Frustration with tailstock alignment on PM1030 lathe

[starr256]

I have struggled with the tailstock alignment on my PM1030 for two years. While I have not done any turning between centers, alignment is needed for drilling as well. and is done frequently. I understand the methods to true it up. The problem, for me, is the design of the adjustment mechanism. You need both vertical and horizontal axial alignment. And the alignment needs to maintained as you run the tailstock quill in and out. The tailstock is a two piece affair, a bottom piece that rides in the bed and a top piece that has the quill. There is a holddown bolt that runs vertically through both pieces to a block steel below the bed to secure the tailstock location. There is no adjustment for vertical alignment, other than shims between the two pieces. The horizontal alignment is done with opposing screws with a small set screw. to "fix" the location. After a couple frustration days trying to get a nonn-tapers turn, I put a test indicator to measure the vertical deviation and dial indicator on a ground test bar to measure the horizonal deviation at the same time. I found that the the vertical alignment was ~0.005" out. I adjusted this with shims between the two tailstock haves. That was easy. The real issue is the fact that the hoorizontal alignment is affected by the opposing screws, the set screw and the holddown bolt. The tension from the holddown bolt tends to distort the alignment is no repeatable ways. The tension on the set screw also modifies the alignment, but in a more predictable manner. Note that the bed itself has been aligned to within 0.0005".

How is this done on other brand/models of lathes?

Comments, admonishments, suggestions welcome.

 

[tazzat]

just make a better tailstock/tailstock loock.
its what you get for 3k..

 

[benmychree]

If the shims that you put between the base and top casting of the tailstock are yielding or spongy, you are going to get poor results with alignment, and you cannot be totally dependent on readings of an indicator, as the weight of the indicator and flexibility of the setup can effect the results, especially in the vertical plane. Ideally, there should be no shims between the top and bottom, also one should check the top of the tailstock quill for paralellism with the bed of the lathe, as this will effect the center height depending on whether the quill is extended or withdrawn. Another factor is the concentricity of the drill chuck you are using, cheap imports may not run concentric with the quill taper.
Bottom line, your lathe's construction is no different than most any other lathe made in modern times. One thing you mention is a setscrew; where is it located and what does it bear upon?

 

[Tozguy]

The tension from the holddown bolt tends to distort the alignment is no repeatable ways.

When adjusting in the horizontal, the holddown bolt needs to allow the top part to slide on the bottom but not allow it to lift off it. The two opposing screws must not interfere with one another. Make sure the opposing screw is backed off enough to allow the other screw to slide the top part but not lift it. Granted it is a crude design.
You also have to be sure that the hold down bolt is perfectly vertical. The block under the bed that the bolt goes through can easily shift around so keep an eye that it stays in position.

I would do the horizontal adjustment first without shims, then do the vertical. Bear in mind that the vertical is much less critical for avoiding tapers. My TS center was a bit high but apparently that's maybe a good thing. Does your manual have good instructions for this?

After trying several different approaches my favorite is to put a deep internal center in a four jaw and slide the TS center up to it. Adjust the TS to get the deepest/best fit in the divot.

 

[Winegrower]

I would say that any method that relies on feel or visual alignment has failed for me when checking with the two collar test. We are talking sub thousandths over feet. It’s a delicate alignment and requires an accurate check.

 

[Tozguy]

Agreed, there are a few ways to get close but none of them replace an actual turning test. I would regard any visual or feel method as preliminary.

 

[T Bredehoft]

Only use an indicator between chuck and tail stock for preliminary adjustments. Adjust horizontal with tail stock locked to the bed/rails. Cut a long piece (longer/better) only at ends one inch long. (dumbell shaped) adjust tail stock to elimination taper between ends. Assume vertical is acceptable. Or, once you have both ends of your test bar the same exact diameter, use an indicator mounted on the carriage to check for height differences. No other way to do it. The best test indicators in the world are not gravity proof. You can't rotate them in a horizontal plane and trust them.

 

[Tozguy]

Adjust horizontal with tail stock locked to the bed/rails.

The bolt locks all parts of the tailstock. But for horizontal adjustment, the top part have to move with respect to the bottom part.
Do I misunderstand your statement?

 

[T Bredehoft]

No, you understand it . The top will move when the base is locked down.

 

[Tozguy]

Can't visualize how that would happen. The locking bolt locks the top to the bottom and to the ways all together.