Hardest material that can be broached with an arbor press and HHS broaches

nt1953 · Jan 19, 2020

I have some lathe parts that I need to make that require two internal 1/4" keyways. The parts are about 1.24" ID and they need to be as hard as I can get them without having to heat treat them after machining. Hardness and toughness are important.

So, how hard can the steel be and still be broached with the tooling I have? I am considering annealed 4340 at Rockwell C25. Any help appreciated?

atex57 · Jan 19, 2020

RC25? Piece o cake! RC35 may be getting tough but 25 is easy.

Ed.

Rickyb · Jan 19, 2020

atex57 said:
RC25? Piece o cake! RC35 may be getting tough but 25 is easy.

Ed.

No problem at Rc37. Heavy truck steering knuckles are Rc 30 to 37 and have broached and cut key ways.

Bill D · Jan 19, 2020

Can they be rough broached before heat treat. then broached to final dimensions after. Or is that too likely to skew the broach and jam things up?
Bil lD

Peter from Holland · Jan 20, 2020

How hard is prehardened 4340
That is the whole idea of pre hardening
Get it as tough as possible but still beeing machinable
And in the old days that meant with HSS
Peter

thermite · Jan 20, 2020

nt1953 said:
I have some lathe parts that I need to make that require two internal 1/4" keyways. The parts are about 1.24" ID and they need to be as hard as I can get them without having to heat treat them after machining. Hardness and toughness are important.

So, how hard can the steel be and still be broached with the tooling I have? I am considering annealed 4340 at Rockwell C25. Any help appreciated?

C25 you could do with hand chisels. If this is for your Monarch, 4XXX "pre-hard" should do fine as-had, JF finish that task, go do the next thing.

Old part has served for how long, and how HARD, already?

You ain't likely to live long enuf to USE it for enuf hours to begin to wear out its replacement, made this year!

The Wizards of Sidney didn't much depend on uber-exotic alloys nor bleeding edge heat-treatments.

They simply made good parts at "best current practice" levels of technology, saw to it they were well-fitted, and made them a tad BIGGER than they needed to be.

Ergo, all parts back of a "Monarch" badge ran at lower stress than less well-thought-out lathes from those who paid less attention to what actually mattered.

Imagine a THREE HUNDRED year "one Hoss, Shay" and ... it wudda been a Sidney, Ohio product.

YouTube

nt1953 · Jan 20, 2020

The old parts can be cut with a file, but just barely. So, is it likely that I can broach a .200 to .250 keyway 2.75 long in steel that has a hardness of C35 with HSS broaches?

thermite · Jan 20, 2020

nt1953 said:
The old parts can be cut with a file, but just barely. So, is it likely that I can broach a .200 to .250 keyway 2.75 long in steel that has a hardness of C35 with HSS broaches?

Welll. WTH do you HAVE for broaching? "Experience" doesn't seem to be all that heavy or you wudda told us already?

And is your "arbour press" a dinky H-F benchtop ...or a multi-ton capable "Grand Old" with ratchet arm .. of the sort we used to check 25-ton punch-press progressive diesets fits with, 50 to .. well "before my shift", but damn.... one old "Day Job" must have been using that old dinosaur from about 1923, and prolly bought it USED, even so?

C35 "by itself", is not the issue. If it is that uncertain, or your experience lies in OTHER areas of the craft than broaching, and/or you have SQRT-FA for equipment?

Make the part, hard as cut-nails if that seems righteous.

Send it out for EDM of the keyways. Cheap enuf postage to send it anywhere on Earth, but USA should do yah.

EDM don't give a damn about hardness. That's a goodly part of why it earns a living on a reg'lar basis.

implmex · Jan 20, 2020

Hi nt1953:
If you can just barely cut it with a new single cut mill bastard file and heavy pressure it's about 50 RC.
That's too hard to broach with HSS.

So if you MUST have it as close to the original as possible in material properties you have three choices:
1) Make it in the soft state and harden it.
2) Do as Thermite recommends and have the keyways EDM cut (sinker for blind ones and wire for through ones)
3) Fuck around half of forever with a single point carbide shaper tool rigged up in your lathe or mill and try to nibble it out in the hard state.

If you judge you can go softer without detriment to the function, then I'd go with 4140 HTSR or P-20 Hi Hard which gets you in the low Rockwell 30's.

If you want to make it in the soft state and harden it, you can choose an air hardening tool steel so it doesn't warp too badly during HT or you can plan to leave stock for finishing and just re-machine it after HT.
I have four favourites I use routinely:
1) A-2
2) H-13
3) 420M Stainless
4) 17-4 PH Stainless

All but the last will go up over 50 RC
17-4 PH at condition H900 gets up to close to 45 RC
All are pretty stable in HT and will not warp badly.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

thermite · Jan 20, 2020

implmex said:
3) Fuck around half of forever with a single point carbide shaper tool rigged up in your lathe or mill and try to nibble it out in the hard state.

LOL! 12" shaper, 7 1/2" slotter, decent HSS broaches to-hand, and even I would EDM the Mike Foxtrot.

Not as if I'm ever going to need more than TWO. One for each of two 10EE. If even I actually BOTHER at all.

Just not worth the f**k around time to set up for when stock sized or custom keyways, either one, are "white bread" common basic-rations, most any EDM shop on-planet.

10 fingers · Jan 22, 2020

I push broach keyways a couple times a week. In general, push broaching is a PIA. Read thru the tips on Minuteman's site. A 1/4 keyway broach takes a lot of force. To reduce chip load I will first push a 3/16 broach thru. Be careful to align larger broach. Regarding workpiece hardness, I wouldn't exceed HRC 36-38.

crooney70 · Feb 8, 2020

implmex said:
Hi nt1953:
If you can just barely cut it with a new single cut mill bastard file and heavy pressure it's about 50 RC.
That's too hard to broach with HSS.

So if you MUST have it as close to the original as possible in material properties you have three choices:
1) Make it in the soft state and harden it.
2) Do as Thermite recommends and have the keyways EDM cut (sinker for blind ones and wire for through ones)
3) Fuck around half of forever with a single point carbide shaper tool rigged up in your lathe or mill and try to nibble it out in the hard state.

If you judge you can go softer without detriment to the function, then I'd go with 4140 HTSR or P-20 Hi Hard which gets you in the low Rockwell 30's.

If you want to make it in the soft state and harden it, you can choose an air hardening tool steel so it doesn't warp too badly during HT or you can plan to leave stock for finishing and just re-machine it after HT.
I have four favourites I use routinely:
1) A-2
2) H-13
3) 420M Stainless
4) 17-4 PH Stainless

All but the last will go up over 50 RC
17-4 PH at condition H900 gets up to close to 45 RC
All are pretty stable in HT and will not warp badly.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Using a HSS broach heat treated by Rayco Tools can broach in materials up to 50 Hrc. It is a proprietary heat treat process that is still a company secret after 73 years. This material could get the job done for you.

Part manufacturer seeks to oust weak machining link | Cutting Tool Engineering

Wobble Broach Tool Test in BioDur 108C (50 Hrc) — Rayco Tools Inc.

crooney70 · Feb 24, 2020

Rotary Broaching: Making Hard Materials Look Easy:

Modern Machine Shop

mhajicek · Feb 24, 2020

Why can't you heat treat after cutting? 17-4 is precipitation hardening, you just bake it at 900°F for an hour to harden it, and it's very dimentionally stable.

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Hardest material that can be broached with an arbor press and HHS broaches

nt1953

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atex57

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