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Issues mandrel bending brass

Whetstone

Cast Iron
Joined
Mar 27, 2011
Location
Providence RI
I very new to mandrel bending, and am experiencing some issues that I’m hoping to get some help with.

Material is 1.5” diameter 385 brass with 0.125 wall. I believe the temper is hard.

Machine is a pines #2
1 ball chrome mandrel


The issue I am experiencing is two fold. One, which is minor is that the diameter of the cross-section of the tube in the middle of the the bend is reducing by about 0.016”. Is this within the acceptable range for what I can get out of a basic machine? I have the mandrel nose about as far forward as I can get, which is about .375” past tangent.

The second issue is more important to solve as these are going to be mirror polished abs the distortion will be noticeable. I am getting a weird stretch at the trailing end of the bend. It looks to be about an inch long abs is a completely different angle. Any ideas what could be causing this? Pictures are of both a 45° and 90° bend.

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I did some more fiddling and moved the mandrel back, which helped with the weird stretch, but now the cross section of the tube reduced by about 040”. Would a two or 3 ball mandrel help with that?


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