Hi,
This is my first post, just starting out with composites. I’ve seen people using UHMW or aluminum mandrels in pre-made head tubes and bottom brackets on bike frames. I think the reason is so that those tubes don’t loose their shape during curing. My question is are they really required or just a good precaution?
Any help or pointers to threads already discussing this (I can’t find any) would be greatly appreciated.
Thanks
People who are in business of making thing don’t do something or use something just because, they do it because they need to
The mandrel is the mould, you can’t form a new moulded shape without a mould!
I now use acetyl as mandrels for things and it’s great. There is a small amount of expansion but this is what you want to help with removing a parallel tube from the mandrel. The acetyl is just sanded really smooth and no release system is needed at all. Parts just fall off.
Hi, thanks for the replies. Sorry I think my first post might not explain what I am trying to understand very well.
Let me ask it a different way. If I make a tube (with a mandrel), or buy a tube off the shelf where the internal roundness and diameter is important, and then I want to bond it to another tube and wrap and cure the joint, should I use a mandrel in the first tube to retain it’s shape while I’m curing the joint, even though the first tube is already cured?
The example on a bike frame is the head tube where the roundness and diameter is important for the bearing seats.
The mandrel or plug is there to stop the tube end from collapsing or distorting under the vacuum/ heat phase. If you are using wet lay up, you will be OK without. If heating, mandrel is recommended as you reach TG of resin, it will soften.
You can just fit and glue the tubes to set your join and then add enough layers across the join for strength.
the mandrels you are talking about are to hold the already set piece at the exact angle so that the next tube can be bonded onto it …
as already mentioned , unless you going to heat the absolute snot out of it , i wouldnt bother …
if you just doing a one off piece, you can use hot glue/ super glue to hold the two tubes together , and then do your filament winding/ clothe layup
There is lots for me to think about there, so thanks for all the replies.