Building 3D track

[Steve_Cornford]

Thanks Martin,
So my first print has finished.
I had arranged 5 copies of the raft on the build plate, and the print progressed I could see that number of chairs displayed on the front panel LCD.
But once finished with the build plate draining, it looks as though I only have 3 rafts!

Now in the wash.
I assume that I should now filter whats left of the resin in the FEP tank (?) as it is sure to have bits in it!
Oh well. It is all part of the leaarning process.
Steve

 

[Martin Wynne]

Hi Steve,

Bad luck.

It's strange to lose 2 whole rafts as they are chunky lumps of resin directly on the build plate.

Are you getting the exposure light over the full area of the exposure screen? During initial setup a logo image is displayed on the screen to check that.

How big were these rafts? The noises you heard may have been caused by the large area of them sticking to the FEP film in the bottom of the tank and breaking away from the plate. If so you will need to drain the tank, filter the resin for broken bits, and remove them from the film.

Did you shake the bottle of resin well before use? You may have an imperfect mix if it has settled in the bottom of the bottle. The instructions say to shake it well, but don't explain how to deal with the fact that it is then frothy when you pour it out. I have learned the hard way to shake it an hour or so before I need it and leave it to settle in the bottle. This is all the typical learning on the job that they never put in the instructions.

How do your Chitubox settings compare with mine?

cheers,

Martin.

 

[Steve_Cornford]

Hi Martin,

I am using the ABS like resin. Perhaps I didnt shake the bottle enough, as it certainly was not frothy!

I was missing the 2nd and 5th rafts.

I will filter remnants before using again, and certainly give the bottle a good shake, a bit like Halfords etch primer rattle can then.

I did get the logo image in the recatngle so I think that was ok.

I used the default chitubox settings, but will check them and compare.

The printed instructions are a bit useless because the screen images are illegible< so had to resort to viewing PDF in order to actually see the images of the control panel!

The Mercury curing looks good in the dark!

Just the job for All Souls Night next week!

At least I have 3 rafts of 20 off, 4mm S1 chairs to play experiment with!

Its just great to see them in the flesh at last.

Cheers
Steve

 

[Steve_Cornford]

When I drained the tank there were two rafts stuck to the FEP . The chairs supports had started printing but it looks like at one end of the raft they got stuck and pulled the raft base off of the build plate.
I have filtered the resin & cleaned up ready for a other go another evening, thanks for the help an e encouragement,
Steve

 

[Steve_Cornford]

My Chitubox v1.9.4 settings

I must be on a different version.

Regards Steve

 

[Martin Wynne]

When I drained the tank there were two rafts stuck to the FEP . The chairs supports had started printing but it looks like at one end of the raft they got stuck and pulled the raft base off of the build plate.
I have filtered the resin & cleaned up ready for a other go another evening, thanks for the help an e encouragement,
Steve

@Steve_Cornford

Hi Steve,

Hmm.

It seems very strange to me that the rafts printed completely, but then parted company from the build plate later in the process. How firmly attached were the successful rafts? Mine are firmly attached to the plate and need the window scraper worked around them to release them.

Did you degrease the plate before using it to remove any traces of grease or contaminants from the manufacturing process? Likewise the FEP film.

I recently purchased a spare build plate. This speeds up an evening's production by printing the next batch of chairs while you are washing and curing the previous batch (assuming the first batch prints 100% and the tank doesn't need to be cleaned out).

When I went on Amazon to order it, I was surprised to find that there were two options for the build plate surface. A sand-blasted finish (as my original plate), or something described as "CNC Turning CD Pattern" finish. I have no idea what that means, and Google is no help, but I assume it means the plate has a finish similar to a CD disk. Which would certainly be smoother than my sand-blasted plates and may not stick so well. Is it possible your printer has been supplied with such a plate?

Yes, I'm still using Chitubox v1.6.5 as supplied with the machine. Also the original firmware (which I believe is also from Chitubox, as is the control circuit board in the printer).

I'm aware that there are upgrades available for both, but I've carried on using the originals for two reasons -- my first results were so good I didn't see any reason to change; and while I'm constantly experimenting with the chair design I didn't want to add a fresh set of variables into the mix. I will try the equipment upgrades when I have got the designs nearer to completion.

The most significant difference seems to be the exposure time per layer -- I'm using 2.2 seconds, you are using 2.5 seconds. That probably doesn't make much difference to the appearance of the chairs, but it might change the dimensions a little, and the fit of the rail, and the fit of the plugs in the sockets. It might also change the required shrinkage allowance:

That's one of my fears with plug track -- that some users might report rubbish results because they are not sticking closely enough to the printing conditions I have been using in creating the program.

cheers,

Martin.

 

[ralphrobertson]

This does happen sometimes Steve. Run it again and it will probably work. The most common problem I have is the print separating slightly from the build plate at one end and from time to time I get a curl at one end too but as usually happens the next try works fine. Its not that often something ends up sticking to the FEP and needs scraping off. One thing I have found is that on my machine it doesn't do to put too much on the build plate, the suction can really make one hell of a noise so I do try to keep a wide border to the edges. Its better to be able to repeat successful prints than tearing your hair out trying to find out why it doesn't work. Keep trying, it will come out right.

I must say I use the supplied Photon slicer (V1.3.6) and have never moved on to working with anything else, this seems to work for the few things I print on the printer. Supports I find hard work so if there is something I want to print with a flat base I print directly to the build plate. Recently I have printed about 100 strips of coping stones in 7mm for the club layout, all printed on the base plate. These did curl up a bit as they cured but putting them in boiling water, then straightening them and then putting them back in cold water sorted that all out. I think a lot depends upon the resin, usually on the bottle there are parameters given for the settings that are supposed to be used.

I hope this helps and keep at it, a resin printer is a very useful tool not only for track making!

Ralph

 

[Steve_Cornford]

Hi Martin,

The three that were left on the build plate were attached firmly, I had to use the yellow plastic scraper supplied.
Or should I have used the metal bladed scraper supplied?

No, I did not degrease the build plate after removing the plastic protective film, nor did I degrease the FEP plate.
So a recomendation to future owners would be to perform a degrease using IPA before first use?

My build plate has a silvery, sparkly mottled finish, so I would assume it is a sand-blasted one.
I think I will order a second build plate and see if i get a choice.

I think you are right about aiming for consistent reults, so will amend my exposure time to 2.2 seconds.

Another aspect might be ambient temperature, and as I have not yet switched on our central heating I surmise that I was operating at less than the recomended 20 degrees minimum temperature.

I let the build plate drain for 10 minutes, and then swopped it onto the 45 degree plastic holder for a further drain before washing.
This operation is a bit tricky, and I think could be improved by having a catch tray supported on legs that slides betwwen the resin tank and the the build plate to catch any drips whilst this process is performed, rather than let the drips go anywhere else.

As far as curing is concerned what duration are you using?
I can imagine that too long and the result would be brittle chairs that would lead to frustration, too short and they might not be strong enough.

Regards Steve

 

[Steve_Cornford]

Hi Ralph,
Thanks for the encouragement.
Actually I was quite please that I achieved a 60% success rate, a bit like my "O" levels!
Steve

 

[Steve_Cornford]

Upon performing a more thorough clean of the FEP plate I noticed when angling the tray about 45° in the reflection of sunlight what appears to be an array of indentations that match the positions of the 100 or so chairs that are on the 5 rafts (20 per raft). Not so much indentations but as though the FEP sheet has been compressed at those points so I suspect that maybe the A4 sheet of paper I used was too thin and this has resulted in too much pressure so I will try a recalibrate.

edit to correct chair & raft numbers

 

[Martin Wynne]

Hi Martin,

The three that were left on the build plate were attached firmly, I had to use the yellow plastic scraper supplied.
Or should I have used the metal bladed scraper supplied?

No, I did not degrease the build plate after removing the plastic protective film, nor did I degrease the FEP plate.
So a recomendation to future owners would be to perform a degrease using IPA before first use?

My build plate has a silvery, sparkly mottled finish, so I would assume it is a sand-blasted one.
I think I will order a second build plate and see if i get a choice.

I think you are right about aiming for consistent reults, so will amend my exposure time to 2.2 seconds.

Another aspect might be ambient temperature, and as I have not yet switched on our central heating I surmise that I was operating at less than the recomended 20 degrees minimum temperature.

I let the build plate drain for 10 minutes, and then swopped it onto the 45 degree plastic holder for a further drain before washing.
This operation is a bit tricky, and I think could be improved by having a catch tray supported on legs that slides betwwen the resin tank and the the build plate to catch any drips whilst this process is performed, rather than let the drips go anywhere else.

As far as curing is concerned what duration are you using?
I can imagine that too long and the result would be brittle chairs that would lead to frustration, too short and they might not be strong enough.

Regards Steve

@Steve_Cornford

Hi Steve,

I haven't used either of the supplied scrapers. But that's just me. They are useful additions to my toolbox, but for both the FDM and resin printers I'm using a cheapo window scraper from the pound shop:

It's just a Stanley knife blade in a holder, but therefore much sharper and thinner than the supplied scrapers. It also has a clip-on plastic blade cover/scraper which has a sharper edge than the supplied plastic scraper.

(It's also a very useful tool for general modelling, cutting and chopping.)

Ralph says sometimes these things just happen. Well maybe, but I think there has to be reason. For the rafts to detach from the build plate they can't have been properly stuck to it when formed. Some possibilities crossing my mind:

1. Tank not properly located in position. There is a slight recess to contain it, but it's quite easy to knock it out of position while tightening the clamp screws. Don't ask! The noises you heard might have been the build plate catching on the tank?

2. FEP film uneven and not stretched tight enough across the base of the tank. It should "twang" when tapped.

3. Build plate not flat. Have you tried a straight-edge against it?

4. If both missing rafts were at one end, build plate not properly levelled, or it moved after levelling. Have you tested the level again after printing?

5. Z-zero not set low enough. When levelling I have the plate tight against 4 small pieces of 80gsm office paper, one under each corner, such that they can be dragged out, but only with some force. After tightening the levelling screws (gradually from one to the other and back, in the order recommended in the instructions), I lift the head and return it to Z-zero to check that the papers are still tight.

6. Contamination on build plate. Before use I always degrease it in the IPA to remove any grease or fingerprints, and blow it dry with an air blaster (or hair dryer). I've had one of these for years, and it's come in very handy recently. It blows quite warm after a while (motor cooling). Unlike hair dryers it has an input filter for clean air:

https://www.amazon.co.uk/Dusters-EG-1000-UK-Electric-Air-Duster/dp/B073F9NY1X

A less expensive option would be aerosol air dusters.

7. Resin not uniformly mixed. My resin is definitely streaky when not well shaken. That may be because it is well past the labelled shelf life (but seems to work fine).

8. Air bubbles trapped in resin. The printing seems to go better if the tank is well-filled. Leaving it to settle after pouring is probably a good idea.

9. Something else.

cheers,

Martin.

 

[Martin Wynne]

Another aspect might be ambient temperature, and as I have not yet switched on our central heating I surmise that I was operating at less than the recomended 20 degrees minimum temperature.

I let the build plate drain for 10 minutes, and then swopped it onto the 45 degree plastic holder for a further drain before washing.
This operation is a bit tricky, and I think could be improved by having a catch tray supported on legs that slides betwwen the resin tank and the the build plate to catch any drips whilst this process is performed, rather than let the drips go anywhere else.

As far as curing is concerned what duration are you using?
I can imagine that too long and the result would be brittle chairs that would lead to frustration, too short and they might not be strong enough.

@Steve_Cornford

Hi Steve,

I don't know about temperature, but it would have been the same for all the rafts, so can't explain why some stuck to the plate and others didn't. I did do some printing one very warm evening back in the summer when the temperature was over 30 degrees, and there was no obvious difference in the results.

The 45-angled drip holder is a very awkward thing to use and needs a tin lid under it to catch the drips while you are positioning it. Lately I haven't bothered with it and just leave the print to drip normally for longer after the printing finishes. This has the advantage that you can leave the red cover on undisturbed while it is dripping, so no risk of stray UV on the surplus resin before it gets quickly dunked in the first wash.

For curing I couldn't find any time recommendations. I have been using 4 minutes for the 4mm scale chairs, which the machine divides into two lots of 2 minutes in each direction. The time would obviously depend on the bulkiness of the model, if UV needs to penetrate a long way through the translucent resin to reach the core. It also means that any model is always going to be more fully cured on the surface than at the core.

In 4mm scale the chairs are quite tiny in comparison with the typical models the Mercury is designed for. I place a ring of 5 upturned fish-paste jars on the turntable and put the rafts on top of them. This lifts the rafts more centrally into the beam of UV light and allows it to reach the underside of the rafts through the glass. Sainsbury's Salmon & Haddock for preference.

I don't think it's possible to overdo the curing unless you left it on for hours. The chairs will continue to harden in ordinary daylight until they get painted, so leaving them in the machine longer simply accelerates that process by a day or two.

With the "ABS-like" resin I haven't yet found any evidence of chairs getting too brittle, even after several months. The situation might be different with the standard resin or other makes of resin.

The most infuriating thing about the Mercury unit is that at switch-on it defaults to UV curing. It would be very easy to accidentally start curing the unwashed parts and begin hardening the surplus resin. It's blindingly obvious that it should default to washing mode at switch on. As it is you have to be very sure that you have switched to washing mode before pressing Go. Also it's annoying that it won't wash without the yellow lid on, which prevents you assisting the washer by swishing about in the tub with a brush.

cheers,

Martin.

 

[Martin Wynne]

Upon performing a more thorough clean of the FEP plate I noticed when angling the tray about 45° in the reflection of sunlight what appears to be an array of indentations that match the positions of the 100 or so chairs that are on the 5 rafts (20 per raft). Not so much indentations but as though the FEP sheet has been compressed at those points so I suspect that maybe the A4 sheet of paper I used was too thin and this has resulted in too much pressure so I will try a recalibrate.

edit to correct chair & raft numbers

@Steve_Cornford

Hi Steve,

I also have such impressions on the FEP film after every print. I think it is a normal part of the process.

It's not possible for it to be caused by too much pressure, because the chairs are quite soft before they are cured. Under pressure they would simply flatten. Recalibrating the zero setting won't make any difference, because by the time the chairs are being formed the build plate is about 5mm above the zero position.

There were some spare FEP films in the the box. I haven't used any of them yet, but clearly the FEP is regarded as a disposable item and presumably this accumulation of marks causes it to become life-expired.

p.s.If you get a 100% print and print again in the same resin, you don't actually get to see the marks or worry about them

cheers,

Martin.

 

[Martin Wynne]

@Steve_Cornford

Hi Steve,

A further thought crossing my mind is that I think you said you were reducing the width of the chair plugs? And I said that I wasn't too happy about that?

The reason is that it increases the area of chair base each side of the plug, which is flat on the underside.

It's very difficult to print anything with a large horizontal under surface. The first layer of which will be printed as a delicate wafer only 0.05mm thick (2 thou). This has to be pulled away from the FEP film by whatever it is attached to below it in the model. If that is a small area in relation to the area of the wafer, there is a chance that the wafer will break from it and remain stuck to the FEP film. Once that has happened the print can't complete properly. The stuck wafer will receive more and more UV exposure and get quite hard and firmly stuck.

This is the reason many models are printed at an angle raised on supports, so that there are no horizontal under-surfaces.

Tipping the chairs at an angle wouldn't work because it would create a reverse under-surface on one side.

In the chair designs I have allowed for all this with angled bottom faces on the plugs, but I can't do that on the chair base, otherwise it wouldn't sit flush to the timber surface. That's why the chair base overlaps the plug by only 1 inch scale all round, and in the larger scales that may need reducing further.

There is also a small horizontal area on the bottom of the chair keys. So far that seems to be working ok (and even that is not prototypical), but again in the larger scales the keys may need to be angled down on the bottom surface (in the opposite direction from the prototype).

I don't know if any of this explains your noises or the marks on the FEP film, but it is worth bearing in mind. Obviously it can't explain why some rafts behaved differently from others.

cheers,

Martin.

 

[Steve_Cornford]

Hi Martin,
My first print was for S1 chairs all with the default dimensions.

The good news is that last night I had another session having thoroughly cleaned the FEP and the build plate, and without changing any other settings (eg exposure time) the 5 rafts of S1 chairs worked perfectly!

After that I produced some other prints, each time cleaning the build plate thoroughly (but did not clean the FEP as I had left the resin in the tank.
All prints were successful. 4mm S1 rafts, EM P1 slide chair rafts,EM LH B switch rafts.

I then produced a new .STL containing S1 chairs with plug width reduced by 0.3mm (to achieve plug width of 1.7mm) so that I could experiment with my out-sourced laser cut timbers and trackbed, also an .STL of same but locator plugs.
Then a print contaning 1 locator raft and 4 S1 rafts printed without problems, but I will need to inspect them closely to ensure that all is well with the chair bases.

My initial conclusion is that it was my mistake in NOT thoroughly cleaning the build plate after removing the protective film, and also not cleaning the top surface of the FEP (it did not have any protective film, only the bottom surface had one)
Once I had cleaned the top surface of the FEP, the IPA did not "wet" the surface, but was inclined to run away, indicating a fairly clean surface to me.

Anyway it feels good to have achieved some successful prints so thank you all for all your help and suggestions

Steve

 

[Martin Wynne]

@Steve_Cornford

Hi Steve,

Great! Glad you have now made a good start.

If you get good results with the narrower plugs (pics?) I might look at doing the same with some of the smaller chairs, for improved angular alignment in the sockets.

cheers,

Martin.

 

[Steve_Cornford]

Will try and take some pictures later today
Steve

 

[Steve_Cornford]

Hi Martin, pics as promised.
4mm S1 chairs plug width -0.3

When I came to use them in the plywood timbers (example of which I have previously sent you) they were in fact too loose@
So I then tried some 4mm S1 default chairs and they were fine.
Steve

 

[Martin Wynne]

Hi Martin, pics as promised.
4mm S1 chairs plug width -0.3

When I came to use them in the plywood timbers (example of which I have previously sent you) they were in fact too loose@
So I then tried some 4mm S1 default chairs and they were fine.

@Steve_Cornford

Hi Steve,

Thanks for posting the pics.

Something strange there. Several months ago I tried my default S1 chairs in your plywood timbers and they wouldn't fit. Just to be sure I wasn't dreaming I have just tried them again and they still don't fit.

As best I can measure, your sockets are 1.85mm wide (code75 bullhead rail is 1.9mm high, and it doesn't fit through).

The chair plugs are 2.0mm wide immediately below the chair base, so it's not surprising they don't fit. They can be forced into the sockets, but that causes the sleepers to swell from 3.3mm wide to 3.5mm wide.

If the sockets were intended to be 1.7mm wide, it seems your laser-cutter is cutting oversize. This is evident in the sockets looking a fraction too long in the other direction. There is a cutter kerf correction available in Templot, it would seem that you may need to increase it.

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 the plug is 6" x 12.5" (2.0mm x 4.17mm in 4mm/ft scale).

The socket dimension (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 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.

How well does the rail fit in your chairs? I'm interested to know if the 2.5 seconds exposure makes any difference.

cheers,

Martin.

 

[Steve_Cornford]

Hi Martin,
You are correct of course, as I made a slight mistake.
I believe I sent you 2 sheets containing a couple of Left Hand B7 OO-SF turnouts and a couple of sections of plain track.
One piece of plywood was 3.2mm thick and only had sockets plus timber labels, the other was 1.6mm thick with both timbers, sockets and timber labels (or in the case of plain track sleepers).
The laser cutting service also supplied me with another piece of 1.6mm plywwod where they had "bunched" a quantity of plain sleepers to show me that by "bunching" the quantity of laser cuts and therefore length of laser cutting overall was reduced, and this dramatically reduces the cost as it is priced mainly by the sum of the lengths of cut.

The two pieces I sent you had been cut from templates exported with -ve adjustment to socket width (from memory -0.25), which when compounded with their quoted kerf of 0.2mm. Based on the theory that their system needed a line drawn in the middle of the kerf, I halved the kerf giving 0.1, but then as there are two kerfs involved in a socket doubled this to give me 0.2mm again. All this theoretically gave me a socket size of 2.0 - 2*0.25 + 0.2 = 1.7mm.
I believe this pre-dated the enhancement to Templot 2D/3D export that added kerf parameters for lasers.

When I went to try out the locators and S1 chairs I made the mistake of using some sleepers from the "bunched" sheet of ply!
Now that you have pointed out your results, I have gone back to basics.

First I measured the height of the nickel silver bullhead rail (obtained from Scalefour stores some 4 or 5 years ago) with a pair of digital calipers and a micrometer screw gauge. This appears to be 1.94/1.95mm.
This rail did not fit in my copies of the sheets I sent you, however it did fit through the sockets of the sleepers from the "bunched" sheet.
These were the sleepers that I used when I used the -0.3mm locator plugs to stick them with gorilla wood glue to the 3.2mm sheet of ply (intended to simulate a laser-cut sockets only sheet of cork underlay).
Having remove the -0.3mm locator plugs I found that the -0.3mm S1 chairs were loose, so then tried the "default" S1 chairs which were a bash fit. Perhaps aided by the fact that the sleepers were glued down.
I measured the width of the -0.3mm locator plus and they appear to be 1.74mm.

I have now gone back to the drawing board and printed a set of S1 chairs and Locator plugs with default settings, and measured the locator plugs before and after curing as being in the range 2.05mm to 2.07mm.
However in doing this I did have to revert the Chitubox software to v1.8.1, as the Mars 2 Pro could not recognice the .ctb file produced by v1.9.4. I tried producing the v1.9.4 file several times but it would not recognise it, despite the day before recognising 1 file produced by v1.9.4. Having convinced myself that it was not something I was doing wrong in the saving or copying process, I googled & found that it was a known problem that either meant upgrading the firmware in the Mars 2 Pro or reverting to v1.8.1, which I did (as it seemd the safer option).

I am still using the default of 2.5 seconds exposure.
(I note that Elegoo seem to recomend 8 seconds for the ABS like grey resin)
I am now in the process of printing another set of S1 chairs and locator plugs, and will then measure these to see if i get any consistancy.

I am thinking that locator plugs are easier to measure than chairs.
I suppose it is the equivalent to etching a 10cm scale
with 1mm increments on an etch design, or for that matter the calibration lines that Templot prints for ensuring our templates are printed to the right size.

Picture of "bunched" sleeper sheet to follow, the design of which was performed by the laser cutting service.

Steve

edited for typos






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