21 century lathe turning question

[DngBat7]

So I am somewhat new to turning. And I purchased a 21 century lathe. I am sure my question apples to any lathe tho. When I feed in the brass, it cuts the brass as expected. So if I pull the brass out and send it back in, without adjusting anything, it take off more, than again, takes off more. So basically I can push the same piece brass on the turner mandrel 4-5 times and finally it stops shaving the brass off. Is this normal?

 

[Dos XX]

Yes. You can play with technique to get the consistency in neck thickness you want.

If you go in real slow, then come out real slow, you will get a really fine finish and as long as you aren't generating heat, you will get consistency. A couple of tricks to avoid generating heat are to use a carbide turning mandrel, use oil, and keep your cutter in ice water between cases. You can use all or some of those to see what you get.

I also have played with running it in fast, like basically jamming it in, for a rough cut, and then coming back out real slow for a finish cut. Same thing applies, try it and see what works best for you.

Also, rpm matters.

 

[DngBat7]

Yes. You can play with technique to get the consistency in neck thickness you want.

If you go in real slow, then come out real slow, you will get a really fine finish and as long as you aren't generating heat, you will get consistency. A couple of tricks to avoid generating heat are to use a carbide turning mandrel, use oil, and keep you cutter in ice water between cases. You can use all or some of those to see what you get.

I also have played with running it in fast, like basically jamming it in, for a rough cut, and then coming back out real slow for a finish cut. Same thing applies, try it and see what works best for you.

Also, rpm matters.

I am using slow rpm. So do I keep going back and forth till brass stops shaving off? Then they should all be the same thickness at the end of the day?

 

[SG4247]

Brass heats up really fast.

So, as it expands, you cut more off...

One smooth pass in then out.

 

[DngBat7]

Brass heats up really fast.

So, as it expands, you cut more off...

One smooth pass in then out.

Even if I turn it at really slow speed? Is there a cutting oil I am suppose to use? Besides some imperial on the mandrel?

 

[Mikemci]

I only lube the mandrel, using a Q-Tip. Feed in slowly and back out slowly. While the brass is still in the drill chuck, I chamfer, debur and spin it in a green scotchbrite pad.

 

[Sniper338]

Your moving too fast, slow down to 1 slow pass

 

[F Class John]

I agree, one clean pass and move on.

And then of course there’s the second question you’ll end up asking or researching which is whether to turn before or after the first firing...

 

[SG4247]

I actually use 30wt motor oil on the mandrel to cool the brass and improve life if the tool.

I use oil on the drive shaft / guide bushing as well.

 

[DngBat7]

Yes. You can play with technique to get the consistency in neck thickness you want.

If you go in real slow, then come out real slow, you will get a really fine finish and as long as you aren't generating heat, you will get consistency. A couple of tricks to avoid generating heat are to use a carbide turning mandrel, use oil, and keep your cutter in ice water between cases. You can use all or some of those to see what you get.

I also have played with running it in fast, like basically jamming it in, for a rough cut, and then coming back out real slow for a finish cut. Same thing applies, try it and see what works best for you.

Also, rpm matters.

Can you get a carbide turning mandrel for the 21 century lathe ?

 

[Kookie]

Can you get a carbide turning mandrel for the 21 century lathe ?

21st Century makes an adapter to use the KM carbide turning mandrels.

 

[arm017]

I agree, one clean pass and move on.

And then of course there’s the second question you’ll end up asking or researching which is whether to turn before or after the first firing...

I am under the impression before the first firing correct?

 

[F Class John]

I know just as many that do it before the first firing as I do after the first firing. The common thinking about doing it after the first firing is that you’ve allowed all the little voids to get filled by some amount of flow before you turn it there by putting off your need to turn them again for a longer amount of time. Typically if you turn them before the first firing you will probably have to turn them again after two or three firings just to knock back the flow. You have to periodically turn them again anyway but the people I know who turned them after the first firing seem to be able to go longer than those that do it before the first firing.