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Clausing 8520 mill refresh

G

GerryinBelleRiver

Well-Known Member
I purchased this mill in the summer of 2019 after looking for one for close to 2 years. Although it was cosmetically challenged it was a fairly tight machine and came with a load of tooling. 20220128_082005.jpg

As I needed to complete a number of machine restorations I put it into immediate service with the intent on tackling a total refresh; clean , paint, shine at a later date.

While the time has come and I spent the morning doing a complete tear down. Ended up with quite the pile of parts. This may take a while. 20220301_111103.jpg20220301_111139.jpg

I did discover enough wear on the lead screw for the y axis to justify replacing it and the bronze nut. It currently has about 12 thou of backlash. If I can not find new ones I may have to make them which might be difficult without the use of a mill. Worst case I will put it back together, make what I need and replace the parts. Will make some accurate drawing of original parts just in case.

Also noted some small gouges on one of the ways but I don't think they will really effect the accuracy of the mill. While I am at it I will probably put a DRO on the mill.

Anyway, trying not to turn a simple refresh into a full fledged restoration. Wish me luck.
 
That is an awesome project. I am currently doing a refresh on a lathe I picked up and likewise trying to not let it 'scope creep' into a full fledged restoration. That is the size mill I have been looking for and wish you the best of luck. will look forward to seeing the progress and final result
 
GerryinBelleRiver said:
I purchased this mill in the summer of 2019 after looking for one for close to 2 years. Although it was cosmetically challenged it was a fairly tight machine and came with a load of tooling.View attachment 21513

As I needed to complete a number of machine restorations I put it into immediate service with the intent on tackling a total refresh; clean , paint, shine at a later date.

While the time has come and I spent the morning doing a complete tear down. Ended up with quite the pile of parts. This may take a while. View attachment 21512View attachment 21514

I did discover enough wear on the lead screw for the y axis to justify replacing it and the bronze nut. It currently has about 12 thou of backlash. If I can not find new ones I may have to make them which might be difficult without the use of a mill. Worst case I will put it back together, make what I need and replace the parts. Will make some accurate drawing of original parts just in case.

Also noted some small gouges on one of the ways but I don't think they will really effect the accuracy of the mill. While I am at it I will probably put a DRO on the mill.

Anyway, trying not to turn a simple refresh into a full fledged restoration. Wish me luck.
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Hey Gerry, if you run into trouble, give me a shout. I'd trust you using my machines in a heart beat - or do it for you. Gotta beat temporary rebuilds all week long!

That said, I've seen quite a variety of parts like that on line. I bet you can find what you need.

Having seen your machine first hand, it's a very worthy project. She is a beauty!
 
GerryinBelleRiver said:
I did discover enough wear on the lead screw for the y axis to justify replacing it and the bronze nut. It currently has about 12 thou of backlash.
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I confess that I am surprised that you think 12 thou is enough to justify a replacement. From what other forum members have told me, that is quite acceptable.

What is the backlash at the two ends? Can a better split nut get rid of the biggest chunk?
 
The majority of the wear on the lead screw is in the middle 4 inches of the screw, hardly any at the ends. A new nut would certainly help.
 
Had the time to clean up the y axis lead screw and nut today. Close inspection shows thread wear in the middle 3 inches of the screw, although not as bad as I first thought.

The real problem wear is in the nut where the threads are worn to a point.

What puzzles me is what looks like a weird diameter of .693 on the screw. When I look at the location for the screw there is plenty of room for a .750 diameter screw.
20220302_123610.jpg

Thinking I will investigate getting a length of 3/4" -10 tpi left hand acme rod and and a chunk of broken to make a new nut. Could always get a LH 3/4-10 tap for that. Anyone here have dealings with McMaster Carr?

Any other suggestions?
 
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Something I have wondered about. For a worn leade screw like yours with all the wear in the middle, does it make any sense to cut the screw to even out the wear and then make a new nut with a profile to match the revised screw and/or modify the nut to fit the new profile a bit better?
 
As a bonus, cutting the thread a bit like that could be "mostly" done on the lathe axis. I'm not sure you would even need a steady to do that. But I'd prolly use one anyway.....

But most likely, it would have to be cut a bit both ways (push & pull).

But if you can get a new screw to fit, that's the easiest.
 
Managed to find the technical drawings from Atlas for the bronze nut. Turns out it is for a 11/16 -10 lead screw. Could not find threaded rod that size but I can find 3/4-10 and I do have the room for a bigger size. Given I really can't single point left hand threads on my lathe that has a thread mount chuck buying threaded rod and reworking it is my best option

Now I need to find a 3/4 -10 lh acme nut I can rework to fit. If all else fails I could silver solder a bronze sleeve in the original nut and tap it the correct size or just get a slug of bronze and make a new one.

In the meanwhile I am continuing with the cleaning and prep for painting
 
GerryinBelleRiver said:
Could not find threaded rod that size but I can find 3/4-10 and I do have the room for a bigger size. Given I really can't single point left hand threads on my lathe that has a thread mount chuck buying threaded rod and reworking it is my best option

Now I need to find a 3/4 -10 lh acme nut I can rework to fit. If all else fails I could silver solder a bronze sleeve in the original nut and tap it the correct size or just get a slug of bronze and make a new one.
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Or bring your bar 45 minutes East and use my lathe. I'd be happy to host you and feed you too. Just gotta put up with a messy shop.
 
GerryinBelleRiver said:
Could not find threaded rod that size but I can find 3/4-10 and I do have the room for a bigger size.
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I think this is what I will end up doing to repair my mill/drill too I just can't see myself conning some poor guy on Kijiji who wouldn't notice the 11 pitch thread that's in there now, and a proper lead screw will cost more than the mill/drill is worth.
 
GerryinBelleRiver said:
Given I really can't single point left hand threads on my lathe that has a thread mount chuck
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Why?

Run the lathe forward and reverse the lead screw and thread from the HS end towards the TS. I should make perfect LH threads for you.

As as general note:

Any time the lead screw and the spindle turn in the same direction ==> RH threads
Any time the lead screw and the spindle turn in opposite direction to each other ==> LH threads

It does not matter if the spindle is running FWD or REV; it only matters which direction the lead screw is turning wrt the spindle if you get RH or LH threads.
 
I bought precision acme threaded rod from McMaster-Carr when I replaced the worn lead screws on my excello. The price was very reasonable for the lead screw stock but the bronze nuts were a bit pricy. They will only ship to a business though, when I order I get it sent to my work.
 
Rauce said:
I bought precision acme threaded rod from McMaster-Carr when I replaced the worn lead screws on my excello. The price was very reasonable for the lead screw stock but the bronze nuts were a bit pricy. They will only ship to a business though, when I order I get it sent to my work.
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Or start a business (on paper).
 
Rauce said:
I think they go as far as saying no residential addresses either… never looked that hard into it though since I’ve always been able to just get stuff sent to work.
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They might say that, but how the heck would they know the difference?
 
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