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DavidA:
Thinking more about this. There may be a snag.
I suspect that this dog clutch will only work when cutting threads that have a direct relationship with the number of threads on the lead screw. I.e. if you have an eight tpi lead screw it will work with 8, 16, 32, 64 tpi threads.
This is related to being able to 'drop in' the half nuts anywhere with 8 tpi lead screw and the above mentioned threads, but the need to use a thread dial indicator for others.
I suspect, but not sure, that it wont work if you were to, say, cut a 5 tpi thread with a 8 tpi leadscrew and then try to re engage the clutch of the chuck is not in the same position it was when the clutch dis engaged.
Readers views welcome.
Dave.
doubleboost:
I think the "clutch" on the lead screw is there in case the lathe is "crashed"
Tool post crashes in to chuck lead screw slips to minimise damage
John
Manxmodder:
--- Quote from: DavidA on March 02, 2015, 07:00:44 PM ---Thinking more about this. There may be a snag.
I suspect that this dog clutch will only work when cutting threads that have a direct relationship with the number of threads on the lead screw. I.e. if you have an eight tpi lead screw it will work with 8, 16, 32, 64 tpi threads.
This is related to being able to 'drop in' the half nuts anywhere with 8 tpi lead screw and the above mentioned threads, but the need to use a thread dial indicator for others.
I suspect, but not sure, that it wont work if you were to, say, cut a 5 tpi thread with a 8 tpi leadscrew and then try to re engage the clutch of the chuck is not in the same position it was when the clutch dis engaged.
Readers views welcome.
Dave.
--- End quote ---
Dave, a single point dog clutch will always re-engage the leadscrew at exactly the same relevant index as it was disengaged from and there will be no variation in the relationship of gear engagement because they haven't been disengaged or had their relative timing disrupted.
It doesn't make any difference to the repeatability of re-engagement if the dog clutch is located directly on the drive end of the leadscew(like the harrison lathes) or if it is located on the input end of the drive shaft for the screwcutting gearbox.
The reason it cant ever be engaged wrongly being that it has only 1 engagement/drive location in 360 degrees of rotation.
Similar single dog setups do exist,one example is shown and described fitted to a Myford lathe in Martin Cleave's book on screw cutting.
Manxmodder:
Agree John, it being a safety device would make perfect sense considering the cock ups that some spotty Herberts in training college can make when inexperience gets the better of them.....OZ.
DavidA:
...It doesn't make any difference to the repeatability of re-engagement if the dog clutch is located directly on the drive end of the leadscew(like the harrison lathes) or if it is located on the input end of the drive shaft for the screwcutting gearbox. ,
You are right , of course.
It would only make a difference if the gear train was disengaged between the leadscrew gear and the headstock gear.
Took me a while to clearly see the point; pun intended.
Dave. :hammer:
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