"squeezing" thin wall brass tubing

I couldnt answer IF you can do it in your lathe, apart from turn it out of the solid. Also I dont think I could do it in my lathe, but I know I could do it in my draw bench. this is 12ft long and will draw a 5ft length of material. Its dated from about 1850 or so. I drawn lots of tube down from big, ie 1/2 in down to 1/4, and 1/4in down to 1/8in od. when you draw metal through a die it is swaged down to the die size with a thou or so of elastic respring. If you drew some tube through a die of the right size then pulled it back out, you then could cut out the bit you wanted. In the older drawing process the drawtongs do crush the tube end so that has to be cut off before it can be used as tube.. As an afterhought, you could turn up a mandrel to fit the internal dimensions of the tube, over that an extenal steel tube to support it lengththe same as the unswaged section. then make a die that you could put on a drill press ,put the mandrel in the chuck, with the tube over this then the collar over this. # Hold in place and bring down the chuck to push the tube end into the die to swage it down, Use a bit of candle wax or oil as a lube. . This should work with the 15tho wall thickness , if its properly annealed ut of a drawing brass, say a 70/30 cu/ZN.

How do you get the large tube trough the smaller die in the first place so the jaws can grab it?

You could resize the tube with a sizing die. This can be done in an arbor press, but you may need to make several dies to reduce the diameter that much. The die would be a hardened ring in a tube that you force down over your tubing. The max squeeze per iteration would be about .020" The ring should be kept as thin as possible in cross section to reduce friction. The lube of choice would be lanolin. Pushing the ring onto the tube is easy, but lifting the ring off the tube requires the tube and ring be held very securely. Be sure to leave enough space in the die to allow the tube to grow in length and it will do so substantially. Steve

A sizing die might work, just like making little bitty wildcat bottleneck brass cartridges -- 3 caliber! Might need two or three dies.

For larger ID I would make a mandrel from drillrod, lube it with case lube or lanolin. Make some smooth rollers for my scissors-type knurler, perhaps with a taper on one side for the transition region. Grab tube and mandrel in a collet, etc. But an .030 mandrel will flex unless you can contrive a tailstock support of some sort, maybe a bit of drillrod with a lubed .031" hole in it that goes in the tailstock chuck.

You may need to anneal the tube before starting.

Let us know how you solve this one!

Make the tube smaller!! Yes I know its a dumb answer but cant help myself . So a serious answer, coming up. you take the tube end, place in a hemispherical depression the tube dia,flatten it down level, then take a round ended piece of steel, tap it down on the flattened tube to make it concave. Remove from the die block , place edge on flat metal anddress down to close up the half round/concace tube end . IE Your folding it on itself, thus making it smaller. Try it on some copper pipe, easy when youve done it once.

The easy way is to take your basic copper tubing cutter, remove the blade roller, replace with a smooth one wacked out on the lathe, then simply spin the tubing, while tightening down the tubing cutter on the tubing until you reach your reduced OD.

Quick, easy and repeatable.

Gunner

I used to spin a reduced neck on 15/32" OD musical instrument tubing in order to start it on the drawbench by annealing the last half inch, putting it in a collete and cranking the back end of an old amstrong toolholder into it. It worked, but it was a kind of dicey process. Eventually switched to driving the ends through the full series of draw rings using a rubber mallet. If driving, make absolelety sure to anneal only the region you are working, or the whole tube will bend!

Don't know how well either process will work at reduced scale.

If you can get an end srunk down smaller than desired, you can try putting it over a sizing mandrel with a step turned in it, and the driving through a sacrificial die... used annealed fender washers to make tapered french horn leadpipes that way. Problem with this method is that it's very hard to get the washer-die off without drawing all the way through, though if you made the step slightly more gradual then you probably could pass the whole tube through it.