Heat Treating Chuck Key

Smudgemo

Smudgemo

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Today I started to build a tube bender for making bicycle racks, but my chuck key that works perfectly in my three-jaw was starting to get damaged in my four-jaw. The large mandrel was too large for the three-jaw. So (of course) the answer was to make a new key that properly fit the four-jaw. I grabbed some 5/16" O-1 drill rod and my brand-new 5C collet square block and had at it. Perfect fit, but now I need to heat treat it.

Chuck Key.jpg

Looking at Tubal Cain's book and a recent issue of HSM, it looks like approximately 20 minutes of dull to cherry red followed by an oil quench and another 20 minutes of 400* oven before a full cool-down ought to be sufficient for my needs. I've got a O/A unit, but figure I'll run a multi-flame tip using propane since it's so much cheaper and my BBQ tank is still pretty full.

Yes? No?

Thanks for any input.

-Ryan

Chuck Key.jpg
 
i have used the same method for"OKIE"hardening before,(no offence intended to Okies everwhere:jester: ),
without the 400* cooldown in the oven after the oil plunge (just covered in a heat blanket and sometimes air cooled too)
the extra normalizing step would be a good addition to the formula though:thinking:
i have not used propane, may take a little longer to get to temp, but i'm sure it would work!

good luck!
mike:))
 
Smudgemo said:
I grabbed some 5/16" O-1 drill rod and my brand-new 5C collet square block and had at it. Perfect fit, but now I need to heat treat it.

Yes? No?
Click to expand...

Why heat treat it? It's much easier and cheaper to make a new chuck key when it wears, than trying to replace the chuck's pinion gears when you wallow out their sockets with a hardened chuck key. Let the key be the sacrificial link.
 
I got the book "Heat treat, selection,and application of tool steels" By William E. Bryson.

Ray C was doing an oven build and suggested that book...it is a good one.

For all the tool steels he recommends a 20 min bake at 1200 deg. On my heat treat oven post (http://www.hobby-machinist.com/show...nt-mounting-amp-TMI?highlight=heat+treat+oven) second pic from the bottom...I opened the oven after 20 minuets at 1200 degrees. Both pieces are O-1 oil harden tool steel, and as you can see there is really not much color to them at 1200.
Instructions in the book say at that point increase the temp to 1500 and hold for 5 min per inch thickness.
Then quench, and he's very specific in not wanting the piece to get below 125-150 deg in the quench and states it's a mater of life or death (for the part) to then get it into the oven for tempering. The tempering oven should be pre-heated so the part never drops below that 125-150 deg mark.

For that chuck key you don't need the whole tool hardened just hardening the end would be fine. If I was doing it that way I'd heat the end to cherry red, quench it and temper it. No need to cook it any long length of time at the cherry red heat (that's actually detrimental).
The tempering is usually much longer (2 hr per inch cross section) I usually use 350 deg but a higher temp will give you a tougher tool with a little loss of hardness.
 
I'd recommend heating the 01 to more of a spring temper than a knife temper,which is what 400 will give you. It will still be quite hard at a 400º temper,and prone to snapping off if twisted hard enough. Or,used to help rotate the chuck.
 
Heat sources.... I tried using a propane torch, then two propane torches.... I finally settled on Oxy-Acetylene, that took longer than I liked. My current project is a router bit, small, thickest part is about 1/4 inch. I wound up putting a short ( 2 in) piece of 2 in conduit on a old soapstone foot warmer. I put the router bit inside the conduit. Heat to cherry red took seconds instead of minutes. As soon as it was red I picked it up (gently) with a pair of pliars and quenced it in some 30 wt non detergent engine oil. It then went in the oven (I try to get as much oll off as I can so the baker in the family won't get oil soaked bread.) I turned the oven on set for 400º. when it got there I turned the oven off and let the whole thing cool to room temp. It works a charm.

Yes, large, thick pieces need soak time, but tiny little things don't.
 
Be aware that kitchen ovens can be off by 75º. I use a toaster oven with a Brownell's thermometer with a long probe on the back. This is inserted through one of the slots on the back of the toaster. It gives very accurate temps. Pre heat the oven so you can pop the part right in there before it cools below 130º( barely able to be held in the hand for long.) Toaster ovens are recommended by some of my heat treating books,believe it or not.
 
If you are making the chuck key out of O-1 or any other "drill rod", DO NOT HEAT TREAT it! It's hard enough and tough enough to use as is.

Doing so is going to make it so hard, that the first time you put a little monkey force into it, it's going to snap off!

If you insist in heat treating it, temper it back to around 40-45 HRC. Any harder than this put it into the next phase zone in metallurgy and make it brittle!

F.Y.I. All of the chuck keys I've reworked in the past were fairly soft on the key end.

edit: I have a key that apparently was heat treated improperly and broke linearally along the shank of the key. didn't hurt the square. I'll look for it and post a picture of it.
 
Thanks for the advice. I guess I assumed some hardening was required, but I'm up for calling this one done. The fit is nearly perfect so it shouldn't spin out in use anytime soon, and it wouldn't exactly be tough to cut off the tip and remake it if it wears out.

-Ryan
 
it's a novel idea but if you need to heat treat a chuck key , you should give up machining and enter the strong man contests
 
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