lumpy FG tube help

I've had decent success making fiberglass tubes over pvc pipe mandrels by hand layup, but I tried adding some vacuum to the process today and got an ugly, lumpy, useless part. What I'm trying to get is a 4' length of tube using a 1-7/8 inch mandrel and four layers of kentex 1708 (stitched 24oz double bias w/mat). I coated the mandrel with wax and then PVA and wrapped it in the cloth as I wet it out and then wrapped the result with peel ply and bubble wrap and 4 mil plastic and added vacuum. The problem I had is that the layup was loose enough that the vacuum caused wrinkles to form as it pushed the layers against the mandrel. I also found that the vacuumed part was much harder to get off the pipe than the open layup version. Any suggestions on how to do this correctly?

Many thanks,

-- Tom.

 

Realistically, you're only making a 4' part, and you're using 24oz. roving with mat you can ditch the bubble wrap. The basic theory doesn't predict a need for flow media, but In a case where the time it takes to draw the resin throughout the fabric is long enough (ie. longer than the gel time) you need to assist the dispersion. You seem to be wetting out the fabric, then vacuum bagging as opposed to drawing resin from a pot at one end of the part, using the vacuum bag to disperse it, and depositing "left overs" into a container at the other end. What ever works for you buddy. Just out of curiosity, how much vacuum are you using?

 

Thanks for the help. I'm not sure how much vacuum I'm pulling. I drilled a series of holes in the vacuum tube and cover them in duct tape until the bag is very tight... My vacuum source is just a small piston pump type compressor that I am using backwards and keeping coolish with a light water mist... I "developed" this set-up to help me clamp glass into a small, deep mold and it worked very well for me there.

If I did a dry lay-up and then infused the resin, how would I keep the glass tight on the tube? I'm pretty sure that the loose fit around the mandrel is what caused the bunching-up problem.

Cheers,

-- Tom.

 

Sorry to reply twice, but I'm actually using stitched cloth (17 oz of 45/45 plus 8 oz mat) not roving.

-- Tom.

 

I was dealing with the same loose cloth problem last night. I was wrapping a tight radius with tape (rudder aft edge) and had to use spring clamps to assist ---they come off fine).
I wonder if dots of crazy glue would help in getting the cloth stretched around to start with? Either that or spiral-winding tape with someone spinning the piece on an inner mandrel?


A.

 

As far as removing the tube from the pipe is concerned,have you considered the possibility that the bag is compressing the PVC tube?Filling it with casting resin may eliminate the possibility.

 

Tsmwebb,maybe its the bulk of resin in the choppy thats gettin sqeezed up? What resin are you using- maybe drop the chop if using epoxy & do some xtra wraps of the stitched, also do you have an envelope of bag up the middle of the mandril- cos you might be compressing the dia of the tube untill the resins set & the vacs off. Regards from Jeff

 

Thanks for the help!

Thanks for all the suggestions. Time permitting I'll give it another go this evening and report back.

-- Tom.