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Dec 20, 2006, 11:24 AM
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Randy Due's Avatar
Question

Vacuum Forming Box Hole Size & Spacing?


From what I've read, the recommended hole size and spacing (for a homemade vacuum form box) is 1/16" on a 1" grid. My box is going to be 12"x18". 1/16" seems small...is this what I should use? Thanks.

Randy
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Dec 21, 2006, 07:44 AM
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I've never bothered with a hole grid. My vacuum boxes are open at the top. The tops are 1/2" Birch Ply taped to the box. This way I can leave a pattern mounted to a top/base and then just exchange tops with different mounted patterns.
1/16" drilled holes are just fine. I use a 6" long 1/6" drill chucked in my portable drill to drill holes, 1/2" apart, around the pattern and then some additional holes 1/2" away from the pattern to pull the material flat around the pattern.
If I need a really good seal, I'll use 1/2" x 1/16" single sided adhesive foam tape around the pattern.
Dec 21, 2006, 09:30 AM
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Very helpful input! That's a good idea. It would save a lot of drilling at one time and stop the need to mask the unused part ot the top. I was planning to use some 3/4" cabinet grade plywood that I'll have left over from making some doors this week in the kitchen remodel. I was wondering if it would work....now I know. What material do you find best for making the moulds? Thanks for the info.

Randy
Dec 21, 2006, 09:36 AM
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LesUyeda's Avatar
I use one hole the size of my vacuum hose, then lay window screen over the area in use to distribute the vacuum. This means you can have a useful area as small as slightly larger than the hole, to the maximum size of the box.

Les
Dec 21, 2006, 09:43 AM
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Quote:
Originally Posted by LesUyeda
I use one hole the size of my vacuum hose, then lay window screen over the area in use to distribute the vacuum. This means you can have a useful area as small as slightly larger than the hole, to the maximum size of the box.

Les
I'm not sure I'm understanding. Are you saying that you drill one large hole in the top, then lay out screen on the top about the size of your mould? Any pics? Sounds interesting. Thanks.

Randy
Dec 21, 2006, 09:44 AM
The Junk Man
Quote:
Originally Posted by LesUyeda
I use one hole the size of my vacuum hose, then lay window screen over the area in use to distribute the vacuum. This means you can have a useful area as small as slightly larger than the hole, to the maximum size of the box.

Les

What he said. I never figured out why people drilled a million holes in the top of their vacuum box. And then have to go and cover them up for all smaller-than-the-box pulls.

Drill ONE hole, trim window screen to the necessary size to accommodate your tool, and Bob's your uncle. For large pulls, I use two layers of screen, but that isn't absolutely necessary.

Tom
Dec 21, 2006, 09:52 AM
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Quote:
Originally Posted by T_om
What he said. I never figured out why people drilled a million holes in the top of their vacuum box. And then have to go and cover them up for all smaller-than-the-box pulls.

Drill ONE hole, trim window screen to the necessary size to accommodate your tool, and Bob's your uncle. For large pulls, I use two layers of screen, but that isn't absolutely necessary.

Tom
Okay, I think I'm getting the picture now. This is all new to me. Most of my stuff has been scratch built foam, up until now....but I'm really needing a more durable material for my AP pods. ABS may be the ticket. My pods will probably need to be about 3"x15". Think the screen method would work? It sounds a lot easier than drilling all those holes. I think I have a roll of metal screen in the shop somewhere.

Randy
Dec 21, 2006, 10:02 AM
The Junk Man
I don't have any pictures, but it wouldn't show much anyway. A box top with a hole in it.

My box has one 1 1/2" (or so, I didn't go measure it, and I drilled it a long time ago) hole. I don't think the hole size is extremely important for the stuff us modelers pull. I'll bet even a smaller hole would do fine.

Tom
Dec 21, 2006, 10:09 AM
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Randy Due's Avatar
Quote:
Originally Posted by T_om
I don't have any pictures, but it wouldn't show much anyway. A box top with a hole in it.



Tom
Yeah, I see your point. Have you ever pulled a part as large as what I'm thinking? I'm wondering how much trouble I'll have, using .06 ABS. Thanks.

Randy
Dec 21, 2006, 10:14 AM
DWFoamies
The screen system that Les uses works great. The woven mesh of the screen allows the air to move through. The screen can be placed over the total area of your former, up to the perimeter seal. I used a woven grid stainless mesh for a large 2x4 vacuum machine and it worked great. Id say a heavier aluminum or nylon window screen would allow enough vacuum to pull the thick ABS sheet, I've used .040 & .060 with no problems. The hole in the center can be the same size as your vacuum nozzle; with a snug fit, you just push the nozzle into the hole.

-Mike
Dec 21, 2006, 10:34 AM
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Quote:
Originally Posted by electric-2000
The screen system that Les uses works great. The woven mesh of the screen allows the air to move through. The screen can be placed over the total area of your former, up to the perimeter seal. I used a woven grid stainless mesh for a large 2x4 vacuum machine and it worked great. Id say a heavier aluminum or nylon window screen would allow enough vacuum to pull the thick ABS sheet, I've used .040 & .060 with no problems. The hole in the center can be the same size as your vacuum nozzle; with a snug fit, you just push the nozzle into the hole.

-Mike

Sounds good! I'm leaving right now to go get some plywood for a cabinet door. After I build the door today, I'll be able to use the scraps for my box. Already have everything else. I think I'll try the screen method...just sounds a lot easier, drilling only one hole. Thanks.

Randy
Dec 21, 2006, 11:01 AM
Registered User
Quote:
Originally Posted by Randy Due
Very helpful input! That's a good idea. It would save a lot of drilling at one time and stop the need to mask the unused part ot the top. I was planning to use some 3/4" cabinet grade plywood that I'll have left over from making some doors this week in the kitchen remodel. I was wondering if it would work....now I know. What material do you find best for making the moulds? Thanks for the info.

Randy
3/4" is a bit thick. After drilling, say 30-40 holes, the drill bit will be burning holes as much as drilling.
I/2" is a bit easier. All my different sized boxes also have a 1/2" dowel for support in the center benieth the top. For my 12" sq. box in the photo, you'll get a sag in the ply when vacuum is applied, so support is necessary.

By "moulds", I assum you mean the original pattern? A mold is what you would make from a pattern. What material? Almost anything you can shape that will hold up to the pressure from the vacuum and the short term heat from the heated mold material. Styrene foams are no good. Balsa is great as is just about any wood that is dry.
Dec 21, 2006, 11:14 AM
The Junk Man
Quote:
Originally Posted by David A Ramsey
3/4" is a bit thick. After drilling, say 30-40 holes, the drill bit will be burning holes as much as drilling....

I think he is passing up the million holes method. One hole is enough.

Tom
Dec 21, 2006, 02:03 PM
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Thanks for all the info! This is all new to me, so I need all the help I can get! It's always nice to hear from people that have already done it. Sorry, the terminology is new to me also. I was indeed refering to the original pattern, when I called it a mould. I was planning to shape it out of wood of some sort...sounds like that will be okay. I think I'll try the one hole and screen method. I wonder if I'll need the additional support under the top if I use the 3/4" ply? Easy enough to add though, so I may just do it anyway. I appreciate everyone's replies. I may have other questions as I proceed.

Randy
Dec 21, 2006, 02:50 PM
DWFoamies
Randy,
No extra support will be needed, the 3/4" ply will work great. Make sure that you get the heavier aluminum or nylon window screen and it's woven. This will allow the vacuum to pass through.
For one off plugs, I use balsa, laminated with white glue if necessary. If it's going to be a critical part, the softer balsa grain will compress and show through the thinner plastics. To prevent the grain from popping, I pull a .010 sheet over the plug, wet/dry sand any profections out and leave it over the plug for your final pull.

Mike
www.BalsaIsBetter.com


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