Back gear cluster replace

[Chris MurphyParticipant @chrismurphy94983]

Hi all,

I posted something about this yesterday and it was a tooth missing from my back gear cluster which sits at the bottom of the headstock.

do I need to worry about a tooth missing even though it still seems to work fine when I use back gear, which is not very often, and if I were to replace the back gear cluster how would I go about it.

has anyone ever done it before, if so, could you give a few pointers.

im reluctant to do the job seeing as it’s working ok, but it may need doing sometime.

also does anyone else use their lathe ok with broken teeth.

the lathes a Myford ml7.

thanks

Chris m

[Chris MurphyParticipant @chrismurphy94983]

[SillyOldDufferModerator @sillyoldduffer]

Have a look at your Gear seems to be missing thread Chris. You've already got some suggestions.

I'd replace the gear rather than mend it, but they are fixable. Problems caused by a missing tooth:

• If the gear is used for threading, the ratio will be wrong with an accumulating error
• The next tooth in line gets an extra-hard whack on each turn causing wear and risk of breakage.
• The bump might cause a periodic visible line on the finish of the job

Depending on what you're doing the effects may be small enough to not matter.

Dave

[Pete RimmerParticipant @peterimmer30576]

If it's apparently working ok, doesn't knock and doesn't leave marks in the work when you're using back-gear, there's no real reason to rush into changing it. Just keep an eye out for replacement gears and bide your time, they will come along.

[noel shelleyParticipant @noelshelley55608]

If you use it with missing teeth others will break off in time and may well damage the other wheels. On an ML7 the job is easier than on the S7 as the spindle can be removed by undoing the 4 caphead bolts NOTE where the shims go and keep them with their respective caps ! If you look at the manual, 51 the back gear eccentric is held in place by a 2BA grub screw in the operating lever. The gear wheel cluster is held on the shaft by a socket countersunk 2BAscrew. I hpe this is will be more clear looking diagram B in the ML7 manual. Good Luck Noel

[Pete RimmerParticipant @peterimmer30576]

Posted by SillyOldDuffer on 02/10/2022 10:09:27:

Have a look at your Gear seems to be missing thread Chris. You've already got some suggestions.

I'd replace the gear rather than mend it, but they are fixable. Problems caused by a missing tooth:

• If the gear is used for threading, the ratio will be wrong with an accumulating error
• The next tooth in line gets an extra-hard whack on each turn causing wear and risk of breakage.
• The bump might cause a periodic visible line on the finish of the job

Depending on what you're doing the effects may be small enough to not matter.

Dave

Your second point is totally incorrect Dave. Firstly, it would only cause a skip if there were no other teeth engaged which you'd need to be missing several in a row for that to happen. Secondly, the back gear is only a mechanism for slowing the spindle. It has no effect on the threading ratios which are all done on the end gears and gearbox if fitted.

[Robert ButlerParticipant @robertbutler92161]

Posted by Pete Rimmer on 02/10/2022 10:13:49:

Posted by SillyOldDuffer on 02/10/2022 10:09:27:

Your second point is totally incorrect Dave. Firstly, it would only cause a skip if there were no other teeth engaged which you'd need to be missing several in a row for that to happen. Secondly, the back gear is only a mechanism for slowing the spindle. It has no effect on the threading ratios which are all done on the end gears and gearbox if fitted.

? Surely the drive for the gearbox comes from the headstock which in backgear operates at a reduced speed otherwise the headstock rpm would make a nonsense of the gearbox output rpm??? for screwcutting???

RobertButler

[Pete RimmerParticipant @peterimmer30576]

Posted by Robert Butler on 02/10/2022 11:24:04:

Posted by Pete Rimmer on 02/10/2022 10:13:49:

Posted by SillyOldDuffer on 02/10/2022 10:09:27:

Your second point is totally incorrect Dave. Firstly, it would only cause a skip if there were no other teeth engaged which you'd need to be missing several in a row for that to happen. Secondly, the back gear is only a mechanism for slowing the spindle. It has no effect on the threading ratios which are all done on the end gears and gearbox if fitted.

? Surely the drive for the gearbox comes from the headstock which in backgear operates at a reduced speed otherwise the headstock rpm would make a nonsense of the gearbox output rpm??? for screwcutting???

RobertButler

No, the screwcutting ratios are driven from a gear on the end of the spindle so if it's turning, regardless of how it's made to turn, the screwcutting will work.

[HOWARDTParticipant @howardt]

I’d say replace. The wear caused by the missing tooth on adjacent gears depends on the diameters of the driver and driven gear. The top of the tooth will scrape the mating tooth and eventually wear all the teeth dependant on the ratio. Also if the teeth are hardened you risk breaking another tooth which may lead to something catastrophic and costly.

[Martin KyteParticipant @martinkyte99762]

Just change the darn thing. Myfords have spares

https://www.myford.co.uk/acatalog/B50.-21-56T-BACKGEAR-CLUSTER–70-1218-40989.html#SID=51

regards Martin

PS this is often caused by using backgear to lock the spindle when changing chucks. (I have been known to do it myself)

Edited By Martin Kyte on 02/10/2022 13:37:55

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