vac forming?

[raser13]

hey guys, got a few noob questions for the masters. i've put together a few vac form models and really like them. i see all of these small resin models being sold for some pretty large prices when compared to regular models. large scale resin models go for crazy amounts. now i realize the cost of resin and silicone makes the prices correct for what they are. i have no problem with that.

what i'm wondering is i want to make some larger scale models, for myself. but i want to make several copies. i've been thinking of getting into vac forming for a while.

first are there plans somewhere for a fairly cheap and decent diy vac former? i need one that can be made compact. i live in an apartment and space is premium. secondly is a male or female mold better for details? and is there something to do to the master to get the plastic to pull into the corners and details.

is there any reason that the guys that do larger models don't vac form the major assemblies and then do resin for the smaller details to save on cost for those larger models?

[raser13]

also would things like clay and silicon molds be able to stand up to the vac forming process with out distorting?

[naoto]

http://makezine.com/projects/make-11/ki ... um-former/
http://makezine.com/2011/09/08/how-to-l ... g-machine/

[Kylwell]

also would things like clay and silicon molds be able to stand up to the vac forming process with out distorting?

Clay maybe, silicon probably not.

With clay the problem is the heat from partially melted sheet. An air hardened clay would be fine. Your usual modeling clays would lose detail between the heat & the draw.

Silicon could handle the heat but would deform during the draw down.

[raser13]

thanks for the info guys. got another one that i thought of while sleeping last night.

you are drawing heated plastic around what ever your master is. would you be able to vac form over a styrene kit part? or would it melt/warp/damage it? and resin doesn't like heat either what about it? is the forming process quick enough that the plastic cools before it can really do andy harm?

i've noticed on the vac formed models that i've done small little "pips" in the corners and in smaller detail spots. did the masters have small holes drilled into them to make the vacuum pull the plastic into these spots better? or am i just getting the wrong idea about this.?

[Johnnycrash]

Plans:
There are more plans available on the net alone than there are people who have built vac-forms. So, you can pick and choose the features you want/need/can afford. Just google search "vacuum former plans".


Bucks:
Female bucks (molds) are always better. But are harder to use. And in most cases, with female molds, it is better to blow mold, than vac mold. That is, you blow the plastic into the mold from above, compared to sucking the air out from below. This is better for the detail, as it tends to be soft when made from a male buck. Thin plastic is easier to form than thicker plastic. The thicker the plastic, the more rigid the part, the softer the detail.

Small holes can be drilled into the bucks to help the plastic lay down nice and snug, and get into those corners and such. The pips are easy to sand off.


Resin details:
Adding resin detail parts to vac-form parts IS a good way to do it. Although, with the flexibility of the styrene, the parts can have a tendency to pop off. So, add the details AFTER the vac-form has been reenforced and sturdy.


Buck materials:
The buck should be made from something hard, and heat resistant. A sealed hard wood, plaster, concrete, metal impregnated resins, and dental stone are good choices. Styrene parts are NOT. They should also be solid, or as strong as possible. You don't want the buck to collapse.


Drawbacks of vac-form:
Removing the part from the backer-sheet - cleanly resulting is a usable part, amount of scratch-building still need to join and reenforce the parts, low/soft details,

[raser13]

thanks johnny, great info i appreciate it.

[Kylwell]

There's nothing quite like the joy of getting a perfect pull only to find it's locked the buck into the plastic.

[Johnnycrash]

There's nothing quite like the joy of getting a perfect pull only to find it's locked the buck into the plastic.

Oh yeah, forgot to mention: NO UNDERCUTS. EVER. Or truely vertical sides.

[modelnutz]

Unless you use a 2 piece female mold

[Kylwell]

There's nothing quite like the joy of getting a perfect pull only to find it's locked the buck into the plastic.

Oh yeah, forgot to mention: NO UNDERCUTS. EVER. Or truely vertical sides.

Yep.

Oh, and your pull will be as detailed as your buck. Seal & polish it if you don't want wood grain or thumbprints to show.

[b5ranger99]

you are drawing heated plastic around what ever your master is. would you be able to vac form over a styrene kit part? or would it melt/warp/damage it? and resin doesn't like heat either what about it? is the forming process quick enough that the plastic cools before it can really do andy harm?

i've noticed on the vac formed models that i've done small little "pips" in the corners and in smaller detail spots. did the masters have small holes drilled into them to make the vacuum pull the plastic into these spots better? or am i just getting the wrong idea about this.?

My first attempt at copying a styrene canopy resulted in the canopy being distorted, since then I always make resin copies of styrene parts and form over the copies.

The small pips around detail parts may be holes drilled in the part or careful placement on the support surface to get good draw down. Also be sure the edge you want to cut is above the support surface, e.g. I add a small (.010") support to all my masters. This is usually enough to to give a clean edge but not enough to trap the master in the sheet.

Good luck.

[Kylwell]

It's best to reenforce the styrene parts. Easiest way to do that is fill it with Aves or some such but that will mean the original can't be recovered.

[raser13]

basically what i had in mind was doing a set of 1/350 sized stargazers in a few different configurations. so the styrene part that i would be copying would be the top of the saucer section on a 1/350 enterprise. i didn't know if the styrene would be thick enough to be able to take the heat and vac forming process. i didn't know if i could hit it with a mold release and have it work. or if the plastic would cool down fast enough not to distort something that thick.

would plaster of paris work well as a mold? just trying to keep costs down while i get used to doing this.

[raser13]

basically what i had in mind was doing a set of 1/350 sized stargazers in a few different configurations. so the styrene part that i would be copying would be the top of the saucer section on a 1/350 enterprise. i didn't know if the styrene would be thick enough to be able to take the heat and vac forming process. i didn't know if i could hit it with a mold release and have it work. or if the plastic would cool down fast enough not to distort something that thick.

would plaster of paris work well as a mold? just trying to keep costs down while i get used to doing this.

[Kylwell]

Depends on how much draw and how thick of vacc plastic.