An Easy Way to Reduce the Mini-Mill’s Z-Axis Backlash

aluminum_tape_20090312

The typical Sieg X2 mini-mill [HF 44991, Grizzly G8689, Micro-Mark & others] has a lot of backlash in the Z-axis. In my case it was .053-inches, which was almost a full turn of the fine-adjust knob.

I heard that putting a shim behind the rack on the column would help by causing it to mesh tighter with the pinion gear in the head. So I decided to give it a try. For shim-material I used adhesive backed aluminum tape that was .0035-inches thick. The tape was easy to apply once the rack was removed. I just stuck a piece on the back of the rack (after cleaning it with brake cleaner to remove any oil), then I burnished it with a piece of metal to make certain there were no wrinkles and trimmed the tape to size and around the screw holes with a utility knife.

I applied only one layer at a time and then reassembled the rack and measured the backlash. After the forth layer of tape the backlash was down to .035 inches, a 34% improvement. But the backlash didn’t improve any more after applying the fifth layer. Plus it became difficult to move the head and very difficult to engage and disengage the quick-adjust wheel. So I peeled that layer back off.

It was probably not necessary, but I applied a final layer of thin clear packing tape over the aluminum since it is generally not a good idea to have dissimilar metals like steel and aluminum in direct contact.

Removing the rack was not hard. I have a short rack held on by just two metric flat head screws, although I have heard that some machines have longer racks with more screws. I recommend that you take care not to lose or damage your screws as you may have trouble finding replacements locally. I managed to drop one of mine in the large hole in the top of the head, just in front of the rack, and it took me a while to fish it out. So you might want to plug that hole with a rag or something. By the way, you can get replacement screws, or almost any other part for your mini-mill, from Littlemachineshop.com.

The screws and rack are easy to remove once the head is dropped down as far as it will go. But to get it low enough you have to disconnect the spring torsion-arm supporting the head. It is not hard, as the spring is not that strong, but there is definitely a danger you could pinch your hand or the bolt could go flying into your face, so take precautions.

I want to make it clear that you have to disconnect the torsion arm from the head, and not the spring itself, which is mounted on the column. I found it easiest to remove the single attachment bolt when the head was positioned so the torsion arm was horizontal. I also put a pile of rags on top of my vise to help protect it and the spindle if the head dropped on it after the spring was removed.

Once the head is down all the way it is simple matter to remove the screws and slide out the rack. When you’re done, just reassemble everything and then lift up the head and turn the quick-adjust wheel until the gears mesh again. Then reconnect the torsion arm.

I don’t know how hard it is to find aluminum tape like I used. I think I bought mine at an auto parts store a long time ago. I know you can buy it online in the US here. There are plenty of other materials you could also use as a shim. Please leave a comment if you try this mod and let us know what you used and what your results were.

4 comments to An Easy Way to Reduce the Mini-Mill’s Z-Axis Backlash

  • Anonymous
    March 16, 2015 at 9:21 PM | Reply

    or use aluminum soda can.

  • tech teacher
    October 31, 2016 at 5:18 PM | Reply

    the worm gear may have backlash. Remove the shaft cover and you will see a universal. Loosen the fine turn wheel and pull on the universal to take up the slack then tighten the wheel back down. With .010 shim behind the rack, I ended up with less than .010 backlash

  • barney
    March 22, 2018 at 2:16 AM | Reply

    my sxt2 is down to zero backlash hard to belive its true to get this right one needs to attack the whole unit and eliminate all the backlash in everything that’s in the z coloum the fine feed that’s is a big problem where bronze bushes need to be made ,,, and where the fine feed fits in the casting opposite side ,,the splines run into the casting creating bore ware a bronz bush is needed there and the splines cut back to to fit in the new bush there is also slop in the bevel gears they need to be bushed to take out all the slack also the the vernier drive rod for the fine feed the small universal needs to be looked at that’s the one under the cover that universal has a job to do ,,, don’t lock it up tight other wise you will creat another problem where the shaft goes through the end block on the vernier drive there needs to have an adjusting screw in the end of the vernier drive to reduce end play right on the other end of the rack gear there is another screw and a pointer this screw has to be adjusted to take out the end play on the rack gear once all that has been done you can adjust the z rack ,,, in my case the rack was not matched to the the gear ,,, this is a serious problem with all the x2 and sx2 machines ,,,, taking hold of the spider handle to operate the z axis ,,, if it feels lumpy in the z mode there is a serious miss match in the gear and the rack ,,, and I only advise an engineer to tackle the problem or some one who knows what he is doing ,,, the lumpiness in mine is all but gone the one sx2 I rebuilt was straight out of the box brand new all problem were removed before I used the machine ,,,and the other thing I got rid of was the sizor lift counter weight ,,, that thing was about as usless as a box of frogs I weighed the head complete and got a gas strut to the apropiat weight not an over weight gas strut ,,, the simple reason , a gas strut that is too strong puts a lot of ware on the vernier drive and the small key that holds the spider hand wheel in place I also made new castellated drive gear foe the drive ((I had a tad of slack)) whilst I was doing it I sorted it now the spider handle slides on the shaft where the keyway is I drilled and put a small grub screw to pinch down on the new key this was also slack fitting that pinch screw took out a tremendous amount of slack after all this work the machine is down to practically zero limits I also fitted the bottom of the columb to the base (( it was badly fitted at the factory)) with all this said ,,, and also heard about the coloum fles that was also sorted with a shoe on the back of the colum which the large nut is and a new plate to stiffen the back up and side screws for tramming ((not that I will ever use the 45 tilt)) I don’t use the sx2 very much all the work is done on the second generation x3 was it worth it I think so altho a lot of people why bother ,, now if I reach for the vernier drive I am confident I can a thow off without any head drop ((( that’s another problem with the x2 sx2 machines a massive problem?? if any one is interested in the gas strut set up I will see if I can get some pictures up some set ups are darn right ugly this set up you don’t notice its right along side the colum ,,, check out the dreaded head drop on this site,,,

  • barney
    March 22, 2018 at 6:31 AM | Reply

    mini mill head drop problems ,,,, is another page

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