Taking the hardness out of steel

[DJ Morrow]

I have a couple of 1/2 diameter round steel rods x 3 feet with some matching recirculating bearings. I intend to use them with some aluminum supports.

I need to drill and tap 3 holes in each one. 8 - 32 to be exact. The rods are hardened. I talked to a machine shop today and the office guy suggested that they would just heat them with a torch to take the hardness out. Since the hardness just needs to be removed from an area only enough to get about a 1/8" drill through, it sounds like he might be going overboard.

Can anyone enlighten me if his approach is reasonable ?

Is there a better way.

Will it really make any difference to remove too much of the surface hardness ?

David Morrow

[Cold Fusion]

I have a problem similar to this. I want to buy some 1.5 inch rock. 60 shafts but they have no tapped holes in the end. Any ideas?

[Konrad]

There is a possibility that the shaft is casehardened, which means only the outer surface is hard, up to about 1/16" deep.
To find out, just grind some off at the end and see if you can file it.
If it's still hard, then you must heat it up to a cherry red, make sure the heat is uniform around the diameter, otherwise it will distort too much, then slowly cool it, stick it in sand or ash.

Konrad

[Cold Fusion]

Yeah, it's case hardened. So could I drill and tap it on a lathe?

[HuFlungDung]

It all depends on whether the shafting is simply case hardened. Commonly, this would be called "induction hardened" or "carburized and hardened" as opposed to "through hardening".

Induction hardened chrome plated shafting (IHCP) I am familiar with. The steel I am thinking of is C1045 grade, not an alloy like C4140, though.

C4140 is likely going to be a very deep hard case, or even through hardened. You should be able to determine this by facing the end of the bar in a lathe.

C1045 IHCP has a soft core. If the supplier cut it off with an abrasive wheel (which is common practise with this stuff), there may be a bit of a hard skin on the cut end. However, if you face off a wee bit (using the lathe), you will expose the soft core and it is readily drilled and tapped.

Drilling through the hard case of this C1045 IHCP is a different matter. You need someone with some patience, and some carbide drills to drill through the case. I would not want to heat this stuff in a small area to soften it, because it will permanently bend the shaft, and you don't want that

You must have a drill press to drill with, and the sturdier the better.
You can drill through the hard case with masonary drills, but they have to be resharpened before first use, because masonary drills have a very blunt edge on the carbide insert. If you have a silicon carbide grinding wheel ("greenstone" as it might be called because it looks green), you can coax an edge onto the bit. If you have a natural diamond wheel, just use that

You might try spotting a starting position with a ball shaped carbide burr, but if you try to drill right through with the carbide burr, my experience has been that it will jam and shatter.
Anyways, drill through the hard case at a size that will completely clear the screw, because you cannot let the tap touch the hardened steel.
Drilling speed for a 1/4 carbide drill in hardened steel might be around 500 rpm. Clean the drill often, but drill dry, do not use coolants (or crack the carbide).

[Cold Fusion]

Here is the rod I'm talking about. http://cgi.ebay.com/ws/eBayISAPI.dll...category=11805

[Ken_Shea]

Cold Fusion could your design provide for a clamping block at each end rather then bolting them.

Just thinking out loud.

Ken

[Cold Fusion]

It could but I would much rather bolt them to the end.

[Ken_Shea]

Since drilling will be easier then tapping how about drilling, then inserting a pre threaded press fit steel insert.

[HuFlungDung]

Cold Fusion.

Ken has an idea there. However, if you don't want to loose length, you would likely want the hole.

Nowhere on the Thompson site does it say what grade of steel they are using. They do say "high carbon" though, which would be different than the C1045 grade I was talking about.

Generally, plain carbon steels are easy to anneal, just heat them up to a very dull red (work in dim light) and set them to cool in the air. You don't need to take it all the way to "fully annealed" to be able to thread it. For end supported rods, I don't think you would be hurting anything to anneal the end for a couple of inches if you had to.

Alloy steels are a different ball game: the alloy content inhibits the change of state required for hardening or annealing. They require extremely slow cool down to get back to a machinable state. This would be a cooldown measured in hours, not minutes. It is practically impossible for the average guy to do.

[Snel]

I would soft plug the hex stock, drill and tap the soft plug first then insert it, then run the tap back thru. If you don't soft plug the stock then make sure you tap drill maybe .005 or .007 over size, my experience is even though the outside is case hardened the inner core is more tough than usual. Don't use a four flute tap either and use thick tapping oil!

Dave

[duluthboat]

Dave,

I would take the rods to a shop that has EDM, they can burn the holes with threads and no other damage to the rods, this is not difficult or expensive

Gary