13" Single Tumbler Metric Thread Kit

[MyLilMule]

Did South Bend ever make a conversion kit to convert an imperial lathe to cut metric threads for the older (1941 era) 13" SINGLE tumbler QCGB lathes?

I'd like to, some day, look at making a set of gears for it, but I'd like to stay somewhat true to what SBL would have done. I would imagine it would need a new banjo, possibly.

I've searched for details but can't find anything. Not even an image of what the threading chart would look like.

Any help would be appreciated.

 

[MrWhoopee]

As for hardware, all you should really need is the transposing gear set and few extra gears needed to cover all the standard metric threads. Original would have been 127/100 transposing gear, but extremely close approximations are possible. I used 80/63 for my Heavy 10L because it already came with an 80. There are several threads on this topic, here's one:

Metric Transposing Gears

When I was lathe shopping last year, I had a list of features I wanted in a lathe: cross feed, tumbler reverse, QCGB and the option of cutting metric threads with change gears. The SB 10K I ended-up purchasing met all those needs well (and I really like it) but I was left scrounging around for...

www.hobby-machinist.com

 

[MyLilMule]

As for hardware, all you should really need is the transposing gear set and few extra gears needed to cover all the standard metric threads. Original would have been 127/100 transposing gear, but extremely close approximations are possible. I used 80/63 for my Heavy 10L because it already came with an 80. There are several threads on this topic, here's one:

Metric Transposing Gears

When I was lathe shopping last year, I had a list of features I wanted in a lathe: cross feed, tumbler reverse, QCGB and the option of cutting metric threads with change gears. The SB 10K I ended-up purchasing met all those needs well (and I really like it) but I was left scrounging around for...

www.hobby-machinist.com

Thank you. I have already read just about every thread I could find. I am very much aware of the 127/100 gear needed.

I am looking specifically for what SBL provided, if in fact they did, for a 13" Single Tumbler, especially the threading conversion chart that may have shown, for each pitch, what selections the sliding gear (if still used), and the QCGB top lever (Left, Center, Right) and bottom tumbler selector would be set. I've seen them for the double tumbler, but never for the single.

 

[MrWhoopee]

Thank you. I have already read just about every thread I could find. I am very much aware of the 127/100 gear needed.

I am looking specifically for what SBL provided, if in fact they did, for a 13" Single Tumbler, especially the threading conversion chart that may have shown, for each pitch, what selections the sliding gear (if still used), and the QCGB top lever (Left, Center, Right) and bottom tumbler selector would be set. I've seen them for the double tumbler, but never for the single.

Once you have the correct transposing gears, the settings for the QCGB (by TPI) should be the same. I believe that if you translate the QCGB settings for the double tumbler GB to their TPI equivalent you can then set your single tumbler to that TPI.

Of course, I was wrong once.

 

[Canuck75]

SB did make transposing gear sets for the 10K right up to the 17" lathes according to my SB lathe accessories catalogue from the 1960s. One would think such a setup should work for your era lathe as well.
I made a 63/80 transposing set and required stud gears from HDPE ( I don't do heavy work). My 1963 10" has a single arm bracket which mounts the transposing set plus the gear into the box. Stud gears are changed to suit. I've included the chart which applies to my lathe. With the 70 ratio QCGB I can cut .2 to 6 mm pitch threads. Should be able to construct a chart for required gears and box selections to get the mm pitches your gear box will produce. Hope this helps.

Canuck75

 

[Canuck75]

MyLilMule,-

I thought I would add another comment. If you look at the original feed chart on my machine you will see that it uses a 40T on the spindle with a 80T intermediate and a 56T on the gearbox. The lead screw is 8TPI. The transposing set plus different spindle gears changes the ratio between the spindle and lead screw such that precise millimetre carriage movement is realized for each turn of the spindle - nothing new there! But to get all the desired pitches seven stud gears were needed, 26/28/32/36/40/44/48, plus the transposing set. The original 56T drives into the QCGB but moved outboard to line up with the 63T gear. Interesting to note that on the QCGB itself only the A to G plunger holes and 1 and 3 numbered holes are needed for the full mm range. Gathering information from posts by other members made this project so much easier. This is just more background but thought it might help.

 

[SLK001]

Yes, they had a metric thread kit for the 13" (IIRC, it was the same one as for the H10).

Here are a couple of pics of the complete kit:

 

[MyLilMule]

Thank you, @SLK001. Are these the best photos you have? Parts of the thread plate are glared over and I can't read it all. That's really the key to the whole thing. I assume the bundle of gears there are just other stud and idler gears?

 

[SLK001]

Thank you, @SLK001. Are these the best photos you have? Parts of the thread plate are glared over and I can't read it all. That's really the key to the whole thing. I assume the bundle of gears there are just other stud and idler gears?

I got the photos off ebay a couple of years ago, so they are what they are. You're correct on the purpose of the other gears.

 

[joeuser01]

Hey all.. I just picked up a single tumbler english thread SB13 lathe and want to accomplish metric threads as well.. MyLilMule mentioned it was difficult to read the attached metric transposing chart, and it is. I believe I've transcribed most of the chart correctly, as below. There could be some errors as 5 & 6, & 3 & 8 look similar. Hopefully we can dig up a better quality pic of the actual chart (along with a full conversion kit so I can cut metric threads!)

SINGLE TUMBLER TRANSPOSING GEAR CHART (6TPI LEAD SCREW)
MM - STUD - IDLER - PLUNGER - TOP LEVER
6.00 - 36 - FIG. 1 - 1 - LEFT
5.50 - 33 - FIG. 1 - 1 - LEFT
5.00 - 60 - FIG. 1 - 1 - CENTER
4.50 - 64 - FIG. 1 - 1 - CENTER
4.00 - 56 - FIG. 1 - 6 - LEFT
3.50 - 45 - FIG. 1 - 1 - CENTER
3.00 - 56 - FIG. 1 - 1 - CENTER
2.75 - 53 - FIG. 1 - 1 - CENTER
2.50 - 30 - FIG. 1 - 1 - RIGHT
2.25 - 54 - FIG. 1 - 1 - RIGHT
2.00 - 30 - FIG. 1 - 6 - CENTER
1.75 - 45 - FIG. 1 - 1 - RIGHT
1.50 - 56 - FIG. 2 - 1 - LEFT
1.40 - 42 - FIG. 2 - 5 - LEFT
1.30 - 36 - FIG. 2 - 3 - LEFT
1.25 - 60 - FIG. 2 - 1 - CENTER
1.20 - 36 - FIG. 2 - 3 - LEFT
1.10 - 33 - FIG. 2 - 5 - LEFT
1.00 - 36 - FIG. 2 - 3 - LEFT
0.90 - 54 - FIG. 2 - 3 - CENTER
0.80 - 48 - FIG. 2 - 3 - CENTER
0.75 - 36 - FIG. 2 - 1 - CENTER
0.70 - 42 - FIG. 2 - 3 - CENTER
0.65 - 39 - FIG. 2 - 3 - CENTER
0.60 - 36 - FIG. 2 - 3 - CENTER
0.55 - 33 - FIG. 2 - 3 -CENTER
0.50 - 36 - FIG. 2 - 6 - CENTER
0.45 - 54 - FIG. 2 - 3 - RIGHT
0.40 - 48 - FIG. 2 - 5 - RIGHT
0.35 - 42 - FIG. 2 - 6 - RIGHT
0.30 - 36 - FIG. 2 - 3 - RIGHT
0.25 - 36 - FIG. 2 - 6 - RIGHT
0.20 - 24 - FIG. 2 - 6 - RIGHT