Metric Transposing Gears

If anyone wants to make this gear, i will post the chart.

Just wondering, other than using the most Helpful chart U provided, is there a Formula/equation to figure out Metric thread pitches turned with an 8TPI leadscrew?

Obviously, there are few common Stud and Screw gears to use....but the Compound gear ratios are confusing me....specially when the Transposing gears come into play.
In addition to that, others have posted % of error (in Thousands/ft) with the Transposing gear sets.....im wondering how to figure that?
So far im aware of 4 different Metric gear sets.....100/127 (being perfect), and others with marginal error....but how much error?
Those other Marginal gear sets: 63/80, 37/47, and 44/56.

Any help with calculating formulas would be appreciated
 
Perfect ratio is 1.27:1 Take the other ratios and divide to get decimals 47/37= 1.27027027...
Error = 1.270707/1.27*100= 100.0213%
 
Just wondering, other than using the most Helpful chart U provided, is there a Formula/equation to figure out Metric thread pitches turned with an 8TPI leadscrew?

Obviously, there are few common Stud and Screw gears to use....but the Compound gear ratios are confusing me....specially when the Transposing gears come into play.
In addition to that, others have posted % of error (in Thousands/ft) with the Transposing gear sets.....im wondering how to figure that?
So far im aware of 4 different Metric gear sets.....100/127 (being perfect), and others with marginal error....but how much error?
Those other Marginal gear sets: 63/80, 37/47, and 44/56.

Any help with calculating formulas would be appreciated
Yes, there are formulas to figure this stuff .... But ...... They hurt my brain and besides, even though there is a slight error, you will be hard pressed to measure it. You would have to thread about 3 feet before the error was noticable. THAT'S CLOSE ENOUGH for anything I do. Also, it can be done buy picking up the gears for around $10 on eBay instead of hundreds of dollars. But if you want to figure it out, it is just a matter of dividing the number of teeth on one gear into the number of teeth on the other gear to get the ratio and do this with all gears in the train to get the total ratio and then divide using the lead screw pitch to get the thread pitch ....... My brain already hurts. I would only calculate if I was making a special proprietary thread ..... Which I will never do ..... I think.
 
Perfect ratio is 1.27:1 Take the other ratios and divide to get decimals 47/37= 1.27027027...
Error = 1.270707/1.27*100= 100.0213%

That said, .0213% error equates to What exactly in Thousands/Foot?

I have no plans on threading extensive lengths either....but just wanted to see in perspective just how much difference(.0000/ft) there was between the different transposing gear sets.

Reason being for the Equation/formula question and how to figure it out, is that i also have a 10" Rockwell that doesnt have the Impossible to fine Metric
25-875 kit....nor can i find ANYone with specifics/pics of it.
Its metric gears are change gears are totally different from most.
I was contemplating fabrication of a banjo/quadrant to allow metric threading....while not having the typical Change gears of a SB, Logan etc...
 
That said, .0213% error equates to What exactly in Thousands/Foot?

I have no plans on threading extensive lengths either....but just wanted to see in perspective just how much difference(.0000/ft) there was between the different transposing gear sets.

Reason being for the Equation/formula question and how to figure it out, is that i also have a 10" Rockwell that doesnt have the Impossible to fine Metric
25-875 kit....nor can i find ANYone with specifics/pics of it.
Its metric gears are change gears are totally different from most.
I was contemplating fabrication of a banjo/quadrant to allow metric threading....while not having the typical Change gears of a SB, Logan etc...
The transposing gears I am speaking of here are only for change gear lathes. You can make or get a set for QCGB lathes but they use other gears in conjunction with the QCGB to get the metric threads. There is a lot of calculations for this. For example, the SB lathe with a QCGB uses the 127/100 combo but comes with several other gears that must be used by following a chart supplied for the gears required and the settings on the QCGB to cut the desired thread.
 
Thought id help others out by posting my latest find for Metric threading on a Logan 10" (and 11"?).

Found a guy on Ebay that was willing to work with me and make up, via 3D printing, some Transposing gears(37/47t) for my Wards/Logan 10".

He has other gears to accommodate the gearset as well: 20T - 32T - 40T - 80T - 100T (for metric threading)

Gear Face Width = .4375" (7/16")
Keyed center bore = .625" (5/8)
Teeth are 16DP

I suppose U can search on Ebay for them or contact Dennis at FDMprints@Gmail.com

Other items he offers: gearsets for Southbend, threading dials; misc gears and a lathe bed clamp/indicator.
 
The errors with alternate gear sets are small. For instance, the 37/47 set will give an error of .0032"/ft; the 44/56 set will give an error of .0327"/ft; and, the 63/80 set will give an error of .0002"/ft. If any set was to be problematic it would be the 44/56, however, you should not notice anything over the length of any normal nut, or any nut, even a long one, running on any length of shaft that you thread using these alternate gear sets.

For what it is worth.
 
Yes, there are formulas to figure this stuff .... But ...... They hurt my brain and besides, even though there is a slight error, you will be hard pressed to measure it. You would have to thread about 3 feet before the error was noticable. THAT'S CLOSE ENOUGH for anything I do. Also, it can be done buy picking up the gears for around $10 on eBay instead of hundreds of dollars. But if you want to figure it out, it is just a matter of dividing the number of teeth on one gear into the number of teeth on the other gear to get the ratio and do this with all gears in the train to get the total ratio and then divide using the lead screw pitch to get the thread pitch ....... My brain already hurts. I would only calculate if I was making a special proprietary thread ..... Which I will never do ..... I think.

Hi. Are these South Bend 9B gears that you can pick up for $10 on eBay? How would one search for them? Thanks!
 
They are S B 9 change gears. They are usually available on eBay. I got mine there for $10 each. Some sellers charge more. ( I see the prices on S B parts going up and up. If there is a demand, the prices go up. )
 
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