Vac form help

[TK-326]

For those with vac forming experience... I need some help.

I am getting webbing on the corners of the boxes I'm pulling for the TantiveIV hallway set for the R2 room at C4.

See the last two images here:

http://chrislee.tv/vacform/tantiveboxes/tantiveboxes.html

The bucks are 18" x 28" x 5" tall. The sheets are 24" x 48".

The catch is that if I wait for enough sag to get a pull, I get webbing. If I try to pull earlier (less sag to decrease chance of webbing) I don't get a pull cause the plastic never touches the platen enough to form a seal.

I know I can sand down the webs, but I have to make 16 of these, and that's a whole lot of sanding if there's another solution...

Any advice would be appreciated. And yes I know I could cut the buck down to less than 5", but then the boxes would not look right.

 

[Gilmortar]

I think your blank is too small on the sides. Up the 24 to about 36 and you shouldn't get the webbings.

what it is doing is stretching so much from what it doesn't have, that it is cooling rapidly and doesnt have enough time to suck it down

After that, if it is still pulling the webs...take a piece of wood, which I so lovingly call the scraper, and right when you pull the plastic down on the buck, throw that scraper on the side when the plastic is still feasable and it should push that webbing down.

 

[TK-326]

I think your blank is too small on the sides. Up the 24 to about 36 and you shouldn't get the webbings.

what it is doing is stretching so much from what it doesn't have, that it is cooling rapidly and doesnt have enough time to suck it down

After that, if it is still pulling the webs...take a piece of wood, which I so lovingly call the scraper, and right when you pull the plastic down on the buck, throw that scraper on the side when the plastic is still feasable and it should push that webbing down.

Thanks for the advice.

By "blank" do you mean the plastic sheet? If so, that's not really an option since that would require rebuilding the machine to accommodate the larger sheet... :lol

I'll try the "scraper" technique tonite. Problem is, the webbing happens on all four corners, so I guess I'll need four scrapers... wish me luck.

 

[Raffles]

I alway found thinner sheet helps. The shape of the formed structure adds a lot of strength to even the thinnest sheet.

 

[Jumpin Jax]

You might also try it a little less hot, or with a more shallow draw. If the material if forced to stretch rather than droop on the mold, you won't get as much slack that becomes webbing.

 

[kropserkel]

Try placing small spheres slightly away from your corners to draw the 'slack'. Pulling plastic like this is a strange science, and one that might not behave the same way twice. Best of luck with your process!

 

[Jumpin Jax]

Try placing small spheres slightly away from your corners to draw the 'slack'. Pulling plastic like this is a strange science, and one that might not behave the same way twice. Best of luck with your process!

Nice!!!!!!:thumbsup Gonna remember that one.

 

[Bradleyfett]

On a large shape like that, its almost impossible to not get webbing. The only reliable solution is to raise your buck (the 'mold') off the table somehow so that the webs are on material that gets trimmed off.

The best way is to cut a piece of MDF (3/4" or thicker) to the exact shape of your buck.

Combine this with LittleOleBountyHunter's 'scraper' method to push the top of the webbing down before the plastic cools

Mark

 

[Great_Bizarro]

When I was making formed faces for signs, we used to use welding gloves and press the plastic around the mold on the corners to stretch it a bit as soon as it hit the mold, then hold it in place for a min. or so till it is cool enough to take the set.

 

[Boba Binks]

Add 1/4" square dowel rod around the bottom of the buck, like a frame. It helps spread the plastic and stops the webbing as you call it.
I am not sure if this will work for the size you are using but it works for my Clonetrooper Belt Boxes. You may want to go larger with the size you have.