Thin brass milling SO3

Anyone have experience to offer on milling thin brass on an SO3? The parts I would be considering would be similar to a half cylinder, milled on one side and then flipped over and milled out. Wall thickness would be 1mm or less when finished. I can mill wood or aluminum or brass to make a jig to support the wall when milling out the inside of the half-cylinder, but I was curious what experience anyone had to offer. Have you done brass? Thin wall? Flipping it over?

Part is ~1inch wide and ~5" long. I’ll probably end up making it a different way, but in my brainstorming I was trying to figure out how to CNC it and got to wondering what could be done on the SO3.


I haven’t done exactly that but indeed I would mill a jig to hold the initial stock, mill the half cylinder, then remove the piece, mill the negative of the cylinder into the jig, flip and tape the part into it, then mill the inside, probably doing longitudinal passes rather than radial (more workholding force/rigidity along the 5" length of the stock than across it)
If you started from a 1" diameter brass rod you would only have 1 side to mill and you would only have to mill a half-cylinder into the jig (or possibly even no jig if you can figure out how to hold a rod onto a V jaw or something), removing the trouble of accurately flipping the part?

I guess one question is “how thin is thin?”.

I’ve done a bit of double-sided milling of brass on my both SO3 and on my Nomad.

My process is to fix a piece of delrin/acetal to the wasteboard and then mill a jig or fixture that can secure the brass in a known position (basically a pocket rectangle). The jig is part of the design project and its corner is used for zeroing. A corner of the jig’s pocket becomes my locator for flipping the actual work.

Thin brass stock tends to be different to thicker stock, where “thicker stock” is 3.25mm or above. This thicker stock tends to be CZ121 or similar, which is soft and very easy to mill - a bit like aluminium.

Thin stock that I’ve found is much much harder - CZ108 or CZ126 - and tends to machine poorly, creating rough edges if the tool parameters are not quite right. It also gets very hot when machining because of the high friction, and that heat dissipates quickly into the work holding, which can affect the adhesion of work-holdings like double-sided tape or masking tape and superglue.

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