Tuesday, December 11, 2012

LeBlond Tailstock Improvement

This article is about a modification to the tailstock on the shop Leblond regal engine lathe. I cant take full credit for the idea as I saw a lathe that belongs to a gunsmith named Ray with a similar modification. As soon as I saw the modification I knew he had the same problem that I have. The issue is with the clamping studs that lock the tailstock in position along the ways. When doing heavy drilling you need to snug these lock fasteners down pretty well or the tailstock just drifts back under the thrust. This sometimes means you have to take a couple of licks with the stock wrench. This entails lifting the wrench off the fastener and repositioning it several times. To further aggravate me the Leblond wrench is only six point and had limited orientations on the hexagon nut. There is a fine line between not enough clamping force and the ability to loosen the lock bolt sufficiently to easily slide the heavy tailstock along the ways without causing a hernia.
I really like to leave the compound rest set at thirty degrees all the time. Its mainly in case I feel the sudden need for threading. At this angle it keeps the dial out of the way for normal turning operations and is ready to go if you want to thread. On our Leblond if the tailstock wrench is on the front lock bolt there is an interference with the compound. Its not a big deal but what it does is make you have to extend the tailstock quill further to reach the work. In the picture below you can see a large space between the tailstock and the carriage. This translates into turns on the tailstock wheel.
  The front clamp bolt works better than the rear one for some reason on our lathe so the wrench ends up on that stud most of the time. All this might seem nitpicky at first glance but it all contributes to delays and frustrating work ergonomics. If you constantly have to lift the wrench off and advance it to another flank and make that two clamp studs then you have taken a few extra seconds to do something that should be a single motion. Other lathe manufacturers got it right when they changed the lever position from horizontal to vertical like this Monarch double E.

I talked to a race car driver about stuff like this and he said the difference in driving a race car and driving it really fast sometimes boiled down to a quarter of an inch of clearance somewhere in the cockpit. A little more room between the shifter and the body translated directly into better lap times. This is the machinist version of the same problem.
The new idea was to link the two clamping bolts together so the wrench could be left on the rear fastener to give maximum throw and clearance to the compound rest. By actuating both clamp studs simultaneously neither one has to be quite so tight to resist the thrust from drilling.
I scrounged around and found a couple of 1-1/16 twelve point box wrenches and had Steve modify them to make a parallel clamping linkage. The wrenches as it turned out were actually pretty hard. He managed to cut them off in the horizontal band saw but when he had to drill the clevis holes through we ended up having to use a carbide end mill. Good American old school wrenches. The clevises are standard McMaster stuff with a set screw as the threaded stud connecting the two clevises.
You can see in this shot that the tailstock is much closer to the cross slide. We decided after testing the linkage out to put a dogleg in the operation handle to give even more clearance in the loose position. We just notched the handle with an abrasive cutting disc and then bent and re-welded it in the new position. With the adjustable link the two clamp studs can be tuned to give whatever feel the operator likes. All in all a good use for a couple of wrenches that hardly ever saw any use sitting in the bottom of a toolbox.

Another way somebody could do this would be to laser or waterjet cut a pair of custom specially curved wrenches that cleared the tailstock casting for even more throw. 
Thanks for looking.

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