metric 2mm pitch thread

[bob531]

Hi , I have a South Bend 9A imperial with a few loose change wheels 30,40 50 and 55. Is there any way of doing a 2mm pitch thread (also possibly 1.5mm )without having to buy anything else? The thread doesnt have to be exact but a reasonable fit.
Ive never cut metric threads on this lathe before.
Ive also seen a couple of compound gears for sale a 80/76 and a 72/18 ,what would these be used for if anything?
Thanks
Bob

 

[kitno455]

Bob, presumably you also have a 20 and a 56 tooth already on the lathe?

allan

 

[bob531]

Hi Allan,
Yes i have the 56 and 20 on the lathe at the moment ,i also have a spare 24 tooth gear on there at the moment ,it was on mine when i got it. So 24, 30 ,40,50 ,55 available plus 2 small ones )both 20 Tooth) which im unsure what they are off.
Thanks

 

[Conrad Hoffman]

2 mm pitch is 12.7 tpi, and the closest standard is 13, which would bind up very quickly. 1.5 mm is 16.93 tpi. 17 would work OK, but you probably can't cut that. The only real way out of this is to get transposing gears, either the big 127/100 tooth, or the smaller 47/37 pair. More here- Metric Threading

 

[bob531]

Ok Conrad thanks,
Any idea what the Southbend 80/76 and 72/18 compound gears ive seen for sale are for??
Thanks Bob

 

[promacjoe]

Ok Conrad thanks,
Any idea what the Southbend 80/76 and 72/18 compound gears ive seen for sale are for??
Thanks Bob

I have never heard of an 80/76 gear. Depending on how you set up the gears, it would be, either .95 or 1.0526 ratio. not sure what that type gear would be used for. It seems kind of useless to me.
The other gear is for the 9N/10K model B and C. Normally, you use a 54/18 or a 72/18 Compound gear, for a B/C lathe. Although they can be used for the model A, They are not specific for that machine.

stay safe and have fun.

Joe.

 

[kitno455]

The only real way out of this is to get transposing gears, either the big 127/100 tooth, or the smaller 47/37 pair

Not true. Gimme a minute.

allan

 

[kitno455]

If you compound two of your existing gears, and move the gearbox input gear to the outboard position, you can make some metric threads. Your error % is too high for precision work, but probably reasonable for the length of engagement of a typical nut. Here are a few options:

20 tooth stud gear, driving 50 tooth, which is compounded with 55, which drives the 56 on the gearbox will turn your gearbox at 1.1 times its normal speed, making the leadscrew act as if it were 3.494 MM pitch. If that does not fit (probably because the 55 touches the nut on the stud gear), you could make the same thing this way: 20 drives 56 which is compounded with 55, which drives 50 on the gearbox.

QCGB MMPT %ERR
112 0.25 0.214
80 0.35 0.213
56 0.50 0.214
40 0.70 0.214
28 1.00 0.214
16 1.75 0.214
14 2.00 0.214
8 3.49 0.214

A bit better combination is available, but only gives three pitches: 20 drives 30 compounded with 40 which drives 55 on the gearbox.

QCGB MMPT %ERR
46 0.75 0.051
23 1.50 0.051
11.5 3.00 0.051

If we pick up another gear or two (perhaps from a Boxford), you could reduce the error still further. Let me know if you are interested in figuring out which to use.

allan

 

[nt1953]

Allan is quite correct. With a few stud gears you can cut threads with pitches from .25mm to 7mm. I have a spreadsheet that works all of this out for a double tumbler 9" if you want it.

 

[Conrad Hoffman]

Hey, pretty good and he seems to have some of the gears to do it! IMO, the error gets bad quickly, but should be fine for a nut.

 

[kitno455]

Those options are not bad, but you could do better with one or two additional gears. If you get the right ones, you don't even need a compound. In particular, I've noticed previously that the 79 tooth gear seems to work some wonders. I think 79 was in the Boxford gear set.

20 tooth stud, 79 tooth screw gear makes leadscrew act like 2.25mm:

GCGB MMPT %Err
72 0.25 0.026
40 0.45 0.026
36 0.50 0.026
24 0.75 0.026
20 0.90 0.026
18 1.00 0.026
12 1.50 0.026
9 2.00 0.026

24 tooth stud, 79 tooth screw gear makes leadscrew act like 2.70mm:

GCGB MMPT %Err
72 0.30 0.029
48 0.45 0.029
36 0.60 0.029
24 0.90 0.029

30 tooth stud, 79 tooth screw gear makes leadscrew act like 3.376mm:

GCGB MMPT %Err
36 0.75 0.029
18 1.50 0.029
9 3.00 0.029

40 tooth stud, 79 tooth screw gear makes leadscrew act like 4.501mm:

GCGB MMPT %Err
144 0.25 0.028
80 0.45 0.028
72 0.50 0.028
48 0.75 0.028
40 0.90 0.028
36 1.00 0.028
24 1.50 0.028
18 2.00 0.028
12 3.00 0.028
9 4.00 0.028
8 4.50 0.028

Looks like G&M might have one on the shelf. http://www.gandmtools.co.uk/product-category/machine-tools/boxford-spares-and-tooling/

allan

 

[michiganbuck]

Surprised no one mentions die cutting if only a few metrics are needed.

Or is this an "Everybody knows that."

 

[bob531]

Hi Thanks for the further replies , i can get further gears such as 32,54, 43 ,46,59, 36 and 60 off ebay and GM tools are likely to have others
. The 127/100 does show up occasionally over here but prices are high. One on ebay at the moment for something like £150 +shipping.
Im only wanting to cut threads for adapters (for tooling ) max. length probably 1" or less. I`m specfically wanting to adapt some MT4 tooling to use in a Alexander mill (Deckel FP1 clone ). So the Deckel s20 x 2 buttress thread will be one thread i hope to cut. As most Mt4 threaded stuff over here has M16 x 2 threads ,that is another but same 2mm pitch.
As some will know Deckel tooling is not cheap so being a cheapskate i hope to adapt some stuff like boring head tooling .etc..

Allan ,yes im interested in what ever would give me the most accurate 2mm thread and one or two other common metric pitches.
Thanks very much
Bob
p.s so if i used a 79 gear and the 20 stud gear ,i can cut 2mm to a 0.026% error with the gear box set to 18tpi ??

 

[bob531]

Nt1953, yes i wouldnt mind the spreadsheet,thanks

 

[kitno455]

So the Deckel s20 x 2 buttress thread will be one thread i hope to cut.

Not likely to find a tap or a die for that one...

p.s so if i used a 79 gear and the 20 stud gear ,i can cut 2mm to a 0.026% error with the gear box set to 18tpi ??

No, you've mixed the 40+79 and the 20+79 charts. For 20+79, you set the gearbox to 9 TPI to get 2mm.

allan

 

[bob531]

Hi Allan, Thanks yeah i did confuse the charts as i was looking at both and got mixed up. I think i understand now. I ordered that 79T gear from G&M.So does that just go on in place of the 56 gear thats usually on?
So am i right in that you cant use the thread dial but you have to leave the half nuts engaged and reverse the lathe?
I have it on an inverter drive so that should be convenient enough.

Bob

 

[kitno455]

Yes, replace the 56 with the 79 (sliding the idler and swinging the banjo as required). You will not be able to thread in the normal imperial manner, where you open and close the halfnuts timed by the thread dial. But, you don't necessarily have to keep the halfnuts engaged. I actually use the same method Conrad mentions half-way down this page: Metric Threading

allan

 

[nt1953]

bob531
I have sent you a PM

 

[bob531]

Well was hoping to try some threads today as the 79t gear arrived from G&M . Unfortunately the bore is slightly too small and the keyway also.
So i have some fettling to do.
At first when i compared it to my other spare change wheels they didnt mesh properly ,though when i tried it with the gears on the 1964 9A (the one i use) it appears fine. The other spare change gears came with a 1941 9A im renovating.
I assumed that the south bend gears would be the same for a 1941 and a 1964 but apparently not.

 

[promacjoe]

The gears are supposed to be 18 DP on all the 9N and 10K model A, B and C. only the model 405 use 20 DP gears. For further information go to,

http://www.wswells.com/data/9_workshop/9_workshop_info.html

And,

http://www.lathes.co.uk/southbend9-inch/index.html

Stay safe and have fun.

Joe.