Wednesday, February 5, 2014

Hitting Hard on Hard

Probably many of us never get a very organized instruction in the theory and use of tools.  What we know just came in bits and pieces.  When I started hanging out around anvils I picked up some tips both in protecting the anvil and in safe use.  The same goes for the hammers and the other types of tools we use.

One of the general principles was that the working surface and edges of tools are hardened and the bodies are softer.  In general we try to avoid hitting hard-on-hard for both tool protection and safe use.  But hard and soft are relative things and not so easy to really pin down.  It may be safe to hit hard-on-hard if we don’t hit too hard.  But that, too, can go down a slippery slope.

A further complication is encountered when we consider the state of the workpiece.  If the workpiece is hot and plastic there is little concern with hard-on-hard because the energy is dissipating in the workpiece through the movement of the mass.  If the workpiece is cold, more energy is dissipated elsewhere in the system and little effective work is accomplished in the workpiece.  The energy dissipates mostly in the hammer rebound movement and to a lesser degree in frictional losses at the contact surfaces and molecular deformation in the tools.

Some energy may go into permanent tool deformation - think of the gradual mushrooming which develops around the annealed struck end of some tools.  What we hope does not happen is that energy is dissipated through fracture failure especially spalling or chipping which can send off a tiny sharp fragment.

The point is we ought to take some time to use our intuition and think about what we are preparing to do and what the consequences might be for working safely and efficiently.

On 11/22/13 I wrote about  working with Kirk Sullens at a BAM meeting.  The project was an ad hoc chasing exercise and we had a limited set of tools which I brought to the meeting.  We discussed how we were going to proceed and I explained I had made the edge tools from various pieces of scrap tool steel so there wasn’t likely to be much consistency.  It would be a game with a lot of wild cards.  He would be striking the tools and I would be doing the holding.  He asked me straight out how I felt about this hitting hard-on-hard.  It seemed to me like a remarkably thoughtful question.  

I made the decision to proceed in a very short time so it is hard to say what actually went on in my mind.  I knew he was a skilled and careful worker.  The workpiece was soft mild steel.  The work was going to be on the delicate end of the force spectrum.  I had used the tools before without any problems.  It was a go and led to a fun afternoon.

Almost always, it seems to me like one idea leads to another and this might be a natural segue to the subject of work hardening but I’ll leave that to another day.

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