# Clausing 8520 mill refresh



## GerryinBelleRiver (Mar 1, 2022)

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.




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. 







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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## JReimer (Mar 1, 2022)

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


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## Susquatch (Mar 1, 2022)

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.
> 
> ...



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!


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## Susquatch (Mar 1, 2022)

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.



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?


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## GerryinBelleRiver (Mar 1, 2022)

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.


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## GerryinBelleRiver (Mar 2, 2022)

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.





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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## Susquatch (Mar 2, 2022)

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?


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## GerryinBelleRiver (Mar 2, 2022)

Took me a couple of minutes but I get what you are saying. That would be an option.


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## Susquatch (Mar 2, 2022)

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.


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## GerryinBelleRiver (Mar 7, 2022)

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


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## Susquatch (Mar 7, 2022)

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.



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.


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## Susquatch (Mar 7, 2022)

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.



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.


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## RobinHood (Mar 7, 2022)

GerryinBelleRiver said:


> Given I really can't single point left hand threads on my lathe that has a thread mount chuck


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.


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## GerryinBelleRiver (Mar 7, 2022)

Susquatch said:


> 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.


Thanks for the generous offer but I have a friend with a well equipped shop only 3 minutes away.


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## trlvn (Mar 7, 2022)

GerryinBelleRiver said:


> 11/16 -10 lead screw. Could not find threaded rod that size


Did you try here?






						Threadall Manufacturing - Home Page
					

My Store




					www.threadall.com
				




They're located in Cambridge, ON so it is at least within the province.

Craig


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## Rauce (Mar 7, 2022)

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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## Susquatch (Mar 7, 2022)

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.



Or start a business (on paper).


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## Rauce (Mar 7, 2022)

Susquatch said:


> Or start a business (on paper).


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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## Susquatch (Mar 7, 2022)

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.


They might say that, but how the heck would they know the difference?


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## GerryinBelleRiver (Mar 7, 2022)

Ya, I  have been down that road with McMaster Carr


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## PeterT (Mar 7, 2022)

Do a search here on McMaster Carr. Much has been written...


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## calgaryguy (Mar 11, 2022)

Susquatch said:


> They might say that, but how the heck would they know the difference?


Abom79 orders from Mcmaster all teh time and his shop (until recently) is behind his house.


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## GerryinBelleRiver (Mar 19, 2022)

Time for an update

Got the parts stripped , primed and painted with one coat. Needed more paint but due to supply chain  issues the base I need is on back order and not expected for 2-3 months. Tried other suppliers with no luck. Maybe I will make a trip over to the USA after April 1st. I could get the colour I need mixed in Tremclad but I find it doesn't harden as well as what I usually use.

Liking the colour, more grey green than it shows in the picture










Having the parts I need for the knee; lead screw and nut sent to my SIL in Florida. She will bring them back when she returns in Mid April .

In the process of deciding on a DRO for the mill.

So for the time present I  am left twiddling my thumbs on the mill project. Plenty of other things to do.


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## Susquatch (Mar 19, 2022)

GerryinBelleRiver said:


> In the process of deciding on a DRO for the mill.
> 
> So for the time present I am left twiddling my thumbs on the mill project. Plenty of other things to do.



Drop dead gorgeous Gerry! I have loved that machine of yours since the first time I laid eyes on it. It seems it only gets better with age! It's lucky to have you for a handler! 

You can always drive an hour east and come see my Ditron DRO. I couldn't beat the value for the money anywhere. Now if I can only drill a few more holes and get an axis or two working......


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## GerryinBelleRiver (Mar 19, 2022)

Susquatch said:


> You can always drive an hour east and come see my Ditron DRO. I couldn't beat the value for the money anywhere. Now if I can only drill a few more holes and get an axis or two working......


I have been following you escapades on the dro installation,  it  must be frustrating not being able to get a hole drilled without complications


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## Susquatch (Mar 19, 2022)

GerryinBelleRiver said:


> I have been following you escapades on the dro installation,  it  must be frustrating not being able to get a hole drilled without complications



Very. 

And then just when I get my mitts on some carbide, I get re-assigned by upper management.


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## GerryinBelleRiver (Mar 19, 2022)

Susquatch said:


> Very.
> 
> And then just when I get my mitts on some carbide, I get re-assigned by upper management.


Been there!


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## Degen (Mar 19, 2022)

Simple suggestion which might save you a ton of money and time.

Slit the bushing nut off center about 2/3's thru.  Drill and tap to set screws into the thinner half.

Re-install the screw and tighten the set screws till the backlash is gone.  This is how its done on Bridgeports and clones.

Believe there is a good video on YouTube.




BTW compression or expansion of the threads work, I've tweaked my to about 0.0003 backlash.


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## Susquatch (Mar 20, 2022)

Degen said:


> Simple suggestion which might save you a ton of money and time.
> 
> Slit the bushing nut off center about 2/3's thru.  Drill and tap to set screws into the thinner half.
> 
> ...



I know this is a common solution, but I've always wondered about it. 

Does the resulting lop sided nut experience significantly accelerated wear on the tight side? If so, how significant is it? 

Wouldn't it be better to spilt the nut all the way through and use three screws to hold the halves together and/or add another secondary nut to the assembly?


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## Degen (Mar 20, 2022)

Susquatch said:


> I know this is a common solution, but I've always wondered about it.
> 
> Does the resulting lop sided nut experience significantly accelerated wear on the tight side? If so, how significant is it?
> 
> Wouldn't it be better to spilt the nut all the way through and use three screws to hold the halves together and/or add another secondary nut to the assembly?


Actually this how Bridgeport did it and on my BB mill its the same thing.  The answer to wear is yes there is some wear but the concept is to just tighten enough to take out the slop and compensate for wear.  On a manual machine this shouldn't diminish life of the machine much because us mere humans can only operate it so fast, however, for those that of us (myself included) that convert these machines to CNC these are going to be a potential reason for converting to ball screws at some time should the nuts wear out as they will function at significantly higher loads and speeds under CNC performance.

Time will tell.


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## PeterT (Mar 20, 2022)

I have the same style of split nut in my lathe. Just a guess but I think it was done that way because its relatively cheap & maybe influenced by access to the set screws to make the adjustment in-situ. Its rather primitive IMO but seems to do the job. I bet nuts were dime a dozen back in the day whereas now could be pita replacement depending on the situation & resources. My Bridgeport clone has more modern axial anti-backlash leadscrew nuts which would wear more evenly around the thread. Not sure, but I think they have been that way for quite a long time. Sometimes the nuts are threaded together & adjusted rotationally. I've also seen some that slide on pins or guides with some form of spring in between.

My lathe adjustment is getting past due for me too. I've been thinking of an axial anti-backlash system using commercial nuts.




__





						1/2 - 10 Right Hand Acme Lead Screws & Nuts for Power Transmission - Roton Products, Inc.
					

Shop 1/2 - 10 Right Hand Acme from Roton Products, Inc. View all of our products and shop online for your power transmission needs.



					www.roton.com


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## Degen (Mar 20, 2022)

The split nut is actual a very functional method of doing things, simple and it works.


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## historicalarms (Mar 20, 2022)

One thing not mentioned yet about the split nut tensioner...it works better on a machine that the nut has worn to the point backlash is noticed because if it is the threaded rod that is worn at the most used spot, when the nut is tightened too tight it will bind on the unworn part of the threaded rod


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## YYCHM (Mar 20, 2022)

This was my attempt at a split nut.....











Ended up being too difficult to adjust properly, so I gave up on it.  Something like what @Degen posted would probably work better.  The problem with having two threaded pieces is that you have to get the initial gap between them right before you attempt to separate them to take the lash out.


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## GerryinBelleRiver (Mar 21, 2022)

historicalarms said:


> One thing not mentioned yet about the split nut tensioner...it works better on a machine that the nut has worn to the point backlash is noticed because if it is the threaded rod that is worn at the most used spot, when the nut is tightened too tight it will bind on the unworn part of the threaded rod


When I  considered this type of fix this came to mind as a potential issue. My lead screw has considerable wear in the middle third with hardly any wear at either end. Tightening the split nut enough to remedy the backlash would probably make either end too tight.


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## GerryinBelleRiver (Mar 21, 2022)

I wanted to clean up the motor for a repaint but noticed the vent holes were plugged up. When I opened the motor to clean it out it was plugged with a fine black, oily power. What you see in the picture is about a third of what I took out. 

I suspect this is all resideu from the rubber v belts over the past 60+ years. 





I have opened up a lot of motors but never one this filty. Reminded me of when , as a young lad we switched from a coal burning furnace to a gas one and I was assigned to clean the old coal bin. My dad said I looked like Al Jolsen when I was done.

Anyway, I  can mark that chore off the list


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