TBC question

[Haynie]

I have been practicing with TBC. If I just chuck up a wood blank I try to turn it round I can sometimes get it there but most of the time the blank stops turning. If I drill and glue a tube in as soon as I touch it with the gouge it stops turning. If I tighten anymore it flares the end of the tube.

I have read the tutorials, the posts, and this is what I get.

I use round metal stock and the 3 jaw chuck so it is not an issue. But I don't just use the metal lathe for metal.

 

[Lenny]

You can use the bushings you would normally use on a mandrel between centers, although I warn you .... If you try a pair of John's TBC bushings you will never want to turn without them again!

 

[Lenny]

Sorry, I didn't notice that you were talking about a metal lathe. Not sure I understand what you are trying to do?

 

[BSea]

And since you are using a metal lathe, you might as well make them yourself.

 

[Haynie]

I am trying to turn between centers. The same as on the wood lathe. I just don't have a live center for it yet.

 

[dennisg]

I believe the live center is a necessary component.

 

[flint]

I did my first turn between centers Sunday and it went well.
I did us a live center. That may be your problem.
flint

 

[Dale Allen]

It seems you are using a dead center on both ends. That's not good.
Without a live center on the tailstock it will just spin on the center and flare the tube.
You can turn the wood by itself that way but it will be slow going because the tailstock dead center will just keep wearing the hole bigger and then you need to tighten it again.
I use a live center on the tailstock and turn blanks round but I need to turn up the speed to do so or I too have to keep tightening it. And, I also first drill the ends with a 60 degree center bit.
If you have the bushings that are stepped that go on a 7mm mandrel, you can use those but it will also slip a lot.
The bushings made for this are tapper bored to match the 60 degree centers so there is more metal-to-metal contact.

 

[azamiryou]

I am trying to turn between centers. The same as on the wood lathe. I just don't have a live center for it yet.

I think what Haynie means here is that he's doing TBC on the metal lathe because he doesn't have a live center for the wood lathe. If I'm wrong about this, it's definitely something you need, regardless of which lathe you're doing TBC on!

In my own studio I've noticed that doing TBC on my metal lathe is much more difficult than doing it on the wood lathe. Same as Haynie observed, the wood stops very easily on the metal lathe. My hypothesis about what's going on is that it's a combination of the tool angles not being great for wood and that the tool holder doesn't react to the "feel" of cutting the way a human does when cutting with a chisel.

I have been able to do it by only advancing the cross slide a few thou on each pass. It's much slower than doing it on the wood lathe. Bushings help - as others have suggested, you can make your own bushings on the metal lathe.

 

[Haynie]

Yes I have a live center for the metal lathe. One for the wood lathe is on the way. I am thinking speed has something to do with it to. My metal lathe is not fast. Tops out at 1200 I think. The wood lathe is much faster. I also agree with Matthew, feel must be a part of it. On the wood lathe I do rely on feel a little more than my eyes when I am turning. On the metal lathe I am relying solely on my eyes.

 

[azamiryou]

In my shop, both my wood lathe and metal lathe have MT2 tapers on the tailstock. Can your metal lathe live center fit on your wood lathe?

Often, the metal lathe live center has a shorter taper, so the ram in the wood lathe tail stock won't eject it. My wood lathe tail stock has a hole all the way through it so I can use a knockout bar to get it out.

 

[Gilrock]

It sounds like when you tried to turn with the tube glued in that you didn't have bushings. You can buy or make bushings that fit inside the tube and have 60 degree taper on the outside for your centers to fit into. Then you should be able to tighten it up enough to prevent the tool from stopping the spin.

When you just want to chuck up a piece of wood I like to use a center that will grab it...my favorite is the Sorby Stebcenter:
Buy 7 8 Diameter 2 MT at Woodcraft

 

[Haynie]

I have something similar and with that things are fine. I have tried using bushings, though they did not have the 60 degree opening. Same problem. Maybe I need to make some with 60 degree openings.

 

[Rob73]

If you try a pair of John's TBC bushings you will never want to turn without them again!

I have a set of Johns bushings. I agree with Lenny they are very good quality. I wish I had them for every project that uses tubes. I have had a little slippage when not using bushings between centers. However, if I just tighten up slightly and take light cuts I'm usually fine. I run into trouble if I try to really take off some material quickly.