Nauman Sinus Punch

I came across these tools which haven’t been called for in quite a while, but when the opportunity arises they are really handy.  I learned this technique from Dan Nauman at a BAM meeting several years ago.  When I got home I made my own tools.  Three were made from coil spring and one was an Allen wrench as I recall.

The pattern I tested came from Dan’s demonstration.  The printed copy is glued to the sheet metal with rubber cement.  I had an ash log just the right height for working - about vise top height.  As soon as the tools were made I tried them out.

I have forgotten the gauge of sheet I experimented with but I think it was 16 gauge and the holes punched easily and cleanly with the slugs sinking into the end-grain surface.  I thought it was a lot faster and more fun than drilling if there were a lot of holes to make.  

The shape of the cutting edge of the punches is important as well as their sharpness.  I don’t know the upper limit of metal thickness for this technique but I’g going to guess that above 14 gauge it would be better to go to a mechanical punch or to drill.

See Dan’s work here:

http://bighornforge.wordpress.com

Punch Lubrication Hazard

This is an incident report of a potentially dangerous shop operation which I experienced. It was not so much a surprise that it happened but the violence caught me off guard.

I was working on a very simple taper candle holder design using a 3” compressed sphere which had been chamfered and textured. I wanted to punch a socket in the center to hold a standard taper candle. This is the link to the source of the compressed sphere stock and images.

http://www.kingmetals.com/productSearch.aspx?SearchCriteria=compressed%20sphere

The first step was making a series of punches to be dedicated to the project. I forged a 3” round taper in a piece of 7/8” round tool steel, polished it, then cut it into three sections of about 1” length and welded on utility handles. After the faces were dressed by putting a radius on the edges I was ready to test them. I did no heat treatment. See illustration.

With an even coal fire heat I put the compressed sphere in the hydraulic forging press, lubricated the punch with the coal dust grease, which I wrote about on the 25th of October, and punched the smallest starter punch. The press moves slowly but is very powerful and the punch sunk a bit deeper than I wanted so it hung up a couple of seconds before I could knock the punch out. It came out at a dull red heat but fortunately did not upset.

On the second heat I followed with the middle punch with no problem. On the third heat, when I began to reverse the press and come off the punch the grease lubrication exploded and backed the punch out for me with the “muzzle flash” and loud bang. The confined work space didn’t give the punch anywhere to go so it couldn’t become a projectile in this case.

This was exciting enough to stimulate some forensic examination. So what are the factors to consider? Without the lubricant the explosion wouldn’t occur. If I had drilled a small through-and-through pilot hole the hot gas would have escaped at the bottom. Perhaps if the punches were wider relative to their length the escape would be easier. Perhaps of the face had more radius - more ball shaped and less flat - no chamber could form to trap the gas.

When I return to the project the plan will be modified in some way which I haven’t settled on yet. Safety First!

http://www.persimmonforge.com/

That’s a Swell Hole

For the past couple of weeks, besides trying to get the lawn to recover after the terrible hot and dry summer, I’ve been finishing a chandelier. I’ve never made one of this style before and have found it to be interesting and challenging. At this point the frame and pendant elements have been constructed and I’m just working on finishing details.

This detail, if not trivial, is at least a very small one. In my opinion I still think it is worth considering and in other cases can create a much more striking visual detail.

In this design the power cord traverses most of the distance between the ceiling canopy and the candelabra pendant inside a tube with rings at each end instead of winding through the more common vernacular chain. After making the rings from 5/16” round and flattening 1” of the tube ends with the hydraulic press, I sunk a center punch mark and then drilled a pilot hole. Working over a narrow vise opening I heated the hole perimeter with the torch and used a handled opening punch to enlarge the hole so that the 5/16” ring could pass through and swing easily. That process necessarily creates the slight bulges along the edges of the flattened area.

It may take a blacksmith to notice a change this subtle but an accumulation of such little details in the design can eventually add up to interesting.

http://www.persimmonforge.com/

Hot Punching

I like to design projects which use hot punching as a technique. There is a little bit of a learning curve to climb before it gets easy but when mastered it is fun to do and the swell around the hole looks nice.

In the earliest days of my metal working experience I visited a smith who owned a historic shop and he offered some advice based on his 30 years of working. I still remember some of those things and one was to keep my punches sharp. I really didn’t understand the significance of that at the time but I became a believer through practice.

Usually I try to set up punching work when I have an assistant to either strike or to hold. Most of the holes I punch are 5/16” or 3/8” round by design. With holes smaller than 5/16” there is more risk of the small diameter punch drawing so much heat it reaches forging temperature and deforms. With holes larger than 3/8” a lot more force is required to create the hole.

If hole position must be very precise I will make a light mark and check the position and make adjustments and eventually set a shallow depression which can be seen of felt at punching heat.

A six pound sledge is my tool of choice for striking. I try to avoid placing the hot workpiece on the anvil until the punch is ready to place so the anvil doesn’t suck heat away prematurely. When the punch is in proper position, vertical and still it is time for a firm blow with the sledge. The punch is rotated about 90º while the hammer is lifted. The the punch is held steady and struck again once of twice until it is felt to “bottom out” against the anvil. Then the punch is cooled in the quench tub.

If the work piece is turned over the darker, cooler, circle is visible if the punch sunk deep enough to form a very thin area which will be the slug. This is where it gets interesting to me. If the punch face is flat and the edge sharp and the workpiece is cool enough when the punch is centered on the dark circle and struck the slug will fall out. In other words, if every thing is just right, it works perfectly.

If the punch is not sharp it acts like a fuller and moves metal back and forth without creating a stress riser perimeter which will break in shear. If the workpiece is too hot the slug mass perimeter will stretch and not shear. With enough practice this gets easy but, for me, never uninteresting. I just notice smaller and smaller details.

It seems like a trivial thing to rotate the round punch but it is an important detail if the hole is to turn out close to perfectly round. It’s sort of hard to dress a round punch so that it is perfectly round. Usually it is a little bit oval. If that is the case the hole will still be round if the punch is rotated while the workpiece is at a forging heat. If the punch is too oval it will be too difficult to twist so there is a limit to the our-of-round which is tolerable.

The body of the punch has a slight taper so the finished hole may have a very slight hour glass shape and each hole may not be quite the same diameter. Finishing holes with carefully made drifts corrects those imperfections.

I own a couple of square handled punches but have rarely used them to punch holes. I don't use many carriage bolts or make many square passthroughs. If I need a square hole I usually make a round one and use the square punch as a drift. Or can it really be called a drift if the tool doesn’t pass all the way through? Maybe it's a mandrel. It could be an opening punch but that sounds like a segue to boxing.

http://www.persimmonforge.com/