Heat treating 4140 rivet squeezer yoke

I'm building a 4140 3" rivet squeezer yoke out of 4140. Here's a couple of pictures as examples:
Yoke itself -
http://www.averytools.com/images/variant/icon/1124.jpg
Mounted on squeezer -
http://www.clearairtools.web.aplus.net/mm5/graphics/00000001/Pneumatic%20Squeezer%20New%20S.jpg
I think of machining the profile from 1/2" bar stock, drilling the holes, and then having it heat treated to Rc 42-46. However, this is my first go at heat treating and I'm concerned that growth and warpage are going to be a problem.
Will this process work or should I heat treat first and then machine/ drill? Is it feasible to drill 7/16" holes through 1/2" of Rc 46 steel?
Thanks for the help, -DC
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With carbide, no problem. Probably with HSS at Rc 46.
Now, I'm going to sit back and hopefully learn from someone that knows this stuff what kind of factors are used to make a part in soft condition that is right when hardened. That would be the right way.
I have had the joy of dealing with a test cell spindle that was tapped with a H2 or H3 tap then hardened. Guaranteed siezed fastener. My boss (now fired) didn't reject it because he was late on the project. Jerk.
Wes
-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
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It's difficult to tell, but the original could have been forged into shape and them machined all over. Mucho stronger that way...

Your hole diameter will change perhaps .003 or .005" It looks like these holes are clearance for some bolts(?), so who cares if the grow or shirk a wee bit? Drill clearance holes with clearance! Make your life easy.
Overall, you're probably not going to have a lot of warpage/growth. It's important to recognise where the important surfaces/relationships are. Clearance holes - not important. The parallelism of your punches - very important.
If the hole at the end of the hook is important, I'd drill undersized (1/64" or 1/32") while soft, and then drill the hole correctly with a carbide endmill once hardened. You'll get pretty good size, and excellent location (assuming your setup is correct to begin with). You can also drill even further undersized while soft, then endmill to 1/64" undersized after hardening, and then use a carbide-tipped reamer (faster) or a barrel lap (slow as shit) to size the hole correctly (to perhaps .0005" or less on the diameter).
Make sure to put a correctly sized block inside the hook as it *will* flex and it *may* flex enough to make your hole in the wrong location, over-sized, or even jam your cutting tools (dulling/breaking them).
As far as flats, you're likely going to have to process the flat at the end of the hook (inside) after hardening. You can get it pretty good with a carbide endmill, or really good with a surface grinder (if you have access to one).
Now, this advice is worth what you paid. There are quite a few places where there could be some "gotcha!"'s but I don't personally understand the function of the unit enough to make that determination.
Good luck. Let us know how it goes.
Regards,
Robin
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Robin,
Thanks for your advice.

You're right, those are holes for bolts that hold the yoke onto the squeezer body. Take a look at this better shot of how the squeezer works:
http://www.rv7factory.com/images/tools/squeezer.jpg
A shaft extends through a hole drilled on the bottom of the yoke and supports the moving riveting die. The hole at the top of the yoke holds the fixed die. When a rivet or other part is part is placed between the dies, the shaft extends the moving die toward the top die until they meet. This particular squeezer is rated to produce a force of 3000 lbs.
In my mind the first important part is that the fixed die hole (3/16") and the moving ram hole (larger) be aligned and parallel. The second part is that the yoke face where the fixed die rests be perpendicular to the ram travel. It sounds like its best to rough these features while soft and then finish cut them after hardening.
I'll be building the prototype in the next few weeks and I'll report back on how it goes.
Thanks again, -DC
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So why did you choose 4140? A machine shop teacher once told me that hardening something does not change its elasticity, just changes how far it will bend before either breaking or exceeding its modulus of elasticity. I hope I got that right. If not someone please chime in and correct me! I got into a discussion on making boring bars that won't "give" a couple of years ago on this ng. I don't think 4140 was very high on the list. I like 4140 a lot and use it for trip hammer dies, hammer heads and jsut general use where I want something stronger than mild steel. But for this application, there must be something better????
Pete Stanaitis -----------------------------
DC wrote:

http://www.clearairtools.web.aplus.net/mm5/graphics/00000001/Pneumatic%20Squeezer%20New%20S.jpg
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You got the first part right. So did your shop teacher. This is a widely misunderstood fact.
But it doesn't exceed its *modulus* of elasticity when you bend it. What it exceeds is its elastic limit. I'd explain, but these terms are better explained in many discussions about them on the web. I'll bet that Wikipedia has a clearer explanation than I could muster on short notice.
The very short take is that the modulus of elasticity is its stiffness, or springiness, before it takes a permanent bend. The elastic limit is essentially the material's yield strength: the amount of force it requires to give it a permanent bend.

It's the same as any other steel, including mild steel. Stainess is 5% or 10% less stiff. To get a stiffer bar, you have to use a material stiffer than steel: usually tungsten alloy or cemented tungsten carbide.
I didn't look at the links below so I'm not commenting on the application here, only on the point you made above.
-- Ed Huntress

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