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HELP !!! What am I doing wrong ?

Old 07-13-2007, 02:36 PM
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Campy
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Default HELP !!! What am I doing wrong ?

What am I doing wrong here. I am trying to vacuum form some wheel pants. I am using .060 PETG. Vacuum is from a 10 gallon shop vac. I am letting the PETG sag about 2 1/4" - 2 1/2" before putting it over the plugs. I have tried twice and both times I have gotten wrinkles. I sprayed the pants to show the wrinkles.

Thanks
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Old 07-13-2007, 03:22 PM
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Ed Smith
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Default RE: HELP !!! What am I doing wrong ?

The plugs are too close together.

Try forming one at a time.

The plastic may be too hot and is falling over the plugs rather than being pulled.

Try warming the plugs if possible, this will prevent the plastic from cooling before the vacuum can push the plastic down.

A soon as the plastic touches the plugs the edges of the sheet must be sealed against the vacuum box.

the sheet must be placed on the plugs with no twisting movement, straight down.

That is about all I can think of right now.

Ed S
Old 07-13-2007, 06:02 PM
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Default RE: HELP !!! What am I doing wrong ?

I agree, plugs need to be seperated as much as possible and the whole thing warmed up befor the vacuum process is started. Have done some with pre-preg fiber glass and it needs lots of wiggle room for the excess materials to get out of the way!
Old 07-14-2007, 05:47 PM
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Default RE: HELP !!! What am I doing wrong ?

Thanks guys. The problem was the plastic was too hot. Once I reduced the sag to about 1 1/2" I had no problems. Actually, with the use of a heat gun, I was able to make both sides at once AND they came out exactly right.

I have another question.

My plugs for the pants have a slight taper from the top towards the bottom (the bottom being slightly larger than the top ). I am having a devil of a job getting the plugs out after the forming. Could it be the PETG is too thick (.060 ) ? Any suggestions for getting the plugs out ?
Old 07-14-2007, 07:15 PM
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Ed Smith
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Default RE: HELP !!! What am I doing wrong ?

Are they stuck or locked in.

Trim off all excess plastic right up to the seam line. The half plug should pop right out. Screw a big woodscrew into the plug for something to grab hold of.

Ed S
Old 07-15-2007, 12:17 AM
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Default RE: HELP !!! What am I doing wrong ?

Just yank those little buggers out with a screw. The plastic will (Should) flex.
Old 07-15-2007, 10:07 PM
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Campy
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Default RE: HELP !!! What am I doing wrong ?

That WOULD work fine (past tense ) with the old plugs. I pulled a second set and wound up severely damaging one of the plugs getting it out.

I read that if you had a part already, you could fill it with plaster of paris and make a plug that way. I decided to try that before going through making another set of wood plugs. The plaster of paris plugs came out fine. I was thinking of sanding a bit more taper to the plug when I sand the "flashing" off around the edges to see if that would help getting them out.

Do the plaster of paris plugs need any type of coating to preserve them ?

I buried a piece of 1/4" square spruce in each plug for strength, however, I am leary of cracking the plug if I screw a hook into the bottom to aid removal. After I let them dry for a couple of days and sand the bottom smooth, any suggestions for removing these plugs after a make a pull .

Also, I think .040 MIGHT be a better choice for material. The .060 are real HEAVY DUTY (about 2 - 3 times the thickness of wheel pants provided in kits). Comments, suggestions ?

Thanks
Old 07-16-2007, 06:15 AM
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Default RE: HELP !!! What am I doing wrong ?

I made plaster of Paris plugs exactly as described. I have had no trouble geting them out of the plastic part. Ensure there are no reverse tapers on the plug that will lock the part in.

Plaster plugs will need no coating for forming plastic over them. They will however need more than two days to fully cure. They may appear dry but for the moisture to completely dry a two to three week period is more likely needed.

Ed S
Old 07-17-2007, 10:24 AM
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Default RE: HELP !!! What am I doing wrong ?

or you can bake your plaster plugs in oven for awhile at 200 degrees & as stated by ED above make sure of no undercuts/reverse Tapers I have seen many a good mold/plug ruined by undercuts
Old 07-22-2007, 10:25 PM
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Campy
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Default RE: HELP !!! What am I doing wrong ?

OK.

Thanks for the tip about baking them. The wife is going to be gone most of the day tomorrow, so I will do it while she is gone. That will save A LOT of questions AND aggrevation

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