Thread: Myford Gear train

I got a chance to check what gear train has been set up on the ML7 and I am stuck as to locating what its been set up for in cutting threads the closest I can find is an obscure No of threads 48.5333 TPI.

The reason for my confusion is that the leadscrew tumblers are 20 & 18 should these not be the same for a return feed of the leadscrew?

photos below of what the set up is with the gear chart that I can find with 48.5333 TPI

Hi

the reverse tumbler gears are 1 to 1 ratio , the middle gear in the tumbler ( 18 ) does not have any affect on the ratio .

In a 3 gear setup, the middle gear can be any number of teeth, it doesnt change the ratio between the top and bottom gears, that is what i understand from reading books Mike

Hi tumblers are there merely to change lead screw direction feed left or feed right. the tpi required is simple driven divided by driver and the no of threads on lead screw.

You're looking at the wrong place in the chart.
You need to find "setup 3"
Driver 25
Driven 1 60
driver 1 30
Driven 2 65
Driver 2 20
leadscrew 70

Stuart

p.s. my maths says you have a 8 TPI leadscrew* so your current gearing would give you 145.6 TPI(thought I wouldnt trust that)

*I worked out the leadscrew from your thread chart so that might not be correct. I assume your Myford has a imp leadscrew?

Stuart,

I agree with 145.6 TPI. I suspect this arrangement has been set up for feeding rather than threading. If my calculations are correct (often doubtful!) this would give a feed of about 0.007" per revolution.

Frank.

Yes a very fine thread , I didnt want to confuse anyone by changing units.

BTW wheelinround "setup"s are at the bottom of the left hand "tool bar" in case you couldnt find them

Stuart

Originally Posted by morrisman

Hi

the reverse tumbler gears are 1 to 1 ratio , the middle gear in the tumbler ( 18 ) does not have any affect on the ratio .

In a 3 gear setup, the middle gear can be any number of teeth, it doesnt change the ratio between the top and bottom gears, that is what i understand from reading books Mike

Mike the middle gear isn't 18 they are 20 the reveres leadscrew gear s 18.

Thanks Mike yes going through Myford book ATM and its what I am understanding also.

j.ashburn

Hi tumblers are there merely to change lead screw direction feed left or feed right. the tpi required is simple driven divided by driver and the no of threads on lead screw.

If the reveres leadscrew gear is not the same as the forward gear wouldn't this give a feed in reveres different to forward? If its set up as a metric thread it would then not come back to original position??

Stustoys

You're looking at the wrong place in the chart.
You need to find "setup 3"
Driver 25
Driven 1 60
driver 1 30
Driven 2 65
Driver 2 20
leadscrew 70

Stuart

p.s. my maths says you have a 8 TPI leadscrew* so your current gearing would give you 145.6 TPI(thought I wouldnt trust that)

*I worked out the leadscrew from your thread chart so that might not be correct. I assume your Myford has a imp leadscrew?

Thanks Stu yes sorry meant to state 8tpi leadscrew and yes Myford still all imperial

Your right on the ball with that layout Stu I will check that no3 layout.


Thanks all this now allows me to start fresh and set up anything from here when I double check what spare gears I have to play with.

Stu you reckon this is more to do with feed rate??

Originally Posted by Stustoys

Yes a very fine thread , I didnt want to confuse anyone by changing units.

BTW wheelinround "setup"s are at the bottom of the left hand "tool bar" in case you couldnt find them

Stuart

Stuart thanks I am still trying to come to grips with this side of things maths and I don't get on but when I have to work with it it seems there is a work around I come too.

As for the softwear I can't open the help file any ideas there??

Franco again thanks

The lathe although last owner was model engineer previous it was clock makers so such tiny threads maybe possible.??

Hi wheelinround

As far as gears go, I find it can help to think of it as how many teeth the gear has moved.
Say you have the tumbler in fwd 25-20-25. the spindle moves one turn, thats 25 teeth. that moves the 20 tooth gear 25 teeth(1.25 turns) which moves the 25 tooth gear 25 teeth(one turn)
Now in reverse 25-18-20-25
the spindle moves 25 teeth, moves the 18 tooth gear 25 teeth, moves the 20 tooth gear 25 teeth, moves the 25 tooth gear 25 teeth.
A long fisted way of saying "idlers do nothing to change ratio"

You cant use tumbler reverse at all* while thread cutting. You reverse the lathe if needed.
(*well almost all?. I am guessing there will be a couple of threads you could).

I dont know the Myford well enough to know if has separate powerfeed. I feel pretty safe in saying that it doesnt have a separate powerfeed shaft. I would also feel pretty safe given the gearing as currently setup that it doesnt have a keyway in the leadscrew for powerfeed?
So that would mean powerfeed uses the halfnuts?
If thats the case then there really isnt a line between "powerfeed" and "thread cutting" they are the same thing just expressed in different ways.

A thread with a 0.007" pitch would be about M1.8 fine and below. I'm not sure a Myford leadscrew would be up to that(though I'm not sure it wouldnt be either).

I've not used that software, just going off your picture. (there may not be a help file?)

Did you find the correct chart?

Stuart

Originally Posted by wheelinround

Franco again thanks

The lathe although last owner was model engineer previous it was clock makers so such tiny threads maybe possible.??

wheelinround,

All things are possible, but for practical reasons you would normally use a standard thread pitch for which taps are already available when screwcutting a small diameter thread on the lathe to avoid having to make the matching tap as well. The only pitches close to 145.6 TPI are the very uncommon 17BA (149.3 TPI) and 0.175 metric (145.25 TPI), and neither is an exact match, though a 145.6 TPI bolt would probably screw into a thin 0.175 metric nut OK.

You can easily check the TPI of the thread or feed which will be produced from any combination of gears using the various gear tooth numbers.

Driven gears x leadscrew pitch = TPI
Driving gears

In your case:

60x65x70x8 = 145.6 TPI
25x30x20

I presume the Myford, like my Brackenbury and Austin, does not have a separate automatic lengthwise feed, so the lead screw is used for this purpose also, by cutting what amounts to various very fine thread pitches. 0.07 inches/rev is a useful mid range feed on a small lathe.

Frank.

Thanks Stuart and Franco a quick read before heading out will post more later.