Reaming Hardened Steel at 55Hrc

[djstedman]

I have a job here where I have to cut 16 .375 diameter x 2 inch deep holes in 4340 at 55 Hrc..

 

Due to the positional constraints of the holes we have to cut the holes hard.. we are currently drilling them and calling them finished but occasionally we get a lot of parts that just doesn't seem to want to drill ok and we end up with out of round / undersize holes..

 

I am looking into possibly reaming them after drilling to sort out the out of roundess / undersize condition..

 

I was just wondering if anyone had any experience with reaming at 55Hrc or above and what kind of experiences you had with it..

 

I have heard that cermet reamers might be the way to go, and I have seen some Guhring HR 500 D HPC Reamers that are some kind of Tialn Coated Carbide reamers that look like they might be kind of promising..

 

Anyhow.. just looking for any input from anyones who has given this a shot in the past..

 

We have tried regular Solid Carbide reamers that we had Tialn Coated without a lot of luck, maybe im expecting too much from them not sure..

 

Anyhow like I said im just looking for some input.. especially if you have had success doing this and have suggestions of a manufacturer / product I might want to try out..

[Pilot Plant Supervisor]

What drills are you using? I have had good luck in some fairly hard Nickel Ti with Kennametal 3 and 4 margin drills. I have not tried them in Hard steel though. The 3 margin made an exceptionally nice round hole.

[djstedman]

We have been using Mitsubishi MZS Solid carbide drills.. most of the time they do a great job .. but as I said every once in a while the material varies or something and we end up with issues..

 

We have always managed to fight our way through those lots, but I just wanted to explore my options, I mean if we can find a good solution for reaming that minimizes job stoppages and or rework of parts it will be more than worth a bit of added expense.

 

After all we always have a lot of other jobs to run at the same time.. and stopping to mess with this one causes all kinds of scheduling conflicts etc..

 

Anyhow still hoping someone might have some suggestions. .

[Pilot Plant Supervisor]

I would still urge you to try a double margin drill of some sort. I think Mitsubishi has the MHS, but not sure about size options.

[mkd]

1. what are the positional and hole size tolerances needed?

2. what grade of 4340 are you using? there is a wide allowance in composition within the 4340 grade. I read in a trade publication years ago, you could specify "bearing grade" for a ridiculous cheap premium. From what you said this is the source of the unpredictability. I would start at the source, talk to various steel suppliers. there is a big difference.

3. are you verifying the hardness between batches? I've seen suppliers totally miss anneal on 30% of a particular batch. 100% check and send non-conforming parts back. amazing how fast they clean-up their act when the parts come back.

[djstedman]

OK so I kind of fibbed a bit .. its not actually 4340 .. its really 300M .. but 300M is pretty much the same composition as 4340 with a couple added ingredients.. but most people look at me funny when I say 300M so I just said 4340 since everyone knows what that is..

 

Anyhow.. the material is certified material provided by the customer and hardness is between 53-55 Hrc certified and checked at incoming inspection into our facility.

 

I have been doing some testing today and I think im getting somewhere.. hopefully will get this sorted out on Monday..

[mkd]

a buddy gets 1000's holes in Inconel with Guhring drills.....

 

good luck

[JAMMAN]

ARRGH 300M is hard to do anything with at any hardness.

 

I would try boring it single point, an insert with less than a .01 radius.

 

I know I have never been able to tap it under 1/4-20 and even with 1/4-20 I drill the hole way over size.