Machining case hardened shaft

[Bryan]

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.

[RayG]

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

[Stustoys]

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

[Bryan]

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/index.php/121/3815_Primus_Trade_Flame_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.)

[Stustoys]

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

[franco]

Ray, I don't have a heat source yet, but I'm considering one of these: https://www.alltools.com.au/shop/index.php/121/3815_Primus_Trade_Flame_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.

[Rowley]

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.

[Dave J]

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.

[Bryan]

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. :think:

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. :wink:

[rusty steel]

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

[Dave J]

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

[jackaroo]

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

[Bryan]

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.

[Dave J]

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.

[Dave J]

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

[Stustoys]

Have you tried turning the case off? If it's really hard you might not be able to. You're going to need to drill a hole at 90deg to the slot as well right? So turning the shaft down will fix that at the same time. I can't think of a way to make it by grinding the case off and having it look much good. Unless of course you have a surface grinder and a way of indexing the shaft.
Stuart

[eskimo]

Ray, I don't have a heat source yet, but I'm considering one of these: https://www.alltools.com.au/shop/index.php/121/3815_Primus_Trade_Flame_Pack_BJ2101.

if the above at all tools doesnt work one of these would
https://www.alltools.com.au/shop/index.php/95/4021_Bernzomatic_OX2550KC_Brazing_Cutting_&_Welding_Kit

[Bryan]

Have you tried turning the case off? If it's really hard you might not be able to. You're going to need to drill a hole at 90deg to the slot as well right? So turning the shaft down will fix that at the same time. I can't think of a way to make it by grinding the case off and having it look much good. Unless of course you have a surface grinder and a way of indexing the shaft.
Stuart

Stuart, a HSS tool just seemed to skate. I don't have carbide, except boring bars. I should pick up some other brazed bits for this sort of situation. Yes cross-drilling for a pin is needed, so reducing the diameter makes sense. I have a belt sander and I'm not afraid to use it. Who said anything about looking good? :) (Actually with care you can do nice work with a belt.)

Eskimo, thanks but the LPG one came up at an attractive price so I've grabbed it. Plus I like that's it's refillable and can also run on other common bottles. Those disposable bottles would get expensive I reckon. If I need more heat later I'll look at alternatives.

[Stustoys]

Well you have a torch now :) no need to try a work-a-round.
Don't forget pictures of the finished article.
Stuart

[franco]

Jackaroo,


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

Primus were pretty well the first to go into the camping and handyman markets with portable gas appliances on refillable and re-usable cylinders. Their appliances were designed to run at full tank pressure without a regulator. Primus gas cylinders have a right hand thread female outlet on the cylinder, and Primus appliances have a right hand male thread to connect onto the cylinder. Since they were first into this market they set their own standard. I assume they used right hand threads because that is what most people were used to at the time.

Most other later makers followed normal industrial practice for fuel gases with a left hand male thread on the cylinder outlet and left hand thread female connectors, usually using a regulator and low pressure appliances.

The high pressure appliances tend to be noisier than the low pressure ones, but when they came out they were competing with kerosene and petrol blowlamps and pressure lamps where the noise level was similar.

Frank

[Bryan]

Stuart, I won't get hold of the torch for a couple of days. I was impatient and did some grinding today. Took ages and dulled two 40 grit belts taking a bit under 2mm off the diameter. Still hard as. Might wait for the torch after all. :rolleyes: And yes, if I don't make a total hash of it I'll take some pics. I'm not documenting the build though because there's plenty of slotters on the web; mine's nothing special. And because it's so distracting to do.

Frank, thanks for the info on gas fittings. Very useful to know.

[pipeclay]

If you have allready taken 2mm of yhe OD and its still hard,I would go for the option of a pice of Mild or H/T bar.

[Stustoys]

I'm with pipeclay, time to give up and buy some bar. Annealing temp could be anything from 770 to 900C, hold for 1 hour, then cool very slowly. (wheelie bin axles are 25mm I think)
Stuart

[Bryan]

Thanks for the advice guys. I picked up some bright bar yesterday.

[RayG]

I'm with pipeclay, time to give up and buy some bar. Annealing temp could be anything from 770 to 900C, hold for 1 hour, then cool very slowly. (wheelie bin axles are 25mm I think)
Stuart


Hi Stuart,

You don't need to hold it at that temp for an hour, just get it bright red (non-magnetic) and let it cool slowly.

Regards
Ray

[Stustoys]

Hi RayG
Good point, as Bryan doesn't want to reharden it over heating it should work.
Stuart

[Dave J]

(wheelie bin axles are 25mm I think) Stuart

I take it you or your neighbors have to drag the wheelie bins out on pick up day. LOL

Dave

[Stustoys]

lol
Not so much of a wheelie bin.... just a bin ;)
Stuart