'Machining' fiberglass

[pugachu]

I have a scratch built 54mm rocket where I rolled the tubes on a 2.125" aluminum mandrel with a mylar release film. I need to make couplers for them rocket, but the off-the-shelf 54mm fiberglass couplers that I can find are ~1.14" OD. they are also a somewhat thin wall, so I don't want to thin them down more. I could get a 54mm thin wall fiberglass motor case from RCS, but then I would be tempted to buy some additional research supplies that I don't need right now..... On my first 54mm min diameter rocket, I cut a slit in the airframe tube, and then fiberglassed the seam on the ID. The finish was rather rough, and it was more of an egg shape cross section, rather than a perfect circular OD. This allowed the joint between tubes to rock back and forth a bit, and lead to some wiggle on the way up.

I currently want to roll up a thick coupler on a 2" mandrel, and machine it down to the right OD for a nice tight fit into the tube.

What is the best way to machine fiberglass? I have a lathe, but I don't know if standard metal cutting tools will be right for cutting fiberglass. It looks like the FW stuff from Wildman is wet sanded by a machine to the final size.

Thanks!

 

[tfish]

Do you or a local buddy have any spent AT 54mm DMS motor cases? They make good couplers.

Tony

 

[3stoogesrocketry]

Do you or a local buddy have any spent AT 54mm DMS motor cases? They make good couplers.

Tony

To build on this, 2 grain dms motor cases are only 19.99 and pre machined to accept glue for a bulkhead

 

[pugachu]

Do you or a local buddy have any spent AT 54mm DMS motor cases? They make good couplers.

Tony

Tony,

Thanks, but I don't have any used 54mm DMS motors. I'd be happy to pay shipping for a used one. I know you like to refill them with swamp gas

 

[pugachu]

To build on this, 2 grain dms motor cases are only 19.99 and pre machined to accept glue for a bulkhead

but if I go and buy a DMS motor case, I will also want to buy a gallon of HTPB, and curative, and liners and a lot more stuff that I don't have time to use

 

[SDramstad]

Get a 54mm stiffy coupler then add fiberglass as needed to hit the right diameter

Nevermind. Smallest one I can find is for a 2.56 inch tube

 

[David Schwantz]

I have chucked a glass tube on the lathe and used my belt sander while turning part

 

[kjhambrick]

@pugachu --

I wonder if you could wind a 0.060 inch wall glass coupler on a 2-inch wooden dowel to make a 2.120 inch OD tube ?

Sand the dowel a tad If you need a smaller ID to allow for release film ...

HTH

-- kjh

 

[spigalau]

Make another tube on your existing mandrel, cut 4 1"sections off the tube, then split vertically the remainder of it, remove 1/16"(or so), insert inside your 4 x 1"sections, and then re-seam it.

Example below is 4"tube that has been split, cut & rejoined.

 

[tfish]

...or....



Tony

 

[lr64]

Use the inside of your tube as a mold for a coupler. You could inflate something to hold the material against the inside of the tube until it cures and becomes a coupler. Of course you'll want some polyethylene or something so you can get it back out of the mold.

 

[Rocketjunkie]

Thanks, but I don't have any used 54mm DMS motors. I'd be happy to pay shipping for a used one. I know you like to refill them with swamp gas

Use a liner from a reload as a mandrel and make a tube the same way as the body tube.

 

[mrwalsh85]

Use the inside of your tube as a mold for a coupler. You could inflate something to hold the material against the inside of the tube until it cures and becomes a coupler. Of course you'll want some polyethylene or something so you can get it back out of the mold.

This. Mylar against the ID of the airframe, or even saran wrap - which is what I'd probably do in a pinch. It will be messy but once you get a few layers to your satisfaction, inflate with balloon and let cure. ID won't be pretty but it'll be good enough for a rocket, I bet.

 

[lr64]

Baking parchment might be a reasonable alternative to mylar or Saran wrap. It doesn't have to be waxed and it would be neater than Saran wrap. Or, alternatively, polyethylene in some moderate thickness.