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Myford ML7RB backgear cluster

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ian j22/02/2019 19:17:44
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259 forum posts
227 photos

What a bad day ! Managed to strip some teeth off the 17 tooth gear of the 17/53 tooth back gear cluster on my ML7RB lathe.

Is it possible to remove and replace the cluster with out the hassle of removing and replacing the spindle. I live in hope!!

Ian

Mike Poole22/02/2019 19:43:33
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1757 forum posts
44 photos

Here is a link showing what you need to do, I don’t fancy your chances of getting that apart with the spindle in situ unless you are a gynaecologist, and getting the gear cluster out doesn’t look as though there is enough room to get it passed the spindle. It may be possible to unbolt the whole headstock and drop it out but I think that could well be more trouble than taking the spindle out. Don’t forget the screw hiding down the back gear lever top detent hole.

**LINK**

Mike

ian j23/02/2019 09:09:32
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259 forum posts
227 photos

Thanks for the utube link Mike, it confirms what I really thought. Looks like I'm going to have to learn how to reassemble the spindle and bearings, I may be back !!

Ian

Brian Wood23/02/2019 09:27:37
1831 forum posts
36 photos

Hello Ian J,

I had just the same misfortune and I'm afraid the only way of getting to it for access is to strip the lathe spindle.

One reassembly tip I think is worthwhile is to put a scratch mark across the lever and boss of the eccentric that swings the back gear up into engagement. It makes correct alignment a breeze when you come to put it together again later. Also, be aware that there are two grub screws that lock the lever in place on the boss.

And finally, another bit of future proofing maintenance which I have incorporated is to run an end mill down the pivot for the combination gear itself to cut a shallow oil groove rather than rely on the drilled hole to provide sufficient lubrication over the length of the close fit of the two components

I hope the repair goes well for you

Regards

Brian.

ega23/02/2019 11:42:04
1103 forum posts
90 photos

Unfortunate indeed! May we know what caused the problem?

Hopper23/02/2019 12:12:02
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3304 forum posts
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Posted by ian j on 23/02/2019 09:09:32:

... Looks like I'm going to have to learn how to reassemble the spindle and bearings, I may be back !!

Ian

They are not terribly complicated. Mark the bearing caps so they go back on the way they came off. Four cap screws and the whole shebang can be lifted out. Be very careful on disassembly to capture and note the small shims between top and bottom bearings on each side so they go back in the same place they came out of.

If you measure your spindle play up and down before disassembly you might even be able to tighten the bearings up a notch by peeling off one layer of the shims, if yours has the laminated shims fitted. Not all do.

And put oil on the bearings and shaft before final assembly so the bearings do not start up dry.

Not much to it really. Pulleys and gears and thrust bearings etc can all stay in place on the spindle.

Edited By Hopper on 23/02/2019 12:13:29

Brian Wood23/02/2019 12:12:54
1831 forum posts
36 photos

Ega,

I think it was down to a session of fairly heavy cutting to reduce a rough 4 cornered piece to round, one tooth from the 17 T gear disappeared completely and presumably fell away into the space below the headstock. The cluster gear is 16 DP but made in cast iron and the hammering effect was evidently too much for it. The break was clean with no sign of fatigue.

I have a new one from Myford fitted now, but the materials used are still the same and I am in the process of cutting a new 17 T pinion on a short shaft in phosphor bronze to salvage the old component as a spare.

Regards

Brian

Hopper23/02/2019 12:22:51
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3304 forum posts
65 photos

Here's one way of smoothing out impact on the back gear when taking interrupted cuts. Credit to LH Sparey for this idea. Crude but it works. Takes up the backlash between gear teeth etc and keeps chuck rotation more constant.

dscn1046.jpg

dscn2084.jpg

Brian Wood23/02/2019 12:30:17
1831 forum posts
36 photos

Hopper,

Thank you, I'll remember that for the next time; a neat trick. I don't like abusing machinery and I don't recall any unusual added noise when the tooth broke off, but it's absence was very soon apparent as the next tooth along took the additional impact from the gap left by the missing tooth

The drive gear from the V belt cluster is in P. Br and I query the design concept regarding the strength of a 17 T cast iron gear in the chain with the anticipated loading that back gearing might be expected to handle; hence my planned salvage with a P Br alternative. Change wheel gearing of that sort of tooth count is usually in steel, much better able to handle the loading per tooth.

Brian

Edited By Brian Wood on 23/02/2019 12:36:14

ega23/02/2019 14:24:35
1103 forum posts
90 photos

Brian Wood:

Many thanks for the cautionary explanation.

I am reminded of GHT's Small Rotary Table:

"After a lot of clonk, clonk, clonk, the base was eventually machined and I believed then that an ML7 would turn anything!"

He didn't say whether he used back gear or Hopper's dodge.

I take your point about the use of cast iron but wonder whether the pressure angle has a bearing on the strength of the 17T gear.

ian j23/02/2019 15:22:29
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259 forum posts
227 photos

.

Thanks for the replies.

Hopper.The ML7RB is basically a super 7 with the ML7 cross and top slide so its the bronze bearing etc type headstock.

I damaged mine by turning a boss on the face of a piece of 1/2"x2"x4" EN1 MS so similar to Brian it was an interrupted cut and maybe a bit to heavy1

Ian

Jan B23/02/2019 17:04:05
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18 forum posts
10 photos

Hello Ian J,

The same happened to me last weekend.

I also came to the conclusion that I have to remove the spindle to get access to the back gear. I am thinking of making a new 17 tooth gearwheel in steel instead of cast iron and fit this to the 53 tooth gearwheel. Does anyone know what pressure angle Myford used, is it 14.5 or 20 degrees? I guess it is DP and not Module. Can I use a module gear cutter? The evolvent profile must be the same, or am I wrong?

Jan

Mike Poole23/02/2019 17:11:45
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1757 forum posts
44 photos

Stripping the myford spindle seems daunting but is fairly straightforward once you understand how it works, the method is explained in a number of places and once you have done it you will wonder what there was to be worried about.

mike

Brian Wood23/02/2019 18:32:13
1831 forum posts
36 photos

Jan B,

The gear size is most definitely 16 DP and I would imagine the pressure angle will be 14.5 degrees.

To my knowledge, the only time Myford deviated from that was with the Super 7 spindle and reversing gear complex, all 4 of those are 20 degree to cater for the tooth loading.

Regards

Brian

ian j23/02/2019 18:49:17
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259 forum posts
227 photos

Just doing a bit of reading on removing and replacing the spindle. When I replace it are the rear bearings still correctly set for the preload and I only need to adjust the threaded collar on the left to set the front bearing clearance?

Ian

Brian Wood23/02/2019 19:20:38
1831 forum posts
36 photos

Hello Ian,

You will have to draw the spindle out of the bearing cluster to remove it over the bed, so I'm afraid you will need to go though the whole set up procedure when you put it all back again.

If you have Myford's handbook with the instructions for setting pre-load and bearing clearance, just do exactly as it says and all will be well. The job is made so much easier if you have a hook wrench to set the bearing cluster collars correctly

Regards

Brian

ian j23/02/2019 20:00:54
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259 forum posts
227 photos

Thanks for that Brian.Yes I have the hand book, hook spanner and even a peg spanner for the LH adjusting collar. Just need to buy the new gear cluster and get on with it!

Ian

Brian Wood24/02/2019 10:14:43
1831 forum posts
36 photos

Hello again Ian J

Last word if you need it.

You do know about the method of holding down the oiling wick in the bronze bearing against it's spring during spindle re-fitting and how to get access to do so?

Good luck with fitting the replacement gear. They are much more utilitarian in appearance now without the six nicely shaped lightening slots in the 53 tooth part; I was rather disappointed to see that.

A silly notion I know and had I made it as a spare part I would have done the same, but it is another example of a quirky little bit of the overall design process in creating the lathe cast aside in the name of progress!

Regards

Brian

ian j24/02/2019 11:40:25
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259 forum posts
227 photos

Brian thanks for the reminder about the needle trick to hold the wick in position.

Yes I noticed the new gear cluster now don't have the lightening slots, I suppose before fitting a new one they could be milled out.

" I am in the process of cutting a new 17 T pinion on a short shaft in phosphor bronze to salvage the old component as a spare. "

How do you propose to secure it to the 53 tooth gear?

You don't fancy making two while your at it ?smiley

Ian

Brian Wood24/02/2019 13:52:42
1831 forum posts
36 photos

Hello Ian J

The non gear end is going to be inserted into the 53 tooth wheel [after turning off the damaged tooth] as a shrink fit and further secured with a two small pins drilled axially into the joint interface. Then the bore will be carefully sized to fit the spindle it runs on.

I note your smiley!

If it was a financially sensible operation I would make another for you but I had to buy the cutter just for this job and then of course the section of P Bronze; taking those outlays together with all the machining work including cutting the gear you could easily afford to buy at least two more spares from Myford even if I barely charged you for my time.

If you have the resources it is not too difficult, it just isn't cost effective to make one offs when you aren't fully equipped to do so.except just for the satisfaction of making your own expensive spare part!

Regards

Brian

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