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Thread: Myford Gear train
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30th April 2013, 10:21 AM #1
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
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30th April 2013, 10:52 AM #2
gears
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
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30th April 2013, 11:15 AM #3Senior Member
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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.
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30th April 2013, 11:42 AM #4GOLD MEMBER
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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?Last edited by Stustoys; 30th April 2013 at 11:54 AM. Reason: p.s
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30th April 2013, 02:19 PM #5Senior Member
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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.
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30th April 2013, 02:53 PM #6GOLD MEMBER
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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
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30th April 2013, 02:58 PM #7
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.ashburnHi 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.
StustoysYou'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??
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30th April 2013, 03:02 PM #8
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.??
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30th April 2013, 03:50 PM #9GOLD MEMBER
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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
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30th April 2013, 05:24 PM #10Senior Member
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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.
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30th April 2013, 06:27 PM #11
Thanks Stuart and Franco a quick read before heading out will post more later.