Pacemaker Blew Out Tailstock Ram Threads!!

[Mike C.]

Was setting up to trim down an impeller wear ring on the old 1943 20" HD Pacemaker last Tuesday. Ran the tailstock ram out as far as possible to get some travel on the carriage and went to where it ran off the screw. No big deal, happens all the time. When I went to retract the ram, it felt tight, so I ran it back out, bumped it lightly with a mallet while turning the wheel and it started to go back in, then got tight again, then loose, then tight, then loose, then tight and quit moving. Swapped to the #$%^ing Summit to get the job done and came back later. Once I got the ram out (no help from the handwheel), I stood it taper down on the bench and the bronze threads fell out, one by one. Flipped it around and removed the bronze threaded insert, which was now just an insert... no threads.

Ordered a chunk of 2.250" aluminum bronze and it came 2.250. No room for error, so just passed a piece of emory cloth down it to polish it up and let it ride. Luckily, we had a 1" 5TPI Acme tap in the drawer! I pulled the wheel and screw out and life suddenly got more difficult. Somebody's brother in law at American must have owned a shop that specialized in 1" 6TPI square thread parts, because that's what the tailstock ram screw is. So much for a simple tapping job. My 4 years of single pointing every imaginable thread form and pitch at the hydraulic shop were about to pay off.

I just rough measured the thread space width at about .085", so I ground a square thread tool for .090 to give a little room if it got tight at the back end. Depth of thread was 3/32nd, so that made it easy. Piloted a 1/4",then drilled a 13/16ths hole. Set up 6TPI on the Leblond and kicked the compound perpendicular to the cross slide. Couldn't take more than about .005" depth of cut without it barking, so just took my time. Went to .1875 on the cross feed (diametral dial on the LeBlond) and then took it on out to .1900, just to be sure it cleared. Tested the screw and it started, but was a tad tight. I knew I had a burr on the entry, so figured I should let it ride. Gulped as I removed the part from the jaws and cleaned up all burrs. It spun on the screw freely with no perceptible play.

Last bit was to set the Cincy horizontal up with a 3/16" radius cutter and cut a groove for the retaining pin. Sure slicker and faster than an endmill.

Got it all back together and the handwheel spins freely until you draw in far enough to eject a center or tool with no tang. It gets a little tight, but nothing you can't deal with one handed.

 

[climb-101]

got any pictures? i will prob need to do this on my pacemaker sooner than later. there isnt much left of the thread in my tailstock.

 

[johnoder]

Thanks Mike, for finding time for that great post. Glad you are back

 

[Mike C.]

got any pictures? i will prob need to do this on my pacemaker sooner than later. there isnt much left of the thread in my tailstock.

It's just stupid straight forward work. Only trick is grinding the left hand thread tool. Make sure to wrap your brain around the fact that the leading side of the tool needs to slope away from the flank of the left handed thread... and that this will be on the OPPOSITE side to what you are used to grinding for a threading tool. As might be expected, an experienced machinist like myself would have no problem with this, right? Nope, I screwed it up and ended up with a clearance on BOTH sides. So, should I ever have to cut a RIGHT handed square thread in the future, I now inadvertently have a tool that is capable of either, lol.

 

[thermite]

It's just stupid straight forward work. Only trick is grinding the left hand thread tool. Make sure to wrap your brain around the fact that the leading side of the tool needs to slope away from the flank of the left handed thread... and that this will be on the OPPOSITE side to what you are used to grinding for a threading tool. As might be expected, an experienced machinist like myself would have no problem with this, right? Nope, I screwed it up and ended up with a clearance on BOTH sides.

Relax, Bro. That's not a "screw up" at all.

Normal practice, back in the day, rather.

Couple or four entire human generations of us "generally" cut threads with no compound on the lathe. "Straight in", IOW. We NEEDED heel clearance both sides.

Only "one way" threading tools I've EVER ground were for use where the thread itself was assymetrical. Butress. Dardelet. etc. Even so, I ground-in heel clearance, trailing side as well as leading out of habit.

Doesn't HARM anything important. Not when yer paid Union scale by the hour, anyway!



But even when time is "your OWN money", the "future-proofing" is pretty cheap.

So, should I ever have to cut a RIGHT handed square thread in the future, I now inadvertently have a tool that is capable of either, lol.

Got it in one. Good on yah!



Purchased inserts, of course "are whatever they are". Order whatever works with whatever you are tooled-up to utilize.