Here is a list of all the postings James G 1 has made in our forums. Click on a thread name to jump to the thread.
|Thread: Boxford STS Screwcutting Clutch|
Thanks for your comprehensive reply - it's amazing how subtle can be the details of a simple mechanism. Certainly as you say consistent lubrication should help - the latest version as discusssed on this thread is enclosed and may effectively have it's own oil bath. Hopefully I'll be able to build it and enjoy the luxury of using it.
Just to say that I am also following this with interest and would be interested in drawings if available.
Is there any advantage in having matching slight tapers on the engaging surfaces of the dog clutch i.e. on the drive dog and the semi-circular end of the recess with which it engages ? The taper would be such as to have the dog more narrow at it's end than at it's base, such that there would be a slight tendency (depending on taper angle) for the clutch to disengage unless held by a detent.
The only dog clutch I have had a chance to examine was a multi-tooth clutch in the feed gearbox of a toolroom type mill and this had a very definite taper on the dog faces, hence my enquiry.
To follow up on the previous excellent description, the most straightforward arrangement is to have the dog clutch turning at spindle speed.
I believe that the shaft where the dog clutch is located must not be running any faster than spindle speed, as this allows for re-engagement at incorrect relative positions.
In the general case, a dog clutch located on a shaft which is running more slowly than the spindle will not work correctly either. This is why a clutch located on the leadscrew will not suffice.
However, if the shaft with the dog clutch is rotating more slowly than the spindle by a ratio of 1/N, where N is a whole number, then I think it will work. e.g. if the dog clutch shaft turns at 1/3 of spindle speed then all will be well. However dog clutch running at say 2/5 of spindle speed will not work.
The above is my understanding from reading - particularly Martin Cleeve's excellent book.
The Boxford 280 and similar lathes have a built-in reduction in speed of 1/3 from spindle to the first accessible shaft of the feed train, hence my interest in the niceties!
That looks great! I would be most interested in any and all details of this mechanism. I have been scratching my head trying to figure a way of doing this internally to the headstock using a dog clutch on the feed and feed reverse gears. This looks like a very neat solution. I think it will apply to other lathes in this series as well such as the 280.
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