09-07-2015, 06:46 PM
(This post was last modified: 09-07-2015, 06:54 PM by Hopefuldave.)
Hi aRM, I don't know these machines specifically, just machines in general ;)
It's unlikely the key would wear, the failure is usually the key shearing or something else shifting and letting it move from its correct position, so...
How much torque the key can take depends on its length and cross-section, and something that occurs to me is that it appears it's only supported by the cross-shaft, hence excess torque will try to force the key and shaft sideways as the quill tries to rotate with the torque applied to the tailstock quill - this would force the cross-shaft out through its bore, bending the grubscrew in its groove and locking it up as you found. Or it could shear leaving you with half(ish) in the quill's groove, the rest in the cross-shaft's groove - this would probably lock the quill up solid and probably badly score either the quill, the tailstock bore, or both :(
The key seems to be all that's preventing the quill rotating, so my instinct says a longer key and a groove cut in the tailstock casting to match the groove in the quill would add a lot of strength to what may be a weak point?
This is just a wild-arsed guess, you understand, but if I were to try that I'd make up a cutter from a piece of HSS the right width to match the slot in the quill and the key, clamp the tailstock down and run the tool back and forth with the carriage, tool held in the toolpost.
If you have a QCTP lowering the tool would be fairly easy, unclamp the holder, rotate the height adjuster a touch, re-clamp taking a few thou" of cut each pass - if you don't have a QCTP you could lay thin (0.002" - 0.003"?) shimstock under the tool, plenty of layers, take a few passes, remove a shim, repeat until deep enough or you die of boredom...
If you should got that route, be sure to clean up and deburr your new slot very thoroughly! Being cast-iron the tailstock casting should cut fairly cleanly, but to be sure...
Hope this helps, rather than confuses!
Dave H. (the other one)
EDIT: Just a thought, if there's enough wall thickness to the tailstock housing, the new key could be positioned at 90 degrees from the original, with a new keyway in the quill - just as strong, maybe easier to cut in the housing as you could adjust the tool into the slot for depth of cut with the cross-slide, but you'd have to also cut a new keyway slot in the quill - if you have access to a mill this wouldn't be such a problem though?
It's unlikely the key would wear, the failure is usually the key shearing or something else shifting and letting it move from its correct position, so...
How much torque the key can take depends on its length and cross-section, and something that occurs to me is that it appears it's only supported by the cross-shaft, hence excess torque will try to force the key and shaft sideways as the quill tries to rotate with the torque applied to the tailstock quill - this would force the cross-shaft out through its bore, bending the grubscrew in its groove and locking it up as you found. Or it could shear leaving you with half(ish) in the quill's groove, the rest in the cross-shaft's groove - this would probably lock the quill up solid and probably badly score either the quill, the tailstock bore, or both :(
The key seems to be all that's preventing the quill rotating, so my instinct says a longer key and a groove cut in the tailstock casting to match the groove in the quill would add a lot of strength to what may be a weak point?
This is just a wild-arsed guess, you understand, but if I were to try that I'd make up a cutter from a piece of HSS the right width to match the slot in the quill and the key, clamp the tailstock down and run the tool back and forth with the carriage, tool held in the toolpost.
If you have a QCTP lowering the tool would be fairly easy, unclamp the holder, rotate the height adjuster a touch, re-clamp taking a few thou" of cut each pass - if you don't have a QCTP you could lay thin (0.002" - 0.003"?) shimstock under the tool, plenty of layers, take a few passes, remove a shim, repeat until deep enough or you die of boredom...
If you should got that route, be sure to clean up and deburr your new slot very thoroughly! Being cast-iron the tailstock casting should cut fairly cleanly, but to be sure...
Hope this helps, rather than confuses!
Dave H. (the other one)
EDIT: Just a thought, if there's enough wall thickness to the tailstock housing, the new key could be positioned at 90 degrees from the original, with a new keyway in the quill - just as strong, maybe easier to cut in the housing as you could adjust the tool into the slot for depth of cut with the cross-slide, but you'd have to also cut a new keyway slot in the quill - if you have access to a mill this wouldn't be such a problem though?
Rules are for the obedience of fools, and the guidance of wise men...
(Douglas Bader)
(Douglas Bader)