Mould making

[sheldon@dingwallguitars.com]

I need to make some simple male/female molds for thermoforming 1/16" ABS.

The shape is a rectangle roughly 1.25" x 4" x .75" deep.

Any suggestions for the angle of taper needed for the sides?

I plan on using aluminum for the moulds, but if I were to try vacuum forming, what material would be best. MDF?

[jgraphic]

Sheldon,

Check out this site for info.

http://www.dow.com/engineeringplastics/tech/guide/display.htm?guide=draft.htm

[donchandler]

Sheldon,
If you are going to use the aluminum M/F molds to press mold the parts, you will need to heat up the molds. If you don't, the cool alum. will suck the heat out of the thin plastic and it will not form or it will cold form due to the force you put on it. This will make some some bad parts. If you are going to press form, use something that is a very poor conductor of heat for the molds. If you are going to vacuum form, aluminum is OK, but you will still have to warm it up some. Otherwise you will throw away parts until the mold has picked up enough heat from the parts, to start working. The vacuum form will not need much draft, since the plastic will shrink upon cooling and come out of the mold easily. (I assume you were thinking of drawing into a female mold)

[gfacer@istar.ca]

Sheldon,

look at http://www.empirewest.com/academy/index.html

This is a good site for design considerations. I haven't read it in a while, but should have the info you need. Jerry's site deals with injection molding. You will need more than 1/2 degree. We use 5% (I think....might be 7%) for the projects we do. Unless you're doing lots of parts, just use MDF sealed with thinned out epoxy (best) or fiberglass resin.

For large runs, aluminum is the way to go.

[gfacer@istar.ca]

Hi again,

That should be 5-7 degrees, not %,

Greg

[sheldon@dingwallguitars.com]

Thanks guys, that's exactly the information I needed. I'm going to try vacuum first.

Any suggestions on how to make a small frame less than 2' x 2', to hold the sheet as it's heating and then provide a seal for vacuum?

Also, I have a couple of vacuum pumps that although can achieve 25" of vacuum, provide much cfm, how practical is a Shopvac?

[gfacer@istar.ca]

Sheldon, how thick is the material (what is the material)?

You don't always need much CFM, and a tank set-up will have the same effect if you do. A shopvac will work OK for some stuff, probably need to get the sheet really good and hot, but I haven't tried it.

As for the frame, for small runs, make it from anything from MDF to angle iron (recommended), and clamp the sheet in. The trick is to get the sheet sealed. Normally this is done with the sheet itself, streching the edge over the edge of the mold. It the top of the mold is flat, you either will be ok or maybe use weather stripping as a one-per-pull sealing aid. Otherwise, two pairs of hands to pull over the form?.... a proper machine as rails that allows the sheet to come straight down with some force behind it.

Greg

[odysseywood@home.com]

Sheldon:
Here is a link to a web site that has information on vacuum forming and thermoforming. They also sell plans for several vacuum forming machines.
http://www.build-stuff.com/

[garbob]

An excellent book on diy vacuum forming is available from Lindsay books in Illinois (815) 935-5353 or their web site http://www.lindsaybks.com/ - they also have tons of OLD books (reprinted) on things like forges and all kinds of lost technology.

The vacuum forming book is one of the best teaching aids that I have ever seen. Includes how to set up two vacuum cleaner motors in series and also a high vacuum source (old bicycle pump, real vacuum pump, a tank that has had the air pulled from it using your car's manifold,etc). Types of materials are discussed with sources. Temperatures to use and how to build vacuum boxes, molds and frames. The neat part is this book recommends using your kitchen oven.

A superb book!

[flyboy]

I'm working with a vacuum forming company to make a gaming table male mold. They said it didn't need any draft angle. Go figure. I'll post more when I see that it worked but they do a lot of work for 30 years now so it must be right.

[Wdyasq@yahoo.com]

Tom,

I think the plastic must 'shrink' BUT, will you please explain the reasoning if/when you find out?

Ron Brown - wdyasq@yahoo.com (mailto:wdyasq@yahoo.com)

If Stupidity got us into this mess,
then why can't it get us out? - Will Rogers

[gfacer@istar.ca]

If its big enough of a piece it'll just pop out due to the flexibility of the material itself. That's my bet

Greg

[flyboy]

More on that vacuum formed gaming table project "without draft angle". Well, it turns out that this post is making me look a lot smarter than I am because when they pulled the test piece for the chip holders they didn't release well. So the 30 year veteran changed his mind about needing a draft on the mold. Now we are sanding some draft by hand.