3D track - fun with laser-cutters

[Martin Wynne]

I think the reason the clip fit work so well on laser cut timber (when the right size socket vales are found) is the clip is acting as the inverted version of the taper IE think of it more like a cross section of a Morse taper lock system.

@Phil G

Hi Phil,

If that's the case, you might do better with snap-fit rather than clip-fit:

You can adjust the taper angle by changing the jut width (amount the tang juts out from the plug):

cheers,

Martin.

 

[Phil G]

Hi Martin,
Good thinking. I will try that as well,
However its possible the clip fit has just enough flex to take exactly the same taper as the kerf is creating. where as with the snap fit setting the jut width exactly right for every socket, bearing in mind wood is natural so not all tapers are likely to be exactly the same. could add even more complexity. Only testing will tell us the answer.
If looking down on the chair in plan view, how wide would it be possible to make the clip?
cheers
Phil

 

[Martin Wynne]

If looking down on the chair in plan view, how wide would it be possible to make the clip?

@Phil G

Hi Phil,

You can make it as wide as you like by changing the jut width.

However, if you make the overall plug width wider than the chair base (8" scale for most chairs) the socket will be visible alongside the chair, and the chair may not sit correctly on the timber surface. If you make it wider than the timber (10" scale for plain track sleepers) the socket will break through the side of the timber.

FDM timbers have a under-cut in the socket wall to allow for the tang. The default sizes have been set to work fine with FDM timbers. Everything is over to you for laser-cutting (until I get a laser-cutter of my own and can test things).

cheers,

Martin.

 

[Phil G]

Hi Martin,
some very interesting findings today, the first one is the speed and the power do most certainly have an effect on the size of the taper created, somewhat surprisingly to me at least, is running at lower power and slower speed makes this taper more pronounced.
we are not talking a great deal here though, for a 2.5 mm thick piece of 3 ply (Gabon faces)10 thou at the top and 6 thou at the bottom of the slot. ( single pass one straight cut)

The next thing is two passes are defiantly better than a singe pass, in fact at at both 21 mm/sec and 25 mm/sec just cutting a single straight line (two passes) I can get a 7 thou feeler to start at the top of the slot and a 6 thou to start at the bottom, so almost a straight cut
the pocket is slightly worse at least 2 to 3 thou when measuring a pocket taper.

The other thing I have found is the ply is remarkably flexible, you can push a 0.15 mm inference fit in and in some cases only see a slight bulge in the ply sides but not always. This needs a lot more trial and investigation to see if a slight interference fit is the right way to go.

With the clip fit plugs I have made, if you force the caliper to close the clip it will leaving the plug body at 1.97mm. my current sockets (best case IE cutting at both 21 and 25 mm/sec two passes) are giving sockets 1.89 mm at the top so we have 0.08 mm of squeeze on the ply side, Its a bit to much, so I need to just open the socket by say .06 total tomorrow. and see what happens.

The other thing is both material thickness and density do have a marked effect on the speed required to cut though, I tried 2.5 mm ply 1.8 mm ply 1.6 mm bass and 1.6 mm balsa not surprisingly balsa is by far the easiest.

The focal point is also very important, I can see why there moving to a manageable z plane option. a focal point difference of +- 0.4 mm will have a noticeable effect on both ability to penetrate and the taper produced. Sometimes wood distortion can be in that range.
will keep all posted with my findings.
cheers
Phl

 

[Martin Wynne]

@Phil G

Hi Phil,

Thanks for that detailed info.

I noticed on part of your test that the sockets are offset in opposite directions relative to the timber outline:

This applies to all the sockets in that row.

This can't be due to rounding effects from the axis stepper resolution, otherwise both sockets would be offset in the same direction.

It seems more likely due to backlash in the drives. Is the belt tight? Did you cut the sockets before or after the timber outlines?

On a laser-cutter, how fast does the head travel between cuts? Is it the same as the cut speed or faster? Travel speed is more likely to affect accurate positioning than cut speed.

Presumably you edited the snibs in CAD? As far as I know I haven't yet released 244a with a double angle on the snibs. Puzzled.

cheers,

Martin.

 

[Phil G]

Hi Martin,
Well spotted there is something definitely off in that corner of my machine, only in the Y axis. the belts are both set with the same tension and are supposed to be the right tightness but I am not 100% that is right. what's odd is its mainly that corner that has the issue.

re cutting sequence its , text first done at max speed of the machine 41.mm sec or 2.5 meters min,
then all the sockets, then it comes back and does the outline profile last.
the sockets you have noticed are the first sockets to be cut.

interestingly the first one with the chair in is actually in the right place, its all the others cutting at 5mm sec and 50% that are off.

re head speed between cuts it's max speed. 41mm/sec

yes I have used cad quite a lot cause, its only 10 sleepers in Templot just copied and then the layers changed so lightburn understands it requires different processing values. re the snib angles I started doing that in cad just days before you had more or less the same Idea, it solves most of the conflicts especially with crossovers First time I have set the snib to zero to cut out the waste piece though.
I may have a play with modifying that a bit, as it would not be hard to generate some "new sleepers" for the P-way gang wagon loads out of the waste material.

Once I am happy with the results I will post the lightburn file, as it would be good to compare same program settings different machines see what happens.
cheers
Phil,

 

[Phil G]

Ps did you notice the gain is going the wrong way? this is just some handy sized scrap that does the job for testing.

 

[John Walker]

Here is my latest cut in:

https://hobarts.com/products/laserplylite-italian-poplar-plywood?variant=43925461237997

It is soft with a good grain and not too smooth. Also the cheapest from Hobarts. I think the birch faced poplar surface is a bit too hard to soak up the stain. For the moment this looks like my preferred material. Pity they don't have it in 1.5mm for my 3mm scale.

This is scale 7 on a 6ft radius. My sleepers measure 59.35 x 5.82 which is not so different to last time with the slightly more expensive birch faced poplar at 59.3 (59.5) x 5.84 (5.833). This is not totally reliable test because I forgot to cut the containing box last. I must make a checklist for cutting. My settings were 0.2mm kerf and 0.6 x 0.6mm nibs. Some of the nibs broke a bit too easily for my liking but that maybe because of my sequence error.

I would have liked an extra smidgen on the gauge but I have decided to move away from the water washable resin so that may change things.

As I already found with the C&L chairs I need to adjust the underside of my printed fishplates to fit over the rail support..

Some of my very strong neodymium magnets have shattered, probably because they move like lightning when they get too close to each other. Now I have chosen the material for my sleepers I will use the other sheet to make some jigs to align the material, honeycombe and cutter and enclose the magnets.

Regards
John Walker

 

[Martin Wynne]

I have decided to move away from the water washable resin so that may change things.

@John Walker

Hi John,

For the chairs the recommended resin is the ABS-Like resins. Tougher and far less brittle than the standard resins.

In particular we have excellent results with this one:

Anycubic V2 water-washable ABS-Like resin:

https://www.amazon.co.uk/gp/product/B0C7BFQZ2C

(It must be the V2 version -- they are mixed up on the page)

To correct the gauge I suggest changing the output scaling a fraction for the laser cut:

The laser-cutter stepper resolution is not likely to be better than 0.05mm per step. Even that requires electronically micro-stepping the motor, which is affected by resonance and load variations, and varies with speed. So it's not possible to get dimensions accurate and consistent to the second decimal place of mm.

cheers,

Martin.

 

[Phil I]

@James Walters

Hi James,

I'm not convinced there is a problem, but without a laser-cutter I can't be sure. If I had a machine, my intended way of working would likely be:

1. make a trial cut in the desired material at the intended power settings.

2. measure the kerf using feeler gauges.

3. set that as the kerf setting in Templot.

4. export a file to make a test piece and measure it (cutting the sockets before the timber outline).

5. adjust the DXF socket size and scaling settings as necessary.


We seem to be going round in circles. Here's some stuff I posted 18 months ago:

---

This is how it is intended to look immediately below the chair base:

The plug dimensions (pink+red) are taken directly from the prototype at 1" inside the chair base all round, so for an S1 chair the plug is 6" x 12.5" (2.0mm x 4.17mm in 4mm/ft scale).

The socket dimensions (green) are then set so that there is an easy fit or small clearance at the sides of the plug, and an interference overlap (red) at each end of the plug to create a bash press-fit. In the FDM bases this causes the plastic to be deformed sideways into the green clearance spaces, creating a firm interference fit and an accurate track gauge. In the CNC milled bases, the MDF material compresses to produce the same result. The idea of a bash fit is that it is more tolerant of variations in socket size (caused by the fixed printer resolution) than a traditional engineering press-fit.

I'm not too sure how this would work best in plywood bases, and without my own precision laser-cutter to conduct experiments it is difficult to find out. I imagine the red overlap might need to be increased to achieve a firm fit, by reducing the socket length. Alternatively you might need to abandon the idea of a press-fit and glue the chairs in place.

---

I don't think anything much has changed with regard to laser-cutting.

For FDM I have since introduced the easy assembly clip-fit option, which allows for a greater socket clearance to accommodate the variations and rounding effects in different FDM printers, while still retaining the chair firmly in the timber. But it still requires a close fit at the socket ends to ensure an accurate track gauge.

All the default socket size settings:


View attachment 8465

View attachment 8464


have been derived from trials with FDM printers, so I would expect them to need changes for laser-cutting (and CNC milling).

I think perhaps I should post a bit more about FDM printing, to restore the balance of discussions here on Templot Club. I'm sure there are more users interested in that than in using smoke and mirrors.

cheers,

Martin.

Having only just started into this, pls excuse me if this has already been suggested and or dismissed somewhere in else in one of the tomes...
The idea I had after reading about tolerance, kerf, fit issues etc with PlugTrack using laser cut timbers was to provide extra vertical fins of a sort, perhaps in pairs, on the long sides of the plug base. These would press into the ply ensuring a tighter fit over a wider range of aperture sizes perhaps. Indeed, maybe the aperture could be made to be a looser general fit? Perhaps there could be more than a pair on each side?

Cheers,
Phil Insull

 

[James Walters]

I've had some fun today cutting timbering bases for my challenge project, and experimenting with pre-painted chairs.
The chairs have had a dusting of a suitable colour from the airbrush, and thus far, I've had no issues fitting the loose outer jaws. The chairs and timbers will all bet a more thorough treatment at the laying stage, but so far it all looks pretty good.
The timber has been coloured with Coloron Jacobean Oak wood dye, applied sparingly with a cotton bud. I think it's a reasonable starting point for later weathering.

 

[Phil G]

Hi James,
looking very good, what type of fit did you use for the chairs?

 

[James Walters]

Hi Phil, I'm using Press-Fit. I've moved the Press-fit adjuster to read 140, so part way between firm and bash-fit which gives a very solid fit which I am most happy with. I'm also using the slightest smear of a school-type PVA on the turnout chairs, as a precaution rather than necessity. Just enough to reassure me, but a tiny amount such that the chairs are easily removable if need be. I thought it worth doing as I'm treating these as test pieces and it will be some time before they are fitted down. My concern was that should the timbering base flex in the interim (especially with rail fitted) that chairs might loosen.
So far so good.

 

[Martin Wynne]

@James Walters

Another laser review from James:

 

[Phil G]

Hi James,
Another good video, interesting how the frame of this offering is all in one piece, I guess the good news you know its square, the not so good news is, that must prevent any sort of expansion of the working bed area. is that right?

I was especially interested in the etching of the arch and the cutting out of the B8.
The obvious question which you did not address on the video, which I can understand why. Is simply which did you find the better machine the Falcon 2? or the Atomstack x24 pro?

Also more out of curiosity, which machine did you use to cut most of the Jubilee project trackwork on? Or the sneak peak of the wagon hoist.
cheers
Phil,

 

[James Walters]

Hi Phil,
I really can't decide which of the two machines I prefer. Both work really well, and both have pros and cons. The slightly larger bed of the Creality machine is a plus, but the Atomstack machine has the laser cross-hair and a more powerful air assist.
I'd be happy with both.
As for my Jubilee project trackwork, that was mostly done using the Creality machine, but there is no difference between the two in terms of quality or cleanliness of cut.
Best,
James