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Randa lathe missing back gear

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Reggie Chant04/09/2020 09:02:37
15 forum posts
2 photos

Hi

I have recently purchased what I believe to be a Randa lathe all though it has no badge. I am a beginner at learning.

I was hoping maybe some one here has a similar lathe who can help me with either being able to find the missing back gear or the measurements for this missing part so I can possibly create the missing part.

Searched on Google but can't find specs only info on lathes site.

I will upload photos

Kind regards

Reggie

old mart04/09/2020 18:15:57
3312 forum posts
203 photos

Welcome, Reggie, I have looked at the Randa lathes on the "lathes" website, not all of them have backgear, although if yours has parts missing, at least the large gear next to the chuck would be present, as it is harder to remove. Finding detailed specs on an old machine like this could be very hard.

Edited By old mart on 04/09/2020 18:17:24

Nicholas Farr04/09/2020 19:41:09
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2955 forum posts
1335 photos

Hi Reggie, as it happens, I still have my fathers RandA model B lathe as shown below, when i gave it a strip down, clean and a repaint, about 28 years ago, which looks the same as what you have.

randa model b.jpg

You will be very lucky to find a gear that you have missing, so you will probably have to make one or get one made by somebody. Although the gear wheel is a 60 tooth 20 DP with a 14-1/2 degree pressure angle, it will probably be slightly larger O/D than your 60 tooth change wheel, assuming you have one of those, but it should be the same O/D as the one on the back end of the spindle.

I have measured the one on my lathe and the O/D is 3.184" (80.9mm or there about) and the width on the teeth is 0.409" (10.4mm), but the boss portion is about 0.482" (12.25mm) but flush with the teeth side at the back.

If you would like a photo or two of it, let my know.

Regards Nick.

Dave Halford05/09/2020 13:38:02
1665 forum posts
19 photos

Reggie,

You might find a Polyvee belt more useful than the inside out vee belt

Reggie Chant05/09/2020 19:34:41
15 forum posts
2 photos

Hi thanks guys for the replies and so quickly. I thought it might be 60 tooth as I have the change gears and that one did fit when the back gear was engaged all though not meant to be there lol. Those measurements you gave are great nick so thanks.

If I have to I will get an engineer's place to make one up as there's no chance in hell I could make one.

Thanks Dave I will look into the belt.

Thanks old mart

I know I won't find another but just having the measurements means I can complete the lathe.

Reggie Chant05/09/2020 19:36:07
15 forum posts
2 photos

p_20200831_171854.jpg

Reggie Chant05/09/2020 19:36:27
15 forum posts
2 photos

p_20200904_084626.jpg

Reggie Chant05/09/2020 19:36:48
15 forum posts
2 photos

Sorry just figured out how to add photos

Nicholas Farr05/09/2020 21:36:58
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2955 forum posts
1335 photos

Hi Raggie, be sure to measure the O/D on the one on the spindle for the one you get made as it should be the same to give correct depth of the teeth. I will say it looks as if the lathe is driven directly from a pulley on the motor, but there should be a counter shaft between the motor and the lathe, otherwise you will having it running much to fast in direct drive. The sort of designs in the photos on the Lathes website should give you an idea of how to configure something.

Regards Nick.

Hopper05/09/2020 23:15:55
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5505 forum posts
137 photos

60 tooth 20DP 14.5PA is same spec as a Myford change gear. You might be able to adapt one to fit. Cheaper than getting one made. Plenty on Fleabay.

Reggie Chant06/09/2020 06:43:48
15 forum posts
2 photos

Cheers hopper

That does make things easier as all I need to do is drill and thread and add a grub screw. Many thanks.

Cheers for the advice nick will look into it. I have been reading the amateurs lathebook which is the only book I found which relates better to these older lathes. I did the measurements for the pulleys and the math to work out speed and the speeds seem to relate to what is mentioned in the book.

All though without a rpm counter I can't be definate and I'm just relying on my math skills. I will read up a bit more and take a look at counter shafts.

Once again thanks for your input folks as I'm only just leaning.

Reggie

Nicholas Farr06/09/2020 09:53:36
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2955 forum posts
1335 photos
Posted by Hopper on 05/09/2020 23:15:55:

60 tooth 20DP 14.5PA is same spec as a Myford change gear. You might be able to adapt one to fit. Cheaper than getting one made. Plenty on Fleabay.

Hi Hopper, I know the Myford change wheels are the same, but Reggie needs a back gear wheel and although they are as best that I can identify as being the same profile, they have a slightly larger diameter, 3.184" as opposed to the change wheels of 3.1" and they do mesh but not perfectly, I guess because of the larger diameter. Below in the photos, I have shown the different diameters with a Myford change wheel that had been fitted to another RandA that I have that was fitted to the spindle, the other photo shows it sitting in the back gear on my fathers old RandA.

back gear 1.jpg

 

back gear 2.jpg

This is why Reggie should check the outside diameter of the one that is on his spindle before investing in any gear.

Regards Nick.

Edited By Nicholas Farr on 06/09/2020 09:54:57

John Hinkley06/09/2020 10:02:10
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1170 forum posts
390 photos

Reggie,

If you want to "try before you buy", you could download a copy of GearDXF (free) or similar program, and print out the result. Stick it on a piece of card/board and cut it out. You can offer it up to your lathe and at least get an idea whether it will fit or not.

Here's a scrennshot of the gear, using the parameters supplied by Nicholas Farr, above. Centre bore is my guess.

RandA gear.jpg

John

P.S. You can get GearDXF from HERE

Edited By John Hinkley on 06/09/2020 10:02:36

Reggie Chant06/09/2020 18:33:20
15 forum posts
2 photos

Thanks guys I'm not home for a couple of days but when I get back will check your recommendations out. The gear app looks handy so will definitely check that out.

I will keep you updated.

Nick I will probably bug you at a later stage about the change wheels configuration for power feed and threading. I'm struggling to understand the setup for this

That one for a later date though

All the best

Update coming soon

Bazyle06/09/2020 22:02:34
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5998 forum posts
220 photos

Not sure what gears are available in the myford range but a simpler solution to a 'special' would be one with a few more teeth say 62 or 64.

Howard Lewis08/09/2020 12:25:27
5228 forum posts
13 photos

A 20 DP gear, 3.184" diameter , theoretically has 63.68 teeth. So a 64T would be a little oversize, and a 63T would be undersize. There are 63T gears available for mini lathes, but being Module gears, and 20'PA would not be suitable.

If there is a similar gear available for a Myford, this would be 20 DP and 14.5 PA so would be suitable if the bore and centre boss are suitable.

Howard

Bazyle08/09/2020 13:31:20
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5998 forum posts
220 photos

Perhaps if somwone has an actual Myford 64 tooth they could measure it as it is unlikely to be exactly on theoretical dimension. Another option is to replace both the larger gears and modify the layshaft bracket to bring it in a bit. Admitedly such a modification is a little undesirable.

Nicholas Farr08/09/2020 19:05:28
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2955 forum posts
1335 photos
Posted by Howard Lewis on 08/09/2020 12:25:27:

A 20 DP gear, 3.184" diameter , theoretically has 63.68 teeth. So a 64T would be a little oversize, and a 63T would be undersize. There are 63T gears available for mini lathes, but being Module gears, and 20'PA would not be suitable.

If there is a similar gear available for a Myford, this would be 20 DP and 14.5 PA so would be suitable if the bore and centre boss are suitable.

Howard

Hi Howard, according to the formula in WPS 17, a 64 DP gear would have a blank of 3.3". I have measured my gears from 40 t0 70 in five tooth steps which they are for the RandA and none of them detract from this formula with any significant amount. The best I can get with this formula for a blank of 3.184 is 61.66, which of course you don't get and even 62 takes it over although only a small amount, but I think there will be no clearance at all. Maybe if Reggie's gear on the cone pulley is fairly worn, a 62 may go, but it's unlikely they will mesh without first releasing the screw in the cone pulley first, that locks it to the spindle.

Regards Nick.

Edited By Nicholas Farr on 08/09/2020 19:20:20

Nicholas Farr08/09/2020 19:12:26
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2955 forum posts
1335 photos
Posted by Bazyle on 08/09/2020 13:31:20:

Perhaps if somwone has an actual Myford 64 tooth they could measure it as it is unlikely to be exactly on theoretical dimension. Another option is to replace both the larger gears and modify the layshaft bracket to bring it in a bit. Admitedly such a modification is a little undesirable.

Hi Bazyle, the layshaft bracket is all part of the lathe casting and there would be virtually no leeway for much modification, the gears as they are don't clear by very much when they disengage.

randa backgear.jpg

Regards Nick.

Howard Lewis08/09/2020 19:16:07
5228 forum posts
13 photos

Hi Nicholas,

Correct! i got my sums wrong, on the basis of 3.184" dia x 20 dp = 63.68 ,and in my haste forgot the +2...

Certainly, I would not want to run gears with Zero or negative backlash, so a 6iT would have a lot of backlashh, unless the gear centres can be reduced (Which I would think is unlikely, and liking to be prototypical, undesirable ).

Howard

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