Thread: Hercus Gearing Problem

Dave,

My ARL came with the metric transposing gearset in it's original cardboard box. I'll have a look tonight and report back in regards to the contents.

BT

Originally the lathe should of been supplied with a 20,40 and 56 tooth change gears,there would also be an 80 tooth bossed idler.

The 20 and 40 tooth change gears are changed between themselves on the Stud gear to give the desired Imperial TPI ,the 56 tooth gear remains on the Screw shaft.

For cutting Metric pitches rangeing from 0.20mm to 6mm you will require change gears of 28,32,36,40,44, and 48 teeth,you will also require the 127/100 tooth compound gear.This gear goes in place of the 80 tooth Idler.You will still require the 56 tooth gear,this will remain on the Screw shaft.the other change gears listed above interchange on the Stud shaft to give the desired pitch.

Thanks Pipeclay,
I didn't get a 40 tooth gear with the lathe. After reading you post and consulting the 'Textbook of Turning' the penny has dropped. I didn't realize that there are two separate gears on the stud. Now I see how the 40 tooth works on the stud and how the metric change gears would work.
Much appreciated,
Dave

Originally Posted by pipeclay

Originally the lathe should of been supplied with a 20,40 and 56 tooth change gears,there would also be an 80 tooth bossed idler.

The 20 and 40 tooth change gears are changed between themselves on the Stud gear to give the desired Imperial TPI ,the 56 tooth gear remains on the Screw shaft.

For cutting Metric pitches rangeing from 0.20mm to 6mm you will require change gears of 28,32,36,40,44, and 48 teeth,you will also require the 127/100 tooth compound gear.This gear goes in place of the 80 tooth Idler.You will still require the 56 tooth gear,this will remain on the Screw shaft.the other change gears listed above interchange on the Stud shaft to give the desired pitch.

Dave,

I'd say Peter has covered it with the answer above. I won't be able to add anything.
It will be interesting to hear how you get on cutting metric threads. I've tried my hand at it and it makes me wish that one of my lathes was metric.

BT.

Thanks Bob. What's the general thought. Is it worth the effort and expense to buy and setup the gears for metric thread cutting? Are you still able to close the gear cover on a 9in Hercus with the 127 compound gear on the banjo? I recall from my tech training (45 years ago) that the method for cutting a metric thread was to reverse the lathe after each cut with the half nuts engaged. Is this a successful and practical option or should I look for a metric machine.

Dave,

Having the half nuts constantly engaged makes metric thread cutting a bit trickier. Most of my imperial screwcutting has utilized a runout groove. It's easy, you disengage the nuts when you hear the load on the motor change. Can't do that with a metric thread and the motor doesn't stop quick enough to enable the use of a narrow runout groove.

My answer has been to cut the threads without the motor, by turning the spindle by hand by means of a hand crank fitted to an expanding mandrel inserted in the spindle bore. It is laborious but it works.The mandrel was featured in one of my posts a few months back.

Hand turning works perfectly for threading to a shoulder or where you may not want a runout groove.

I don't know about the cover. I've left it open during my metric efforts.

Buying a metric lathe is an expensive option. Depends on the amount of screwcutting you plan on doing. I hadn't had the need to cut any metric threads until I acquired my metric mill six months ago.

Bob.