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

Reggie,

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

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.

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

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

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

Hi Bazyle, with regards to moving the existing 60 to the inside, isn't a straight forward option, as the thickness of this gear is slightly wider than the gap that the original gear goes into, plus the bore is 1" and the layshaft is only 5/8". I don't know what skills Reggie has, but of course there may not be any suitable gears to give a close reduction to what it should be, that will fit the centres. I further more don't know why the lager diameters with what appears to be a 20 DP gear were used, maybe there was a miss calculation in the original design, and perhaps after having a large batch of lathe beds ready for fitting out, these gears were the cheapest compromise. However, I have had a bit of a study of my RandA this morning and there seems to be a fair amount of backlash to make it worth while for Reggie to try a Myford 62 tooth change wheel and he may or may not have to either relieve the root of the teeth with a file and or skim the tops of the teeth, although these are slightly thinner than the original and will leave a small projection of the layshaft, which may make it awkward to fit a retaining screw between the shaft and the gear, but a suitable washer could be glued on the to the boss to bring it to the correct thickness and thus level with the end of the shaft.

The photo shows a Myford 25 tooth change wheel sitting on top of the gear attached to the cone pulley, while you can notice the slight difference in the diameters, the profile and depth of the teeth do not show any significant difference. The second photo shows a 65 tooth original change wheel in the cone pulley gear.

Regards Nick.

Edited By Nicholas Farr on 09/09/2020 11:44:55

Hi Reggie, the RandA "A" type has the same gears, so look out for one of them also with all the gears on.

Sadly this one has all the gackgears missing.

Regards Nick.