Atlas Horizontal Mill Bushing Help

[wa5cab]

I can think of several ways to hold the pulley with the bushings installed but if the "holder" is going to be a 6" lathe, the only one that you have room for is going to be an expanding mandrel. And I suspect that it will take two mandrels as if you cut the mandrel to fit the bushings as they are now and bore out one bushing, the mandrel might be too small to hold without wobbling in the now larger ID bushing when you turn the pulley around to do the second bushing.

In any case, be sure that you use a carriage stop to prevent you from running the boring bar into the mandrel.

As far as how much to remove, first you need to accurately measure the spindle outside diameter in the region of the pulley and the inside diameters of the two bushings. Then you need to pick the class of fit, and look up what the clearance range should be. Reference pages 1540, top of 1541 and the table on page 1544 of the 21st edition of Machinery's Handbook. 1540 and 1541 define classes of fits. In my opinion, the spindle pulley bushings and spindle need a class RC6 or RC7 fit, where "R" means Running and "C" means clearance. For a nominal shaft OD and bushing ID of 0.71" to 1.19", the clearance between the shaft and the bushing should be between 2.5 and 5.7 Thousandths. That's for a Class RC7 fit. RC6 is a little tighter. And for both classes, the clearance requirement increases and decreases with diameter. In any case, you are probably looking at more like removing 3 to 5 thousandths than 1 or 2 (but note that that is on the diameter, not per side). Which increases the probability that you will need two of the mandrels to do the job. Unfortunately, "I cut it off twice and it is still too short" is only funny in the comics. Fortunately, clearance here has no effect on machine accuracy and the Chinese mandrel sets are relatively cheap. Unfortunately, I have not seen the individual mandrels for sale.

 

[jster1963]

I can think of several ways to hold the pulley with the bushings installed but if the "holder" is going to be a 6" lathe, the only one that you have room for is going to be an expanding mandrel. And I suspect that it will take two mandrels as if you cut the mandrel to fit the bushings as they are now and bore out one bushing, the mandrel might be too small to hold without wobbling in the now larger ID bushing when you turn the pulley around to do the second bushing.

In any case, be sure that you use a carriage stop to prevent you from running the boring bar into the mandrel.

As far as how much to remove, first you need to accurately measure the spindle outside diameter in the region of the pulley and the inside diameters of the two bushings. Then you need to pick the class of fit, and look up what the clearance range should be. Reference pages 1540, top of 1541 and the table on page 1544 of the 21st edition of Machinery's Handbook. 1540 and 1541 define classes of fits. In my opinion, the spindle pulley bushings and spindle need a class RC6 or RC7 fit, where "R" means Running and "C" means clearance. For a nominal shaft OD and bushing ID of 0.71" to 1.19", the clearance between the shaft and the bushing should be between 2.5 and 5.7 Thousandths. That's for a Class RC7 fit. RC6 is a little tighter. And for both classes, the clearance requirement increases and decreases with diameter. In any case, you are probably looking at more like removing 3 to 5 thousandths than 1 or 2 (but note that that is on the diameter, not per side). Which increases the probability that you will need two of the mandrels to do the job. Unfortunately, "I cut it off twice and it is still too short" is only funny in the comics. Fortunately, clearance here has no effect on machine accuracy and the Chinese mandrel sets are relatively cheap. Unfortunately, I have not seen the individual mandrels for sale.

I can think of several ways to hold the pulley with the bushings installed but if the "holder" is going to be a 6" lathe, the only one that you have room for is going to be an expanding mandrel. And I suspect that it will take two mandrels as if you cut the mandrel to fit the bushings as they are now and bore out one bushing, the mandrel might be too small to hold without wobbling in the now larger ID bushing when you turn the pulley around to do the second bushing.

In any case, be sure that you use a carriage stop to prevent you from running the boring bar into the mandrel.

As far as how much to remove, first you need to accurately measure the spindle outside diameter in the region of the pulley and the inside diameters of the two bushings. Then you need to pick the class of fit, and look up what the clearance range should be. Reference pages 1540, top of 1541 and the table on page 1544 of the 21st edition of Machinery's Handbook. 1540 and 1541 define classes of fits. In my opinion, the spindle pulley bushings and spindle need a class RC6 or RC7 fit, where "R" means Running and "C" means clearance. For a nominal shaft OD and bushing ID of 0.71" to 1.19", the clearance between the shaft and the bushing should be between 2.5 and 5.7 Thousandths. That's for a Class RC7 fit. RC6 is a little tighter. And for both classes, the clearance requirement increases and decreases with diameter. In any case, you are probably looking at more like removing 3 to 5 thousandths than 1 or 2 (but note that that is on the diameter, not per side). Which increases the probability that you will need two of the mandrels to do the job. Unfortunately, "I cut it off twice and it is still too short" is only funny in the comics. Fortunately, clearance here has no effect on machine accuracy and the Chinese mandrel sets are relatively cheap. Unfortunately, I have not seen the individual mandrels for sale.

Excellent advice! I will probably be using my South Bend !0K for this one but my Atlas 6" is still not out of the question. Thank you very much and I'll keep everyone informed......

 

[Moderatemixed]

Hey jster. I’m about to start the same restoration as you, and ironically I’m right seat on the ‘37 up here in Canada. Looks like I’m going to have some time to do the project over the next couple of months. You might try putting it into a vice and if you have a cylinder hone, Chuck it into your drill and hone a couple thou off. I would think that putting it into the four jaw of the lathe will work fine but if it is just to “fit” the hone or and expanding reamer might just do the trick..... Cheers. Derek


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[wa5cab]

I don't think that I would do that (use a hone). Were it not for one thing, I would have already suggested clamping the pulley assembly down to a drill press or vertical mill table with a half inch spacer with a hole in the middle so that a brake wheel cylinder hone could just barely start coming out the bottom but not run into the table. That one thing is that although the oil hole in the pulley supposedly bypasses the bushings, they are Oilite. And using a hone rather than a sharp reamer could smear the ID surface, plug up the pores and make the bushings effectively the same as solid brass.

 

[Moderatemixed]

And that is a remarkably good point. I just watched Kieth Rucker, (Vintage Machinery on YouTube) I assume that you are likely familiar, he used the hone to enlarge a couple of “guide ways” and thought I’d bring it forward. That said your point is very valid. Cheers


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[wa5cab]

Thanks. If your mill or drill press has enough headroom, you could clamp the pulley the same way only use an adjustable reamer instead of the hone.

 

[jster1963]

Hey jster. I’m about to start the same restoration as you, and ironically I’m right seat on the ‘37 up here in Canada. Looks like I’m going to have some time to do the project over the next couple of months. You might try putting it into a vice and if you have a cylinder hone, Chuck it into your drill and hone a couple thou off. I would think that putting it into the four jaw of the lathe will work fine but if it is just to “fit” the hone or and expanding reamer might just do the trick..... Cheers. Derek


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The mighty '37? Awesome! I have a few years in the 737-200. That's the old round dial bird. And yes, I do believe we will have lots of time in the shop in the near future! Crazy.

I did it! I just used my 4 jaw chuck in my South Bend 10K. I was worried about marring the pulley surface. But all is good! I will post pix in a separate post.

Stay warm up there and fly safe......

 

[jster1963]

Thanks. If your mill or drill press has enough headroom, you could clamp the pulley the same way only use an adjustable reamer instead of the hone.

I got it! I'll post below. Thank you for all of your help....

 

[jster1963]

Well ladies and germs I did it! I was able to use my 4 jaw chuck in my South Bend 10K and dial it in. I was worried about marring the pulley, but I didn't chuck it with "Chuck Norris" torque and it worked great.

I bored out about .005" after measuring it and the spindle. .005" of the ID is really small so I took my time. I hope to put the head stock back together tonight or tomorrow.

Thank you all for you help. I have a spare bushing just in case.....

 

[jster1963]

And that is a remarkably good point. I just watched Kieth Rucker, (Vintage Machinery on YouTube) I assume that you are likely familiar, he used the hone to enlarge a couple of “guide ways” and thought I’d bring it forward. That said your point is very valid. Cheers


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Of course I watch Keith Rucker! I just watched him today. There are a couple of guys you have to watch on Youtube that have great videos on restoring this machine. I'm posting as well. Mine will not be as in depth as some but more than others. I hope to have mine up and running soon. I have lots of parts to make too.

Thanks for the reply and good luck with yours........