Thread: Machining case hardened shaft

I want to mill a slot in a shaft but I think it's case hardened. Is it possible to anneal case hardening? If so, what would be the procedure? Thanks.

Hi Bryan,

Same as for any HC steel.

Just heat it up to bright red (like you would if you were hardening) and let it cool slowly. A bucket of sand works well.

Of course, if you have a carbide cutter you can probably mill it without annealing.

Regards
Ray

I just thinking aloud here guys.
As the case will likely be very thin. Could you carefully grind a flat on the shaft to the width of the slot, that would get rid of most of the case in the middle of the slot. Then cut an undersize slot with a slot drill followed by cutting each side with a end mill to full width.
Just might work? Stupid idea?
Stuart

Stuart, grinding through the skin is something I was considering. How thin do you think it would be? 1mm? I'm not sure I understand your milling procedure. The slot will go right across the end of the shaft so I should be able to just use an end mill?

Ray, I don't have a heat source yet, but I'm considering one of these: https://www.alltools.com.au/shop/ind...me_Pack_BJ2101. Do you think that would have enough grunt? The shaft is 25mm, and I'd need to soften maybe 40mm of it. This would be an example of the biggest sort of heating job I'd expect to be doing. I'm guessing it would be fine for heat treating smaller parts? Silver soldering would be a handy capability too. (Sorry, I'm sneaking in a different question here.)

Sorry Bryan I thought you were cutting some sort of keyway in the shaft.
The case depth could be anything, maybe as thin as 0.1mm but maybe much more. Not sure how I would go about cutting the slot you want. How accurate does it need to be?

Stuart

Originally Posted by Bryan

Ray, I don't have a heat source yet, but I'm considering one of these: https://www.alltools.com.au/shop/ind...me_Pack_BJ2101. Do you think that would have enough grunt? The shaft is 25mm, and I'd need to soften maybe 40mm of it. This would be an example of the biggest sort of heating job I'd expect to be doing. I'm guessing it would be fine for heat treating smaller parts? Silver soldering would be a handy capability too. (Sorry, I'm sneaking in a different question here.)

Bryan,

I have one of those Primus torches - very good for heating small stuff like obstinate nuts etc. and for soft soldering, but I seriously doubt you would be able to get 40 mm on the end of a 25 mm shaft red hot to anneal it.

I have not tried silver soldering with it, but expect it would be OK for smaller compact items without much mass to heat.

Frank.

I beleive once you anneal case hardening you will be unable to get it back again.
Some case hardening is very thin and heating it to anneal it may burn right through the surface
Rowley.

Hi Bryan,
I have the handle and the medium burner out of that kit and heat steel to red hot for oil dipping all the time. I can heat a bar around about 20mm round x 150-200mm long to a red glow. I have the full flame burner nozzle but have to get the jet for it.
I have mine hooked up to a small (2.5kg I think) bottle with a 5 foot hose. If you go this way I would recommend getting a larger bottle as I think it would get expensive with the small bottle supplied in that kit.
Most welding shops have these parts separate and the hoses to match, I think you could get set up for under a $100 with a cheap bottle from Kmart, BigW or a camping store etc. If you have a BBQ you could just buy the adapter and use the bottle off that for now and it would last a really long time.

Dave

EDIT
For stuff smaller than the size listed above you can get the steel to a bright red.

Hi Rowley. That part of the shaft doesn't need to be re-hardened so it wouldn't matter. But without the right heating device it sounds like grinding might be the go. Stuart it doesn't need to be super precise, but I'd like it a known width with square sides and a reasonable finish. So I'd like to mill it if possible. It's just a pivot for a handle on a slotting attachment. I'll need to cross-drill the shaft too, so that might get fiddly. There are other options. I could clamp something onto the shaft, or screw into the end, but either would throw my linkage length out.

Frank, thanks, that's about what I expected. Probably a worthwhile jigger to have around for the smaller stuff though. PS: Dave thanks for the info. We have big LPG bottles for our water heater.

Hello Bryan,
Forgive me if this is a stupid suggestion,but could you use another piece of shaft which is not case hardened? Maybe something like 4140 or EN26 if the shaft needs to be tough,or even just bright shaft. Russell

Hi Bryan,
Just come back from the shed doing a test for you and anyone else thinking about buying a propane torch.
I heated 40mm on the end of a 300mm long piece of 28mm round bar, it took 8 minutes to get it were it is in the pictures.

I brought a proper propane hose years ago and it only lasted about 5 year before becoming brittle and cracking. I just replaced it with some oxy hose I had laying around and when it becomes brittle I replace it.
You really only need the hand piece, neck, nozzle, barbed fitting for the handle and a fitting to go onto your tank. The other things in that kit wont get used, like the paint stripper nozzle, I have 2 in the cupboard and don't use them because they can be dangerous stripping paint on a house by putting flames into the cavity.

Dave

Hi Dave, direct connection to the bottle, no regulator on the line, would this be ok?

Dave you're a legend!

Russell, not silly at all. Just trying to use what I've got. If I screw it up I'll have to buy something. Thanks for the suggestion.

Jackaroo,
I have had this running for over 20 years but I did pick up a gas fuse for cheap a few years ago and tried it, but it wouldn't let enough gas through to make it work.
The regulating is done in the jet in the nozzle, I have even tried it off the BBQ hose and got the same result a small flame with no heat.

Bryan,
No problems, I hope it helps to make up your mind.
I know what it's like, to not know if something will do the job you need.

Dave.

Originally Posted by jackaroo

Hi Dave, direct connection to the bottle, no regulator on the line, would this be ok?

I will just add if you look at the unit in the link posted above, you will see the cylinder and the neck with the valve on it. There is no regulator in between and this is a commercial kit and the hot nozzle is closer to the bottle than mine is with the lead on it.

When I originally bought the hose and fittings from local gas place around here I took my new hand piece in and said I wanted to connect it to a cylinder. They supplied me everything I needed with no mention of a regulator and said to connect it directly to the cylinder the way it is set up now.

Dave