Help: vac-forming spider webs!

[rogue_artist]

I am working on Death Star Trooper helmets, formed on a 2'X2' vac-machine. I reproduced the comm-box form; making 6 resin copies. But when I set the little buggers on my platen, I got spider webbing from each one to the adjacent.

I reduced it to 4 of the forms, still on a 2'X2' platen. Huge waste of plastic and space, but time is an issue. Even with 4 forms I STILL had spider webbing! What the heck???

What causes spider webbing? How can I stop it?

thank you,
-Jason

 

[Rhett J Martin]

How thick's the plastic?
That may be an issue . . .

Also, how powerful's the suction?

Truth-be-told, you'll always have webbing the on any box of some sort, but you could solve it by putting the box on a wider riser, and with a few holes drilled into the riser, the airflow should take care of the webbing, or atleast move it downward! This worked like a charm years ago when my ghost trap cartriges were vacformed.

 

[CustomCreations]

Its normally due to the following:
A: Your former is too tall or thin, or both, in relation to its width
B: Your plastic is too hot ( it only needs to 'bounce'- not sag.....
C: Your formers are too close together
D: you may need to experiment with air holes , and having your formers mounted on a base.
I often paste this link up but it is a really good source of basic info:
http://www.crclarke.co.uk/Support/pdf/thermo.pdf
ALso, if you have the control over the vacuum pump, and you can see the webbing likely to happen you can stop the process and re-use the sheet.

http://www.crclarke.co.uk/Support/pdf/mould.pdf

Mucking around with the above points should reveal the source of the problem...
HOpe this helps !
D

 

[rogue_artist]

Fantastic, thank you!!!

Im working on .06 smooth-on-smooth ABS. The boxes are (estimating off the top of my head here) probably 6" long by 3" inches wide. Height at the tallest (the problem area) is probably 4 to 5 inches. So yeah, I think you guys have hit the nail on the head with a couple points. The shape most definitely is very tall and thin, compared to the width. I think I was letting the plastic get too hot for another.

I will add block risers with air holes drilled in them. I have also been considering hallowing my resin form where the detail is most demanding and not reproducing well. I doubt .06 will break my forms. Is "form" the correct term?

Its been raining all day. Tomorrow, I hope its nice so I can get out to the shop and have at it once more. Im not one to be so easily defeated! :love

BTW I love Ghostbusters! Im glad to se it become a big costuming thing! I may join you guys one day

 

[Superkrates]

If the the webbing (spiders) is only happening between the parts, it can be eliminated by widening the gap between the parts or using a 'push-assist' before vacuum is applied. Often a gloved hand, pressing on the heated plastic (between the parts) will do the trick. If webbing persists, a custom shaped push-assist can be made from block wood and should be sized to remain away from the part a distance no less than the height of the part where it webs (four parts would need a tool that looks like a 'plus symbol').

 

[Superkrates]

...considering hallowing my resin form where the detail is most demanding and not reproducing well. I doubt .06 will break my forms. Is "form" the correct term?

It's the vac pressure, not the plasic, that will crush your mold if you hollow it out. Just drill some nice small holes (1/16) in the low spots to vent the trapped air - that should bring out the detail.

 

[rogue_artist]

It's the vac pressure, not the plasic, that will crush your mold if you hollow it out. Just drill some nice small holes (1/16) in the low spots to vent the trapped air - that should bring out the detail.

Ah! Okay. Thats easier then hallowing it out too