# Anti backlash mod for X2 mill



## homebrewed (Aug 3, 2017)

I've been working on a scheme for reducing backlash on my X2 mill for some time.  After some false starts I believe I've done it.  It is a variation on an approach used on the Sherline CNC mills, where each table axis has two, not one, lead screw nuts.  In the Sherline design (sorry, I don't have any photos) for each axis there is a second nut on the exterior of the table, and it is in close contact to the table..  Its outer diameter is knurled with a fairly coarse knurl.  The nut engages a thick washer whose OD also is knurled.  The washer is fixed to the table with a bolt.  To adjust the backlash, the bolt is slightly loosened and the washer is rotated to turn the feed screw nut, sort of like a pair of gears.  In this manner the external feed screw nut is moved in or out to adjust   the backlash.  Once the backlash is set, the bolt is tightened.

I know, verbal descriptions can be hard to unravel.  But I think the attached photo will clarify things.  It shows a second feed screw nut (modified from a nut I bought from LMS).  The photo shows the underside of the right-hand side of the table.  The nut was drilled with a 1/16" hole to accommodate a short length of piano wire that was bent at the end.  The other end of the piano wire is attached to an adjuster that has a slot cut in it.  To set the backlash, the screw in the slot is loosened, then the adjuster is moved to tighten/loosen the nut.  BTW I also made an end plate so the external nut had a "landing pad".  The stock mill table is open on both ends so it was necessary to fabricate this piece.  It was made from a piece of ground steel plate.  I had to D/T two holes to mount the plate on the table.  It was an interesting exercise to align the hole in the plate so there was no mechanical interference with the lead screw.  I made a number of prints using Inkscape, which, on my system, seems to produce pretty accurate to-scale prints.  I used the prints to do some trial fitting so I could avoid any major d'oh! moments. 

Unlike the Sherline approach, due to the limited range of my adjuster scheme it is necessary to do a trial fit of the the nut so you know where to drill the hole for the piano wire.  But I think there should be enough adjustment range to accommodate a lot of wear.  Of course, you could always drill another hole in the nut when you need to...


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## jdl6mm (Aug 3, 2017)

Well I may be blind or just don't understand, but I don't see a knurled nut or washer on there. 
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## chip maker (Aug 3, 2017)

I'm also a bit lost . I think a few more photos to show the set ups would be helpful. I don't get the nut and washer because there isn't any photo to show the setup and I guess I don't understand the part mounted on the end with the piano wire? To me all that does is put pressure own the lead screw making it harder to turn but how does that take out the backlash? Maybe with more info I will get a better idea of the operation and if this is something I could do to my mill also.


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## homebrewed (Aug 3, 2017)

jdl6mm said:


> Well I may be blind or just don't understand, but I don't see a knurled nut or washer on there.
> Sent from my VS987 using Tapatalk


My version doesn't use a knurl.  It's got a length of piano wire, one end of which is bent to 90 degrees.  That end goes into a hole I drilled in the nut.  It is not glued or pinned:  it is free to rotate in the hole.  The slotted piece is moved back & forth, which turns the nut -- which in turn moves closer or further away from the end plate.  In use, I loosen the bolt in the slotted piece, then move it to minimize backlash without making it too difficult to turn the crank handle.  Then I tighten the bolt.  See my reply to Chip Maker for another photo of the pieces.


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## chip maker (Aug 3, 2017)

homebrewed, I didn't get or see any other photos to see how you have this set up. Your reply does make a bit more since but still can't get how it works out to remove the backlash. Is the bracket bolt a cam that lifts to make the lead screw tighter? By the other photo all I get is that the piano wire is moving across the threads of the lead screw. I'm also not sure where the nut is and how it works if the wire is just free to move.


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## homebrewed (Aug 3, 2017)

Chip Maker said:


> I'm also a bit lost . I think a few more photos to show the set ups would be helpful. I don't get the nut and washer because there isn't any photo to show the setup and I guess I don't understand the part mounted on the end with the piano wire? To me all that does is put pressure own the lead screw making it harder to turn but how does that take out the backlash? Maybe with more info I will get a better idea of the operation and if this is something I could do to my mill also.



Chip Maker, please see the attached photo.  It shows the individual pieces:  a steel backing plate, the lead screw nut, the slotted piece with the piano wire, and a standoff.  The steel plate has a hole in it for the lead screw.  To assemble, the handwheel/bearing assembly on the X axis is removed, the plate is slid down the lead screw and bolted into place.  The external LS nut is then threaded onto the LS and run down to the plate.  I found it easiest to temporarily re-attach the hand wheel and turn the LS while holding the nut.

Before drilling the 1/16" hole in the nut I ran it down the LS and marked the spot with a felt tip pin.  I chose the location to maximize the amount of adjustment with wear in mind.  The piano wire piece is free to rotate in the hole (it has to, in order for the design to work).

The system is similar to the split nut mod, where the nut is slotted so it can be compressed & therefore take out the slack in the nut.  Another approach uses a purchased Acme anti-backlash nut, which has two nuts and a spring to apply pre-load between the two nuts and remove the slack.  The split nut is a cheap way to go but you have to take the table apart to adjust it.  And the commercial anti-backlash nut would likely require some serious modding to install it.  My scheme just requires two drilled/tapped holes in the end of the table, to mount the steel plate; and can be adjusted without disassembling the table.  To adjust, I loosen the screw holding the slotted piece then either rotate the nut by hand or push/pull the slotted piece until the backlash is minimized.  Then tighten down the screw.  The 10TPI thread means the adjustment can be a little fiddly but it's not too bad once you get a feel for how things work.

Some might wonder why I didn't just use a set screw to hold the nut in place.  But you have to remember that the nut is threaded onto the LS.  The sideways force from the set screw would increase the drag, and also push the LS sideways.  Designs to avoid this seemed to introduce their own complications so I went with the scheme shown here.  

BTW this mod DOES slightly reduce the range of motion on the X axis, by ~1 inch or so.

I have not done this mod to the Y axis of my mill because it's not nearly as easy to do (there is no spacing between the table and bearing block).  If any of you decide to try it, you should strongly consider adding thrust bearings as well.  They make a large improvement to the Y axis.   If I were to do that I likely would also try to get a little more range on the Y axis.


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## homebrewed (Aug 3, 2017)

Correction:  my mill is a true-inch machine so the lead screws are 20TPI, not 10TPI.  Apologies for any confusion I may have caused.


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## chip maker (Aug 3, 2017)

OK now that I got the photo I fully understand how this works. Really a very simple fix except for the drilling and plate install. Thanks for the photo and better explanation as now I completely understand the conversion and seems it would work out on my mill as well.  I will for sure look into how to make it work on my mill. Thanks !!!


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## jdl6mm (Aug 3, 2017)

Oh, so when you move the slotted piece back or forth, it turns the nut to take up the backlash. I see now, I think. Does it tighten or loosen against the carriage?

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## jdl6mm (Aug 3, 2017)

Not the carriage per say, but the bracket you made for the carriage

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## homebrewed (Aug 3, 2017)

jdl6mm said:


> Oh, so when you move the slotted piece back or forth, it turns the nut to take up the backlash. I see now, I think. Does it tighten or loosen against the carriage?
> 
> Sent from my VS987 using Tapatalk


Yep, that's how it works.  It tightens and loosens against the steel plate that is bolted to the table.  If you take a look at your X2 you will immediately see that the plate is required for this to work.  BTW the plate is 1/8" thick, seems plenty stiff for this application.

I've found it is fairly easy to adjust.  One small refinement I did after the initial install was to replace the philips head screw with an allen cap head -- it's much easier to loosen/tighten.  To get a screwdriver on the philips head I had to run the table much further over to the right.

I've got DROs installed on my mill.  With the AB mechanism adjusted reasonably tight, pushing/pulling on the table only produces .001" of motion according to the X axis DRO.  The mechanical turns dial has to turn .002-.003" before the DRO reading changes by .001".  Before the mod I was seeing .005" of table motion and the turns dial had to move .010" before the DRO readout would change by .001".

Aside from removing the table to drill/tap the mounting holes for the steel plate, the most involved part of this project was turning the lead screw nut down so it was perfectly circular.  I made an expanding mandrel out of aluminum to fit the ID of the nut, installed it in my lathe (a micromark 7x12) and took it slow, since it was an interrupted cut in steel.  I also cut the nut in half (with my parting tool) so I had an extra in case I screwed something up.  That also reduced the extent-of-motion penalty imposed by the mod.  Even with half the number of threads it's plenty beefy.

The other half of the nut can't be used to mod the Y axis because it uses left hand threads.  If I just put a right-handed LS in there I still would have to buy a matching nut, since there must be TWO nuts per axis to implement the mod.

One potential issue is if you have a substantially worn lead screw.  Since the two nuts are separated by several inches, it's possible that the outer nut could be in a less-worn portion of the LS, compared to the inside nut.  The result would be a variable amount of backlash that depends on the table position.  My mill is fairly new so I haven't noticed a problem but YMMV.  It could be an excuse to get another lead screw


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## mikey (Aug 3, 2017)

Seeing the original Sherline adjuster might make things easier to understand. Initially, Sherline was looking for a way to just lock the Z-axis lead screw nut down so they added a lever that threaded onto the lead screw and locked onto the main lead screw nut: 




Then someone got the bright idea that if they used a bar to adjust the lever's position they could use the locking lever as a backlash adjuster. They just drilled a hole in the end of the lever handle, added a sliding bar that was lock-downable and voila, an adjustable backlash adjuster thingy.




I have this device installed on my Sherline Z-axis and it works. On the Z-axis, back lash is not about how much play there is when you turn the hand wheel; its about what happens when the cutter engages the material in a cut. If back lash is excessive, the entire spindle head can move to the degree of that backlash. This results in the end mill/cutter gouging into the work piece. This Z-nut adjuster thing prevents that by tensioning the nut so that the head cannot move much. 

As you can see in the second picture, the lever locking knob is loosened and the lever itself is adjusted until backlash is all but eliminated. Then the knob is locked down. The knob and the bar is attached to a separate block that is screwed into the side of the headstock.

Prior to installing this nut adjuster, I would lower the cutter down below the required depth of cut and then back the head up to my desired setting. This took most of the backlash out of the system and the cut would proceed without mishap. After installing the adjuster, I can just dial in my depth of cut and the head does not move and no more crashes have occurred. So, as simple as it is, it works.

What homebrewed seems to have done is to substitute the lever for a pin. As long as you are able to attain enough leverage with the pin to keep the nut in place then this will work. If not, you can add a lever arm and use that to improve it's function.


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## homebrewed (Aug 4, 2017)

mikey said:


> Seeing the original Sherline adjuster might make things easier to understand. Initially, Sherline was looking for a way to just lock the Z-axis lead screw nut down so they added a lever that threaded onto the lead screw and locked onto the main lead screw nut:
> 
> View attachment 239091
> 
> ...



Thanks for the info!  I had not looked all that closely at the Z axis on the Sherline -- it's quite a bit different from the table setup.  The X2 mill's Z axis drive is completely incompatible with the Sherline design, but the design could work for the X and Y axes (on the other hand, Sherline didn't do it that way for X and Y).  The main thing is to arrange things so the backlash can be removed while providing enough leeway to accommodate wear.


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## homebrewed (Aug 4, 2017)

I've been thinking about how the Sherline Z axis approach could be used on the X2's X axis.  It could permit use of a less-modified feed screw nut for the external nut, but would require a slightly different assembly procedure.

In the normal assembly procedure the LS nut is installed into the saddle first, then the LS+table is screwed into it.  But, since the external nut's profile has not been altered, it can't rotate on the LS shaft.  As a result, it can't be moved into its proper place.  It, the lead screw, steel plate and internal LS nut must all be installed into the saddle first (and installed so the backlash can be removed with suitable adjustment).  The steel plate would have to have two holes in it so the set screws for the inner LS nut can be accessed.  

In this approach the table would be slid onto the saddle in a separate operation, then the gib, bearing block and handwheel installed.  As Young Frankenstein said, .....It.....Could.....Work....


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## mikey (Aug 4, 2017)

I know nothing about the X2. Does it not have a split leadscrew nut that allows you to dial out backlash? If not, then maybe you can fabricate one. Of all the ideas that I have seen for backlash elimination on a manual machine, the split leadscrew nut is the best. My Emco lathe has split leadscrew nuts on the cross slide and compound and both can be adjusted to zero - zero - backlash, while turning smooth as silk. Might be a consideration.


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## homebrewed (Aug 4, 2017)

mikey said:


> I know nothing about the X2. Does it not have a split leadscrew nut that allows you to dial out backlash? If not, then maybe you can fabricate one. Of all the ideas that I have seen for backlash elimination on a manual machine, the split leadscrew nut is the best. My Emco lathe has split leadscrew nuts on the cross slide and compound and both can be adjusted to zero - zero - backlash, while turning smooth as silk. Might be a consideration.



The X2 does not have a split leadscrew nut so would need some machine work.  My reluctance to go that route is based on comments others have made w/regard to doing a split nut mod on mini-lathes.  The nut appears to wear fairly quickly, requiring frequent adjustment.  Since the X2 leadscrew nut is buried inside the table it would be a PITA to adjust the nut (you'd have to disassemble the table).  This would be particularly unhandy if you have added a DRO, like I have.  That's the main reason I was going for something that could be easily adjusted.


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## mikey (Aug 4, 2017)

Oh, okay. It was a thought.


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## homebrewed (Aug 4, 2017)

mikey said:


> Oh, okay. It was a thought.


Well there are a zillion machines out there, who could know the ugly details on all of them, right?  As an X2 owner (or a VW owner) I am pretty familiar with the compromises/faults those things have.  For instance, the X2 doesn't have tapered gibs .  I'm happy to get input from other sources because I sure as heck don't know everything, maybe there's yet another approach that is way better.  You don't know what you don't know.


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## Wreck™Wreck (Aug 5, 2017)

Is the axis in question under NC?


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## homebrewed (Aug 5, 2017)

Wreck™Wreck said:


> Is the axis in question under NC?


Please clarify "NC" and I will tell you


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## Wreck™Wreck (Aug 5, 2017)

Numerical Control
CNC


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## homebrewed (Aug 6, 2017)

Wreck™Wreck said:


> Numerical Control
> CNC


Ah.  No, at least not yet.  I have steppers, drivers and a PSU but nuttin' else yet.  From what I've seen most folks who do a CNC mod go the extra distance and use ball screws.  But if you're on a tight budget or aren't sure just how useful CNC would be to you, it certainly is feasible to use the standard feed screws.  The Sherline CNC mill does.


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