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pntrbl
03-26-2007, 11:04 AM
I'm running a 15" test cut on a piece of 1" mystery steel with a collet and a dead center in my turret. Getting a .015 taper but the parts that's got me surprised is the small dia is at the turret end.

Not sure what to do next .......

SP

SGW
03-26-2007, 11:07 AM
Sounds as though either:

1. The lathe bed is twisted or
2. The tailstock center is offset.

Check #1 first and be sure the lathe bed is set up properly. If that checks out, move on to #2.

DeereGuy
03-26-2007, 11:56 AM
I'm running a 15" test cut on a piece of 1" mystery steel with a collet and a dead center in my turret. Getting a .015 taper but the parts that's got me surprised is the small dia is at the turret end.

Not sure what to do next .......

SP

pntrbl, with a test piece that long you need to first make sure you bed is level side to side. Then align your tail stock. You will need a machinist level to check the bed. A carpenters level will not measure with enough accuracy.

Crap should have read SGW's post a little closer....I have duped exactly what you need to do from SGW's post.

Lew Hartswick
03-26-2007, 01:25 PM
I'm running a 15" test cut on a piece of 1" mystery steel with a collet and a dead center in my turret. Getting a .015 taper but the parts that's got me surprised is the small dia is at the turret end.

Not sure what to do next .......

SP
Small at the tail stock end means the tailstock is to the front. Move it back.
...lew...

SGW
03-26-2007, 02:09 PM
...assuming the lathe bed isn't twisted. Make sure the lathe bed is set up correctly before you mess with the tailstock.

chipmaker4130
03-26-2007, 02:12 PM
I think you'll get the most accurate reading for tailstock set-over if you turn a short piece on centers after level checking the bed as noted above.

Gordon

DR
03-26-2007, 02:42 PM
It wouldn't be a surprise if the turret hole is not on center. A good percent of turret tooling is adjustable to compensate for off center turret bores.

Assuming the turret bore is off (and not a twisted lathe bed, etc) an adjustable boring head mounted in the hole can act as a centering device. Even an adjustable drill holder could be used with a center made from drill rod.

Turrets are not generally used to hold centers. This is not a big problem to worry about.

Is your lathe one that migh have been available with a conventional tailstock? If so, try to get one for centered turning.

pntrbl
03-26-2007, 07:15 PM
I just double checked cuz it's good to be thorough, but I'm still aligned within .0005. That's across the top of the V's with a VIZ 8" machinists level. How level it is to the ground varies with the time of day but that's a different story! LOL! I tried ....

Probably the turret. I was expecting to find it wide of the mark tho because of the way the gibs are arranged. The screws are in the front so as the gibs wear you'd expect the turret to move towards the back. Not forward.

But it's a rotating part on top of a sliding part on top af a movable base which is a long way from a one piece tailstock. I've already checked this hole twice but I believe I'll try another just to see if it's different. If they're at least consistent I think could skin the rear gib on my belt sander and move it all over some.

When I get a 4-jaw and the necessary skills to do it I'll be wanting to rebore all 6. But that's down the road a bit.

Meanwhile the Mission from God to be a machinist continues. :)

SP

pntrbl
03-26-2007, 09:41 PM
I got to the bottom of another one guys. I tried a 2nd hole in the turret with the same results and was starting to attack the gibs when I got the idea of switching them. When I put it together I assumed they were the same and paid no attention. But we all know what happens when there's 2 ways to choose ....

About the time I slipped the back one in the front and realized it was fatter I knew I was gonna be OK. That came up with an .005 wide test cut but .002 of that "save yer butt" brass shimstock behind the rear gib fixed that.

As near as I can tell my turret will hold a dead center within .001 of spindle center 18" out.

Gettin' happier with this old machine all the time.

SP