Thrust bearing modification to mini lathe compond slide.

[ian_in_the_midlands]

Since new, I have had problems with the dial sticking on the compound slide.
I can not see how the design should work; winding the slide away from the handle relies on contact between the bracket and the dial. The friction will always try to grab the dial.
I could never trust the dial so have had to resort to a DRO made from a tyre depth gauge.

I wanted to have a go at fixing this with the option of returning to standard if things didn't work out, so I purchased a needle roller bearing, a compound slide feed screw bracket, and dial.

The two mounting holes were deepened in the bracket to allow clearance for the screw heads before boring out a recess for the bearing. I did plan to leave a couple thousands of an inch of the bearing proud, but something went wrong as when I tried the bearing for fit, it was flush.  Easily fixed by a small recess around the collar for clearance.
Everything assembled, and now slide feels much better. Only .075mm backlash, so wasn't far off depth with the boring.
Hopefully the bearing will not suffer from ingress of muck. The gap is tiny so I do not think this will be a problem.

[Chuck in E. TN]

Ian, can you please post the part #/specs and source of the thrust bearing you used.
 
Chuck

[ian_in_the_midlands]

I purchased the parts from Arc Euro Trade.

http://www.arceurotrade.co.uk/Catalogue/Bearings/Needle-Roller-Thrust-Bearings
AXK1226 + AS + AS Needle Roller Thrust Bearings - 12x26x4   AXK1226ASAS   £3.84    

I have concerns about the modification for 2 reasons:
1. For the price of a £3.84 bearing, why do they not fit them when they build them?
2. Why can I not find details of other people doing this modification?

Have I missed something?
If it does develop problems, at least parts for the mini lathes are easily available.

[Manxmodder]

Don't think you have reason to panic Ian,these type of roller thrust or ball thrust cup bearings are common enough in crosslide  assemblies. They are fitted to my Harrison L6.......OZ.

[steampunkpete]

winding the slide away from the handle relies on contact between the bracket and the dial.

No - The thrust generated by pulling and pushing the slide by turning the handle is countered by the collar on the shaft being contained in a pocket created by the recess in the the back of the bracket.

The dials must NOT touch the bracket. If it does, that is why it sticks. It might also stick if a small bit of swarf or grit has got between the dial and bracket.

Because the handle turns both ways and both pushes the slide away and pulls it towards the handle, it would need TWO thrust bearings, one to take the thrust in the pull direction, and one in the push direction.  If you follow the link in ArcEurotrade's page to the example of how it is done, you will see it calls up TWO needle roller thrust-bearings.

By using only one it seems that you have a set up that works in one direction, but in the other works on the same principle as the standard arrangement - but it isn't really clear from your description what you have done. You seem to have machined the dial - is that so?

Like other people I have solved the problem of friction and backlash by using a ball-race. Ball-races are not intended to take significant thrust, but for a mini-lathe the forces are low enough not to cause an wear problem. See my post in MadModder showing how it was done on my cross-slide.

[ian_in_the_midlands]

Hello Pete,
I agree with what you say if you were talking about the cross slide, but the compound on mine works in a different way.
If I remove the handle and the collar, the lead screw will pass through the bracket - is yours the same?
There is no recess on my bracket.

I also agree - 1 ball race only works in 1 direction, but luckily this is the direction I was having the problem with.
Fitting a second bearing to work in the other direction would be more difficult because the bracket fixing bolts are in the way. I am sure it can be done, but I have no issues when winding the compound slide in that direction so 1 bearing is all I needed.

[Chuck in E. TN]

Ian, I hadn't done it yet as I hadn't found a suitable and affordable bearing. Now that you have found the spec, I see that VXB has them for under $5 US. Will definitely try this mod.
 
Chuck

[ian_in_the_midlands]

Hi Chuck,
Are you seeing the same problem as me: The graduated collar sticking and not reliably turning with the handle? Before you order your bearing, it may be worthwhile measuring the diameter of the hole in the collar. I seem to remember reading somewhere that some are 10mm.

[Manxmodder]

Hi Ian, can I ask does your graduated collar have any means of adjusting the amount of friction between it and the spindle.

On the Harrison dials there is a grub screw which loads a spring and acts on a small brass disc which creates an adjustable level of friction between the graduated dial and the inner spindle collar.

I have included a link to image showing a similar set up which uses springs and a couple of ball bearings.....OZ.

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRw&url=http%3A%2F%2Fbbs.homeshopmachinist.net%2Farchive%2Findex.php%2Ft-53703.html&ei=GOezVJ7HBsTrUoKRg5AI&bvm=bv.83339334,d.d24&psig=AFQjCNFLhbwyTR0j4fGcvdh5d1KhGCkh4A&ust=1421162186654916

[ian_in_the_midlands]

A bent spring is used to allow the collar to turn, whist applying the tension to hold it in place (item 45).

[steampunkpete]

Hello Pete,
I agree with what you say if you were talking about the cross slide, but the compound on mine works in a different way.
If I remove the handle and the collar, the lead screw will pass through the bracket - is yours the same?

Mine is the same - I had forgotten it was different to the cross-slide.

I have already modified my cross-slide with a ball race, and you have prompted me to do a similar mod to the compound.

The way I did it was to use a 10mm ID x 15mm OD ball race. The collar was turned off the lead-screw and the bearing fitted with Loctite. A 15mm recess was bored in the back of the bracket, and the lead-screw + bearing loctited in. Because the lead-screw sits about 3mm further out than before I turned up a suitable spacer to go under the handle. Re-assemble and job done in under an hour.

Pete

[steampunkpete]

Since new, I have had problems with the dial sticking on the compound slide.

p.s. I had the problem after I applied some grease to the friction mechanism, and now I've seen your post I understand why. Lubricating the friction mechanism means that the torque generated by friction between the dial and the bracket can exceed the break-away torque on the dial - so the dial ceases to rotate with the shaft and sticks to the bracket.

The quick cure is to de-lubricate the friction spring / dial and apply a smear of thin grease to the dial / bracket interface. That worked a treat for me.

[ian_in_the_midlands]

Thanks for the feedback Pete. Your earlier post had concerned me a bit.
I hadn't thought about doing it that way - it does give you the advantage of the bearing working in both ways.

I am sure the root cause is as simple as oil/grease on the friction spring.

[steampunkpete]

Sorry the response was a bit late, it was a combination of a big birthday & early retirement with consequent gallivanting and getting the mod done so that I was confident that it worked before I posted it.