Offset key for Sherline Lathe Headstock - need one made

As @Bob Korves frequently reminds us, it is important to know if you actually have a problem before trying to apply a solution that may be permanent. We have to positively identify what the problem is, how severe it is and then we can figure out what we need to do about it. Some folks might pooh pooh us Sherline guys for fussing about stuff in tenths but these machines are capable of working to those tolerances so I ignore them.
 
I held a dial test indicator in the lathe chuck, set the indicator's arm on the tailstock quill, then turned the lathe chuck to indicate the position of the tailstock quill relative to the axis of rotation of the headstock. (Similar to doing shaft alignment on rotating machinery) The reading of concern to me was the total indicator reading from one side to the other side, which was 0.010", indicating 0.005" "offset" of the tailstock relative to the headstock.
 
Forty Niner said:
I held a dial test indicator in the lathe chuck, set the indicator's arm on the tailstock quill, then turned the lathe chuck to indicate the position of the tailstock quill relative to the axis of rotation of the headstock. (Similar to doing shaft alignment on rotating machinery) The reading of concern to me was the total indicator reading from one side to the other side, which was 0.010", indicating 0.005" "offset" of the tailstock relative to the headstock.
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OK, the only issue with that test is that the weight of the indicator arm will cause sag, leading to a reading that appears that the quill is lower than it really is. Side to side reading will probably be good. (edit) Wait, I was assuming you had an indicator stand magged down to the chuck, or and indicator arm. If you have the indicator itself in the chuck, that should be a good reading. The arm weight of an indicator holder causes sag.
 
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I'm trying to remember where I saw it but it was a fully adjustable tailstock setup for a Sherline. I thought about getting one for mine but was not that far out of alignment. and had already done some tapers I needed in other ways when I saw it. It could be adjusted hor and vert. For some reason I think it was on Ebay. It might help you if can find one.
 
Found something on it. A2Z use to do one of the adjustable tail stock. But do not think they are around any more, the last time I went looking for them.
 
mikey said:
Make an accurate live center and then find a position where it is the most accurate. I made an interchangeable tip live center that is really accurate - zero run out with the standard 60 degree tip and almost zero with an extended tip - that was as precise as I could make it. Then I did numerous cutting trials while turning/indexing the live center in the tailstock ram to find the position that had the least amount of run out. The arbor and internal taper of the tailstock ram has tolerances, too, and there is a position where the live center has the least amount of run out. I found that position, confirmed it in multiple trials, then punched a witness mark on the tailstock ram and the live center arbor. I just need to align those marks when I use the center and it works really well for me
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So, Mikey, I pondered on your experience. Obviously, if you were able to index your live center, you have some slight offset of the morse mount and the center. If they were dead true to each other it would make no difference how you place it in the tailstock. I think I can make that work for me too.
I am thinking about buying the Sherline "tailstock spindle extender" and modifying it so that there is some (just the right amount) eccentricity between the ends. Then I can place it in the tailstock in a position that will eliminate the tailstock offset. Mark that position and voila!
 
kvt said:
Found something on it. A2Z use to do one of the adjustable tail stock. But do not think they are around any more, the last time I went looking for them.
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Tis a shame they aren't around. They had some clever products.
 
Bob Korves said:
OK, the only issue with that test is that the weight of the indicator arm will cause sag, leading to a reading that appears that the quill is lower than it really is. Side to side reading will probably be good. (edit) Wait, I was assuming you had an indicator stand magged down to the chuck, or and indicator arm. If you have the indicator itself in the chuck, that should be a good reading. The arm weight of an indicator holder causes sag.
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Yes, I understand sag. (Sag can be measured and sag can be compensated for, but that is another topic) Picture a dial test indicator being held by the dovetail in the end. Just a short stem type holder. This chucked in the lathe headstock. Indicator arm sweeping the tailstock quill bore or od. Very little weight. Quite stiff. Sag probably less that .001 TIR. Sag is the same on the sides, so side to side readings are unaffected. My offset problem is side to side. Not much problem vertically. I believe the numbers I get.
 
Forty Niner said:
So, Mikey, I pondered on your experience. Obviously, if you were able to index your live center, you have some slight offset of the morse mount and the center. If they were dead true to each other it would make no difference how you place it in the tailstock. I think I can make that work for me too.
I am thinking about buying the Sherline "tailstock spindle extender" and modifying it so that there is some (just the right amount) eccentricity between the ends. Then I can place it in the tailstock in a position that will eliminate the tailstock offset. Mark that position and voila!
Click to expand...

I actually own that tailstock extender thing and did not find it useful. It magnifies the offset if you think about it. Trust me; I've been down the exact road you're on and I feel your pain! It may be that your tailstock is not off by that much and it may also be that your OEM live center can be clocked to mitigate some or all of your offset. The only way to tell is to make a test bar and figure it out. Oh, and I've also done the "put the indicator in the chuck" thing to sweep the tailstock. A test bar is vastly more sensitive, at least in my hands. Like I said, I've been down this road before.
 
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