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Myford ML10 main screw skating

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Michael Gilligan14/01/2021 13:28:22
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Posted by Robin King on 14/01/2021 12:15:53:

Michael,

Your sanity is our highest priority, of course! Maybe this'll help?

The original manufactured form of these gears is with a near semi circular form tooth machined into the bronze gear circumference so that the teeth effectively wrap part way around the leadscrew. They are not in simple straight cut sprocket form. I can understand that at first sight it might appear that the gears are excessively worn, but probably not so; that's how they were made. Thinking about it and in light of using mine for nearly forty years the only way that the teeth will wear excessively is if the gears are prevented from turning while the leadscrew rotates, either manually or due to seizing, but otherwise they are free to turn therefore wear should be minimal, assuming reasonable lubrication, adjustment, and normal handling. I'd still look at cleaning, adjustment and lubrication as the first steps before investing hard earned cash on a new set.

.

Many thanks for that Robin yes

The remaining issue is ... Why does Myford in Mytholmroyd not supply them in that form ?

MichaelG.

Grindstone Cowboy14/01/2021 14:32:14
490 forum posts
44 photos

Just went out and took a couple of photos of my ML10 - apologies for the quality, it's currently stored in a neighbour's garage and not easy to get at - and the gears look just like the ones that Michael G linked to. It's a fairly late model, and in excellent condition.

img_3787.jpg

Usual photo rotation problem!

So this begs the question, did the design change over the years if Robin King's have a semi-circular profile?

Rob

Edited By Grindstone Cowboy on 14/01/2021 14:33:33

Michael Gilligan14/01/2021 15:07:21
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Very interesting, Rob

... I think we might need one of Jason’s [unless another volunteer steps forward] clever 3D models to explain the requisite tooth shape !

MichaelG.

Oily Rag14/01/2021 16:26:54
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126 photos

That looks to me like a spur gear with a slight helix angle to mate closely to the leadscrew (picture posted by Rob). A cheaper way of mating what is a 'worm' (leadscrew) with a right angle driven system, than producing a wormwheel. The gear can be cut in the normal way by a hob or simply by a B&S type form cutter by angling the component by the value of the lead angle.

The apron gears on my Raglan are formed this way which mates with the power feed worm wheel, meanwhile the rack and pinion for the hand drive of the saddle is a normal 'zero offset' spur gear as the rack's lead is equal to the pitch.

So, in conclusion I think Bob's problem is that the gear has been 'over engaged' in the past and the root of the leadscrew thread has worn the tips of the pinion gears. Maybe the original pinion gears were straight cut, which on a closer look at his photograph there is a suggestion this is the case) - in which case the wear will be more concentrated as the pinion gear flanks will be single 'point' loaded rather than having a slightly lower stress level with a 'lead angle' pinion gear matching the appropriate lead angle of the leadscrew.

Martin

Hopper15/01/2021 00:36:36
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5174 forum posts
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If you wanted to squeeze the last life out of those gears without buying new, you could possibly put a shim between the apron and saddle so the upper drive gear is moved down lower and thus closer to the leadscrew for better engagement. Then replace the worn lower gear with an oversized Delrin roller, as all it does is stop leadscrew deflection so does not need to engage teeth for any reason. YOu would then have to adjust the half nuts to engage in the new position.

It would be worth checking that the bolts holding your apron to the saddle are tight. If loose they could be allowing the whole apron to tilt, making the drive gear a loose mesh with the leadscrew, which could be the cause of the worn tips on the gear in the first place.

If you buy new gears, it would be worth shimming the apron so the new gear engages to the full tooth depth to avoid a repeat of the problem..

Hopper15/01/2021 01:16:45
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PS. Looking further at the pictures in the original post , it does appear that perhaps the original gears were throated worm gears made with the curved tops on the teeth for better engagement. The lower gear seems to have the same curved tooth tops so seems to be possibly original? Perhaps the new ones available today are made as the cheaper to manufacture straight variety?

If that is the case, then definitely try shimming between the apron and saddle to get fuller gear engagement. I know I had to put shims in that location on my ML7 to get the best engagement of both halfnuts and rack gear.

 

Edited By Hopper on 15/01/2021 01:19:54

Bazyle15/01/2021 09:47:52
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5780 forum posts
216 photos

Just realised that GC's picture is upside down. So perhaps the idler gear is the same as the handle gear - after all it would make sense to mass produce teh same rather thatn have two differnet ones, so perhaps it is possible to swap them over, or use teh lower one and preplace it with a plain roller or flat plate as used on other lathes to oppose the push of the half nut.

Robin King15/01/2021 10:09:27
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1 photos

Looking at it again, Hopper's description as 'throated' is much better than my misleading one of 'semi circular', so apologies if I've over elaborated it and caused confusion.

The centre distance between leadscrew and handle spindle is fixed, leaving the only adjustment available by rotating the lower gear eccentric shaft. I'm a bit cautious about the idea of being able to 'over engage' that gear with the underside of the leadscrew given the small diameter of the shaft and limited leverage available to achieve it. The means of rotating it are not clear from the Myford drawings so I can only assume (dangerous word, that) it's by finger pressure on the underside of the gear once the shaft retaining grub screw is loosened. Has anyone ever done it?

Michael Gilligan15/01/2021 10:25:34
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17299 forum posts
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Posted by Robin King on 15/01/2021 10:09:27:

Looking at it again, Hopper's description as 'throated' is much better than my misleading one of 'semi circular', so apologies if I've over elaborated it and caused confusion.

[…]

.

No problem, Robin ... I just took it as ‘artistic license’ and assumed [that dreaded word again] that you meant it was just like Bob LAG’s photo.

... I must admit, however, that I would love to see the original Myford [Beeston] drawing for the tooth profile.

MichaelG.

Bob LAG15/01/2021 10:40:06
5 forum posts

Bonjour,

First I would like to express my admiration for the technical erudition of all of you and the kindness of your welcome! Respect and chapeau bas!

Reading all your comments, I think that the best should be that I buy the gears and to make the test.

May I abuse of your patience?

https://drive.google.com/file/d/1Nr-qM2C_h3LdqgnnZOefmtHJvaVubSUD/view?usp=sharing

MG gave me a link for the 121 pinion but i can't found the 122 on the QSANEY website.

Does someone know where to find the eccentric 122 pinion (imperial)?

Thx

Bob

Hopper15/01/2021 11:01:49
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5174 forum posts
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Posted by Robin King on 15/01/2021 10:09:27:

The centre distance between leadscrew and handle spindle is fixed, leaving the only adjustment available by rotating the lower gear eccentric shaft

The upper gear is adjusted by shim between the saddle and apron.

Hopper15/01/2021 11:03:24
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5174 forum posts
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Bob, I dont know where you can get a lower gear. But it should be possible to use an upper gear in the lower position if you mount it on the different spindle. They appear to be the same gear.

Grindstone Cowboy15/01/2021 12:23:10
490 forum posts
44 photos

Yes, apologies for the orientation - leaning over from the back of the lathe, holding a torch in one hand and trying not to drop my phone . But from what I could see, the two gears are the same (at least on the outer circumference).

Rob

Robin King15/01/2021 14:08:23
115 forum posts
1 photos

Michael - 'artistic license' - that's very generous of you, thank you.

Hopper - If you shim between saddle and apron do you then not also upset the relative positions of half nuts and leadscrew in the process? Maybe I'm not thinking that through properly.

To clarify part numbers for Bob's benefit - reference 122 is the 'eccentric shaft' not the gear. The lower gear - referred to on the parts list as a 'counter pinion' is reference 119. There are two different versions of this - one for 8tpi imperial (A6513), or metric 3mm pitch (10296). The numbers in brackets are the original Myford part numbers. The other numbers 119, 222 etc that I mentioned earlier are more correctly the part reference numbers used by Myford on their drawings.

I would assume (!) that both pinions are the same, but, the lower one appears to be free to rotate on the eccentric end of the lower shaft and is shown retained by a circlip, reference 123 (Anderton external type, 5/16 inch). The upper pinion is fixed to the handle spindle but no details are given of the fixing method; press fit?

Howard Lewis15/01/2021 14:37:40
4426 forum posts
8 photos

Pure guess work, but being a Myford, the gears may be 20DP and 14.5 PA like all the changewheels.

If so, unless the gears are "throated" to match the Leadscrew, would it be possible to make replacements?

Taking the DP as being 20, and knowing the number of teeth, calculating the size of the blank should be simple. As long as the tooth count exceeds 12 finding a cutter should be fairly easy (For starters, RDG could possibly be one supplier of a suitable )

Howard

Dave Halford15/01/2021 17:30:06
1287 forum posts
12 photos

Bob may need to buy 2 of the 121 upper shaft parts and remove the gear from one them and ream to produce a running fit for the lower shaft.

Thinking about making a gear, the DP would be whatever fitted into an 8tpi thread, but as the thread is used as a rack would you use a rack cutter or 19 is it? to match the tooth count.

It can't be involute can it?

Edited By Dave Halford on 15/01/2021 17:35:18

Edited By Dave Halford on 15/01/2021 17:36:20

"Bill Hancox"15/01/2021 19:32:47
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257 forum posts
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I recently replaced my transverse gear assembly as the brass gear was in a condition similar to yours. I ordered the new assembly (gear and spindle as per Michael Gilligan's link). After several confusing emails concerning acknowledgement of my order and subsequent shipping info, I finally received the item. When I opened the package, the contents fell apart in my hand. I needed to knurl the steel spindle in order to establish a tight press fit for the gear. This is what it looked like when it finally arrived from Myford.new myford transverse.jpg

Hopper16/01/2021 00:33:49
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5174 forum posts
114 photos
Posted by Howard Lewis on 15/01/2021 14:37:40:

Pure guess work, but being a Myford, the gears may be 20DP and 14.5 PA like all the changewheels.

If so, unless the gears are "throated" to match the Leadscrew, would it be possible to make replacements?

Taking the DP as being 20, and knowing the number of teeth, calculating the size of the blank should be simple. As long as the tooth count exceeds 12 finding a cutter should be fairly easy (For starters, RDG could possibly be one supplier of a suitable )

Howard

The gear will be a special DP to match the linear pitch of the leadscrew.

If you cut a worm to match a Myford 20DP gear it is some oddball TPI and certainly not a straight 8tpi like the leadscrew. I did this exercise when making the Versatile Dividing Head using a Myford 60T gear some years back but dont remember the specific pitch that matches 20DP.

But the correct pitch can be calculated by the usual methods if wanting to make your own gear. The Acme thread on the leadscrew is close enough to a 14.5 degree PA rack profile for practical purposes.

Hopper16/01/2021 00:39:17
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5174 forum posts
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Posted by Robin King on 15/01/2021 14:08:23:

Hopper - If you shim between saddle and apron do you then not also upset the relative positions of half nuts and leadscrew in the process? Maybe I'm not thinking that through properly.

Ah, yes. I think you may be right. I was thinking the Myford had adjustable half nut alignment but from dim memory (matches the rest of my brain!) the adjustment is only on one half nut relative to the other to limit clamping force on the leadscrew so would not affect overall alignment. My apologies for the confusion.

What I was thinking of is that you then must clamp the halfnuts together on the leadscrew and adjust the shimming of the apron to fill any gap there so the halfnuts engage in alignment. With the ML10 you are then stuck with the traverse gear where it is. So might still be worth checking the apron alignment as halfnuts could be out of line also. It certainly looks as if that gear is not fully engaged and thus has worn on the tips and is skating now. A new one might do the same in time.

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