Help me Choose Steel for Part

T

The Mighty Ginsu

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Aug 11, 2016
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My question is not about knives, but the subject is something people here know a lot about.

I have a Chinese arbor press. One of the teeth on the ratchet gear is damaged. The company that sold me the press appears to be out of business, and the gear is not the same size as gears from other Chinese presses. I think I'm going to have to make my own gear.

This gear will have to be hardened and tempered. I'll have to cut it from 3" or 3.5" bar.

What's a good steel for this purpose? Should I be okay if I just cut the part, heat it, quench it, and throw it in the oven for a while?
 
The Mighty Ginsu said:
My question is not about knives, but the subject is something people here know a lot about.

I have a Chinese arbor press. One of the teeth on the ratchet gear is damaged. The company that sold me the press appears to be out of business, and the gear is not the same size as gears from other Chinese presses. I think I'm going to have to make my own gear.

This gear will have to be hardened and tempered. I'll have to cut it from 3" or 3.5" bar.

What's a good steel for this purpose? Should I be okay if I just cut the part, heat it, quench it, and throw it in the oven for a while?
Click to expand...
S45C ?
 
A weld would be soft, so it would deform when I used the press.

Big pieces of S7 are not popping up when I search.

I have seen web sources saying 4140 is a good gear steel, so maybe that's the way to go. I can get a piece for under $20.

Now I have to figure out whether it should be case-hardened or just plain hardened.

Thanks for all the help.
 
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Have you looked at regular rack gears? You may be able to find a rack and pinion gear to fit/replace what is currently there.

If not, 4140 should work as well as anything.
 
4140 can be through-hardened, or it can be flame or induction surface hardened (carburizing isn't necessary at that carbon content).

Most of what I see is 4140 surface hardened to 45-50 HRC. Through-hardened gears are usually softer than the surface of surface-hardened gears

Also:
With moderate hardness (through hardened), you could do your finishing cuts after hardening - although that's likely unnecessary.
Don't temper too high, lest you encounter tempered martensite embrittlement.
It's often advantageous to have your pinion fail before your rack. Be sure that the existing pinion actually is hardened, or plan to replace your rack eventually too.
If you don't have gear cutters and an indexing head, it may be a better value to buy hobbed stock.
Precipitation hardening or maraging alloys may offer lower distortion during heat treatment after machining.
 
Thanks for the replies.

An arbor press gear is not a standard gear. It has teeth that are sloped on one side. It's really a pawl, but they call it a gear. Maybe the Chinese people who made it didn't know the word "pawl." You can't buy a standard gear and shove it in there.

I haven't bought stock for a new pawl yet. I found I could mill some material off the old pawl and restore it so it worked. I was surprised that carbide would cut it. Guess it wasn't all that hard, which may explain why it deformed in the first place.

I may get some 4140 and make a new pawl. Sounds like through-hardening will work as well as anything. I will report back when I get around to doing the job.
 
Can't go wrong with 4140 here, but if it was me I would use A2. Easy to machine and air quench is nice to heat treat for a gear
 
If it's just one gear, I'd be inclined to do a repair.

Drill through the centre of the tooth and insert two dowel pins in side by side.

or
Preheat, Arc Weld or TIG stainless rod, then re machine the tooth ( which could be done with angle grinder and files)

or
Burr to clean metal and Bronze Braze in the whole gap, then re machine the tooth

Youtube has some nice examples
 
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