Sherline lathe, Kerk screws and Moglice.

I have had a Sherline CNC lathe with a 24" bed (approx 16" of Z) for a few years. It also has a 13" cross slide (also known as a Sherline mill table). My plan is for gang tooling at some point, mostly just for fun. That being said the Sherline is quite a capable and convenient machine for the jobs it is capable of. Anyway like other Sherline owners, I want to modify and or attempt to improve on the original product.

(1) Stock Sherline couplers gave me a problem or 2 over the years.

Either they were frozen to the stepper shaft upon disassembly and required forces that destroyed the coupler.

The taper of the leadscrew and the coupler didnt have enough contact area and therefore slipped (regardless of technique employed to insure their fit, more on that later possibly).

The shaft of the coupler or lead screw would physically break, both have occurred. Of course at different times.

Upon disassembly of the CNC stepper mount (stock Sherline stuff) I notice the inner bearing stands proud. The bore accomodates the bearings ID but not its flange. Since I am improving things, this will be first. My intent is to bore the mount to allow the bearing flange to seat flush. This in turn will allow me more room for the next iteration of coupler.
Before
Attachment 250778
After
Attachment 250780

As I mentioned above. I have snapped a screw before. It looks like this ;-)
Attachment 250782
This isnt a problem to recover the coupler but the screw is toast.

My thought on this was to ditch the taper. I then proceeded to thread the ID of the coupler to 1/4-20 (the same thread as a Sherline lead screw). This did work well and eliminated slippage. It still used the grub screw to bind to the stepper shaft. I still didnt like the helical design and its tendency to stick to the stepper shaft. (Yes I used antiseize to no avail).

During this time I had purchased some Kerk motion screws from EBay.

I use these on my A2Z mill and have been very impressed with their performance and accuracy over the years. (different specs but same product basically)

The sets I purchased were advertised as used 1/4-20 lead screws and nuts. They neither measure 1/4-20 or 6mm. (I dont see 1/4-20's in Kerks catalog). Being that Mach can measure and calibrate steps per unit this isnt an issue.

Here is a pic of the screws. Btw they are coated with Kerkote, a low friction high wearing layer. The reason I suspect the screw measures neither metric or imperial.
Attachment 250784

They are nice screws with very smooth motion. However the OD of the nut is larger than allowable to use in the cross slide, even with extensive machining. There simply isnt the room. More on this later.

I could use this screw for the Z and it would likely work well. I could thread the ID of the standard Sherline lead screw nut to the thread of the Kerk nut. I dont like the diameter or the pitch though for the Z. The Z of a Sherline is a 3/8" screw. Still up in the air on a solution here.

So these new screws present a few new issues. Their diameter and thread is not familiar to me. I still suspect the coating. Plus the coating is a lubricant of sorts and will complicate the ability to attach a coupler securely.

My plan here is to thread the lead screw to 1/4-20 in the areas where couplers and thrust adjustment nuts will go. This will remove the coating and allow me to use standard fasteners in those areas.

I have acquired a different type of coupler from Ebay. I bought a smaller bore size so I would fit them on both sides.

Attachment 250786

I purchased these for 3 reasons.

I could use the clamping feature of the coupler to tighten the (soon to be internally threaded coupler) on the matching thread of the lead screw. If necessary loctite could be used also.

On the stepper side of the coupler I could use a grub screw along with the clamping feature. A win win in my book.

I could remove the stepper without destroying the coupler.

I turned the end of the coupler to fit inside the ID of the thrust bearing to keep the lead screw centered. I intend to do the same for the nut on the opposite side of the thrust bearing too.

Attachment 250788Attachment 250790

Then attached to the screw.

Attachment 250792

You will notice on the coupler there are 2 levels to my cut.

1 centers the screw in the ID of the bearing.

The other assures the coupler is contacting the bearings inner race and not the shield.

I will have to mill a clearance area for the adjustment nuts on the bottom of the mill table first. You can see there is no clearance for the flats or a wrench.

Attachment 250794

You will now see the diameter of the screw doesnt match the ID of the bearing. This is where the thrust adjustment nut will have a turned collar like the coupler does now.

On the outboard side I built a bearing support for the screw. Mostly to eliminate the whipping. Being that this lathe has a 13" mill table, the screw extends unsupported much further than normal.

Attachment 250800Attachment 250802

This is a little close up of the nut in relation to the carriage.
Attachment 250804Attachment 250806Attachment 250808

Seeing there is no room to actually install the nut. I would also need to machine the base of the cross slide. Another solution is needed.

I had heard of Moglice a few times but really found no info. I called them. They were very thorough, helpful and informative.
Attachment 250810
Attachment 250814
This is 1 of their kits. I paid 57.00 plus shipping. I plan on using this in conjunction with the Kerkote screws. Stick around for the process and hopefully improved operation of my Sherline lathe.

Turns out there is an acid brush and a stir stick for the epoxy. Nice complete kit.

Today I removed the carriage in preparation for the Moglice. I removed the small threaded insert inside the carriage. I will use it as a plug/centering device for the screw while the mixture hardens. I will use the separator/release agent on those parts too. I will even wrap the nuts on each end with a layer of teflon tape as a precaution.

Attachment 251078Attachment 251080

While I was there, I modified this tube right under the spindle and bed. I bored it and installed a small bearing. I then turned the end of the Z screw to fit the bearing. It really does nothing but minimize the clatter from the whipping of the screw.

Attachment 251084Attachment 251086Attachment 251088

Also just as a plan B or back up. And since I had an additional screw left. I threaded the internal bore of the stock Sherline Z nut to 12mm x 1.50. The external thread size of the anti backlash nut. Unfortunately that screw is a 6mm or 1/4-20 coated (very close either way) and I dont think it sturdy enough for Z. However I had an additional nut and the tap on hand, so why not?

Attachment 251090Attachment 251092

I have now cleaned all of the parts. Applied the liquid separator to both lead screws and centering nut. I wrapped a layer of teflon tape on both end plugs.

Attachment 251124Attachment 251126

Those 2 holes on the top of the carriage are the injection ports. I have a similar process for the Z nut. I bored it internally. This will allow the Moglice to ooze around the screw.

I mixed the Moglice and injected it in both the carriage and the Z nut. We will know in 24 hours!

Attachment 251134
Attachment 251136Attachment 251138

I barely used any of the Moglice to do both areas but 50 grams is the smallest you can purchase.

Anyone interested?

Of course we are...

Great then, here goes.

If you look at post #10 you will see where I am readying the carriage for the Moglice.

I wasnt entirely ready for the fluidity of the epoxy/Moglice. It did leak from any opening.
If I had it to do again I would prep a little more. Really make conical seals that screwed onto my lead screw and sealed against the carriage. That being said, it seems to have worked pretty well. I applied a few layers of the wax/release agent to the lead screw prior to injection. If I would have really followed the directions I would have bored the passes out to be larger. Moglice has a recommended thickness. I didnt heed it on the Z lead screw nut and it failed. The carriage is working. Removing the screw was an exercise in patience. It was tight and remained so. I then got the Bon Ami as suggested and lapped the screw nut combo repeatedly. Each successive time it loosened up a small amount. Since I am using an existing screw there is wear, you can hear the change in fit. A very small difference but a difference none the less. At this time I do have the cross slide mounted on the bench. It does feel very well fitted. I havent measured or quantified it yet. I am of course still suspicious of its durability. I have a few pieces to fab to make it work like I intended or hoped.

Now for the Z. I mentioned it failed. Well i do believe that is my fault. I drilled out the stock Z nut just a few sizes, still leaving a trace of the original thread. This was an error. Devitt Machinery (the distributor of Moglice) gives a specific clearance. I didnt prepare well enough for that axis and with the short amount of thread engagement of that nut. I cant imagine it could take the load.

I ended up using plan 2 on the Z, using the anti backlash nut threaded into a stock Z nut. This is a 1/4-20 thread. I hate that thread and the reduction of speed it causes . I just found a lead screw and nut that is 1/4-10, so I might be updating the Z.

Here is a preliminary test of the X axis. I will use an indicator later and show the results.

Oh and sorry for the video quality.

Preliminary Moglice testing - YouTube

Dunno how I missed this thread before. Like most Sherline owners, I've searched high & low for a viable backlash remedy.

Did you get anything else done on this project? Great info & pictures; please keep it coming!

Milton

I am following this thread. Your methods could also be applied to reduce backlash on my X1 micro-mill. Keep on the good work and, please, keep us informed, we are starving for more information.

Thank you,

kreutz