www.TK560.com

[RFC]

Went ahead and tried my first pull of the .020" flocked styrene. I was pretty happy with the results but I am experiencing the common problems from what I have read.
I have webbing in the corners:





And even though I am using dual vacuums (a 4 hp shop vac & a decent canister vac) I am not getting crisp tight inside corners.
I am heating the styrene in a gas oven for 4 minutes at 300 degrees and achieve about 2.5 to 3" of sag across the sheet:



Here is a shot of the plug I made which will form liners for display cases I build.





Also, here is a shot of the table or platten that I fabricated.



Any help would be appreciated. Thanks, Bob
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Cheers, Bob

[Fredo]

Bob, search "webbing", there are a lot of threads that address the problem your having, and ways to prevent it....
I'm surprised how well the flocking holds up, what a quick easy way to make display trays for any shape you want. Guns, knifes, whatever needs displaying..... Never thought of using flocked plastic........Fredo
_________________
If someone has a gun and is trying to kill you,
it would be reasonable to shoot back with your own gun...The Dalai Lama..Seattle 2001

[Fredo]

Bob, your platen will seal better if you add some 1/2" weather stripping to the platen were frame contacts the platen.... Don't strech the tape when you put it down, over lap at the corners, and cut with a razor blade. Perfect fit every time..............Fredo
_________________
If someone has a gun and is trying to kill you,
it would be reasonable to shoot back with your own gun...The Dalai Lama..Seattle 2001

[RFC]

Thanks for the tips Fredo, so you feel that I may be loosing some vacuum around the plastic frame. Ok, its worth a shot. I guess the next step is to raise the plug with a spacer maybe a half inch and see if that moves the webbing down farther on the part.

What if I taped off the outer area of vacuum holes only leaving a row around the plug? Would that help to draw the plastic tighter to the bottom of the plug on the outside. I need that area to be a crisp tight corner.
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Cheers, Bob

[spektr]

Ok. you need a spacer under the tool. it probably needs to be at least an inch tall and beveled 45 degrees. The base needs to be larger than where it contacts the tool. The webbing is due to poor tool design.. easily Fixed.. Also note that vacuum forming is a stretching process and that webbing is where you are trying to pull plastic down where it is overstretched. give us better pics of your tools.. oh yeah, the frame should never sit on the platen.
if that happens the frame is too small. the vac shutoff is established between the plastic sheet and the platen face.

[RFC]

Spektr, I have included some close ups of my frame and platten. The platten surface is 1/2" above the stop for the frame. The bottom
frame is 1/4" thick and the top frame is 1/8" thick so when the plastic is hot and the frame is lowered, the plastic makes a good tight seal against the platten.




There is about a quarter of an inch of platten sticking above the center line of the clamping frame.



As far as the tool is concerned, I don't know what better pictures I could give other than what I have shown already. It is really nothing more than a tray type design. The tool measures 7" x 11" x 1". And I copied it from an old existing example that I had for design and measurements.




So this spacer should be tapered like a pyramid? I can make it an inch tall but how much bigger than the base of the tool should it be?
Any suggestions as to how to get the sheet to pull tighter in the inside corners?
Thank you for helping me with this, I do appreciate it.
_________________
Cheers, Bob

[spektr]

Yes , the spacer should be shaped like a pyramid. this gives the plastic somewhere to go and almost always handles webbing. As far as getting tighter corners, you need real vacuum. Shopvacs and vacuum cleaners get you maybe 4 inches of vacuum, they are all about volume and not suction. REAL vacuum pumps with tanks and plumbing are easily above 25 inches. You should also look at how well you sealed the tooling. You wont notice it with shop vacs, but small leaks will terrorize you at higher vac points. I suggest you use a few coats of shellac on anything that doesnt touch plastic, it plugs porosity in wood and mdf well. Silicone window caulk also does amazing things..

You also might make it easier on yourself by removing 1 frame guide leg from the vacuum box. you dont need it. Move in this way. push it against the back, slide it to the right until you hit the post, go down. this is simpler than being real accurate to get all the guides at the same time. Speed to tohe platen matters.....

Scott.

[RFC]

Thanks again for the tips. I want to build the spacer for the tool next. Should I make the top of the pyramid the same size as the bottom of the tool or should it be like a half inch bigger all around and then taper down from there?
_________________
Cheers, Bob

[spektr]

You are looking to do 2 things.. To stop webbing AND perhaps even more important, establish the Part Trim Line. Its's a bitch to cut a 90 degree transition well, 45 degrees however is a snap. SO let the 45 degree spacer be your friend. Make it the same size as the base of the tool and 1 inch larger at the platen face. 3/4 inch will work also if you cant find 1 inch mdf anywhere. That should get you home free....

When you design tools, try to remember that you need to cut them out of the blank, so make it easy on yourself and use angles to create parting planes and aid the plastic in forming without turning 90 degree corners....

Its in the setup Baby....

Scott.

[RFC]

Scott, thanks for the education. I am gluing up some wood tonight and will trim to size and cut the bevel tomorrow.
_________________
Cheers, Bob

[jdougn]

Interesting project, how's it coming along with the webbing.
dn
_________________
DougN - Just in case you're wondering, I got my "rating" legitimately... by posting aimless drivel, useless advice, and pointless questions.

[RFC]

Two things to report.
First, I glued up some cabinet grade plywood I had laying around last night to make the 1" thick riser. Bad move! Tonight I tried to saw the bevel and the saw just shredded the top layer of the plywood laminate. Looked like crap and I should have known better. So I will have to get a piece of MDF as you suggested and try it again.

Secondly, I am remaking my tray insert tool. I did not like the overall size of my finished part....slightly small all over. I already have the parts cut and glued up. If I am going to do this correctly, I better get my tooling right on before I finish size the riser.

Give me a couple of days guys, I gotta work for a living and this is my hobby so only have a couple of hours at night. Saturday I'll give er' hell.
_________________
Cheers, Bob

[spektr]

Just sand the plywood, the angle isnt critical and the surface finish is outside the finished part trim line.. Make it EASY on yourself As far as making the tool smaller, depending on how much smaler, belt sand or plane the outside edges. If the wall around the tray gets too small, add a small strip of material to the outside edges.. Superglue and Hobbyshop basswood or plywood will space the OML edges outboard for you..

KEEP IT SIMPLE.....

Scott.

[RFC]

Scott, the problem was that the tool was too small.... I thought the finished flocked tray insert would finish larger but it was too loose in the wooden display case.
I have already completed the new tray insert tool and the finished part size should be right on.

Sat. I will complete my riser and and try another pull. I do understand the K.I.S.S. principal but I over do everything...detail freak I guess
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Cheers, Bob

[jdougn]

Hey Bob, how does this liner fit into the display case? Does it fit tight to all 4 sides or is it free standing?
dn
_________________
DougN - Just in case you're wondering, I got my "rating" legitimately... by posting aimless drivel, useless advice, and pointless questions.