# Threading Problem



## ddickey (Jun 7, 2017)

So I need to turn some 5/8-32 threads. I set up my gears and place my change gears in the correct position. I check double and triple and then check again. Everything is correct according to this chart.
I measure the threads to be about 11tpi. 
Any idea what I should check?


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## Bob Korves (Jun 7, 2017)

It appears you are using a diametral pitch chart instead of a TPI chart...


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## ddickey (Jun 7, 2017)

I was wondering what that meant. It appears then I can't thread 32TPI?


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## Bob Korves (Jun 7, 2017)

In the upper chart it shows 16, 8, and 4 TPI, which are in the same ratio group for 32 TPI, would need to reduce the drive train ratio by a factor of 2 (slow down the lead screw by 1/2) and otherwise use the setup for 16 TPI.  If we knew the lead screw pitch and the tooth count on all the gears in the train to make 16 TPI, along with what additional change gears you have available, we may be able to come up with something that would do 32 TPI.


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## Wreck™Wreck (Jun 7, 2017)

Before threading check the lead, this is easily done on a small lathe that allows rotating the spindle  and gear train by hand. Put the gear box in the desired lead, in your case .03125, close the half nuts then rotate the spindle until the lash is gone, place an indicator on the carriage and rotate the spindle by hand 1 revolution and the motion of the indicator will tell you the actual lead. Most people do not have an indicator that will resolve to 5 decimal places so 16 revolutions of the spindle will yield .500" of travel for 32 TPI. 

On lathes with an automatic spindle brake this is more difficult, you will not be able to rotate the chuck by hand with the brake on.


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## Tozguy (Jun 7, 2017)

ddickey said:


> So I need to turn some 5/8-32 threads. I set up my gears and place my change gears in the correct position. I check double and triple and then check again. Everything is correct according to this chart.
> I measure the threads to be about 11tpi.
> Any idea what I should check?
> View attachment 235018



I'd try the 10 selection or the 104 selection.


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## mikey (Jun 7, 2017)

Do you have the change gear set for your lathe? If not, is it available?


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## ddickey (Jun 7, 2017)

I have all the gears.


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## markba633csi (Jun 7, 2017)

What Bob said, also, the 6,12,24 group might provide a path- depending on the gearset.
Mark S.


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## joshua43214 (Jun 7, 2017)

Things that will be very helpful in getting a good response:
A decent pic of the change gear set up.
A list of the gears that are already installed.
A list of what gears you have on hand.

I agree with the others, no reason this can't be done easily enough since you can turn 16TPI.
Some lathes have wonky set ups, your lathe is already a bit unusual in that it gives a plate for DP (a nice feature IMO).

Typically, a lathe will have a gear at the spindle, a gear at the gearbox, and an idler gear in between. All you have to do is get the gear at the gearbox to run at 1/2 speed for the 16TPI setting.


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## Bob Korves (Jun 7, 2017)

That lathe TPI chart has numbers on it that I wish were on mine, like 27...


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## MarkM (Jun 7, 2017)

Good day,  Is your lathe the pm 1440GS by chance? If so Please give us a review of your thoughts.  It is one of the three I have narrowed it down to.  If it isn't what is it? Cutting a worm is some thing I would like to do and it would be great to have the ability to cut DP and Modular gears. with actual proper leads would be great.  Worm and Worm gears are found in reduction boxes and such


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## ddickey (Jun 7, 2017)

In no particular order.
45,43,38,36,35,34,33,33,30,27,29,27, 28,36,28,28,26 & an idler not sure what size.
No on the PM. 2000 ACRA.


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## ddickey (Jun 7, 2017)

Changed the gears back to another tpi as I didn't like the way the other gears were.


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## Bob Korves (Jun 7, 2017)

ddickey said:


> In no particular order.
> 45,43,38,36,35,34,33,33,30,27,29,27, 28,36,28,28,26 & an idler not sure what size.
> No on the PM. 2000 ACRA.
> 
> ...


OK, Great!  Nice assortment.  Also need to know what the A,B,C,D,E stand for...


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## ddickey (Jun 7, 2017)

The position of the gears.
	

	
	
		
		

		
			





Big one on the bottom right is E. Behind that is C. Above and on the inside is B, outside is D. Above that on the outside is A. Behind A is the one that never changes.


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## Bob Korves (Jun 7, 2017)

As it is set up now it appears to have compound gearing.  That is confusing me.  Do you know what thread it is set up for now?  Is it a metric lathe, that is, does it have a metric lead screw?  Can you post pics of all the charts that you have not posted so far?  Do you have a manual for the lathe?


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## ddickey (Jun 8, 2017)

I have it set up for 28 TPI.
No imperial lead screw. 6TPI.
No manual.


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## joshua43214 (Jun 8, 2017)

Thanks a lot, the pics really help.
Something is not adding up right if I am reading your explanation correctly (I probably am not)
Would you mind please setting it up for 16TPI and posting the pic of it?

Thanks
-Josh


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## ddickey (Jun 8, 2017)

It is also set up for 16TPI. Just need to change the change gear knob(s) or dials.


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## Bob Korves (Jun 8, 2017)

What is the factory model number for the lathe?  Lathe size, too.


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## ddickey (Jun 8, 2017)

It is a 2000 Acra-Turn LG 13-40.


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## Bob Korves (Jun 8, 2017)

No luck finding an online manual for that model number...


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## joshua43214 (Jun 8, 2017)

Since there is nothing obvious we can do with the gears, I wrote a script that would check all gear combinations using the 16TPI thread group.
Sadly, there is no solution given your gear set, there are solutions if you have two 45 tooth gears 

A = 30 B = 45 E = 45 D = 27
30/(45/27)/45 = 2/5 which is half the ratio for 16TPI


Spoiler: code





```
from __future__ import division
A = [45,43,38,36,36,35,34,33,33,30,29,28,28,28,27,27,26]
B = [45,43,38,36,36,35,34,33,33,30,29,28,28,28,27,27,26]
D = [45,43,38,36,36,35,34,33,33,30,29,28,28,28,27,27,26]
E = [45,43,38,36,36,35,34,33,33,30,29,28,28,28,27,27,26]
U = [45,43,38,35,34,30,29,26]
def GearSolver(a,b,d,e):
    ratio = a/(b/d)/e
    return rati0
     
r = range(len(A))
for a in r:
    for b in r:
        for d in r:
            for e in r:
                ratio = GearSolver(A[a],B[b],D[d],E[e])
                if ratio == (36/90):
                    print "A = " + str(A[a]),"B = " + str(B[b]),\
                    "E = " + str(E[e]),"D = " + str(D[d])
```





Unless someone chimes in with the answer before I get back to it, I will reverse engineer the entire gear train and have the script check all the other knob positions.
Should not be too hard to do. We know that when you cut a 6TPI thread, the lead screw turns 1 full revolution every time the spindle does. The 1/2/3 lever continuously doubles the speed of the lead screw (2 is twice 1, 3 is twice 2). The I/II/III lever has the following ratios I:II = 3:1 and I:III = 3.5:1


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## ddickey (Jun 8, 2017)

It's possible that gear next to the A gear the one that doesn't get moved is a 45, but I guess that doesn't do us good.
Thanks for doing all that.


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## Bob Korves (Jun 8, 2017)

joshua43214 said:


> Since there is nothing obvious we can do with the gears, I wrote a script that would check all gear combinations using the 16TPI thread group.
> Sadly, there is no solution given your gear set, there are solutions if you have two 45 tooth gears
> 
> A = 30 B = 45 E = 45 D = 27
> ...


Thanks for doing the math, Joshua!


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## joshua43214 (Jun 9, 2017)

So I wrote up a bit of script, it is a bit ugly and slow.
it might have errors, but it seemed to predict some stuff correctly.
There are 23663 different gear/lever configurations total that will cut 100 different thread pitches (2-100TPI).
There are 228 different gear combinations that will cut 32TPI, but most of them are probably physically impossible to set up. I don't like these numbers, they imply to me something is wrong with the code. It does predict some correctly, but it might be including ones it should not.
I filtered the list to put smaller gears in for B and D, I suggest trying ones that use the bigger gears in A and E.

Let me know if they work and I will upload the code snippet and a csv with all the combos.
pos I pos 2 A = 29 B = 26 D = 27 E = 43 TPI = 32
pos I pos 2 A = 28 B = 26 D = 28 E = 43 TPI = 32
pos I pos 2 A = 27 B = 26 D = 29 E = 43 TPI = 32
pos I pos 1 A = 45 B = 26 D = 29 E = 36 TPI = 32
pos I pos 1 A = 43 B = 26 D = 28 E = 33 TPI = 32
pos I pos 1 A = 35 B = 26 D = 29 E = 28 TPI = 32
pos I pos 1 A = 35 B = 26 D = 28 E = 27 TPI = 32
pos I pos 1 A = 34 B = 26 D = 29 E = 27 TPI = 32

Good chance I am tired and made some stupid mistakes...
-Josh


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## ddickey (Jun 9, 2017)

Thanks I'll try some. It will have to wait until next week though.


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## markba633csi (Sep 21, 2017)

Joshua you are the man! How are you with Arduino code? 
Mark S.


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