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Backlash Eliminators: What to expect?

gargamel

Aluminum
Joined
Mar 22, 2012
Location
Boston, MA
I have been playing with the backlash eliminator nuts on my 1950's era Cincinnati Toolmaster. I can dial it to about 0.003" of backlash and still get smooth turning action on the leadscrew, but if I try to snug it up more than that then the screw binds and does not want to turn. Is 0.003" considered to be about as good one can expect from these types of devices, or should I be able to bring that closer to 0 with the magic touch? Despite being 70 years old this is a low hours machine in great shape, so I don't think that wear on the screw is an issue in this case. It does not seem to matter where I am on the leadscrew when I adjust the backlash, same story all across the travel.
Preempting the claims that I can do good work even with much more than 0.003" of backlash: Agreed. This is not about needing it to be better, but a general question on the function of the backlash eliminators.

Thanks,
Mike
 
With most feed screws and lead screws that's about as close as you can get. The thread form of the screw and the nut may not be perfeclty matched due to wear and the alignment of screw and nut may not be absolutely perfect, this leads to a very rapid increase in friction once you get binding on any part of the length of the nut and any part of the threadform.

Most folk would be very happy with that amount of backlash on a new mill if it didn't have ball screws. :D
 
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Back in the day I only used a few mills with backlash eliminators and would rate 0.003'' as very good going.

P.S. those mills had been ridden hard and not been given the best feed or stabling
 
Thanks Mark & Limi. You've confirmed my suspicions. Just figured I would ask as I have not tried adjusting one of these before.
 
I thought the tool master was an opposing nut sprung cartridge affair, though the one I have hasn’t been tinkered with, however I have the square shaped one made in France.
Mark
 
Think it was sold as a climb milling thingy from memory, there’s definately somthing about climb cutting and the backlash exterminator, mind I can break cutters conventional milling, I’ve not pulled the table off mine, I should I suppose, add the leftover bits to the “ that will come in handy bin”, I like leftover parts, they’re so useful for fixing the thing you just fixed
Mark
 
Thanks all. For posterity, I'll see if I can dig up some pictures of the relevant mechanism from the Cincinnati docs. its a bit hard to photo no, but i might have one from when the table was off.
 
Think it was sold as a climb milling thingy from memory, there’s definately somthing about climb cutting and the backlash exterminator, mind I can break cutters conventional milling, I’ve not pulled the table off mine, I should I suppose, add the leftover bits to the “ that will come in handy bin”, I like leftover parts, they’re so useful for fixing the thing you just fixed
Mark

I know that Kearney & Trecker promoted their back-lash mechanism for that very purpose (climb milling).
 
Yes, it might tighten up a bit with more use. I am just finishing putting the machine back together after a teardown for moving into a restricted access (read basement) space. Im sure there were slight shifts and alignment changes for the components after cleaning out all of the old hardened oil and putting things back together.

After a few months of use, you will be able to set it tighter, maybe down to .0015 ...Phil
 
Check the bearings that are controlling the thrust, too.

No bearing on the right-hand side, only the left apron is currently installed. Seemed like it would be easier to get at the mechanism before putting the right side apron back on. Good point though, I'll poke it again after putting the RHS apron back on.
 
Attached should be a couple selections from the user manual for this machine relevant to the backlash mechanism. Looks like their official term is "anti-backlash", and my wording of "backlash eliminator" was maybe optimistic.

Improved climb milling is also specifically called out as a benefit.

ToolmasterBAcklash2.jpgToolmasterBacklash1.jpg
 
I know that Kearney & Trecker promoted their back-lash mechanism for that very purpose (climb milling).
It’s interesting, I have a tool master mill with the slotter on the back ( that’s been very very handy, no more fileing holes square, making dies, marvellous gadget, it’s not got the guts of the 36” shaper but I like it, I’d like a 36” too, but don’t think that’s on the cards)
Anyway I had a K&T mill in my shop in work, and the tool master I now have, some spooky similarities, I was short a green and silver lever handle for the Cincinnati, it’s the same as the K&T, which I promptly removed and replaced with a black knob, it’s as if K&T and Cincinnati had some common ground?
Mark
 
I would guess that's about as good as you're going to get with a lead screw and not a ball screw. I could be wrong though.
 
A machine with that much use will usually have more wear in the mid part of the travel than at the ends. A typical place to start is set for .005" on an end, then check at various points along the travel. I have seen as much as .020" or more backlash difference between the end and middle. Remember that the difference is a loss in accuracy. If you measure travel over the range, you will find that the actual travel falls behind in the worn part and catches up at the other end.

Bill
 
It depends quite a lot on the materials used in the screw and nuts. Bronze nuts as used on Bridgeports, have a tendancy to wear the screw severely. cast iron nuts as used on some other machines (like my Beaver) wear the nut in preference to the screw.
 








 
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