MT 6 1/2 One Piece Dead Center

[erikmannie]

Here is the taper in the spindle nose. I measured as carefully as I could and I came up with .0240”/inch of (radial!) taper.

The precision ground, female taper in this spindle nose is 2.60” long.

This reducing sleeve came with the lathe. The precision ground, male taper on the sleeve is 3.10” long.

The precision ground male taper extends .572” beyond the spindle nose:

 

[erikmannie]

The male taper is 3.10” long, but it is sticking out .572”, so only 2.53” of the sleeve is engaged.

I measured the female taper as 2.60” long, so I calculate that .070” of the smallest diameter section of the female taper is not engaged by the reducing sleeve.

I will now measure the diameters on the factory reducing sleeve that actually see engagement.

 

[erikmannie]

The top of the sleeve has an OD of 2.7670”, and the bottom has an OD of 2.6250”.

So it tapers .1420” over 3.010”, for a radial taper of .0236”/inch.

 

[erikmannie]

When I measured the interior earlier, I came up with .0240”/inch. When I measured the exterior, I came up with .0236”/inch.

The contradiction here is that few weeks ago I chucked up the factory reducing sleeve and, using a toolpost-mounted dial indicator, I came up with .0256”/inch taper. I made 3 dead centers using that datum, and they all fit perfectly.

Anyway, I see that I have plenty of data now so I will start cutting & see what the taper attachment is set to (I measured it last night at .0255”/inch).

 

[erikmannie]

I am turning between centers & I will allow the dog driving pin to get this close to my tool shank.

Also, the 4” lathe dog will get this close to the gap bed.

 

[erikmannie]

I am only able to take .020” lubricated cuts at 250 RPM, .005”/rev feed on this 4140 prehard.

I am also getting chatter on the tailstock side.

I am going to switch to HSS. When I tried to go up to 380 RPM (using A6 carbide here), the chips were dark purple (so too hot).

 

[erikmannie]

I saw that the tailstock quill was sticking out way longer than necessary. I fixed that, and the chatter seems to have gone away.

Now I have switched to HSS. I lowered the RPM to 180, and my DOC is .010”. The whole setup seems much better behaved.

 

[erikmannie]

It took me 2 hours to reduce the diameter by 0.415”. With the HSS, I ended up at 130 RPM with .030” radial cuts.

I just switched back to carbide & I will try cuts of .030” or greater. However, a cut of .025” with the carbide at RPM caused this awful chatter. I will increase the RPM to 180 now for .030” cuts.

 

[ddickey]

A lathe that size you should be able to take .150" DOC easy on prehard.
How long is that piece? Finish looks horrible.
What the diameter? What's your feed rate?

 

[erikmannie]

The piece was 10” before I faced each side about .050”. The diameter started out 4”. My feed rate is .005”/rev.

At this point, I’m just trying to get the diameter down to 2.800”. I am really kicking myself for not starting out with 3 inch bar!

The finish was nice with the HSS. These carbide inserts obviously call for deeper cuts.

I realize that the finish is absolutely horrendous. I have to think that that is because of the .020” DOC for the carbide.

Maybe my insert needs to be rotated: