What would be a better way to do this...

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#1

What I’m trying to do:
Create an ID controlled tube with flanges on both ends. Later bearing cups will be pressed into the tube ends and seat against the flanges. I only care about the ID tolerance and creating a decent flange. The OD can be ugly because it gets processed later.

My strategy:
I turned a pair of straight mating mandrels (uhmw) on the lathe, fixed them together on a shaft, waxed, wrapped with CF, epoxy, peel ply, vacuum bagged, cured…thought i could pull the mandrels out…having way too much trouble getting the second part of the mandrel out. Like it’s not coming out.

What should i have done:?
I assume i should have tapered part of the mandrel…But is there a way better way to attack this?

Thanks,

-Kyle-

#2

Is that a bottom bracket shell?

I’d probably try putting some PVA on the mandrel. It’s an easy and cheap first step although you might have some slight trouble keeping the surface really uniform if you don’t spray the PVA.

#3

Drill a hole thru mandrel and put an air fitting into it so you can push the mandrel out. Then press the other side out. If those mandrels are teflon or other plastic they should come out. If nothing else coat with a semi-pern release.

#4

Enve Composites have off the shelf tubing of the diameters you are after. You are on the right track, my mandrels are aluminium and I also use some vacuum bagging film in the centre section which can help removal. I also use semi perm release. I will be offering up a road tubeset for like minded builders soon.

#5

Thanks for the feedback. Sounds like i just need a different mold release and maybe an air fitting.

The small part is a bottom bracket shell and the longer one is a head tube shell. I’ve bought tubes from Rockwest before which were nice but spendy. I didn’t know ENVE sold just tubes. If i can get the mandrel out easier i think this method will be pretty cheap and help hold the part in the jig for layup with the rest of the bike frame.

Thanks guys!

#6

Are there lathe marks in the mandrel? It might be UHWMwhatever, but if you have physical ridges perpendicular from the direction you are pulling the mandrel out of, the resin will be locking into those machining lines, and gluing it there!! Sand and polish if possible. You should not need any release on PE/PP plastic.

#7

Yes, A lot of the time plastics are hard to machine without leaving small ridges or variation in diameter. I prefer to use aluminium.