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drivetrain ratios

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sorceror10/10/2020 13:58:28
6 forum posts

If 2 gears are the same diameter and number of teeth, but one is 20DP and the other is 24DP would the FDR be the same ?

Brian Wood10/10/2020 14:00:40
2287 forum posts
37 photos

What is FDR please?

They will not run together as a pair, the DPs need to match

Edited By Brian Wood on 10/10/2020 14:03:07

sorceror10/10/2020 14:08:30
6 forum posts

FDR is final drive ratio.

The gears would not be run together.

i,m trying to change to a 20DP geartrain from 24DP as 24DP gears are unobtainable, but want to keep the same ratio's to the leadscrew.

Edited By sorceror on 10/10/2020 14:09:13

JasonB10/10/2020 14:09:12
19135 forum posts
2105 photos
1 articles

FDR Feedrate?

They will run together but not for long as both will wear badly but ratio will be the same as if matching DP

Roderick Jenkins10/10/2020 14:54:29
1974 forum posts
510 photos

The gears are defined by the number of teeth and diameter. 20DP and 24 DP gears of the same number of teeth will have different diameters or if the same diameter they will have different numbers of teeth.

If you have 2 gears of different DPs tied together on the same stud, one being driven by a gear of the same DP and the other driving a gear of the same DP then your FDR will be fine.

This is the technique that Martin Cleeve used to fit a 127 tooth gear to his Myford.



Brian Wood10/10/2020 14:55:46
2287 forum posts
37 photos


They can't both be the same diameter and have the same number of teeth, the 24 DP wheel will be smaller in diameter for the same number of teeth if that is chosen as the governing parameter.

If I remember the earlier post correctly, Sorceror has a 24 tooth wheel and a 127 tooth wheel, both in 24 DP. He could retain those to run together and operate the first part of the train in 20 DP as Martin Cleeve did, having a 20DP and 24DP pair coupled together to make the transition


JasonB10/10/2020 15:24:43
19135 forum posts
2105 photos
1 articles

I was basing it on same number of teeth.

Not sure about the statement that 24DP are unobtainable, don't know the pa but you can by 24dp gears or as you only have two might as well scrap those and get some cheap MOD1 gears and do the whole geartrain in that.

Keith Long10/10/2020 15:39:03
849 forum posts
11 photos

24dp change gears do come up from time to time on EBay, I've bought a number from that source. I think Exe lathes might have used them, but stand to be corrected on that. The gears that I've purchased have has a 7/16 in. bore, but that is pretty easy enough to change.

As Jason says above, 1MOD (MOD1) are readily available and very similar diameter to 24dp, but won't run meshed with them. As well as being available for the various mini lathes they are also available from other sources, particularly suppliers that sell parts for home build robots. One supplier that I've done business with and been happy with their products is Technobots, but I'm sure that there are many more, try checking with bearing suppliers as they usually do other drive train products as well.

Brian Wood10/10/2020 15:44:23
2287 forum posts
37 photos


I agree with you, a whole new set in MOD1 would simplify the whole business


JasonB10/10/2020 15:45:15
19135 forum posts
2105 photos
1 articles

I'd go with someone like Beltingonline for most of them, a 50T would be half the price of a 50T Myford gear and if you saw it in half then you can get two out of one which makes it 1/4 the price. SC4 127T from ARC is £22.

Leave all the gears that are in the head 24DP and just change from the output shaft down to the leadscrew which are the ones you will want to be swapping about for screwcutting.

sorceror10/10/2020 17:57:33
6 forum posts

Thanks for all the reply's, just needed to confirmation of my thinking.

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