Experimental 3D plug track - up to version 244c

[Martin Wynne]

Hi Martin,
out of interest do you know if James will be showing Laser cut timber or FDM made timbers at S4rum?
PS thanks for the instructions on part bricks working my way though that.
cheers
Phil

@Phil G @James Walters

Hi Phil,

James says he is intending to have some laser-cut plywood bases with him, and also Templot running on a laptop, but he can answer fully himself.

He should also have some sample FDM bases from me, some chairs, and some filing jigs for folks to look at. Maybe an assembled FDM turnout. Assuming of course I get my act together in the next few days and get it all ready.

There is a lot that needs explaining from a 5-minute chat about plug track -- so there will be a big QR scan code, so that folks can come here on their phones and get the full info. Here it is:

Mainly James will be doing his own demonstrations, including the P4 Finetrax kits which are the current big thing in the Scalefour Society:

cheers,

Martin.

 

[Martin Wynne]

there are so many unfinished loose ends

One of which I was well aware of, but to which I haven't been paying enough attention.

I came to the end of a reel of FDM filament, and started a new one. Same make and type of polymer, same colour. Just from a later batch: eSun PLA+ brown.

I printed the exact same file on the Neptune2S and was a bit surprised that from the old reel the chair sockets had been a fraction loose, but from the new reel they were far too tight.

The problem wasn't difficult to find:

old reel filament diameter: 1.72mm
new reel filament diameter: 1.78mm

That's not much difference (2 thou), and within eSun's claimed spec: 1.75mm +/- 0.05mm.

But it's enough to make a significant difference to plug track. The filament diameter is a critical dimension because it gets squared in the calculations of polymer flow, so small changes make a big difference:

1.72 / 1.78 = 0.9663

0.9663 x 0.9663 = 0.934 = 93.4%

That means that to correct for the change of filament it is necessary to change the Flow setting in the slicer to 93.4% of what it had been for the previous reel. i.e assuming 100% previously:

It is particularly critical to get the flow right for plug track, because I also use this setting in Cura:

which is showing in yellow because that is way above the expected range up to 100% max.

What that does is to allow the printer to print narrow walls accurately (such as the socket walls) which are significantly narrower than the nozzle diameter (0.4mm) by carefully reducing the flow rate along them.

What to do about all this? I can't imagine many users wanting to do filament volumetric calculations every time they change a reel, and make consequent changes in the slicer settings.

It will at least be necessary to measure the diameter when starting a new reel, and ideally before each fresh job. So a suitable caliper or micrometer will be a tool needed for FDM plug track. I imagine most users will already have one -- inexpensive digital calipers are often available from Lidl, etc.

The measured diameter could then be entered in Templot. Which could adjust the socket clearances to allow for the change in polymer flow. Leaving the slicer set on 100%. Then it's only necessary to re-export and slice the file if making multiple identical parts.

So that's yet another tickbox and a chunk of code for me to write.

Either way, it's unlikely to be a perfect correction. There will likely also be batch-to-batch changes in the polymer thermal and shrinkage characteristics. And a change in diameter may affect the speed at which it is fed through the extruder gears. And I haven't kept any records for the consistency of diameter throughout a reel. But it would probably go most of the way to correcting for the filament change and be a usable result. Only a full trial and error test will get a perfect result.

cheers,

Martin.

 

[James Walters]

Hi Martin,
out of interest do you know if James will be showing Laser cut timber or FDM made timbers at S4rum?
PS thanks for the instructions on part bricks working my way though that.
cheers
Phil

Hi Phil,

I hope to have example of FDM and Laser cut timbering, and hopefully a full turnout of each. Maybe even some working point rodding, if I can un-stick the run I've just ballasted over.

Best,

James

 

[Michael Woods]

One of which I was well aware of, but to which I haven't been paying enough attention.

I came to the end of a reel of FDM filament, and started a new one. Same make and type of polymer, same colour. Just from a later batch: eSun PLA+ brown.

I printed the exact same file on the Neptune2S and was a bit surprised that from the old reel the chair sockets had been a fraction loose, but from the new reel they were far too tight.

The problem wasn't difficult to find:

old reel filament diameter: 1.72mm
new reel filament diameter: 1.78mm

That's not much difference (2 thou), and within eSun's claimed spec: 1.75mm +/- 0.05mm.

But it's enough to make a significant difference to plug track. The filament diameter is a critical dimension because it gets squared in the calculations of polymer flow, so small changes make a big difference:

1.72 / 1.78 = 0.9663

0.9663 x 0.9663 = 0.934 = 93.4%

That means that to correct for the change of filament it is necessary to change the Flow setting in the slicer to 93.4% of what it had been for the previous reel. i.e assuming 100% previously:


View attachment 6770


It is particularly critical to get the flow right for plug track, because I also use this setting in Cura:

View attachment 6769


which is showing in yellow because that is way above the expected range up to 100% max.

What that does is to allow the printer to print narrow walls accurately (such as the socket walls) which are significantly narrower than the nozzle diameter (0.4mm) by carefully reducing the flow rate along them.

What to do about all this? I can't imagine many users wanting to do filament volumetric calculations every time they change a reel, and make consequent changes in the slicer settings.

It will at least be necessary to measure the diameter when starting a new reel, and ideally before each fresh job. So a suitable caliper or micrometer will be a tool needed for FDM plug track. I imagine most users will already have one -- inexpensive digital calipers are often available from Lidl, etc.

The measured diameter could then be entered in Templot. Which could adjust the socket clearances to allow for the change in polymer flow. Leaving the slicer set on 100%. Then it's only necessary to re-export and slice the file if making multiple identical parts.

So that's yet another tickbox and a chunk of code for me to write.

Either way, it's unlikely to be a perfect correction. There will likely also be batch-to-batch changes in the polymer thermal and shrinkage characteristics. And a change in diameter may affect the speed at which it is fed through the extruder gears. And I haven't kept any records for the consistency of diameter throughout a reel. But it would probably go most of the way to correcting for the filament change and be a usable result. Only a full trial and error test will get a perfect result.

cheers,

Martin.

Hi Martin - for reasons that are too complex to explain I have two Anycubic Vyer FDM printers....purchased about three months apart but effectively the same model. I use the same filament and the same slicer, swapping memory cards as and when.


One printer just prints faster than the other.....no idea why. On a short length of track one consistently finishes five minutes faster....both produce the same result. I suspect that it is down to different chip sets or stepper motors. But you could imagine a situation where the results are different. My thoughts are that there are multiple variables here and it is not possible for you to try and smooth all the variables, at some point it is down to us (the end user) to make this work......What you have built for us is brilliant but you can only do so much. As you say the physical properties of the filament may also vary....

 

[Martin Wynne]

So that's yet another tickbox and a chunk of code for me to write.

Another day, another button:

cheers,

Martin.

 

[genixia]

One of which I was well aware of, but to which I haven't been paying enough attention.

...

old reel filament diameter: 1.72mm
new reel filament diameter: 1.78mm

...

That means that to correct for the change of filament it is necessary to change the Flow setting in the slicer to 93.4% of what it had been for the previous reel. i.e assuming 100% previously:

...

What to do about all this? I can't imagine many users wanting to do filament volumetric calculations every time they change a reel, and make consequent changes in the slicer settings.

It will at least be necessary to measure the diameter when starting a new reel.

That's a key tenet of FDM printing though - every reel needs to be calibrated for flow. Better filament manufacturers maintain a higher tolerance in diameter. +/- 0.02mm is a fairly typical "good" specification. You reels would (just) meet a +/- 0.03mm specification. I'm not sure what eSun claim (it doesn't seem easy to find on their webpage, which could in itself be telling). I know that I have so far found Sunlu PETG filaments to be fairly consistent with their diameter (all measured within +0.02/-0mm against a claimed +/-0.02mm), although my experience is still rather limited so perhaps take that statement with a statistically-correct sized grain of salt.

I don't think you need to worry about this in code. Ensure that it is documented that FDM printers need flow calibrations for each reel, and those calibrations are essential for the correct fitment of Plug Track, and move on. This really isn't your problem to solve - it's the Slicer's. Adding options to Templot is likely to add confusion around the issue without bringing benefits.

I've just printed two sets of bases for B sized turnouts with V-8 crossings. The first was with default timber settings and used 28g of filament. The second was with widened and thickened flanges to test ballast reduction techniques you suggested before, and used 46g of filament. The first would allow for about 40 turnouts per reel, the second about 20. I really don't think per-reel flow calibration is a burden here.

 

[Paul Boyd]

I don't think you need to worry about this in code. Ensure that it is documented that FDM printers need flow calibrations for each reel, and those calibrations are essential for the correct fitment of Plug Track, and move on. This really isn't your problem to solve - it's the Slicer's. Adding options to Templot is likely to add confusion around the issue without bringing benefits.

Hi Martin,

I tend to agree with Ian here. If FDM users are already calibrating the flow for different reels for other work, isn’t also having these settings in Templot going to potentially double-calibrate, leading to more confusion?

Templot just needs to take it as read that the printer is calibrated for flow, perhaps with a reminder message? After all, when I”m producing a CAD drawing for something to be made by a machine shop, I take it as read that their machines are maintained to produce what I draw.

Cheers,
Paul

 

[Martin Wynne]

I don't think you need to worry about this in code. Ensure that it is documented that FDM printers need flow calibrations for each reel, and those calibrations are essential for the correct fitment of Plug Track, and move on. This really isn't your problem to solve

@genixia

Hi Ian,

That would probably be the correct approach if I was doing this commercially, but I'm not. It really is hard work to get that point across.

I'm doing this as a hobby for my own enjoyment. I put stuff in Templot because I want it for myself and it's stuff I enjoy tinkering with. I like to get things working well for myself, and equally well for others who want to join in the fun.

I have promised several here that I will make it easy-peasy to do the 3D printing for plug track, and I don't want to let them down. I doubt that would include doing volumetric calculations and calibrations -- I think most folks here are more interested in building track than getting into a new 3D printing hobby. The 3D printer is just a tool to that end. But it all takes time to get done, and having a 75-year-old brain isn't helping -- I keep making silly mistakes.

You reels would (just) meet a +/- 0.03mm specification.

Checking on Amazon I see they are now claiming +/-0.03 mm :

https://www.amazon.co.uk/gp/product/B07FQ75QG2

I took the +/-0.05mm from an old eSun box, about 3 years old, and should have checked the current specs. But even at +/-0.03mm it is enough to significantly affect the fit of the chair plugs in the sockets, so worth doing something about. If someone comes here saying their plugs won't fit in the sockets, I want to be able to help, rather than telling them to go away and calibrate their printer.

But like everything in Templot it's optional -- you don't have to click on anything you don't like the look of.

cheers,

Martin.

 

[Martin Wynne]

p.s.

I have now ordered some of this for comparison:

https://www.amazon.co.uk/dp/B07Y5K1TB5

Because it's on offer, it's claimed +/-0.02mm, and it looks a better colour for timbers than the brown or grey options from eSUN. We shall see.

Martin.

 

[genixia]

Even at +/-0.01mm, the difference between the minimum and maximum equals in a 2.3% difference in flow, which in turn might be enough to throw the fit off. Further compounding the problem is that almost no-one has the tools necessary to measure to that accuracy anyway. Even if their caliper/micrometer has the resolution, most won't have the necessary repeatability or accuracy. For example, genuine Mitutoyo Absolute Digimatic 0-6" calipers have a resolution of 0.01mm, a repeatability of 0.01mm and an accuracy of 0.02mm. If that's what a high quality set trusted by Blue Chip industries achieves, one can only wonder about cheap Amazon options.

The reality is that we care most about resolution and repeatability. After we get one filament dialed in, a comparative measurement often suffices to make adjustments. Even that might not be enough though - a resolution and repeatability of 0.01mm is effectively +/-0.005mm, which could change flow by nearly 1% before the caliper reading changes.

If that proves to be problematic in practice for Plug Track, a better way to measure flow is by weighing a known test print of about 10g. Anything that prints fast and reliably, we only care about its mass. Once you have flow dialed in with one filament for good Plug Track fitment, print that test print, label it and store it safely. Copy, label and store the slicer profile used to print it too, and never modify it again. When you change reels, reprint using that profile and compare their masses using a milligram scale. Affordable $50 milligram scales typically have 1-2mg repeatability, but even if they were only repeatable to 10mg, that represents just 0.1% of 10g, giving you a factor-of-10 better measurement than that achievable by quality calipers. Even better, we are now measuring actual extruded flow and immune to short-length diameter fluctuations (which can be problematic when measuring filament diameter). By using comparative mass measurements we make most of the potential printer and slicer errors common-mode such that they cancel each other out and simultaneously remove any reliability on scale accuracy.

Obviously that only works directly for filaments of identical densities. Theoretically, compensation could applied for other filaments if you knew the densities, but most manufacturers only quote densities in 0.01g/cm^3 resolution. With eSun PLA+ being 1.23g/cm^3, that least significant digit represents 0.8% of the density, so the moment you apply that compensation you'd introduce the potential for at least that much error (again). That is a shame, since the manufacturers should be able to control and measure density much better than diameter. If they specified the density to another significant digit, then it would be a reliable method.

Also, be aware that whilst PLA, ABS, PETG, and some other filament types are usually fairly pure chemistries (dyes not withstanding), the chemistries of modified filaments (such as Silk filaments, PLA+, and those containing carbon fiber or wood particles) are very much manufacturer-dependent. You might be able to directly compare PLA or PETG test prints of reels from different manufacturers (with an initial physical fit verification), but you probably shouldn't do so with modified filaments.

The easiest option is to find a manufacturer and filament that you like and trust, and stick to it to minimize possible variations and allow for comparative measurements to be most reliable.

 

[Phil G]

Hi Guys,
i have been reading the last few posts with some interest, I have to say I am I little bit confused.
In so far as there is a lot of info on the net and with you tubes, all comparing the true size and dimensional stability of filament rolls. Its generally taken as read that the filament diameter even from the more accurate suppliers will have a tolerance during the extrusion of the filament itself, with most people commenting if you measure in enough places most of the stated tolerance can be observed.
I.E. a tolerance of +/-0.02mm on a 1.75mm roll would be expected to be observed at some point in the roll if enough measurements were taken.

We should also not forget that PLA+ is a slightly hydroscope material (hence to vacuum sealed bag and the small packet of silica gel found in most new rolls) Martin my suspicion is the big difference you have observed from your old Esun PLA+ to your new roll has as much to do with the hydroscopic nature of the product and how that impacts the material as it goes though the nozzle, as much as a difference in measured filament size.
It will be interesting to see what you make of the Sulu product.

 

[Martin Wynne]

a tolerance of +/-0.02mm on a 1.75mm roll would be expected to be observed at some point in the roll if enough measurements were taken.

@Phil G

Hi Phil,

That's why I suggested measuring it before the start of each job and entering the diameter in Templot before exporting the STL file. Most folks would probably be happy with that, rather than changing the settings in the slicer for every job.

It's not ideal, and it gets very confusing if you are going to save the STL and want to re-use it at a later date with a different reel or filament, or post the STL here or elsewhere for others to use. Generally if Templot has adjusted the export for a specific filament diameter it is a one-time STL to be used there and then and deleted afterwards. A fresh STL can easily be created later if you have saved the BOX and BGS3 files. There is a function in the menu to save only the templates for a brick / all bricks by grouping them:

I'm going to continue with this idea and see how well it works, while I have enough supplies of two very different filament diameters to test it on. It may or may not make it into 241c.

The object is not to get into the wilds of FDM printing, but to produce usable plug track by having chair plugs which fit properly in their sockets. The other dimensions are not so critical, apart from the need for the connector clips to engage correctly.

cheers,

Martin.

 

[Steve_Cornford]

Turnout Operating Unit thoughts
The operating bar (as opposed to any cosmetic stretcher) needs to be constrained in the vertical plane(z), it should be free to move in both the horizontal planes(x,y).
The 45 degree angle of the ribs were introduced to overcome a possible FDM printing problem.
In some of the pictures of prototype stretchers, the stretchers intrude into the space below the timber tops.
If we assume that in the model we are laying the timber bases onto some sort of trackbed that is at least 3mm thick, how about having a TOU that sits under the timber base, in a slot cut out from the trackbed?
Imagine if the flanges of the two relevant timbers were extended so that they joined up, the would provide a smooth flat surface on the underside of the timber base, and an operating bar below that would be constrained from moving vertically.
There would obviously be a couple of holes, through which the operating pins protruded.
Taking the switch template but shortening it so that it just contained the two timbers either side of the operating bar, and reducing the depth of the timbers to match the height of your trackbed, and reducing the depth of the flanges, could make an upside down U shaped container that fitted under the turnout, matching the geometry of the turnout.
The operating bar would sit in this trough as it were.
The operating bar could be the same standard size for all switches, lets say 4mm wide, equivalent to 12" which should fit in the gap of A,B and C switches.
Steve
edited to correct dimensional typo

 

[Steve_Cornford]

Another day another doodle!

Steve

 

[Steve_Cornford]

Mockup of an FDM base with extended flanges & operating holes

Mockup of operating bar to sit below timberbase

The operating bar can have a servo drive hole between the blade pin holes or can be extended either side and driven from there.
Steve

 

[Winander]

Interesting idea Steve, but wouldn't burying it so deep be a problem if it malfunctioned?

Richard

 

[Phil G]

Hi Steve,
it looks like your kind of halfway to integrating something like James Walters turnout servo drive unit. At which point some of the mechanism needs to be accessed from the underside anyway.
I see this more as a three element concept, all of which can be integrated. In order to do that I see the turnout switching mechanism as the link,
the first step is a std turnout, the link involves making new parts and then changing some components, and the final stage is the servo integration
phil,

 

[Martin Wynne]

@Steve_Cornford

Hi Steve,

Does this idea help:

Extended clip-fit plugs with tangs omitted, glued into timber.

Cross pieces through the openings could retain your subterranean slider.

FDM-printed extensions below the webs are not practical for printing, but you could do the above now. The openings are quite small, so metal bars across might be better than plastic. At present the size of the opening is hard-coded, but the vertical dimension (currently 1.3mm clear) could easily be made adjustable in a deeper plug, allowing a more substantial cross piece.

The lower edges of socket holes would need some cleaning up with a craft knife, but not difficult or critical.

P slide chairs, so printing a batch would be interchangeable for any switch.

cheers,

Martin.

 

[genixia]

Suggestion: Change the default for flanges at the ends of a timber brick to be disabled by default. That allows the flange width/thickness to be changed without affecting the space available for clips at the ends.

The images below are of the same B turnout exported to be printed in two parts, first with default 3D timber settings, and then with widened/thickened flanges that would reduce ballast needs, as discussed before, with no other changes.

The widened flanges don't leave enough space for the clips to work. Also, if they are widened enough to ensure that every gap is filled, they will conflict with each other, requiring modification.

It is possible to solve this using the Shove Timbers functionality to disable those flanges, and then the clip has consistent space available to it there regardless of flange width and depth. I think it likely that the vast majority of timber bricks are likely to have a clip added there so disabling them by default would save a lot of work for anyone straying from the defaults.

Along the same line of thinking, disabling the flanges on each side of the tie-bar could be achieved in the same manner to ensure a consistent volume there for your latest hold-down mechanism ideas.

Ian.

 

[Martin Wynne]

@genixia

Hi Ian,

Thanks for your thoughts. Lots to think about there.

Automatically doing anything with the end timbers on a brick is a bit problematic. Templot doesn't actually know which timber is a brick-end timber. That's why they still have the end webs for example. If I knew which was an end timber I would have removed those, although in practice they are easily snipped off.

Sure it knows which are the end timbers on a template, but a brick might include a dozen different templates, especially for a formation such as a tandem turnout with multiple partial templates. Knowing which templates terminate the brick in various different places is tricky -- just knowing how many such places exist is difficult. No doubt I could write something to find all the end timbers, but getting it to work reliably in all possible track formations and orientations would be a challenge.

But the main point is NOT to put clips between the timbers if you can possibly avoid it. Most of the time you can avoid it, putting them outboard on assorted splints and slabs as required, like this:

That's quick and easy to do, the exact positions are not critical. and the wide spacings increase the alignment accuracy with the next brick.

The purpose of the timber flanges is to stiffen the timbers where the thin socket walls weaken them. If you attach a clip to a timber without a side flange, you are using the weakest part of the brick as a means of attachment, which is less than ideal.

The tommy bar part includes a hole for a 1mm veneer pin which can be used as an aid to alignment if desired, corresponding to target marks on the paper templates. They are much easier to use if located outside the tracks.

But sometimes a clip between the timbers can't be avoided, and I'm currently re-working the clip functions to make that easier. The current functions are little more than the original kludges to prove the concept.

On the subject of minimising ballast requirements, that result doesn't look too appealing to me, but I will see what others think. In essence it is similar to the CNC-milled option, where the depth of milling can be made quite shallow if desired:

But I feel sure the scenic department will be able cover up all the webs, splints, clips, screw heads, dropper connections and other gubbins without adding too much weight. A layer of crumbled cork doesn't weigh much -- a lot less than all that plaster they will be spreading across the hillsides. Only the top half-millimetre needs to be a layer of proper ballast.

Thanks again.

cheers,

Martin.

 

[genixia]

That makes a lot of sense. In the search for easy-peasey would it then make sense to design the default shape of the clip pair such that they will side-mount without needing any additional sprues? The claws will already do that, but the tommy bar won't. If the tommy bar was an 'H' shape with unequal lengthed sides, then it could (and could mount either side). Also, if space between the timbers isn't an issue for the preferred location, then the tommy bar could be squarer and thus stronger. (Actually, the whole clip pair could be longer to make it easier to connect to templates and stiffen up the connection). Keep the existing shape as a (non-default) option for when someone is forced to go between the timbers.

I'm just learning how to use pegs and notches. It would be good if dropping a clip at one of the available peg locations 'just worked'. Double-Track center perhaps?

 

[Martin Wynne]

That makes a lot of sense. In the search for easy-peasey would it then make sense to design the default shape of the clip pair such that they will side-mount without needing any additional sprues? The claws will already do that, but the tommy bar won't. If the tommy bar was an 'H' shape with unequal lengthed sides, then it could (and could mount either side). Also, if space between the timbers isn't an issue for the preferred location, then the tommy bar could be squarer and thus stronger. (Actually, the whole clip pair could be longer to make it easier to connect to templates and stiffen up the connection). Keep the existing shape as a (non-default) option for when someone is forced to go between the timbers.

@genixia

Hi Ian,

Funny you should say that. I'm already looking at a sort of H shape for the shaft of the tommy bar -- the outer vertical being in effect a replacement for a missing timber flange without any risk of fouling the claws. With an option to widen it to something which could be attached directly to the timber webs when outboard of them.

I'm just learning how to use pegs and notches. It would be good if dropping a clip at one of the available peg locations 'just worked'. Double-Track center perhaps?

You can already do that, more or less. Put the peg on the desired peg position (CTRL+F8 to slide it along). Put the notch under it. Add clip at notch.

Will be changed to using the locator instead for the clips soon. More about the locator at template > symbols (feed droppers, gaps ) ...

cheers,

Martin.

 

[genixia]

Here's a mockup of a concept that I thought of earlier - a 2-dimenstional connector capable of connecting the ends of two timber bricks, two parallel timber bricks, or both simultaneously. The center of the connector is at Double-Track Center. The size and jigsaw shape might need a little tweaking to optimise connections and to avoid webbing conflicts. I didn't put any pinholes in it either.

 

[Martin Wynne]

Here's a mockup of a concept that I thought of earlier - a 2-dimenstional connector capable of connecting the ends of two timber bricks, two parallel timber bricks, or both simultaneously. The center of the connector is at Double-Track Center. The size and jigsaw shape might need a little tweaking to optimise connections and to avoid webbing conflicts. I didn't put any pinholes in it either.

View attachment 6810

@genixia

Hi Ian,

That looks good, but if you can get it to work I shall be amazed. Been there, got the T-shirt!

It's next to impossible to find tolerance settings which allow a round FDM component to fit accurately in a round FDM hole. The two options available are too loose or too tight, and just opening the window while printing is enough to switch from one to the other. At the very least it will need some corner relief across the inside corners.

I tried running a drill through the hole to improve accuracy, but the side opening pulled the drill off-centre and made matters worse.

An important feature of the tommy bar design is that the claws can flex slightly if needed without affecting the alignment. In the fact the best fit is achieved when they do flex just a fraction.

Bear in mind also that the spacing between adjacent tracks is not a constant. Nor are they always straight or parallel or on concentric radii. Or square-on to the build plate, making it inconvenient to align the brick boundaries across multiple tracks.

cheers,

Martin.

 

[Steve_Cornford]

Hi Martin,
I accidently chose "Real > V crossing > Parallel" and got this result:-

Steve

 

[Martin Wynne]

Hi Martin,
I accidently chose "Real > V crossing > Parallel" and got this result:-
View attachment 6818
Steve

@Steve_Cornford

Hi Steve,

Yes, that's one of the many loose ends I do know about. Chairing is not yet done for parallel crossings. I think I did mention it a few months ago, maybe at a Zoom meeting.

Parallel crossings as implemented in Templot are very seldom used and I have been minded to remove them entirely. The snag with that is that it would break any legacy BOX files which do happen to use them. But it's one for the back burner I think while I have so many other loose ends to deal with.

In the meantime you can use the return curve button instead (at the top of the trackpad).

Thanks for reporting it. Those chairs in fresh air are a bit puzzling.

cheers,

Martin.

 

[Steve_Cornford]

Sorry Martin, it was an accident, but having spotted the fresh air chairs thought it worth reporting.

Am I correct in thinking that the "real > timbering > exit track timbering > exit timbered" which generates S1J chairs is on your "to do" list?

Steve

 

[Martin Wynne]

Am I correct in thinking that the "real > timbering > exit track timbering > exit timbered" which generates S1J chairs is on your "to do" list?

@Steve_Cornford

Hi Steve,

Yes it is, but I have forgotten to do anything about it. Sorry about that, I remember you mentioned it before. I will get it done soon.

In the meantime there is a trick you can use to get long timbers with sockets for ordinary S1 chairs if that's what you need. Go to real > V-crossing options > customize V-crossing > vee rail...

Change "number of timbers spanned by vee rail" to say 12 or however many long timbers you want. You must change the relevant size for the crossing angle (or change all of the sizes).

Please do post reports of anything you notice. Just because I know about something in theory doesn't mean I haven't totally forgotten about it. There should be a note in my notebook, but where have I put that?

cheers,

Martin.

 

[Martin Wynne]

p.s.

I have now ordered some of this for comparison:

https://www.amazon.co.uk/dp/B07Y5K1TB5

Because it's on offer, it's claimed +/-0.02mm, and it looks a better colour for timbers than the brown or grey options from eSUN. We shall see.

Martin.

.
Sunlu filament now arrived. Also some Jayo brand PLA+ which turns out to be the same stuff from the same company -- same packaging, same labels, same specs and same user notes on the box. The difference is that it costs less because it is on a cardboard spool instead of plastic, with a much smaller range of colours. But you get 10% extra -- 1.1Kg instead of 1Kg. So combined with the lower cost it is worth getting.

But my idea that the Sunlu "wood-coloured" filament might be better for timbers than brown or grey was way off. It's actually beige -- ideal for concrete sleepers when we get that far. In the meantime it will come in handy for the filing jigs.

But the Jayo filament is excellent. It's grey, slightly darker than the eSun grey and with an earthy colour tinge which probably makes it the best colour for timbers of any that I have tried:

https://www.amazon.co.uk/dp/B0BHYZJQY9

It will need painting of course, but if you can start with a colour somewhere near it makes it a lot easier.

It's almost spot-on at 1.755mm dia. (0.0691" on my Mitutoyo micrometer) and a test print at 100% flow in Cura has turned out fine. The clip-fit chairs all clipped straight in. Just a fraction of end-play in a few of the sockets which I have now tweaked in the code.

So that's a positive result.

cheers,

Martin.

 

[genixia]

Here's a mockup of a concept that I thought of earlier - a 2-dimenstional connector capable of connecting the ends of two timber bricks, two parallel timber bricks, or both simultaneously. The center of the connector is at Double-Tring

...
It's next to impossible to find tolerance settings which allow a round FDM component to fit accurately in a round FDM hole. The two options available are too loose or too tight, and just opening the window while printing is enough to switch from one to the other. At the very least it will need some corner relief across the inside corners.
...
An important feature of the tommy bar design is that the claws can flex slightly if needed without affecting the alignment. In the fact the best clip-fit is achieved when they do flex just a fraction.

Bear in mind also that the spacing between adjacent tracks is not a constant. Nor are they always straight or parallel or on concentric radii. Or square-on to the build plate, making it inconvenient to align the brick boundaries across multiple tracks.

cheers,

Martin.

Have you played with the Slicing Tolerance experimental option in Cura? The idea to use rounded joints was just a musing, I'll try playing with it a bit to test feasibility some more.

One reason that rounded joints might be desirable is that square angles are more difficult to print than rounded angles for several reasons. First, the kinetics of the move require one axis to decelerate to a standstill and at that exact moment for the other axis to accelerate from zero. Any latency in that transition results in a non-square corner. Also since axis acceleration isn't infinite, it is thus impossible for the nozzle to maintain a constant speed across the bed as it traverses the corner. Because the acceleration is finite, there is a definite point in time where the nozzle isn't moving in either axis. To avoid over-extrusion (and blobby corners), the filament flow must also decelerate into the corner and then accelerate out of it. Unfortunately, there is a distance between the extruder and nozzle, containing a volume of pressurized molten filament. That pressure has its own inertia, so the pressure changes and thus extruder velocity changes must be made in advance of the corner or you end up with non-square corners again. Those pressure changes are dependent on both print velocity and filament viscosity (and hence temperature). Problems related to them are made easily noticeable by printing something with square corners (such as a timber base) and turning the initial layer print speed up. The first thing that will go wrong is you'll start to lose adhesion with the plate at sharp corners.

Advanced builds of Marlin, and all builds of Klipper firmware contain an option to tune those pressure changes, (Linear Advance and Pressure Advance respectively), but they are only compensating for the problem, not solving it.

Anyway, with that all out the way, it probably doesn't matter for clips - all the timbers are square cornered anyway, and we can't really get away from that!

 

[Martin Wynne]

But the Jayo filament is excellent. It's grey, slightly darker than the eSun grey and with an earthy colour tinge which probably makes it the best colour for timbers of any that I have tried:

https://www.amazon.co.uk/dp/B0BHYZJQY9

It will need painting of course, but if you can start with a colour somewhere near it makes it a lot easier.

I've been try to find a name for this colour. There are lots of greys here:

https://www.color-meanings.com/shades-of-gray-color-names-html-hex-rgb-codes/

As best I can judge from my monitor, it is somewhere between "Rustic Grey" and "Echo":

With remaining bullhead track now largely receding into the undergrowth, plug track is surely something of a rustic echo?

cheers,

Martin.

 

[James Walters]

Here's an idea for the collective gene-pool. I've not really thought it through so am dropping it here for the hive mind to ridicule.

How about laying FDM track bases upon a sub-base of cork, foam or whatever, and then placing another sheet over the track base with lasered cut-outs for the timbers? The top layer would obviously need to be thin enough to allow for ballasting and could be very loosely glued down, perhaps at the edges as a variation on the floating track bed concept.
Taken to the extreme, the sleepers/timbering could be made very thick indeed to allow for, say, a 6mm thick cork top layer.
Might this be an effective means for deadening unwelcome track noise?

As I say, it's just a quick thought jotted down to save it slipping my memory. But I think I might give it a try on a little test track.
It's obviously not for everyone, but could be worth an experiment, especially as the FDM bases allow us to fix them down with pins rather than buckets of PVA.

Happy for you all to ridicule me on here or to my face at Scaleforum.

 

[Steve_Cornford]

Hi James,
Not quite sure I understand your suggestion. Any chance of a free hand sketched diagram?
Steve

 

[James Walters]

Of course, I've got to go a meeting right-now, but I'll send a sketch after I've drawn one in the meeting.

 

[Phil G]

Hi James,
with this idea is the cork solid or has the FDM/Laser cut ply been relived by part etching the timbers to create a recess.
Second comment how well can you glue ply onto top of FDM made timbers?
cheers
Phil,

 

[Phil G]

Sorry just to clarify I meant part etch the timber shape in the cork, thus allowing the cork to snugly fit the timbers in the part etching.

 

[Martin Wynne]

First, the kinetics of the move require one axis to decelerate to a standstill and at that exact moment for the other axis to accelerate from zero. Any latency in that transition results in a non-square corner. Also since axis acceleration isn't infinite, it is thus impossible for the nozzle to maintain a constant speed across the bed as it traverses the corner. Because the acceleration is finite, there is a definite point in time where the nozzle isn't moving in either axis. To avoid over-extrusion (and blobby corners), the filament flow must also decelerate into the corner and then accelerate out of it

@genixia @AndyB

Hi Ian,

Have you actually tried any of this? I went through it a few years ago when I was trying to get detailed chairs FDM printed. I couldn't get any of it to make the slightest difference. Andy has done much better than me at getting FDM to work for chairs, by simplifying the chair detail and weaving the rail fractionally from side to side.

In a real-world timbering brick extracted from a track plan, the vast majority of rectangles will not be square-on to the build plate. This applies to the chair sockets and the connector clips. Even a single one-off turnout is likely to be curved, a little or a lot. At a corner in that case, one axis keeps moving while the other changes direction. If the nozzle doesn't stop moving there is much less risk of blobby corners.

For the sockets the corners are not really a problem because the plugs have a generous corner relief. Likewise the clip tommy bars. This is especially the case for the CNC-milled sockets which have radiused corners. The main consideration for the sockets is the dimensions rather than the corners.

In any event, Templot has no control over any of this, it would be for each user to experiment with their own printers. I can imagine that a majority of users will use a standard profile from the slicer which came bundled with the printer -- even if that's Cura and I post a suggested Cura profile. So I have to find designs and settings which will work reasonably well with the typical standard profiles.

Your clip idea might work if the tabs are made hexagonal or octagonal in a round hole -- something to try when I get a chance.

Thanks again.

cheers,

Martin.

 

[James Walters]

Hi James,
Not quite sure I understand your suggestion. Any chance of a free hand sketched diagram?
Steve

I hope this explains it better. Starting to have my own doubts now though.

 

[James Walters]

Hi James,
with this idea is the cork solid or has the FDM/Laser cut ply been relived by part etching the timbers to create a recess.
Second comment how well can you glue ply onto top of FDM made timbers?
cheers
Phil,

Hi Phil, does the sketch make it clearer?

 

[Martin Wynne]

@James Walters

Hi James,

That would solve Ian's problem with the volume of ballast needed. It means if dropper wires are pre-fitted they would need to have holes drilled through the base to drop through, rather then being bent to run to the side of the track for easy connection.

Many timbering bricks could be tricky to fit it in place, something like this for example:

But there is no requirement to use the same construction method everywhere. This idea might be fine for plain track, but be omitted for areas of pointwork, which could use crumbled cork instead of sheet material (search "cork granules" -- from pet shops, used for animal bedding).

cheers,

Martin.