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Cincinnati #2 universal head: terrible surface finish after dis/reassembly of spindle

Dope

Cast Iron
Joined
Jan 16, 2016
Hello friends,

I have a new-to-me 1938 Cincinnati 2MH with the universal/toolmaker's overarm.

20201214_234718.jpg

I had to disassemble and reassemble the internals of the overarm, which took forever with shimming the bevel gears for backlash and wear pattern. But everything seems pretty good now, the machine works and cuts nicely. However, the surface finish is abysmal. I realize the machine likely has lots of wear so it's possible I'm just asking for too much here, but I figured I'd see if there's anything I can do. What I'm most concerned about is that there is a collar at the top of the vertical spindle that seems to allow you to preload the bearings. If I crank down on it a bit, the spindle is resistant to turning and stops immediately when power is removed, for example. Too loose, and I can move the spindle up and down slightly.

I'm guessing there is some procedure to setting the correct amount of preload, however after weeks of searching I'm not able to come up with any sort of manual for this. Anyone have any tips or pointers?

Also, as I was typing this, I realized that the main bearing around the spindle might just be trashed. I went over to the machine and the spindle does have the tiniest bit of movement side-to-side. I've got a long-reach facemill arbor on it right now so there's plenty of leverage to produce a little movement, by hand. Guessing this might be a more obvious solution than I originally realized?

Dope
 
You should buy a maintenance manual for the machine as Cincinnati had the best disassemble and assembly manuals. They give the maintenance man the correct way to do everything. I suspect you have the bearings in backwards, a spacer missing, bearings not seated correctly. Worn bevel gears are very difficult to align. It may cost you $ 150.00. But well worth the money.
 
You should buy a maintenance manual for the machine as Cincinnati had the best disassemble and assembly manuals. They give the maintenance man the correct way to do everything. I suspect you have the bearings in backwards, a spacer missing, bearings not seated correctly. Worn bevel gears are very difficult to align. It may cost you $ 150.00. But well worth the money.

Believe me, I understand, I spent the last 3 weeks disassembling and reassembling the machine over and over to try to get the gears meshed well. Made a ton of custom shims along the way. I think it's pretty close now. Long story short, sure, I'd love a maintenance manual, but I have spent the last two months looking and have found nothing. If you know where to get them, I'm all ears!

Dope
 

Thank you, those are indeed pretty close. Unfortunately there doesn't seem to be any information regarding my situation.

Having said that, I started messing with the machine a bit. I turned the large nut on top of the spindle 1/8 turn at a time and examined the effects. The surface finish cleaned up quite a bit, and I was able to take increasingly heavier and heavier cuts as I tightened the nut. I was using a 4" facemill and was getting chatter at .050" DOC (and a terrible surface finish at only .020" even), and by the end I was taking .175" cuts with no chatter. Unfortunately couldn't go beyond that, I was maxing out the motor (1HP on a static phase converter so roughly .67HP). Surface finish always has a tiny bit of chatter in it when focusing a bright LED light right on it, but I suspect the bearings are a bit trashed (they are a bit crunchy and loud). I have two sets of bearings for this machine so I swapped them out and it helped but only so much. Expecting much out of 80 year old bearings is probably a bit excessive.

Anyway, tightening the nut definitely increased the drag on the entire gear train but I can still turn the motor over easily by hand so I'm not super concerned. Will have to see if anything's heating up with prolonged usage. No idea how loud a machine like this should be in the first place, this is my first experience with anything but a bridgeport (which is very quiet).

Dope
 
Often you have to tighten way past preload to seat the bearings into the bearing counterbore or running, work, and temperature makes preload slack, come loose again with the bearing moving. No. you don't want to leave it that tight. Once bearings are well seated the preload is set and stays there.
You might crank it to 200-inch pounds or 20 foot-pounds I Don't know the spec..loosen and then bring it back up to 12 or what. ..
That is why the actual spec is good to have.
 
Often you have to tighten way past preload to seat the bearings into the bearing counterbore or running, work, and temperature makes preload slack, come loose again with the bearing moving. No. you don't want to leave it that tight. Once bearings are well seated the preload is set and stays there.
You might crank it to 200-inch pounds or 20 foot-pounds I Don't know the spec..loosen and then bring it back up to 12 or what. ..
That is why the actual spec is good to have.

Interesting, thank you. I've got it at about 30ft/lbs I'd say (hard to tell, the nut is tightened with a pin wrench which I don't even have the right size for, so I'm kinda doing guesswork at the moment). I've been doing google research and people are talking numbers all over the place. Some say 10ft/lbs, some say 100ft/lbs+, but that's for all kinds of different machines so it's not super helpful. Anyway, it's dragging slightly but still spins smoothly and cuts somewhat decently. I agree though, I'd love to have the actual spec/procedure.

Dope
 
20201224_181549.jpg

20201224_181205.jpg

Pics of how the surface finish looks now. This is just junk mild steel so I'm not too worried about the "smeared" look. The second picture shows what I'm talking about though, still a little bit of chatter in there. I wish I had taken pictures before, it looked like about a 16 grit finish.

Dope
 
I was thinking what Buck said as I read your answer. The bearings have "preload", meaning tighter then bearing seated. No slop. I was also thinking you should ask in the Cincinnati Forum as there are exports in there who may not read this forum. Someone may have the exact machine and the parts and repair manuals. Merry Christmas. Rich
 
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I was thinking what Buck said as I read your answer. The bearing have "preload", meaning tighter then bearing seated. No slop. I was so thinking you should ask in the Cincinnati Forum as there are exports in there who may not read this forum. Someone may have the exact machine and the parts and repair manuals. Merry Christmas. Rich

Good idea Rich. Merry Christmas to you too brother.

Dope
 
Pulling the bearings to seat is the higher-pressure..once seated back off and then set, they don't need very much. very likely over three fingers tight will be too much...but that is just thinking about grinding spindles, not Mill spindles.

pull tight to seat is if the bearing goes into a shoulder stop counterbore.. If it doesn't then don't worry about that

So finding the spec is good/important, from book or spindle hand..

The photo doesn't tell much because we don't know what kind of cutter you are using ,or the condition of the cutter.

Duplex bearings often go a certain way and some can not go the wrong way or they may fail. unsure you may need to put them on a plate check to be sure your intended way gives zero movement when they are laded (pushed together)..and that the inside shoulder is the right way.

Precision bearings have an eccentric Mark ( might be a star, a circle or some other symbol) to be liked up with each other all in a straight line row even if they are far apart.

Be sure any threads can very smoothly hand spin/turn past the place where they might get tight.

Dont know what kind of bearings you have and I am not a spindle guy
 
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Are you sure the bevel gears arent jammed in mesh......this is the commonest result of refitting bevels .......if well worn ,they should have lots of backlash.

So, what I did, especially since in almost all cases there were no strict bearing surfaces and such (bearing lands on shafts were 10-20% bigger than the bearings themselves), I just put everything back together "close enough". Then I shimmed it based off of a guide I found for setting wear patterns and backlash on used spiral bevel gears. I ended up with roughly .005" of backlash in each spiral gear mating pair. Are you thinking that's too little and I should take some shims out? The entire assembly from the motor shaft to the spindle moves smoothly by hand so I'm assuming I'm not getting any binding/jamming. But I could be wrong. What should I look for, any ideas?
 
Part 2: The Installation of Bevel Gears - YouTube

I have also lapped the bevel gears in place with Timesavers Lapping compound on some Gleason 116 Finishers. I have also tested Sunstrand Stub lathes pretty much as they show in the video, using red lead. You can use bluing or lip stick too if you don't have anything else.

Part 3: The Installation of Bevel Gears - YouTube


Haha, I don't normally keep lipstick in my purse but I'm curious if any others admit that they do. OTOH, it's an opportunity to go hit up on the receptionist. No, not the 73 year old. The other one.
 
Are you sure the bevel gears arent jammed in mesh......this is the commonest result of refitting bevels .......if well worn ,they should have lots of backlash.

You know, I read this and it kinda clicked, so I started looking into it. I know the final set of bevel gears that actually drive the spindle had backlash on the very low end of the scale (about .004"). It was acceptable, as far as I could tell from looking up the specs on similar gears, so I didn't think anything of it.

However, in thinking how the bearing preload works for the spindle, where you tighten a very large nut at the top of the spindle, it's sorta drawing the spindle upwards, which maybe could be putting pressure on that bevel gear mesh. Turns out, that was exactly correct. Maybe the bearings just weren't seated perfectly or something, but the mesh had closed to exactly nothing, no backlash at all. In fact, when I took it apart, I had to remove .030" worth of shims to get the geras to stop jamming. So something had moved quite a bit. The good news is, the surface finish cleaned up dramatically and the drag on the spindle reduced significantly. The bad news is, there's still quite a bit a chatter - especially on hardened steel.

Here's some mild junk steel, using a 1.25" 3 flute indexed end mill. There are a couple passes, each with a little more preload each time (from bottom to top).

20210101_224536.jpg

Once I got it to this point, I tried some AR500 (what I primarily machine). Again, a little more preload for each small segment (from right to left this time). This was with a 1.5" 6 flute indexed end mill.

20210102_211835.jpg

As you can see, not great but still a dramatic improvement. Adding more preload doesn't seem to produce any more rigidity or improve the surface finish, so I stopped with that. Not sure what's up with the slight chatter in the finish, I assume the original 83 year old bearings probably have some wear, along with the rest of the machine LOL

Interesting, the lines present in the chatter. Not sure what's up with that. I paid $850 for this machine and planned on using it to rough out big pieces of hardened steel so I'm not super worried I suppose.

Dope
 
Dope, try reducing your spindle RPM significantly. Those chips are dark blue and you might put less stress on things if you slow it down. If that helps improve the finish, try compensating for the lower RPM by increasing the feed rate.
 
Dope, try reducing your spindle RPM significantly. Those chips are dark blue and you might put less stress on things if you slow it down. If that helps improve the finish, try compensating for the lower RPM by increasing the feed rate.

Oh believe me, I understand. I was running .75 and 1 IPM at about 250 RPM. The blue chips are because AR500 is an extremely tough material and the shearing action produces a lot of friction. When I was running mild steel in the top picture, it was bright silver chips.

Dope
 
On thing I can see ,is the gears have been set for a certain minimum backlash......this is a sure fire way to break teeth......bevels must be set to maintain previous running contact,if this backlash is reduced to some supposedly desirable dimension,then the gears will run on the toe or heel of the teeth ,and tooth breakage is certain when heavy loads are applied.
 








 
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