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Chrome-Moly-Nickel steel

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Hello

I need to remove about 8 thou from the diameter of some 7/8" rods of the above material.

What is the best way of going about it on a lathe please?

The current finish on the rods is impressively smooth. Needle rollers will be running
on the reduced diameter surface, so I need to get an appropriate finish.

Regards
Doug
 

Comments

#2
I would turn to about 0.001 to 0.0005 oversize using a nice sharp tool bit with about 0.030 nose radius, about 300 RPM and 0.0015 feed, use a carbide tool bit if you have it and then finish with a file and emery cloth. I like to hold the strip of emery cloth on the file to get a nice flat surface. File a bit then measure, rinse, repeat until it's on size. Measure at several points down the surface as you are doing this so you are working on the large parts. Makes a nice smooth bearing surface.
 
#3
Hello Jim, thanks for the reply.
Regards Doug
 
#4
Needle bearings will not run successfully on a unhardened shaft for any significant amount of time, the shaft will be "brinelled", that is, roughed up with lines parallel to the axis; the inner race for needle bearings need to be up in the 60s Rc.
 
#5
Please explain the hardness? These shafts are quite hard and a file bounces off them.
 
#6
If a file bounces off of it then it is probably around R60C or better, and that is hard, really hard.

I take back what I said above, you MAY be able to turn it with a carbide tool bit. Slow the lathe down to its minimum speed and see what happens. If the pin is that hard, this is really a grinding job.
 
#7
Your description of the steel does not give any specification as to the alloy or hardness; is the file a new sharp one?; if it is truly so hard as to cause a sharp file to skate over, it will not be machineable by normal means, it would take an extremely hard grade of carbide, ceramic or PCD tool to accurately cut it and provide a smooth finish, or also it could be finished by cylindrical grinding. Specifying the elements of the alloy says little about its hardness or suitability for a specific use.
 
#8
Unfortunately I cannot be more specific at this time about the hardness. I will try and track back to the source and see if I can find out what he used. But by the sounds of it, doing 80 of them would wreck my lathe if I tried to use carbide tools. As far as grinding, I would rather not have to buy a grinding attachment and don't want all that carborundum right through the lathe, I doubt I would ever successfully eliminate it.
 
#9
80? That's a lot, I might do 1 or 2 on the lathe, but for 80 pieces I would drag out one of the surface grinders and get it fired up. You might try turning one piece to see if you can cut it, but if that doesn't go well then grinding on a real grinder (cylindrical, surface, or tool & cutter) would be the only real option. As you said, all of that grit in the lathe would not be a good thing.
 
#10
Hmmm. Looks like I need to find another way. The advantage of converting them to metric was that I could use a needle roller with a seal at one end. The equivalent in imperial is very difficult to find. They are listed, but nobody seems to be able to source them.
Either that or I use a standard imperial bearing with a separate seal.
The last option although dearer may be the only choice.
Thanks everyone.
Doug
 
#11
80? That's a lot, I might do 1 or 2 on the lathe, but for 80 pieces I would drag out one of the surface grinders and get it fired up. You might try turning one piece to see if you can cut it, but if that doesn't go well then grinding on a real grinder (cylindrical, surface, or tool & cutter) would be the only real option. As you said, all of that grit in the lathe would not be a good thing.
Yes, grinding is best done on machines designed for grinding ---
 
#12
From the description, I suspect that you have chrome rod, which is used for hydraulic cylinder shafts. It is medium carbon steel which has been plated with hard chrome and ground. You will not be able to turn the chrome plating, though if you take a deep enough cut, you can get underneath the plating. Surface finish is also critical for needle rollers.

Here's a comprehensive treatment of the types of bearings and requirements.
https://www.ntn-snr.com/sites/default/files/2017-03/needle_roller_bearings_en.pdf

Your best bet is Thomson Case 60 shafting, which is available in both metric and imperial. It's the stuff to use for needle roller and linear bearing applications. https://www.thomsonlinear.com/en/products/shafting/quick-shaft-products

There are also inner races (hardened and ground bushings) which will work for this application that can be pressed on a shaft.
https://www.astbearings.com/inner-rings.html
 
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