Hobbymat MD65 – Thrust bearings on leadscrew

[Harry MParticipant @harrym12848]

Good evening everybody

So nice to be here ! I recently acquired a Hobbymat MD65. Seems to be a nice mini lathe, even though it has some issues that are not too difficult to overcome.

I 've seen that more than a few people have done the "thrust bearings mod" on the leadscrew handle. Therefore, I purchased some AXK1226 thrust bearings and tried to fit them. Unscrewed the handle, fitted the bearings, and then put the handle back on.

The problem is, that the assembly is either way too tight – and the leadscrew cannot move at all, or it has free play – backlash. I see that the way the handle is attached is not proper – I guess a keyway would be a better option than a screw-on handle, but it is what it is.

Any ideas on how thrust bearings can be fitted and backlash adjusted on the leadscrew ?

Thanks in advance !

[Harry MParticipant @harrym12848]

[DiogenesIIParticipant @diogenesii]

The mod has been done to mine (although I'm not entirely convinced how much value it has – there is already a thrust bearing at the headstock end).

Be that as it may, I'm not sure that it's simply a question of 'sticking them in' and doing it all up again – I'm more-or-less certain it requires 'metal-off' the ?outer?inner? collar.. .possibly in a first for this forum, I have to admit that a certain amount of Speyside precludes me wanting to go and look now – I'll go and check for you in the morning..

The end-float problem is a question of trial, error, 'feel' and patience, I'm afraid – the best advice is to not overtighten the locknut, but only nip-it-up enough to stop the handwheel unscrewing.. ..do it, re-do it, move it a bit and do it again, eventually it will come right..

[DiogenesIIParticipant @diogenesii]

Okay – there's a recess that is cut in the round 'bearing block' that is screwed to the square endplate at the tailstock end.

..without measuring up (I have to go to work) I can see that the main issue is that the bearing is of a larger diameter than the boss that bears the adjustable collar – I think the collar must have had a face skimmed to provide a running clearance, which could be part of your 'binding' problem – I'll measure later and see what has been done.

In closing (for now), I must point out that it's not a practical proposition to remove all backlash from the carriage leadscrew using the standard components – a little clearance is necessary in order for things to move freely, and on mine this translates to about an eighth-of-a-turn at the handwheel. In practice this is not a problem, there are established methods of compensating for backlash on manual machines, maybe someone with a little more time will provide a fuller answer, or can point you in the right direction!

[Harry MParticipant @harrym12848]

Thank you for the quick reply !

If you could do some measurements, that would be great !

I will try to get rid of the spring washer that's behind the tighting nut – and then replace the nut with a nylock nut. Maybe this in addition with a little slack on the handle would do the trick

Hmmm, seems that I have to figure out how to compensate backlash then, to make it right

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Harry M, I've not got a thrust bearing on my hand wheel end. As DiogenesII has said, all a matter of adjustment and allowing a slight clearance. I've had no issues with using it without the mod.

Regards Nick.

[DiogenesIIParticipant @diogenesii]

Hi Harry.

The recess in the round 'bearing block' is approx 3.75mm deep (housing a bearing + two hard washers total thickness 4mm) – so outer washer sits c. 0.25mm proud of the face. Bearing is a 1226, I think – the recess is 27.30-ish diameter…

The handwheel 'boss' upon which the adjustable collar is located seems to be unmolested, lengthwise – the collar is (as near as I can tell with feeler gauges) c. 0.15mm or so shorter than the boss, so that there is clearance for it to rotate without binding when the complete assembly is all in situ and tightened up. Hope this is clear / makes sense.

I have some reservations whether the boring of the bearing block will be feasible unless you have access to another lathe to do it on, or can find a spare (or even make one).

As Nick says, and I hinted at the beginning, I'm not at all sure that much is to be gained – the greatest thrust comes when cutting (towards the headstock), and the bearing already fitted at that end of the leadscrew takes care of that – at best this will only ease the action of returning the saddle to the 'tailstock end' – a circumstance which is only really coping with the resistance of the carriage – if the action of moving the carriage feels stiff, recheck the adjustment of the saddle clamp and setting screws.

If you do decide to go ahead, DO check all measurements with & against the fittings on your own machine to check that everything will fit and work together as expected.

PAY particular attention to the depth of the recess and the relative position of the shoulder on the leadscrew – the bearing must seat in the bottom of the recess, and not on the leadscrew shoulder!

Kind regards

D.

Edited By DiogenesII on 16/11/2021 06:44:11

Edited By DiogenesII on 16/11/2021 06:50:22

[DiogenesIIParticipant @diogenesii]

[Harry MParticipant @harrym12848]

Thank you so much Diogenes ! The measurements and the photos are really helpful. I will try making a spare block – and see how it goes

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