Soft high speed steel

[JasonBModerator @jasonb]

Further to my suggestion of using old drills, I have been reliably informed that some of the larger sizes particularly with taper shanks may be friction welded with just the business end in HSS and the shank in something else. Which makes sense as it keeps the cost down.

[Hollowpoint]

On Hollowpoint Said:

Another option might be to harden the cutting edge of the silver steel very hard and leave the rest of the shank unhardened. It might help prevent breakages at least.

Agreed. I’ve done this many times with various tools etc, and it seems to work fine.

[Vic]

On Vic Said:

On Hollowpoint Said:

Another option might be to harden the cutting edge of the silver steel very hard and leave the rest of the shank unhardened. It might help prevent breakages at least.

Agreed. I’ve done this many times with various tools etc, and it seems to work fine.

I’ve done the same, but would be difficult in this instance, the cutters are 30mm long, maximum diameter around 12mm.  My propane torch will heat the lot.  Gas welding torch might do it.

Vic, you have grasped the problem, unlike some, brittle cutters in the smaller sizes, <6mm (AF).  That’s why I would like to try HSS or similar.

 

 

 

[John MC]

On John MC Said:

On Vic Said:

On Hollowpoint Said:

Another option might be to harden the cutting edge of the silver steel very hard and leave the rest of the shank unhardened. It might help prevent breakages at least.

Agreed. I’ve done this many times with various tools etc, and it seems to work fine.

I’ve done the same, but would be difficult in this instance, the cutters are 30mm long, maximum diameter around 12mm.  My propane torch will heat the lot.  Gas welding torch might do it.

Vic, you have grasped the problem, unlike some, brittle cutters in the smaller sizes, <6mm (AF).  That’s why I would like to try HSS or similar.

 

 

Not a problem, harden the whole punch and then temper the part you want just toughened by watching the colours run as you apply heat to the non cutting end or am I missing something?  BTW in my experience HSS is just as brittle as silver steel if hardened and then not tempered.

 

Tony

 

[John MCParticipant @johnmc39344]

Not a problem, harden the whole punch and then temper the part you want just toughened by watching the colours run as you apply heat to the non cutting end or am I missing something?  BTW in my experience HSS is just as brittle as silver steel if hardened and then not tempered.

Tony

The way I heat treat the tool is to heat up to around 900C, quench in oil.  To temper , I heat a steel plate about 5 – 600c, sit the tool on it and monitor with a non-contact thermometer, this can happen rather quickly so I lift the tool on and off the steel plate to try to “soak” the tool at the required temperature, then quench again.  I find that if I temper much above 200C, the tool blunts too quickly, rotary broach or whatever.

I have, maybe wrongly, always considered that heat treatment means hardening and tempering when discussing steel?

I was hoping someone could explain the forces involved in rotary broaching.  Clearly, the primary force is axial.  But, because the cutter is angularly displaced form the centre line of the machine, how big is the secondary force trying to push the tool back onto the machines centreline, if, indeed, there is one?

Again, I thank those who have taken the time to contribute to this thread, useful or otherwise.  As is usual, the thread has “taken a walk” at one point, whether to buy or make tooling.  I’ll make a tool as a means to an end, not as a primary interest.  As I did with the rotary broach when all that was commercially were expensive commercial products.  As is often the way, commerce has caught up with me, rotary broaching equipment is readily available at affordable(?) prices.  Should I buy new kit or carry on with what I have?

[VicParticipant @vic]

Could clamping the cutter in a larger block of steel stop anything other than the very tip of the tool getting to the required temperature before quenching? Just a thought.

[not done it yetParticipant @notdoneityet]

Quenching in oil will not fully harden steels.  Quenching in water and salt solutions will harden it more completely.  But that would leave the whole tool brittle and likely to shatter if struck with a hard hammer.  Oil quenching, without further tempering, is likely best for both hardness and toughness.

[Vic]

On Vic Said:

Could clamping the cutter in a larger block of steel stop anything other than the very tip of the tool getting to the required temperature before quenching? Just a thought.

Good idea.   I watch the US programme “Forged in Fire”.  It’s like Great British Bake Off except they make knives and swords.  Part of the challenge is choosing the steels and manipulating their heat treatment to meet a requirement.   Sharp delicate weapons and choppers are different.  What’s wanted is a very hard edge on a tough base.  The base mustn’t be brittle.

Various ways:

• Selecting Oil, Water or Brine to quench.   Oil results in a less hard, less brittle tougher blade, good for chopping.  Water produces a hard brittle blade.  Good for mixed work.  Brine produces a very hard, very brittle blade, good for scalpels and razors.  Depends on the steel too, the best choice depends on the desired result.
• Controlling the temperature by insulating those parts of the tool that mustn’t be brittle with clay.  Very similar to Vic’s suggestion.
• Mixing metals.  For example by forge welding a hardenable steel sheath over a mild-steel core.  Only the outer sheath responds to heat treatment, and takes an edge, and the mild-steel is good at absorbing shocks.   Sometime 3 different steels are layered: very hard outer, tough middle, on a soft base.   The billet ground to knife shape.   Hacksaw blades are made this way: the blade is tough, slightly hardened to reduce wear, and only the teeth are HSS.  Don’t know how the heat treatment is applied: I guess the HSS part resists heat well enough to be welded on.

Skilled work, requiring time and temperatures to be judged accurately and matched to the steels used. Getting it wrong causes cracks, chips, warping, delamination, blunting and shattering.    Part of the fun is testing the blades, done with gusto!   Is the blade still sharp after a machine drives the point into an oil-drum?  Will the blade shatter when whacked into a block of ice?  Hours of good work often ends in failure because the heat-treatment wasn’t spot on.

My daughter enjoys it too: not sure what she sees in a load of muscular sweaty men wielding hammers…

Silver-steel meets most of my needs without fuss.

Dave

[John MCParticipant @johnmc39344]

To hopefully conclude this thread this is how I am going to proceed.  I’ve been gifted a small piece of annealed M2 tool steel that I will make a 4mm AF hex. cutter.  For heat treatment, a basic quench and temper.

I am told that this particular piece of tool steel came from a now defunct toolmaking firm. They didn’t do the heat treatment , but occasionally, they would  heat treat a tool if need be, a flame being the heat source.  Apparently it worked well enough to get themselves out of a fix!  I’ll do the same. The gifter has done this and tells me he has had reasonable results, a tougher tool which is just what I am after.

When I made the rotary broach the “drawing” was a sketch that was altered as I made the tool.  I have just used  2D CAD  to layout the geometry of the tool.  From this I can see that the side clearance of the cutters can be reduced a little.  That should help with resisting the secondary forces involved in the process.

Since starting this thread I’ve broached several hex. holes, 8mm AF in mild steel, silver steel cutter now chipped, will make a new one.  And a 14mm AF hex hole in Al/alloy, much bigger than I intended the tool to be used for, it went well.  Next job will be 4mm in stainless steel, I’ll just tool steel for the tool.

Again, thanks for the replies.

[Author]

Posts