Sherline Tailstock Misaligment

tomw

tomw

Registered
Registered
Joined
Jan 24, 2015
Messages
239
Dear All,

I have a Sherline 4400 Lathe, purchased new back in February. In doing some work between centers on a very thin piece, I discovered that my tailstock appears to be misaligned. The misalignment is enough to taper a 2" piece 6 thou. I did some tests, and this 6 thou taper over 2" occurs when using 3/8" stock as well. The tapering is uneven, and there is a ton of chatter when cutting near the tailstock, diminishing as you move towards the spindle.

My spindle is aligned perpendicular with the lathe axis. A 4" long brass 1/2" diameter rod will have .0005 TIR when machined using only a chuck (not between centers).

I took a photo of the tailstock with a live center against the spindle with a dead center.

IMG_1145.jpg

The misalignment also helps explain why I keep getting slightly off-center holes when I drill on the lathe. I thought it was my technique.

My question is how much misalignment should I expect. Is this pretty standard for Sherline? If so, I am surprised, because all of their other features seem very precise for a machine of this price.

Sherline offers adjustable tailstock holders. Given this degree of misalignment, I am going to have to buy all of them. This will make the lathe much less fun to operate, as I will have to do the alignment each time I switch between centers and drills.

Thank you for your help.

Cheers,

Tom
 
Hi Tom,

Is that picture looking down on the alignment of the two centres? That is, you need to adjust your tailstock in the same direction as the cross feed.

or.....

Is that picture looking from the front of the lathe towards the back (along the same direction as the cross feed). That is your tailstock centre is higher than your headstock centre, and you would need to shim the headstock up?

other things:
-are you certain that there are no chips in the headstock or tailstock tapers?
-have you ever re-turned the point on your headstock live centre to match exactly your spindle centre?

-brino
 
Brino,

That is looking down. The tailstock center is very lightly used, and gives me the same look as an unused (except for this project) dead center.

I took the tailstock apart and cleaned everything, readjusted the gib, etc. I made sure the tapers were clean on the centers and the tailstock and spindle bores. No change in the alignment. It is still off by 12 or so thou.

Thank you for your help.

Tom
 
Hi Tom,

Looking at the page here:
http://www.sherline.com/setupins.htm

It looks like the tailstock is not adjustable, which is why you mentioned the "adjustable tailstock tool holder".

Did you go thru the headstock alignment procedure?

The only other ideas are chips between the headstock/tailstock and bed ways.

Hopefully another sherline owner will jump in with some knowledge.

-brino
 
My Sherline 4400 is over 20 years old and I've used the live center thousands of times and have nowhere near this amount of run out, either with the old style tailstock or the newer one so this is unusual. I think you need to isolate exactly what the problem is, Tom.
  • It can be the brass tailstock gib. Try removing the gib altogether and push the dovetail against the way to see if this improves things.
  • It can be the machining of the dovetail of the tailstock. The above will help sort that.
  • Since the offset is the same with the dead and live center it is not likely to be a bent morse taper on the live center but it might be a burr or debris in the morse taper socket.
  • The tailstock body itself may be warped for some reason.
  • The ram may be distorted or the morse taper is inaccurately cut for some reason.
  • The morse taper of the tailstock may be off for some reason. You can put a test bar between centers and index the live center in various positions to see if it is off. My tailstock definitely has a position where the live center runout is reduced so I marked the center and the ram.
My Sherline live center was okay but had a TIR of 0.0008. I bought the adjustable live center and while it can be made to run more accurately it is a bear to align. Every time you remove it and replace it you have to realign the thing, which is a royal pain. My solution was to make my own live center with replaceable tips. It has near zero run out with the 60 degree point and only about 0.0002" TIR with an extended tip. I cannot post pics for some reason; PM me if you need them.

In any case, you have an issue but I'm not sure what it is. Maybe check the list above and we can go from there.
 
If you are holding a 1/2 thousandth TIR over 4", your headstock should be aligned. The .006" taper would result from a .003" offset which Sherline may deem acceptable. The unevenness of the taper could arise because of mounting the piece in a chuck. Normally in cutting tapers using an offset, the work is mounted on a headstock center and driven with a lathe dog. By using a chuck and an offset taper, you would be introducing a bend in the part which will change as you turn the part. It would also explain the chatter you are experiencing.

Tailstock misalignment can come from two factors: there can be an offset parallel to the ways or the tailstock could be rotated. The latter would be indicated by a change in the amount of offset as the tailstock ram is advanced or by having different offsets for different lengths of drills.

About ten years ago I was doing some lathe work with very small features (drilling .009" holes in stainless, e.g.). I designed and made an adjustable chuck for the tailstock based on the "Set Tru" lathe chuck design principle and using a 1/4" Albrecht chuck. I had four adjustment screws which allowed me to dial in the runout on the chuck. I also had four adjustment screws from the back which allowed me to zero out any angular misalignment. I then made my own mini live center with a 1/4 straight shank.

It may be that Sherline's adjustable tailstock tools are similar in design.
 
Is this the 4400 or the 4000, I have both. You said It is new in the last year, I would take the picture and send it to them, I hate to say it, They have been good to me and tried to fix and make up for things I have had problems with on my new one. But it almost seems their QA has fallen into a bad state at times. They say they put each one together and check it but if that was the case why are there so many problems. Another person had problems with his new MIll as well. I had problems with several things when I got my new 4400 in Dec. often I do not use the Tail stock so I have not check it. I guess I should. The adjustable tail stock that I have seen, it is actually for use on a mill, and attaches to the T slots. I have seen several on the web actually make an adjustable tail stock to replace the original by cutting the top off, then using a heavy piece of alum angle. They machine it where they can hold it to the old base, and adjust left and right, And if need by they can also adjust up and down. The one thing you have to worry about is keeping it level to the bed as well. That way when you do drill with it you drill straight and level.
From the look of the picture I it is not the brass gib on the tail stock, but rather the Alum on the back side of the tail stock, Ensure there is not any chips etc in the edge of the dovetail. It can happen, Check to see that it seets properly. Even a glob of bad grease can cause some alignment on the back. Also, make sure that the GiB on the front is putting enough pressure on it to keep it moved over properly. Note at least it is better than the old tail stocks which used a pinch method which was often out of alignment.
One of the other things to check is to see if the head stock is correct. I do this by attaching a gauge to the cross slide then checking down the side of a precision drill rod to see if there is any change from the head out. If there is then the head is a little out of alignment. Some times there is a little bit of play in the alignment bar on the head stock so you may be able to adjust that out.

Good luck and let us know what happens
 
Thank you all for your replies. I am quite certain the problem is not in the tapers for either the spindle or ram or the centers. I cleaned and checked them all. I will do some additional checking tomorrow and also contact Sherline.
 
I had that same problem with my 4400. I had to use a wooden mallet on the headstock to tweek it with the alignment bar in it and tightened down. Also I found that using the thumb screw that locks the ram pushed it off center as well. I drilled and tapped the opposite side and made a thumb screw to be able to center it up. If you do that, make sure you deburr the hole on the inside of the tailstock so you don't scar the ram. Also, don't forget to loosen the screw before moving the ram. I need to replace mine but worry about the quality of a new one. Good luck
 
Steve,

Thanks for the information. I already aligned the headstock. The alignment screw on the rear is a good idea.
 
You must log in or register to reply here.
Back
Top