Sherline Tailstock Misaligment

[Forty Niner]

You show the second GIB to be secured with 10-32 screws. Am I right to assume that these will be cap screws of some sort and that there will be two vertical and two horizontal? And that when tightened, they will securely assure that the GIB will be, so to speak, an immovable part of the tailstock casting? If so, then the design looks like it could work. I looked at my tailstock and unfortunately see that there is not enough meat to incorporate your design to my existing tailstock, and like you said, would require a modified casting.

If it requires a modified casting design to incorporate your design change, then it might also be just as easy to make a tailstock the same way that they have been made for larger machines. They can be adjusted horizontally with screws and vertically with shims. A simple design that has worked well on other lathes for a century.

I think for my tailstock I would only need to have about 0.003" shaved/machined from the angled surface on the opposite side from the existing gib in order to obtain really good alignment. Mine only needs to come towards the operator a smidgen. I don't have the cutter or a good enough milling machine to make that cut though. I keep thinking, but have not come up with a better solution.

I go crazy thinking about the tailstock alignment

 

[Karl A]

I am biased, of course, but I feel I have solved a nagging problem with tailstock misalignment.

Please examine the image and pick it apart at will. Challenge me in what I have come up with. I think I can explain any questions one may have as to how it all works.

I think that you have solved the problem conceptually. I think that your idea is ingenious. Unfortunately, it requires participation by Sherline -- which does not seem to be forthcoming.

I wonder whether a simpler version of your idea can be implemented by hobbyists on existing tailstocks, using a Sherline milling machine. I am thinking of a thinner gib installed without a top shim and without the top screws. In this simpler version, the tailstock would be milled to require a side shim. In other words, after the modification the tailstock would be misaligned forward, and a side shim would be added to move the tailstock back toward better alignment.

I looked up the Sherline tailstock gib: sku 40112, $ 15.86. Perhaps a Sherline tailstock gib can be milled thinner for this simpler version of your idea.

 

[Karl A]

I have been pursing a different approach to achieving better tailstock alignment. It is to make a spindle that contains a Morse taper with the opposite misalignment of the tailstock. The idea is to cancel the existing tailstock misalignment with an intentional spindle misalignment.

Today, I received a blank tailstock spindle that I ordered from Sherline. On my order, I specified "not ground to OD, not stamped with rule, no slot". It arrived that way.

Unfortunately, the diameter of the blank tailstock spindle is only 0.625". I not sure that I will be able to turn it down to both fit the ID of my tailstock and include the 4 to 5 thousandths horizontal offset on the Morse taper to counteract the tailstock misalignment. The ID of my tailstock is 0.6192".

 

[blu73]

Forty Niner,
You are correct in that there would be two cap screws in both the vertical and horizontal directions. When properly shimmed and secured, the second gib becomes an immovable part of the tailstock base. Your observation on the lack of enough stock to incorporate this modification on a stock Sherline tailstock is in line with mine.

Karl A,
Yes, it does require involvement and expense on the part of Sherline, and yes again, Sherline doesn't seem to be interested. I have not had any replies from Sherline other than the one from Karl Rohlin, so I don't know if this has been discussed with anyone else at Sherline, or if Karl is actually the final word.

As far as the thinner gib that could only be shimmed at the rear, that is an alternative I hadn't thought of. If the gib was properly sized, the tailstock would be too close to the operator side. In my thinking, that would be the more desirable condition to start with. Adding shims to the far side of the gib would then force the tailstock away from the operator. By staggering the shims, it should be possible to "twist" it also and achieve that last bit of alignment. I think my only concern with a thinner gib would be the amount of material that would be available to add the tapped holes to secure the gib and shims well enough to ensure no movement of the gib and shims in relation to the base of the tailstock. Going to have to give that one more thought.

You stated in your next posting (#53) that you were able to acquire a tailstock ram from Sherline in an unfinished condition. I wonder if it is also possible to buy a gib from them with no holes added. If the idea of a thinner gib works, it would relieve someone trying this modification from having to drill holes in locations that had to match any that were in a stock gib.

Well then. At the moment it looks like there may be an alternative that doesn't require involvement by Sherline. This is precisely what I was hoping for. A different point of view that brings to light something I had overlooked. This is starting to get interesting.

 

[Karl A]

blu73,
I wonder how many lathes Sherline sells per year, and what percentage of buyers care about the tailstock misalignment and/or are not satisfied with the adjustable tailstock tool holders. Perhaps if I was in Karl Rohlin's position, I would make the same decision: to not implement your idea. As a hobbyist, I am like Forty Niner: "I go crazy thinking about the tailstock alignment"

I have not measured amount of twist at the bore of the tailstock casing on my lathe. I plan to do so. Up until now, any twist hasn't seemed to matter, being that the tailstock ram (called "spindle" by Sherline) is wobbly inside the tailstock casing. I measured 1.2 thousandths clearance between the ID of the tailstock casing and the OD of the tailstock ram. I intend to make my new tailstock ram fit tighter.

In regard to buying a gib without holes, I doubt that Sherline is willing to sell one. On the webpage for ordering a tailstock spindle (sku 40270, $23.66), Sherline states, "The tailstock spindle is ground to fit each individual tailstock case. Please measure your tailstock spindle OD and enter the dimensions in the box below.
If no dimensions are entered the spindle you receive will be between .618-.619"
Instead of entering an dimension, I entered "not ground to OD, not stamped with rule, no slot". I imagined that Sherline has tailstock spindles in inventory that are not ground, and consequently such spindles are not stamped with a rule and do not have a slot. In contrast, I expect that all the tailstock gibs that Sherline has in inventory have holes.

I don't think that the holes in the gib matter for implementing your idea. The holes are vertical, and I expect that they would be milled off to make the gib thin enough to use on the tailstock at rear side of the lathe.

I am glad that you are pursing an idea for improving tailstock alignment that others, without access to a wire EDM, can implement.

BTW, a new tailstock casing (sku 40111) costs $46.03.

 

[Karl A]

This photo shows a mock up of how I plan to turn my new, unfinished tailstock spindle [ram] from Sherline.

The set up has a 4-jaw independent chuck, the Morse-taper half of an adjustable toolstock tool holder to hold the ram on the left side, a dead center in an adjustable tailstock custom tool holder to hold the ram on the right side, and a 1/4-inch turning tool. (I will be able to position the holder for the turning tool closer to the ram.)

The set up allows the ram to be mounted with an intentional amount of runout, to achieve the desired amount of misalignment of the Morse taper in the ram (to counteract the existing misalignment of the tailstock) when the ram OD is turned down to fit the ID of the tailstock casing.

I don't expect the existing threads of the ram to work after turning it down with the intentional runout. After turning the ram, I plan to drill the existing threads out of the ram, press fit a plug, and make new threads in the plug that are concentric with the OD of the ram.

The final step will be to mill a slot down the side of the ram, in the correct location on the circumference to cancel the existing misalignment of the tailstock casing on the lathe.

I think that I need a better 1/4-inch turning tool -- one with optimum angles for steel, and a small nose radius for removing 0.001 to 0.004" from the ram OD. I am still working on modifying a belt sander for grinding my own tools.

 

[Forty Niner]

Sorry to say this, but I don't think that setup will accomplish what you want. It will only allow you to offset the headstock end, not the end you show running on the dead center in the tailstock. If you back off the dead center, the setup could be made to offset the entire length of the spindle, but it probably would not be stiff enough to cut on. You would need something like a 4 jaw chuck mounted on a live center on the tailstock to get that end held and offset.

Or make a plate with a threaded nub that would go into that end. The carefully put a center in the place where it is needed. Maybe you could drill the center of that plate with the setup you have, having set the offset up using the 4 jaw and insuring that the entire length is all wobbling the same way the same amount at the same time.

 

[Karl A]

Sorry to say this, but I don't think that setup will accomplish what you want. It will only allow you to offset the headstock end, not the end you show running on the dead center in the tailstock. If you back off the dead center, the setup could be made to offset the entire length of the spindle, but it probably would not be stiff enough to cut on. You would need something like a 4 jaw chuck mounted on a live center on the tailstock to get that end held and offset.

Or make a plate with a threaded nub that would go into that end. The carefully put a center in the place where it is needed. Maybe you could drill the center of that plate with the setup you have, having set the offset up using the 4 jaw and insuring that the entire length is all wobbling the same way the same amount at the same time.

You're right. Thanks.

I have a second 4-jaw independent chuck.

I like your suggestion of a plate with a threaded nub.

 

[Forty Niner]

OR, just face the end of a threaded bolt so it is smooth, then screw it into the spindle, then drill a center into that to hold the tailstock end?

 

[Karl A]

OR, just face the end of a threaded bolt so it is smooth, then screw it into the spindle, then drill a center into that to hold the tailstock end?

Yes. Faster and easier.

The bolt needs to have left-handed threads, though. The threads in the ram are 1/4-20 left-handed.