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Gear size

Speed of spindle gear

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Carl Dorling18/04/2017 17:41:11
50 forum posts
43 photos

Hi unfortunately it's too close to the hole that's already there ,I will need to rethink this as it appears not as simple as just gearing it down .

Brian Wood18/04/2017 17:48:41
1529 forum posts
35 photos

Hello Carl,

Plug the first hole and drill again, I rather expected that since we are only taking about the difference 4 teeth makes to the true position. After that it should be correct.


Carl Dorling18/04/2017 18:37:17
50 forum posts
43 photos

I see your point ,yes ok I will give that a go probably should have gone that way instead of being lazy and assuming the 34t gear would work. I still need to find some gears at a very small cost as this project has a cash limit if it climbs to much I may as well bought a better lathe !!!

Brian Wood18/04/2017 19:39:11
1529 forum posts
35 photos

Well yes it did in a way, but brought along with it a whole host of troubles in its wake.

​I don't know how you measured the relative centre heights for this headstock compared to the tailstock, but they do need to be aligned vertically fairly precisely; we are talking about only a few thou. When you have the current crisis settled you can look into that, the solution is though a good deal easier if the tailstock is low as I've said.

​Regards Brian

Hopper19/04/2017 11:42:22
2522 forum posts
40 photos

Instead of filling the existing stud hole and redrilling, could you perhaps make an eccentric stud that screws into the existing hole but positions the tumbler mechanism that little bit closer to the spindle? You could set it in the correct position and loctite it in place.

Brian Wood19/04/2017 15:55:16
1529 forum posts
35 photos

That's another rather more refined way of doing the adjustment Hopper. It does also have the problem I've overlooked so far in that the locking pin holes for selecting forward/reverse could also finish up in awkward places.

​As Carl has already observed, he has opened a can of worms with mixing up these headstocks and set himself a lot of work to try and recover from it.


Carl Dorling20/04/2017 20:46:37
50 forum posts
43 photos

Thanks to everyone for offering advise can I ask could I just change the tumbler output gear .

Brian Wood21/04/2017 09:23:09
1529 forum posts
35 photos

Hello Carl,

​Which is that one please? If it is the one that the small fibre gears drive then this is the gear you need to change to match the 34 tooth gear you fitted to the spindle.

​I am though sure you will find that there is then no longer space between them to fit the carrier and fibre gears as those clearances were designed for a 30---30 pair.

Can you post an end on view of the situation so that it is possible to see the gears you have and count all the teeth?


JasonB21/04/2017 10:07:33
12658 forum posts
1147 photos

Brian, the earlier photos show 25T & 20T on the output of the tumbler with the 25T meshing with the smaller gears so the old setup would have been 30spindle / 25tumbler. This can't be recreated with a 34T so Carl would need 36T on the spindle and 30T on the tumbler to get back to the old 30/25 ratio.


See post from 18th April at 1.02 and my reply after.


Edited By JasonB on 21/04/2017 10:26:30

JasonB21/04/2017 10:47:00
12658 forum posts
1147 photos

Carl, while altering that picture above I was looking at your gears a bit more closely.

Is the gear shown on the spindle the 30T or the 34T?

My reason for asking is two fold

1. It does not look to be the same gear profile as the others, maybe different DP or even MOD and a different pressure angle.

2. If it is the larger 34T then it is not meshing with the tumbler when the lever is down as can be seen in this brightened photo

no mesh.jpg

Brian Wood21/04/2017 10:48:11
1529 forum posts
35 photos

Hello Jason,

​Thank you for labelling your picture, I saw those earlier but without a full view on the gears I was not sure that the final gear had 25 teeth. Carl had also talked of 30 teeth, I think in that position so you can I hope see where confusion lies.

​The correct matching would then will be 25 T on the spindle, via the two tumbler gears [tooth count irrelevant except that they fit of course] driving a 25 T output gear which is currently mated to the 20 T gear drive to the change wheels.

​What Carl now has instead is a 34/25 overdrive ratio to the change wheels, the screw cutting will be all to hell and the only ways it can be rectified is to either build in another correction of the opposite phase in the change wheels [ie 25/34] or find space in the geometry he has created by fitting equal tooth count gears top and bottom in place of the 34 and 25 T gears. Only then will his screw cutting tables will be correct again. There are other geometrical complications with axles positions for different sized idler wheels for the reversing action and the locking pin location to hold the mechanism engaged in neutral, forward and reverse, all of which might change.

​And yes, now that you mention it Jason, there is something distinctly odd about the meshing of the spindle gear to the small 18 T idlers; I had spotted it too in your enhanced picture.
​Regards Brian





Edited By Brian Wood on 21/04/2017 10:52:01

Carl Dorling21/04/2017 20:27:01
50 forum posts
43 photos

Hi all just so as to clear the confusion I have created. the spindle gear is 34t and I believe to be MOD 1.25 it is not at its optimal position in relation to the 18t tumble gear I have decided to create a new tumble lever , it will be a v shape with the tumble idle gears fitted on opposite sides with a 34t gear on the tumble spindle so going back to 1-1 ratio I hope!!!!!

Brian Wood22/04/2017 09:01:11
1529 forum posts
35 photos

Hello Carl,

​That sounds like good progress, but it would better if you fitted a known 20 DP 34 tooth gear in place of the 1.25 Mod gear you have . The pressure angle on Mod gears at 20 degrees do not run well with 14.5 degree pressure angle DP gears and superficially all might be OK for a while but I suspect wear will be high as a result If you do the maths, 20 DP is equivalent to 1.27 Mod.

​This is an old piece of Myford equipment and I am pretty sure the first stage gears will be 14.5 degree angle, unlike those on Super 7 lathes which used the slightly squatter 20 degree DP versions

Good luck anyway

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