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Discussion Starter #1
I need some hard surface 20mm metric tubing to use for swingarm axles. I've tried everywhere I know & am drawing blanks. I'm thinking that something like a 4140 steel or a 400 series stainless would do the trick, but I'm wide open as long as it has a hard surface for the needle bearings to run on.
 

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My Torrington catalog provides the following info regarding shafts for needle bearings:

Minimum shaft hardness is 58 Rockwell C.
Shaft diameter for a nominal 20mm is 19.987mm to 20.000mm ( 0.7869" to 0.7874" ).

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IMO, 4140 won't get up to 58 HRc, and even if it did, it would be very brittle.
Same for 400 series stainless.
I don't think you'll find any tubing that's going to be up to the job.

My recommendation is 8620 steel.
You can start with some 13/16" bar stock and get it rough-ground or turned down close to the final diameter.
Talk with a centerless grinder to find out how close you need to get.
Heat treat and case-harden.
Final grind to the desired diameter.

That's a bit of a project.
 

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mcmaster has some, but it is just carbon steel

Part Number: 50295K41 $23.47 Each
Type
Metric Carbon Steel Seamless Tubing

Material
Carbon Steel

Shape
Single Line

Outside Dia.
20 mm

Outside Dia. Tolerance
±.08 mm

Inside Dia.
16 mm

Wall Thickness
2 mm

Maximum Pressure
3,610 psi @ 68º F

Operating Temperature Range
-5º to +572º F

Metal Bendability
Bendable

Rockwell
B75

Temper
Soft (Annealed)

Tensile Strength
Low

Metal Construction
Seamless

Metal Flareability
Flareable

Sterilize With
Not Rated

Specifications Met
Deutsche Industrie Normen (DIN)

DIN Specification
DIN 2391

Compatible Fittings
Compression Bite Seal

Length
6'
 

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Speeddog said:
My Torrington catalog provides the following info regarding shafts for needle bearings:

Minimum shaft hardness is 58 Rockwell C.
Shaft diameter for a nominal 20mm is 19.987mm to 20.000mm ( 0.7869" to 0.7874" ).
I wonder if this application would need to be that hard, it is not like a spinning shaft at 30,000rpm. It is just several degrees up and down slow oscillation.

Also, 58RC is really damn hard. If the shaft was thru hardened to that, I would think the impact strength would be low, and it would be very prone to hydrogen embrittlement and fatigue cracks (our suppliers do not like to make fasteners over 50RC for this reason). Or, is the 58RC just for the surface?

There are other ways to get good surface hardness other than heat treating, like QPQ nitrocarborizing for example.

mitt
 

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Unfortunately, the lack of rpm is more of a problem than a benefit.
The impact loading is pretty severe on a swingarm pivot.

Yes, 58 HRc is very hard.
Anything through-hardened to that would be very brittle, I wouldn't use it for a swingarm pivot.

The 8620 will through-harden to about 100ksi yield strength, at about 25 HRc.
Case-hardening will get the surface layer ( about .040" - .060" ) up to 58 HRc or so.

Unfortunately, my best metal book is at work, and I'm off today...
 

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mitt said:
You get time off ? :police:

mitt
I did 3 60hr weeks in december, and didn't get to take the holiday vacation I'd planned.
I'm a bit burned out and there's shyte I've got to take care of today...
So I took a day. ;)
 

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Discussion Starter #9
I was hoping that some of you tech guys would pipe in, but I'm hoping for something I can just buy without going thru all the time (and expense) of hardening it. Is there any kind of tool steel that I would be able to just buy off the self?
 

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Make it out of whatever steel is convenient and have it hard chromed.
This gives a very hard surface without heat treat being necessary to develop the steel's microstructure and mechanicals.
Heat treat will require straightening and/or finish grinding.
Talk to the chrome shop for the hard chrome thickness.
Typically you use about .0015 ".

http://www.metricmetal.com/products/rn2391.htm

I would use 4140 to get reasonable strength and toughness without heat treat.
 

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Discussion Starter #14
Once again the DML comes thru & Speeddog get's the award. I order from McMastersCarr all the time & had no idea they carried that.
dakinebusa - we must have done the same searches because I already tried the Parker steel people for 4140. Unfortunatly, they are out of 20mm 4140 for about 7 weeks & the stuff they're getting will be anealed.
 
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