Buck for vacuum forming

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fragarock

New Member
Hi,

I'm starting my research into vacuum forming a lens for a helmet that I'm working on and would like your input.

I have a model that I can 3d print for the buck. Given the higher temps that are involved in melting PETG for the lens, is there a suitable 3d filament that could hold up to the temps without melting?

Or after printing and cleaning up the buck, I could cast it in a resin if that would maybe be more durable.

Thanks for the help.
 

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computergeek

Active Member
I've never personally vacuformed off a raw 3D print, but if you used a filament like ABS or PETG, hollowed the model out, and filled it with plaster, it may work a few times. I believe the forming temperature is going to be less than the melting temperature that the printer uses, but the buck will not live nearly as long as resin.

If you're looking to do a production run, molding and casting in resin is definitely your best bet. It gets expensive though
 

fragarock

New Member
I've never personally vacuformed off a raw 3D print, but if you used a filament like ABS or PETG, hollowed the model out, and filled it with plaster, it may work a few times. I believe the forming temperature is going to be less than the melting temperature that the printer uses, but the buck will not live nearly as long as resin.

If you're looking to do a production run, molding and casting in resin is definitely your best bet. It gets expensive though
This would be to make 5-10 lenses, figuring the first few will be throw away as I test the process.

I like the idea of casting in resin just for the experience of learning how to do it.
 

Psicorp7

Sr Member
RPF PREMIUM MEMBER
If you are doing your own printing, you can print a negative mold. Then give it a nice coat of mold release and pour your Ultracal into it. If you design the negative mold to come apart correctly you could probably reuse it too.
 

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lmgill

Sr Member
While the 3d printing a mold is clever, if your print isn't perfectly smooth, your vacuum forming tool (buck) will not have a perfectly smooth surface, which will be an issue when trying to make a clean visor in clear material. You can sand and smooth the gypsum, but this is time consuming and these material are not easy to sand.

Another option,
Make your positive 3d printed buck, vacuum form a thin piece of styrene over it (.030"), trim the pull to the bottom edge of your buck, then pull a thicker piece (.090") of styrene over that. Now take the thicker pull and pore some type of gypsum into it. (hydrocal, ultracal, hydrostone...)
The first thin pull will help smooth out you buck.

You can use this technique for either material choice for your finished buck. Just remember to apply some type of wax and mold release to the styrene if you use something other than Gypsum.

Material choice for the buck:
The advantage of a gypsum over plastic is you can preheat the gypsum and this will assist in getting a smoother pull in your clear material. We use Hydro-stone often for thermo-forming tools. It's very hard and when fresh, carves very nicely.
The advantage of plastic/ resin (I would use a Bondo/resin mix, filled with rigid foam) is you can sand and add to it with more bondo.
 

flimzy

Sr Member
I wouldn't vacform a 3D print, the heat even with thin sheet permeate into the mold/buck you'll get rounded corners if not collapse in no time. I have a Formech machine so maybe with a homemade vacuum cleaner machine the pressure would be less and you don't have to worry about things like using plaster. Never use plaster in a professional vac former unless it's been oven-dried, the heat and vacuum will suck the moisture out of the buck and it will sit in your pump (rust trap) for long-lasting bucks Devcon epoxy is the closed to having a metal mold. one good trick for lens or glass-like part is to first suck over a.25mm sheet this can give you a cleaner surface. or another way is to cover your buck in velvet.
 

lmgill

Sr Member
I wouldn't vacform a 3D print, the heat even with thin sheet permeate into the mold/buck you'll get rounded corners if not collapse in no time. I have a Formech machine so maybe with a homemade vacuum cleaner machine the pressure would be less and you don't have to worry about things like using plaster. Never use plaster in a professional vac former unless it's been oven-dried, the heat and vacuum will suck the moisture out of the buck and it will sit in your pump (rust trap) for long-lasting bucks Devcon epoxy is the closed to having a metal mold. one good trick for lens or glass-like part is to first suck over a.25mm sheet this can give you a cleaner surface. or another way is to cover your buck in velvet.

I have never had any of these issues and my 40 years of thermoforming.
The amount of heat in styrene (the thicknesses I referring to), will not transfer enough heat to the printed part to be any issue what so ever (provided you are not pulling many parts one after the other), and provided the part is printed with internal support, crushing it will not be an issue.
While moisture may be a slight issue, unless you were doing production runs all the time with plaster, not an issue at all. Moisture would transfer into the storage tank, not the pump, as the pump, while in operation, is consistently transferring air through itself.
Would not cover you vacuum forming tool in velvet (only 100% silk). This works for drape forming, (wool felt work better) but vacuum forming is too hot and would leave mark off on the part.
 

zorg

Master Member
I've vac formed many petg pulls, the temp you need is way below the temp the 3d print materials need to melt.

The number one tip I can give is the buck needs to be PERFECTLY smooth. 1 spec of dust will show as a bump in the petg. Any blemishes at all will be transferred to the lenses and spoil it.

I would 3d print a negative like piscorp7 suggested, cast a plaster buck and sand it super smooth.
 

flimzy

Sr Member
I have never had any of these issues and my 40 years of thermoforming.
The amount of heat in styrene (the thicknesses I referring to), will not transfer enough heat to the printed part to be any issue what so ever (provided you are not pulling many parts one after the other), and provided the part is printed with internal support, crushing it will not be an issue.
While moisture may be a slight issue, unless you were doing production runs all the time with plaster, not an issue at all. Moisture would transfer into the storage tank, not the pump, as the pump, while in operation, is consistently transferring air through itself.
Would not cover you vacuum forming tool in velvet (only 100% silk). This works for drape forming, (wool felt work better) but vacuum forming is too hot and would leave mark off on the part.
IMG_1105.JPG
I've only been doing it 3o so year so I dow to your superior knowledge
 

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wtyler3

Active Member
RPF PREMIUM MEMBER
I have about 10 different helmet visors I need to form. All have 3D printed bucks.
I got a small former that is made out of wood and uses a shop vac. The sheet holder is MDF, and I believe that in order to get a proper heating of the sheet in an oven the temp needs to be around 280 degrees? That temp came form several folks I know who do it like this.

MDF will survive that kind of temp? feels like I need to re build it out of AL....
 

Duncanator

Sr Member
I have used wooden sheet holders with success. I wouldn't use them for mass production tho.
You do have to watch out for them getting too hot. I don't know what the flash point for MDF is, but that is something to keep in mind. They also can warp from the heat as well - yet another reason why they aren't the best.

Short answer: Yes, wood can work, but be careful.
 

wtyler3

Active Member
RPF PREMIUM MEMBER
Thanks for the reply. I really need a solid former but at the price point I would have to make one and I dont have the time for that these days.

The Centroform seems to fit the criteria but 1500 bucks for the unit without the pump, etc seems a lot to pay... I cant figure out why they are so expensive.
 

Duncanator

Sr Member
Thanks for the reply. I really need a solid former but at the price point I would have to make one and I dont have the time for that these days.

The Centroform seems to fit the criteria but 1500 bucks for the unit without the pump, etc seems a lot to pay... I cant figure out why they are so expensive.

It's a specialty product, and liability is a factor.
 

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wtyler3

Active Member
RPF PREMIUM MEMBER
Well, I tried it out today and it worked!! I actually got a test lens.
I left the sheet in the oven too long so had to peel it off the rack, Maybe 5 mins at 280 for .60 PTEG sheet... So need ot dial that time in the oven in a bit. I could not see the droop in the sheet.
So the question now is,
1. What do you guys use to cut out the lens from the sheet? I used a dremel, but now need to buff and polish the edges to make them look ok I presume?
2. What is the secret to getting a nice clear lens to see through? Am I using to thick material?
 

HyePo

New Member
I have never had any of these issues and my 40 years of thermoforming.
The amount of heat in styrene (the thicknesses I referring to), will not transfer enough heat to the printed part to be any issue what so ever (provided you are not pulling many parts one after the other), and provided the part is printed with internal support, crushing it will not be an issue.
While moisture may be a slight issue, unless you were doing production runs all the time with plaster, not an issue at all. Moisture would transfer into the storage tank, not the pump, as the pump, while in operation, is consistently transferring air through itself.
Would not cover you vacuum forming tool in velvet (only 100% silk). This works for drape forming, (wool felt work better) but vacuum forming is too hot and would leave mark off on the part.
somehow i double posted.... please see next post
 

HyePo

New Member
I have never had any of these issues and my 40 years of thermoforming.
The amount of heat in styrene (the thicknesses I referring to), will not transfer enough heat to the printed part to be any issue what so ever (provided you are not pulling many parts one after the other), and provided the part is printed with internal support, crushing it will not be an issue.
While moisture may be a slight issue, unless you were doing production runs all the time with plaster, not an issue at all. Moisture would transfer into the storage tank, not the pump, as the pump, while in operation, is consistently transferring air through itself.
Would not cover you vacuum forming tool in velvet (only 100% silk). This works for drape forming, (wool felt work better) but vacuum forming is too hot and would leave mark off on the part.
I have read your suggestions and will attempt to do similar. I too have been trying to make bucks w/o having to have them cnc on aluminum which is way too costly for the small production runs I do. I have built my own machine (its a variant of the HobbyVac) where its 220v 12x24 which I use to produce various car dash panels for gauges... I am having the buck positive printed now (was going to use silicone mold and then try various substrates until I found one that would not warp. I used a silicone mold and some BJB metal filled epoxy resin and it still bowed up after first use.. I need the bucks to lay flat on the platen. I also do not use a tank in my machine, the two-stage 12cfm pumps pulls near 29.7 direct, although I do find myself changing the oil quite often. thanks for the suggestion. can't wait to try it all out.

12x24-Former.jpeg
 
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Pro Mod

Well-Known Member
RPF PREMIUM MEMBER
I have about 10 different helmet visors I need to form. All have 3D printed bucks.
I got a small former that is made out of wood and uses a shop vac. The sheet holder is MDF, and I believe that in order to get a proper heating of the sheet in an oven the temp needs to be around 280 degrees? That temp came form several folks I know who do it like this.

MDF will survive that kind of temp? feels like I need to re build it out of AL....
280 degrees rather too hot! Cast acrylic forms around 160 deg C, extruded 170 deg C, and PET 82 deg C.
 
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