Hobbymat md65 – how remove female leadscrew coupling?

[theelous3Participant @theelous3]

Hi folks, first post so hello first and foremost 🙂

 

I picked up a hobbymat 1985 in excellent condition, but I need to get in to the leadscrew’s female drive coupling to work out some gunk that is giving the carriage some sticktion and inconsistent motion.

 

There is a spring steel clip deep inside, there is maybe 1mm gap, and it’s a few mm deep. There are no eyelets, not that any c-clip pliers could ever fit in. The only thing I’ve been able to get at it with is a scalpel blade, but it just continues to lift a tiny amount and snap back in to place. It’s impossible to take a picture of it.

 

I’ve given a model, drawing, and manual drawing (the part is 9 on the manual’s illustration).

 

 

 

[DiogenesParticipant @diogenes]

I’ll go and refresh my memory after another coffee and report back..

..Have you managed to find any of the older ‘Hobbymat’ or ‘MD65’ threads that used to be on this forum?

I think it’s probably true to say that 99% of all known carriage / traverse issues arise from the superficially inscrutable ‘pinch-‘ and ‘press-‘ bolt adjustment system on the back..

[bernard towersParticipant @bernardtowers37738]

Is it round wire or flat if it is round it might just be a firm knock off and just holds the part in place for normal use.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi theelous3, it’s a bit of a fiddley job, but the best way I’ve found is to get the ends of the clip, lined up with one of the dog clutch gaps, and then using a small watchmakers type of screwdriver, lift out one end and then work it out by turning the leadscrew as you go, but you may need two screwdrivers.

 

Getting it back in is easy, using a bit of 15mm copper tube, but the tube will need to have a cut along its length.

Regards Nick.

[DiogenesParticipant @diogenes]

Yes, that exactly.

 

 

[theelous3Participant @theelous3]

@diogenes @nicholasfarr14254 thank you very much. Sometimes knowing something is possible is all that’s required to get it done. I removed the clip with scalpels and an inverted broken key extractor lockpick.

 

Strangely however, the coupling remains retained. It slides a small amount, and seems to come against a shoulder, presumably the groove on the leadscrew for the retaining clip ring. I’m wondering if there is a nack, actual method, or I should attempt to force it – perhaps there is a small burr I can shear – but that would be surprising considering someone put it on there in the first place.

 

My removal method for prosterity’s sake:

 

Scalpel A to lift the end away from the shaft and create a gap through which scalpel B could slide, between the shaft and the clip. Then keeping B in place, removing A and sliding an inverted key extractor pick with as much angle as possible through the dog crenelation under the ring. Remove B. Pulling the ring away as far as possible, reaching and driving the leadscrew as described by nicholas above.

[DiogenesParticipant @diogenes]

It’s probably a burr – the trick is to exert a balanced ‘pull’ or ‘pry’ on it with no sideways forces – it being imperative not to bend the shaft, of course.

The kind of co-axial ‘sharp tug’ that controlled use of a slide hammer can deliver would be my own first choice.

For lack of that tool, I might fabricate something like a bearing puller / ball joint splitter, but gently does it – there should be little or no real resistance to the pull of a thread – if it doesn’t slide straight off and with great ease, something is amiss and you should investigate further before applying any real pressure.

[theelous3Participant @theelous3]

Something ia certainty amiss. I’ve given it (relatively) considerable force. A bearing puller was my thought as well, I might fab something up.

 

It’s worth noting that perhaps 90% of my rubbing issues actually stem from the clip its self rubbing on the coupling. With the clip removed, the coupling spins freely as the carriage is turned. I filed and slightly loosened the clip with some improvement, but it’s still not satisfactory.

[DiogenesParticipant @diogenes]

I’ve not known the clip to cause problems – maybe worth stepping back and looking again at other aspects of the machine – for example, a lack of sufficient freeplay of the leadscrew handwheel at the R/H end, or binding of the saddle – either through adjustment or misplacement / deformation of the plastic ‘gib’ – both of these things may cause axial ‘loading’ of the leadscrew.

Another source of leadscrew binding is overtension of the two inner grubscrews in the front of the saddle – the tips of these register in dimples in the tubular ‘nut’ to prevent displacement, but only need to be very gently nipped up – overtightening deforms the thin wall of the ‘nut’ and ‘pinches’ the leadscrew.

[theelous3Participant @theelous3]

I appreciate that it sounds strange but I believe I have eliminated everything else. With the gears removed and only only the leadscrew thrust bearing, two lock nuts, coupling and clip installed, when rotating the handle the carriage couldn’t be smoother in both directions. With even light finger pressure, just enough to hold the coupling from rotating, the jank begins, and through my finger I can feel the intermittent little scratching and grabbing.

 

Repeating the same test with the clip removed, the jank is nowhere to be found. I can flick the coupling and watch it spin very freely many rotations. It stops dead when clipped. It could be a burr or something on the inner face of the coupling, or burrs on the leadscrew groove similar to what is likely holding on the coupling, but it’s clip related either way.

 

Worth noting I think this machine has probably only seen an hour of use if even. No wear anywhere, the original brazed tools the previous first and only owner bought with it are still wax sealed bar one, which shows little use.

If there is a break in period that usually wears these kinds of things in, it hasn’t happened yet.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi theeolus3,the first photo below, shows what it looks like with both parts of the dog clutch are removed.

The only thing that controls the leadscrew end float is a washer at the handwheel end, and the one on mine is 2.41mm thick.

I would think the only reasons your piece won’t come off, is either a burr on the ring groove, or some gulling between that piece and the leadscrew. The leadscrew will only come out of the lathe at the hand wheel end, but with the hand wheel removed, the leadscrew should be able to be pushed the other way, giving a gap of about 5mm between the thrust bearing and the lathe headstock.

Removing the taper pin through the collar, may let you get a couple of pry bars or a plate for a puller behind the thrust bearing and the headstock.

Regards Nick.

[DiogenesParticipant @diogenes]

Theelous3, I take your point.

I think if you can fabricate some means of popping the carrier off, hopefully all will be revealed.

Apologies for erring on the side of caution!

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