Replacing the lead screw and nut on a mill.

I have never seen a boring head quite like that. At first glance it looks a little bulky. But looking at the dials it must be a pleasure to use. Any info on it? Great job on the nut btw.
 
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Hello Eightball, the boring head was designed by George Thomas and is outlined in his book "The Model Engineers Workshop Manual". It is a pleasure to use providing very accurate increment adjustments. I made this about four years ago and it is the only boring head I use.

Regards,
Jim
 
Thats certainly great work. I'll have to try and find that book or some plans on the boring head. I love those big ol adjusting knobs. It does look very user friendly.
 
Jim,

Very impressive article and machine work. I have a few questions.

Where did you get your lead screw.

Can I get a left handed one for my lathe.

Can I get a hard chromed lead screw so it wont wear.

Can all this work on both x and y axis be done from the top or do you need access to the underside of the mill.

Thanks

John
 
Hello John: Let me try to answer your questions. The lead screw blank I used for this project came from Enco, they stock lead screws blanks in a variety of sizes in both right and left hand threads. Another source that I have used in the past is Roton. In my experience the difference between "acme threaded rods" and "lead screw blanks" is the consistency of the thread and the finish of the thread which provides smooth operation from end to end.

If you use acetal for the nut you will find that wear is very limited. If you want to consider more exotic material then check out the offerings at Roton. You might want to consider ball screws.

Your question on access is a good one and not one that I have considered. I have replaced the "X" axis on my mill but not the "Y" axis. The "Y" axis is on my do list but not quite at the top yet. I believe that needed access can be had from the top although as I say I have not attempted that part of the process yet.

Thank you for your questions and let us know how you do on this project.

Regards,
Jim
 
JimSchroeder said:
I own a Grizzly G3368 mill/drill which has seen a considerable service during the four years that I have owned it. The G3368, like most Chinese mill/drills mine uses a cast iron lead screw nut. Cast iron is only suitable in this role for light duty usage. Over time the backlash has increased to 0010-0.015”. Some of this backlash is due to play in the bearing assembly which has no preload, the rest is due to wear of the nut and the screw. I believe this is a fairly typical situation for this type of equipment with four years of regular use. I explored the various options on how to repair this problem and have decided that first a new lead screw is needed since the cast iron nut has worn the lead screw in the center portion where most of the use is. And second, the bearing assembly needs to be properly installed with preload so that this does not become a source of backlash in the future.
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Hi Jim,
sorry to dredge this old post up again, but just have a question in regards to your grizzly, is it a clone of the RF-31? I have a clone, unsure of actual brand due to lack of nameplates, and trying to see how close your dimensions will be to mine before pulling my table to bits. Hoping that if yours is a rf31 clone your design will slot straight into mine. Going to undertake this project as my backlash is around 30 thou. Thankfully i picked this machine up cheap ($400) and i believe the nut is severely worn and appears to have been never oiled in its life
 
Does the Delrin nut still require standard lubrication under normal operation? Great write up. Thanks, Mike
 
JSimmons22250 said:
Hi Jim,
sorry to dredge this old post up again, but just have a question in regards to your grizzly, is it a clone of the RF-31? I have a clone, unsure of actual brand due to lack of nameplates, and trying to see how close your dimensions will be to mine before pulling my table to bits. Hoping that if yours is a rf31 clone your design will slot straight into mine. Going to undertake this project as my backlash is around 30 thou. Thankfully i picked this machine up cheap ($400) and i believe the nut is severely worn and appears to have been never oiled in its life
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Hello JSimmons, you are dredging up old posts, I had forgotten about the Acetal nut project of which this was only one of three or four that I did. Acetal is a wonderful material for these types of nuts. It requires little if any lubrication and its wear characteristics are much better than the cast iron nuts that come on most of these machines. I am not sure if my lathe is a copy of yours or not, even if it is that does not mean the dimensions will be the same.

There are two points that need to be foremost in you planning for this project. The first is the length of the lead screw from bearing to bearing. I replaced the cast iron thrust bearing in the right end with a ball thrust bearing and made some allowance for adjustment. Keep in mind that backlash is the result of wear in the both the thrust bearing and the lead screw nut. The other critical item is the position and orientation of the lead screw nut in its housing. When you heat form the nut the lead screw will in all probability be ever so slightly off both in center and radial angle. This has to be taken into account when you install the new nut and lead screw else you find that it binds. If the vertical/horizontal position is off the binding will increase as you approach the end of travel in both directions. If the angle of the nut is off you will have excessive drag in both directions.

Removing and tinkering with the nut position is tedious but once it get it correct that is the last time you will have to worry about your lead screw probably in your lifetime. I am advancing in years and my memory is not as good as it once was so if I have made a mistake or an omission please forgive me. I have not been active in writing or doing new projects for machines for some years now and am sort of out of touch. I hope this helps, if not write back and I will give it another go.

Jim
 
FOMOGO said:
Does the Delrin nut still require standard lubrication under normal operation? Great write up. Thanks, Mike
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FOMOGO, I use a drop or two of oil once or twice a year so the answer is not much. I have these nuts on my lathe and mill with great success.

Jim
 
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