Rigid filament for very thin parts

Help with printing with specific plastic filaments.
idiot
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Rigid filament for very thin parts

Post by idiot » Sat Apr 16, 2016 7:58 am

Hi, I'm making a speedo needle for a friends classic car, I tried a test run in Alloy 910 and given how thin the needle is at the end, I feel it had too much flex and would probably bend when stopped and resting on the stop bar.

Other potential filaments I have already are ABS and PLA which I hope will do the job although I think PLA has the risk of softening in the summer sun and ABS might still be too flexible on the thin point.

He's passed on a couple of other people from the owners clubs he's joined to me, some who want clear needles, so I'm thinking T-Glase or polycarbonate could be potential filaments, although I've never used either and don't know if they're easy enough to print with at such small dimensions or if they'd be up to the job.

I've bought a .3mm nozzle to make them with, as the .5mm couldn't go thin enough to print them of sufficient quality, at least not with a910.

Any recommendations would be most welcome, thanks.

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piercet
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Re: Rigid filament for very thin parts

Post by piercet » Sat Apr 16, 2016 9:18 am

A spedometer needle is going to be extremely difficult to 3d print. You are almost certanly either going to need to make it thicker than the stock one, or attempt to print it out of polycarbonate. Polycarbonate is not easy to print. T-glase is basically PLA, which will have the same melting concerns.

You may be better off printing mold masters. then casting a silicon mold over them and then using that mold to cast epoxy resin replacement parts. I think thats the only way you are going to get sufficient strength.

idiot
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Re: Rigid filament for very thin parts

Post by idiot » Sat Apr 16, 2016 9:36 am

Thanks for the reply. I think you're probably right, molding and casting isn't something I've tried yet but it's certainly something I've been interested in trying for a number of parts I've got waiting in the pipeline.

Do you think polycarbonate will be up to the task? Can it be printed with a .3mm nozzle?

I've also seen another filament called HD Glass, which looks like it's a modified PETG, but claims high toughness and low elasticity. I've never used PETG but it's my understanding that it's quite a flexible, bendy material.

I've read about people using alloy 910 for making threaded bolts which are claimed to work well, I'd have thought if it works for threads it would work for the needle, which is .5mm W x .33mm H at the tip (almost certainly thicker than a thread) but it had quite a bit of flex in it. I'm going to send my friend some printed with it anyway to see how it works but I have my doubts.

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piercet
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Re: Rigid filament for very thin parts

Post by piercet » Sat Apr 16, 2016 9:45 am

Polycarbonate is difficult to print mainly because of the moisture issues and warping issues. If you get it hot enough, it should go through a .3mm nozzle. You may even be able to make it go through an even smaller nozzle if you can find one, which you might need to do for this application.

The main issue you are going to run into with other fillaments is the lower melt point. In a hot day inside a car dash, things get extremely warm. Something that thin with a lower melt temperature is just going to droop or even puddle.

idiot
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Re: Rigid filament for very thin parts

Post by idiot » Sat Apr 16, 2016 10:09 am

I live in Britain so temperatures may not be as extreme as in the US, although it's sure to get fairly warm locked in the dash anyway in the summer sun or in the winter with the blowers on. Point taken though, as mentioned in my OP it's something I'm worried about, PLA is probably ruled out.

I'll look into the difficulties of printing polycarb, it may be unfeasible if it saturates like the nylon filaments. The unit where my printer is traps a lot of moisture, I had to build a dry box I bring home with me every night just to print alloy 910 properly.

With regards casting epoxy into a mould, would it really be essential to remould off a print out of silicon? Couldn't I just print the mould from nylon (or alloy 910) which epoxy doesn't bond well to anyway, and spray it in the stuff they spray injection moulding moulds with, which I believe is silicon based?

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piercet
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Re: Rigid filament for very thin parts

Post by piercet » Sat Apr 16, 2016 10:45 am

You can print the mold, you are going to have the fine detail of the layer ridges present in the resulting cast. You would likely get a superior final part by printing one part, filling, sanding and coating in clear until it is smooth as glass, then taking a silicone mold of it. For a small part like that, you can use automotive RTV silicone transmission seal stuff to make the mold to hold down costs though. Just need to find a suitable mold shell and a flat piece for the top, or cast a 2 parter, etc.

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Re: Rigid filament for very thin parts

Post by ttabbal » Sat Apr 16, 2016 11:51 am

If you are making a mold anyway, how about ABS with acetone smoothing before making the mold? Unless there is small detail that might be lost, it might be a good way to get a smooth part to start from.

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Re: Rigid filament for very thin parts

Post by idiot » Sat Apr 16, 2016 2:48 pm

I was actually thinking of cutting corners even more and printing the mold cavity at .1mm bigger in all dimensions and using filler primer to remove the lines. That's if I print the mold itself.

I'm interested about making a silicone mold from a master part. Has anyone on here done it or can point to a decent guide?

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Re: Rigid filament for very thin parts

Post by piercet » Sat Apr 16, 2016 3:56 pm

I've done more than a few of them. I usually make 2 or more part molds, so I start with a mold frame made of rectangular Lego blocks. You want a shape that you can flip over, so its better to make a fully symmetrical box than to make an odd shape. Once I have the box with at least 20mm worth of margin around the part, I then build a base of modeling clay, press the part in about halfway ( or to a natural separation point) and then use a piece of hot glue gun stick to make a pour spout, and 2 scrap pieces of 3d printer filament to make air vents. I also use a few small marbles to make mold alignment marks.

Once that all looks right, I pour silicone into the mold, covering the piece by at least 20mm. Silicone only sticks to silicone, so you don't need to prep the part aside from making sure it is smooth.

After the silicone sets (8 hours +/- 4 depending on size, type of silicone, amount of hardener, etc) you pull the completed mold half out, remove all the clay and the marbles, but leave the vent pieces, pour spout form and the part itself. Put the entire mold half back in the Lego frame with the silicone on the bottom

Next liberally coat the entire silicone mold surface with petroleum jelly. This will cause the new silicone mold half you are about to pour not to stick to the one you already made. Pour new silicone and allow it to set.

Now you should have a completed mold. Separate it carefully, trimming any stuck pieces of silicone with scissors. Remove the mold core part, the vents, the pour spout core and then use a sharp pair of scissors to ensure the pour spout and vents are totally clear of obstruction. Your mold is now mostly ready. Usually at this point I cut a set of thin plywood or partical board mold support sidewalls and find some clamps to keep the mold together.

If you did it right, you should have two or more mold sections that lock together using marble shaped tabs. You can now pour almost any castable plastic or resin into this mold

There are a bunch of good tutorials on the process on Youtube or instructables. For a simple part with a flat side, you can just use a plastic bottle a bit bigger than the part, cut it in half, fill it with silicone and press the part into it, flat side up. I generally prefer a two part mold even in that scenario to get a better final surface quality.

Once you get more proficient you can play with adding dyes and metal or stone powders to your resins and make things that feel like metal parts, etc.

idiot
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Re: Rigid filament for very thin parts

Post by idiot » Sat Apr 16, 2016 5:43 pm

Wow, that's a great write up, thanks a lot.

I think that details just about everything, I'm only left with one or two questions.

Do you allow the clay to harden before pouring the silicone over it or can you do it straight away whilst the clay remains soft?

The air vents I assume should be up near the top of the mold near the pour hole? Also, considering a piece of 3mm filament is probably wider than 80% of the needle itself, would some pieces of thin wire suffice?

I would assume it will be difficult not to over fill the mold, causing some resin to overflow out of the mold cavity and into the air vents/pour hole? Causing there to be some sort of sprue which will need cutting off the finished product?

Last but not least, would there be any advantage using a syringe to fill the cavity under pressure, also eliminating a lot of the potential for the resin to overflow up the pour hole?

Thanks so much for your help and advice.

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