How much allowance for grinding when heat treating?

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LocoJerome
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How much allowance for grinding when heat treating?

Post by LocoJerome » Sun Nov 27, 2016 12:09 am

All,

I have some 4140 axles that I am turning and I am going to heat treat it and then grind to final dimension. Does anyone have a recommendation on how much extra material I should leave prior to heat treating in order to grind it to a nice finish for a needle bearing to run on? These will be axles for the pilot truck. The needle bearings I have are designed to run on a 0.625" shaft.

Thanks for your help!

Harold_V
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Re: How much allowance for grinding when heat treating?

Post by Harold_V » Sun Nov 27, 2016 2:57 am

Depends on the quality of your work, really. If your centers are well placed (not eccentric) and you have the pieces heat treated properly (to prevent bowing), .015" should be plenty. If in doubt, add five more thou.

Is it safe to assume you have a proper cylindrical grinder? If you expect to accomplish this task with a tool post grinder, I'm not sure it's a good idea. Grinding work dry presents a lot of problems that are avoided by flood coolant, and that's a definite no-go on a lathe.

I'm going to assume you will use a cylindrical grinder. It's a good idea to lap the centers before grinding. That eliminates the possibility of out of round grinding. Been there, done that, so I know the value of lapping centers.

It's important for you to keep lengths and center depths close, if not identical. That helps minimize the introduction of taper, once you have the grinder set properly. Not important for one piece, but if you have several to do, it can prevent some aggravation.

Harold
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110HLW
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Re: How much allowance for grinding when heat treating?

Post by 110HLW » Sun Nov 27, 2016 8:04 am

Hi Jerome, I agree with Harold, .015-.-.020 is good. But I would consider case hardening just the journal over hardening the hole axle. In a derailment a hardened axle could break.

Case hardening just hardens the outer surface (about.060).48-52 Rockwell hardness should be good for your needle bearings and you can still turn to finish dia. with the right grade of insert.
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LocoJerome
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Re: How much allowance for grinding when heat treating?

Post by LocoJerome » Sun Nov 27, 2016 9:27 am

Thanks guys!

I pretty much expected a reply like Harold's and while I wouldn't mind playing around with hardening. Thanks for the detailed response. And axle breakage was also a concern of mine. So with those things in minds, I think I'll just take the easy route and buy the matching hardened sleeves for the need bearings, loctite them on and be done with it.

Hudson Honey
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Re: How much allowance for grinding when heat treating?

Post by Hudson Honey » Sun Nov 27, 2016 11:11 am

Smart move. That route will do the job fine. Use bearing and sleeve retainer

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Fender
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Re: How much allowance for grinding when heat treating?

Post by Fender » Sun Nov 27, 2016 2:04 pm

I was under the impression that case hardening was normally employed with low-carbon steel such as 1018. Alloys such as 4140 have enough carbon that they are going to harden all the way through (to some degree) if one tries to case harden them.
Dan Watson

LocoJerome
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Re: How much allowance for grinding when heat treating?

Post by LocoJerome » Sun Nov 27, 2016 2:38 pm

I think I'm going to try a little different route. The shaft in the needle bearing is 5/8" and by the time I remove enough for the sleeve the diameter will be too small. I don't want significantly increase the bearing OD to allow for a larger sleeve so I'm thinking about using 5/8" ground case-hardened shafting. I'll have to make a sleeve for the middle of the shaft to provide the necessary thrust surfaces and then loctite that in place. The only downside I'm seeing is that I won't have a shoulder to press the wheels up against but since they are flush with the end of the shaft I'm not concerned about getting them into the proper position.

Glenn Brooks
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Re: How much allowance for grinding when heat treating?

Post by Glenn Brooks » Sun Nov 27, 2016 2:51 pm

Harold_V wrote:Depends on the quality of your work, really. If your centers are well placed (not eccentric) and you have the pieces heat treated properly (to prevent bowing), .015" should be plenty. If in doubt, add five more thou.

Is it safe to assume you have a proper cylindrical grinder? If you expect to accomplish this task with a tool post grinder, I'm not sure it's a good idea. Grinding work dry presents a lot of problems that are avoided by flood coolant, and that's a definite no-go on a lathe.

I'm going to assume you will use a cylindrical grinder. It's a good idea to lap the centers before grinding. That eliminates the possibility of out of round grinding. Been there, done that, so I know the value of lapping centers.

It's important for you to keep lengths and center depths close, if not identical. That helps minimize the introduction of taper, once you have the grinder set properly. Not important for one piece, but if you have several to do, it can prevent some aggravation.

Harold
Don't want to hijack the thread, but as a point of technical learning, how does one normally check the concentricity of the centers when grinding to tenths? Also assume a relatively small size center drill to center drill 5/8" holes for axle journals, how would one correctly lap such a small hole?

Thanks
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Harold_V
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Re: How much allowance for grinding when heat treating?

Post by Harold_V » Sun Nov 27, 2016 4:22 pm

Glenn Brooks wrote:Don't want to hijack the thread, but as a point of technical learning, how does one normally check the concentricity of the centers when grinding to tenths? Also assume a relatively small size center drill to center drill 5/8" holes for axle journals, how would one correctly lap such a small hole?
I don't recall ever checking concentricity, but any misalignment is generally corrected when the centers are lapped. Done properly, a center lap is employed. It's a device that resembles a small throat drill press, but instead of mounting drills, a center lap is mounted in the spindle, which has a dressing attachment, to true the center lap. The lap is typically made of fine aluminum oxide in a resinoid matrix. It tends to be quite stable, retaining form nicely. In lieu of a table, a center lap machine has what might be called a tailstock, which is mounted to a vertical slide, and can be located to accommodate the length of the part(s) in question. The center of the tailstock has the typical 60° form, and is concentric with the lap. Any misalignment of the original centers in the part are then corrected by applying the slowly spinning lap as the part is located by the center in the tailstock. The part is held by hand. Lapping proceeds until the entire surface of the drilled center has been corrected. It's very obvious when one has accomplished the task, as it is visually observable.

Where I was employed as a precision grinder, the center lap was branded as Excello.

Incidentally, when working as a grinder, it becomes all too apparent how much error is created when machining. Rarely is a center concentric with the related work, although it is generally close. Finish grinding exposes all manner of discrepancies.

Harold
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hudson
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Re: How much allowance for grinding when heat treating?

Post by hudson » Sun Nov 27, 2016 5:03 pm

Hi,

a center grinder which is still manufactured by
Henninger:

http://www.henningerkg.de/wp-content/up ... 2000Kd.pdf

best regards,
hudson

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BigDumbDinosaur
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Re: How much allowance for grinding when heat treating?

Post by BigDumbDinosaur » Mon Nov 28, 2016 12:57 am

LocoJerome wrote:So with those things in minds, I think I'll just take the easy route and buy the matching hardened sleeves for the need bearings, loctite them on and be done with it.
Those "sleeves" (technically, they are "journals") are supposed to be a light press fit to the shaft. No anaerobic adhesive is required, or desired.
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BigDumbDinosaur
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Re: How much allowance for grinding when heat treating?

Post by BigDumbDinosaur » Mon Nov 28, 2016 1:01 am

Fender wrote:I was under the impression that case hardening was normally employed with low-carbon steel such as 1018. Alloys such as 4140 have enough carbon that they are going to harden all the way through (to some degree) if one tries to case harden them.
That is correct. Medium and high carbon alloys are generally through-hardened and then drawn back to the desired hardness level. It's not a simple process to properly carry out and almost always produces some warpage due to uneven cooling of the piece during quenching.
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