13" QC Gearbox Retrofit

I'm considering a retrofit of a single tumbler gearbox to my 1919 gap bed 13" SB. But is this going to be like building the pyramids?

1) Can the box be mounted just by (precisely) drilling some holes, or is it more involved?

2) Can the original leadscrew be modded or is finding a decent screw from a QC machine the only practical route? Or maybe fabbing one starting w/ leadscrew stockk?

3) Will the original banjo work or is a special QC banjo required?

4) Will the big cast iron guard door still close or will the box interfere?

5) What other gears and auxiliary parts beyond the geabox itself and its internal parts will be required?

The point is to be able to dial in feed rates w/o swapping gears. Doubtless it'd be easier to fit a DC gearmotor w/ a 90 degree head to the tailstock end of the leadscrew. But she's a nice old machine in surprisingly good shape, and wiith a well done conversion from overhead shaft drive. The QC box would be more in the spirit of things.

Thanks in advance.

But is this going to be like building the pyramids?

Click to expand...

Probably - if the bed was never machined for such. I.E. they don't sit on rough cast iron. They do sit on a precisely planed pad or pads.

The 1913 How To Run A Lathe is a whole book of Series O - none of which have a QC. Maybe things were different a little later

I can't recall the members name but recently someone did just that with a 10L gearbox since the leadscrew of the early 13" was apparently 8TPI.

Edit- I think it was dcstang67 or something like that

I think you should use a double tumbler gearbox if at all possible. The single tumbler box uses a straight banjo with sliding gears, that needs a hole in your gear cover. The double tumbler might be able to use your existing gears and banjo.

The leadscrew can be modified to have the correct features on the end. The trick will be supporting and mounting the box in just the right place such that it lines up with your leadscrew. You would need some pretty detailed measurements to ensure that will work.

allan

Addl Info

The lathe does indeed have 8tpi leadscrew--does that differ from later SB 13s?

The banjo is single arm w/ sliding gears and no crook on the end. Info plate on front makes no mention of compounding; stops at 40tpi.

Do these data bear on best choice of gearbox?

Thanks.

Later 13" lathes used a 6 TPI leadscrew. You could likely adjust for difference by changing the stud gear.

allan

I was able to find dcstang67's posts re adapting a 10L gearbox to his older SB13. My take is that he used the 10L box because he happened to have one on hand--a big advantage--but not a factor in my case. He was able to make it work, but not w/o some finagaling.

A single lever 13 box sounds like it'd involve about the same total trouble, including making or finding gear(s) to resolve the 8tpi vs 6tpi leadscrew issue. This box would also have the advantage of looking the part.

The underside of the front way feels very smooth, certainly smooth enough to mount a gearbox. But drilling the holes and getting the box in the right location, its axis pointed right at the right hand lead screw support nearly 6ft away sounds a little delicate.

I don't want to take offf the legs and headstock in order to put the bed on a mill to drill the mounting holes. The only way I can think to do a nice job of drilling would be a fixture with removable drill bushings that would hang off the front V-way and could be tightened w/ screws from below. If this was made w/ care, the mounting holes would end up parallel with the front way and locate the box the correct distance from the front way. Drill with a hand-held drill using a tap-driill size bushing, tap with a major diameter bushing, and I don't know yet about the countersink. The headstock is definitely in the way--it'd be a job for the angle drill or else a very long bit.

I dunno, maybe that DC gearmotor driving the right hand end of the leadscrew is a better idea.

Once you have determined how to locate the position of the holes for mounting the gearbox, you could take off the headstock, and then use a magnetic base drill mounted to the carriage to get them precisely vertical and parallel with the ways. Use the same drill to counter bore the holes.