X Axis

Once again, the internet was my friend and I did a lot of research on how to manage the X Axis on such a small lathe. Some have even put the screw outside the cross slide, but I did not like the idea of swarf getting into the ballnut. So, I found a neat design, wish it was my idea!

I did make a small change by electing to go with direct drive instead of mounting the stepper motor inboard and using a timing belt. My mill uses timing belts and I am sure this is the reason for some backlash, so I bought a larger motor and will use a flexible coupling.

This will mean that the motor will stick out quite a bit at the front, but I dont really see that as an issue. I can always go back to belt drive later if this is a problem.

In machining the saddle to accept 15mm outside diameter ballscrew, I moved the centre of the hole down about 3.5mm so the top of the ballnut will clear the cross slide (Img 1-2).

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For securing the ballnut, I used 1/8 BSW cap screws (Img 3-5) because I had them on hand. The fact that they are a little larger than the 3mm standard was a help as well as I did not want to break a tap. This was a prime concern as I had already broken a 6mm tap in one of the holes for the z axis fixed ballscrew mount.

Everyting fitted quite well when assembled (Img 5).

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I am making the extension for the slide out of aluminium. If need be later, I can redo in steel.

I used the 2 existing 5mm tapped holes for the turntable for the compound as well as another 5mm at the other end. Maybe I will add some extra screws later.

Getting the holes in the correct positions (Img 6) was quite easy after measuring. I used a laser edgefinder (Img 7) to locate the edge and used the digital readout on Mach3 (Img 8) to position the holes and counterbores.

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Img 9-11 shows the aluminium plate fitted to the cross slide. The 2 widest holes line up with the oil nipples on the slide. I just made this large enough to fit the oiler in the hole.

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Next task was to machine the bracket for the fixed ballscrew bearing. Luckily I had the right size drill for this (Img 12), then I cut a keyway so I could remove the bracket without removing the ballnut from the cross slide (Img 13). Then the pocket was cut so the bearing fitted into a recess (Img 14).

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Holes were tapped 1/8 BSW to secure the ballnut bearing (Img 15), and mounting holes for the stepper motor were tapped M5.

Everything seemed to fit ok (Img16). I will be away at a shooting competition this weekend, but I should get the X Axis finished Monday.

The bearing mount was then drilled and tapped for 2 x M10 button head screws (Img17).

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Mount fitted nicely to the cross slide(img 18-20). I tested the slide using my battery drill, and the slide moves really well under ballscrew.

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Stepper motor mounts were next on the agenda and was drilled to match the M5 holes tapped in the mount and slide (Img 21). I drilled one to suit the tapping drill size (4.2mm) so I could use this as a guide to hand drill and tap the holes in the cross slide. I do not have enough Z travel to be able to drill this part using my mill.

Now the stepper is installed and wired to the G540. Then I set the steps per mm, then checked backlash. I jugged the axis in, then set the dial indicator to zero and than ran in 10mm (IMG 22) then back 10mm (IMG 23) with a G0 code. This shows zero backlash, so I'm a happy camper. This is much better than my mill which is geared 2:1 with a timing belt.

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MOV 24 shows the X axis moving with a G0 code! There is 80mm of travel, heaps for a lathe of this size.

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All good things must come to an end, and that was the case for my 8mm ballscrew! After about a year of use, the ballnut suddenly disintegrated! I am rebuilding the X axis to use a 12mm ballscrew connected by timing belt. Pics to follow soon.

The new 12mm ballscrew is much more durable than the original, fitting it was not too difficult. This now has a 2:1 pulley system with a timing belt. The plastic cover attaches with Velcro and was cut from a 2 litre plastic milk bottle!

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