Heat treating question...

[Chris D]

Hi Guys,

I am going to be making a small spindle for a tiny machine. I planning on using a scaled down version of an R8 collet but the top portion will be different - much different. Either way, that part doesn't matter much relative to what I am trying to figure out.

This collet will be about 3 inches long and about 3/8" in diameter. I would like to heat treat it so that it lasts for a while (till I come up with something better). I have plenty of machining experience, but about zero heat treating experience. I don't even have much in the form of anything to do heat treating.

I have a propane torch (kind used for plumbing & soldering). I can get some fire bricks to make a small enclosed area to contain the heat. I know that small, long pieces like this can also turn into funny shapes after heat treating.

Can anyone suggests a good material choice for this, and if you don't mind, a method of heat treating it based on what I have here in the home shop?

Thanks a bunch!

Chris

[mxtras]

4140HT would be an excellent material to use for this application but I am uncertain of the exact procedure for oil quenching. I don't think the propane is going to get you enough heat unless you introduce some oxygen - like in a kiln arrangement. Is that what you are proposing?

Most of my experience with heat treating this material is carbon Nitriding and that was left up to the heat treating department. I am positive Google would yield substantial results on methods and specifics.

Scott

[keebler303]

you probably want a cromoly steel 4140, 4340, etc. as far as heat treatment you will need around 1600 F temperatures. A propane torch ain't gonna cut it, not to mention it is inaccurate. I would think you could get it heat treated locally for not too much money. If you figure out how to get that high of a temp. then you are set. Hold the part at the high temp for 30 min or so to get it thoroughly heated. Then pull it out of the furnace and drop it in a bucket of oil to quench it. Then you will want to temper it around 8-900 F for an hour or so, followed by air cooling. the temperatures governing your heat treatment will depend on the phase diagram for the alloy you use.
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Good luck
Matt

[Mcgyver]

for something accurate like a spindle, you'd (imo) have to grind it after heat treating because you are right, the heating and rapid quench will move the metal around. If you just want something a little tougher, use a pre hardened chrome moly.

the main benefit is it will not easily suffer dings and bruises and will wear better. In a diy environment, do you really need this? what would have to be hardened in a commercial project is often just made from mild steel in a diy environment, with no degradation in quality as 1) its one careful user, and 2) its a low duty cycle (less wear concern). This may not apply to your use, but there have been many homemade spindles made of the years without hardening and grinding

PS, disagree regarding propane, you can heat treat steel with propane/air. granted it doesn't have btu's of other gases, but flame temp is more than enough for cherry red - i do it all time with cutters etc. I have o/a but prefer propane for heat treating because its a little easier to control. for a spindle, I'd consider sending out, that is if i didn't take my own advise and leave it soft

[Geof]

I suggest going with Mcgyver's advice and leaving it soft. You probably can get it hot enough with propane and oil quench it and if you are lucky it won't warp or crack. But the devil is in trying to temper it because that needs better temperature control than the heating and quenching; if you overdo it you are right back at soft with something that has almost certainly warped and if you underdo it you are too brittle.

Regarding the material you could make it from C1045 ground shafting. It is partially hard, a bit of a challenge to machine but doesn't ding up the same as annealed chromoly.

[Chris D]

Thanks guys,

This isn't a spindle - rather it is the collet. But I think I will go the route of using it soft. At worst, it will get beat up and dinged up and I would have to make a new one.

I don't have the best lathe for turning it, but can do alright with it. I don't have any means of accurate grinding so that would be a problem too. Warping is almost assured with this based on your comments and my "gut instinct".

Soft it is - will order up some 1045 and give it a go.

Thanks
Chris

[WhiteTiger]

If you want to skip heat treatment look for a metal supplier that handles LaSalle steel. The stuff you want is called ETD150. It's physical properties are such that magnum rifle actions can be made from it as it is shipped from the mill.


Tiger

[One of Many]

A few other ideas. If it is that small, I'd consider converting an MT2 or MT3 collet/broken shank drill etc........ into your needs. There are other junk things you could buy at a scrap yard to get the pre-heattreated factor. As long as you can cut them, it's a cheap way to go.

S7 or other air hardening materials don't get the warpage as bad. Checking for the critical temp is said to be at the point it turns non-magnetic. Be aware that some magnets go bad around high temps too, so it can be a false test.

If you cannot heat it evenly, I wouldn't bother with the HT. If a home shop can get a good 10 years of use out of some of the import R8's, which many are not hardened. I doubt your home made version will be much worse for wear. Besides the greater risk of runout. Of course, if you finished off the ID in the spindle to size, then split the grip body, that should not be much of an issue either.

DC

[jingham]

Don't forget about the environment the part will be used in. Work hardened Stainless Steels can do the job if your going to be doing any water based coolants with the collett.

[dertsap]

use a chunk of drill rod ,it will have way less tendancy the warp out of shape , you can use a propane torch and bricks if the part is small enough ! but you will need to know which color shade the part has to be when you quench it , (steel changes many colors as it cools down ) , straw color is what i used to use for some abused assembly tools , it is hard but boarder line brittle
drill rod is hard enough that you will probably get away with not heat treating

check this pdf for the proper heat for yor application
http://www.bvwt.org/PDFs/Hook%20Tool.pdf

[motomitch1]

Pre hardened and tempered 4140 is used extensively in most industry sectors for a wide range of applications such as:
Adapters, Arbors, Axle Shafts, Bolts, Crankshafts, Connection Rods, Chuck Bodies, Collets, Conveyor Pins & Rolls, Ejector Pins, Forks, Gears, Guide Rods, Hydraulic Shafts & Parts,Lathe Spindles, Logging Parts, Milling Spindles, Motor Shafts, Nuts, Pinch Bars, Pins Various, Pinions, Pump Shafts, Rams, Sockets, Spindles, Sprockets, Studs, Tool Holders, Torsion Bars, Worms etc..

Pre hardened and tempered 4140 can be further surface hardened by flame or induction hardening and by nitriding.

[NC Cams]

Find a local heat treater who does small batch stuff.

We have a guy locally who does small stuff as in jig and fixturs out of 4140 for $25-$35 per batch. Forget the propane deal. Flame harden with oxyacytelene (heat to cherry red and oil quench followed by 300-400F draw).

If you harden and draw 4140 you can easily get Hrc 48-52. 4140 PHT is Hrc 28-32. Nitride after H&D" and it will soften it as nitriding is typically ABOVE draw temp as nitride is at 900F or so.

Look at some air hardening steels (A prefex) as they only need to be austenitized and air quenched. They tend to NOT distort like other quenching mediums tend to cause.