Gear size

[Carl DorlingParticipant @carldorling51660]

hi all could someone help me with a problem I have on my ML 4/5 hybrid I have now fitted a tumble reverse but it is in a lower position than on the original headstock ,so I have had to fit a larger gear to the spindle instead of 30tpi it's 34 tpi what affect will this have on my overall gearing .

[Carl DorlingParticipant @carldorling51660]

Speed of spindle gear

[Martin ConnellyParticipant @martinconnelly55370]

If it just acting as an idler then none. Think of it as one tooth on the spindle moving the tumbler one tooth around. The result is the first driven gear moves around one tooth regardless of the number of teeth on the tumbler.

Martin C

[JasonBModerator @jasonb]

With the larger gear is on the spindle it can't be acting as an idler, it will be a 34T driver rather than a 30T

Feed rates will be higher and thread pitches coarser

 

Edited By JasonB on 17/04/2017 19:22:43

[not done it yetParticipant @notdoneityet]

what affect will this have on my overall gearing .

JB is correct. Every thread will be 34/30 of what you might have expected. A disaster in the making, I would guess. It is teeth, not tpi btw.

Likely better to reposition the tumbler to suit, than change the spindle gear. Otherwise, somewhere in the drive chain you will need to alter the ratio from current to 30/34 (or 1:0.882). Can it be done? I have no idea, but doubt it!

[Neil WyattModerator @neilwyatt]

Usually the spindle gear is matched by another one below the tumbler with the same number of teeth to keep the same ratios.

Can you modify the tumbler so it uses a 34T instead of a 30T?

Neil

[Martin ConnellyParticipant @martinconnelly55370]

I misread the original post, I thought the tumbler was the 34 tooth gear. A 30/34 combination added into the drive train would correct the error from the larger gear on the spindle but this additional set of gears would require the tumbler to be used in the reverse position for normal forward motion. You would also need to add a mounting for it.

Martin C

[JasonBModerator @jasonb]

No being a Myford man what size gears are on the tumbler? if there is enough room ctr to ctr you could change the pair of them to compensate for the 34T. You would want to do both not just one to keep the original ratios in both directions.

Edit

Forget that, it would be the output gear on the tumbler that would need to be adjusted to compensate for the 30 to 34 change as the two smaller gears on the tumbler are just idlers. So question is what number of teeth is that gear?

Edited By JasonB on 18/04/2017 08:29:54

[Carl DorlingParticipant @carldorling51660]

I believe the tumble output gear is 21t but I will check so if I change that to a 34t it will correct the problem.

[JasonBModerator @jasonb]

No you would need a 23.8T to get the same ratio as 30/21 from the 34T

[Neil WyattModerator @neilwyatt]

More likely 20T on the tumbler output to give a 30:20 ratio., otherwise your change gear ratios for normal screwcutting would be really odd.

If so changing to 33 and 22 would work.

Where's Brian Wood!?

Neil

[Anonymous]

Surely the tumbler gears are just idlers, so they have no effect on the overall ratio? To compensate for the 34/30 'error' one would need to introduce a 30/34 ratio elsewhere in the gear train.

Andrew

[Brian WoodParticipant @brianwood45127]

I'm here Neil!

​I agree with Andrew, the tumbler reversing wheels are just idlers and have no influence on the gearing ratio.

Carl is now talking about fitting a 34 T gear in place of the lower 30 T gear. That will force him to change the two tumbler idlers as well as they will no longer fit in the space left for them, and since they run on fixed centres other smaller sizes will give him a virtually impossible meshing headache as well.

​It might be easier altogether to put the original 30 T gear back on the spindle and make a new mounting position for the tumbler reverse. It is that or live with having to include a 30/34 gearing correction elsewhere to get screw cutting results that are correct

​Brian

[Carl DorlingParticipant @carldorling51660]

Hi all I have checked the tumble gears it's off a ML7 and they are 20t and 25t am I correct in thinking I only need to change the 20t gear

[Carl DorlingParticipant @carldorling51660]

Forgot to mention there are pics of the setup

[JasonBModerator @jasonb]

Looks like the 25T is the one that meshes with the two tumbler gears so that does not give an easy swap over

Nearest whole number options would be 36T on the spindle and a 30T on the tumbler lower stud as this would give the same 1.2:1 ratio as the original 30/25

Edited By JasonB on 18/04/2017 13:05:07

Edited By JasonB on 18/04/2017 13:11:25

[not done it yetParticipant @notdoneityet]

Suggestion. You need a different tumbler arm/holder/reverser thingy to the one you have? 30 teeth on both spindle and driven gear (from the tumbler) and possibly different tumbler gears?

Not a myford person, but did they ever change the DP of their gear trains?

[Carl DorlingParticipant @carldorling51660]

Do you think that I may have just created trouble when I could of just used a banjo setup without the tumble reverse option

[Brian WoodParticipant @brianwood45127]

Hello Carl,

​Being brutally honest, yes you have, but to dump the useful tumbler reverse is a retrograde step. If you can reposition the tumbler reverse and fit equal tooth count gears top and bottom, you will be back as Myford intended. That will mean using two gears other than 34 teeth, it might mean creating a new tumbler carrier, but the change of headstock height has brought this about.

​That now raises a further question. Is the tailstock height now 'low' compared with that of the headstock? It is worth checking before you find out by trying to drill with it. Correcting that is a case of fitting a suitable height packer between the shoe and tailstock body.

​Brian

[Carl DorlingParticipant @carldorling51660]

Before fitting the ML5 headstock I took lots of measurements it all lines up as it should 3 1/2" centre hight I tried using the existing pre drilled hole at the back of the headstock to locate the tumble reverse this is set to low which requires the 34t gear on the spindle so as you say it needs re thinking. As the lathe came minus a headstock I thought this would be a good upgrade?

[Brian WoodParticipant @brianwood45127]

Hello Carl,

​Can you create another hole in the correct position to suit the tumbler reverse fitting with it engaged as it should be with the original 30 T gear? If so, that will solve this problem.

​As for my concern over tailstock centre height, I had assumed the ML5 headstock was of a different height to the ML4 version. I still think it would pay you to check that aspect again after you get this gearing sorted out

Regards

Brian

[Carl DorlingParticipant @carldorling51660]

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 WoodParticipant @brianwood45127]

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.

Brian

[Carl DorlingParticipant @carldorling51660]

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 WoodParticipant @brianwood45127]

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

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