Looking for more of a description of what is actually happening when we pound in a new set of pins.

Yes, I agree that excess heat generation of the pin via friction caused by rapidly spinning the pin into place changes the wall of the holes. It seems to be a chemical change in the thousand's of an inch of the material surrounding the pin. The wood can scorch, glue resins can melt, etc.

But is pounding all about temperature management or is there some other benefit? Certainly, the physics of pounding the pin roughens the inside walls of the hole as the pin thread is forced, under heavy friction, past the wood. Then is pounding and pin tightness all about the roughened fibers?

What if temperature was managed as the pin was slowly spun into place? Without the roughened fibers, is this why we don't spin a pin into place as it is the roughened fibers that increase the coefficient of friction?

What is the effect of adding talcum powder (french powder), or rosin, and or other fluids such as varnish or shellac? In the pounding process, it would seem that these materials would get mostly rubbed off of the crest of the thread and accumulate in the root of the thread? How does this act as a benefit?

Also, let's assume that the drilling of the hole is straight, reamed and the proper diameter.

We pound because it yields the results, but WHY?

Mark

Greetings,
Driving pins in is the fastest, easiest, least damaging way to do it. Cutting threads in the block by screwing the pin in will give a looser torque, take longer, be more expensive.

In short, we hammer pins in because no other way has been found that gives better results.
Regards,

Thanks Ed,

Perhaps that is my real question? Why does the pin, cutting its own threads, give us looser torque? If even managing temperature, is it that the pin polishes the sides of the hole in the process? Is it that the pounding process roughens up the wood?

We do it because it yields us the fastest results, but WHY is it more effective than threading the pin in?

I am about to pound in a set of Dimond pins and am pausing to actually get my head around what is happening at the interface between the pin and wood that makes pounding more effective long term.

Regards,

Mark

Basically as Ed said...its because this is the way it's ALWAYS been done.

One could also reason that it is within the same physics (partly) as driving a nail into the wood (but I'm not making a 1:1 comparison here). The wood fibers compress and then to some degree exert inward pressure on the pin.

Turning the pin in would generate LOTS more heat and would tend to glaze the inside. Consider how hot the pins are when you take them out (and that's in a compromised block!).

Try it both ways in a scrap piece and report back.

Pwg

I have tried it both ways. Pounding seems tighter, probably because it forces the wood outwards which then contracts around the pin, as opposed to cutting threads. But the one that I did by screwing in the pins still holds quite well. Of course, I screwed them in with a bit brace.

Thanks Peter,

You got me thinking of the thermodynamics of the two systems. I think I'm understanding the core differences that leads to the extra heat generated by the pins upon removal (twisting) compared to the heat generated by the pins when being pounded. Here is my logic. The reason for the difference is that the surface that the pin (say the leading thread) actually travels different lengths under friction. When pounding, the point of the pin travels linearly, say 1.5 inches under friction into the block. When being twisted it would be 1.5 inches (to the same depth in the block) + the rotational distance of about 11.3 inches. So the difference of distance under friction of twisting is about 7.5 times longer than the frictional linear distance of pounding. Hence the extra heat. Let me know if my logic is in the right ballpark.

So now back to the original question. If temperatures were kept in tolerance when twisting, would the pin have more torque or less torque than pounding and why?

Definitely am going to run a few tests here in about a week. Will share my findings.

Regards,

Mark

Mark, energy (work) is calculated by multiplying force by the distance over which that force is applied. Here the force is the resistance of friction and the distance is how far the surface of the pin travels against that force. So yes, your logic is good. If you wanted to estimate the exact amount of energy generated by turning a pin you could measure the force it takes to turn the pin from the end of a tuning lever and multiply that by the distance the end of the lever travels.

Just for fun let's make up some numbers. Suppose your lever is 1 foot long and you turn it 10 times, and the average force to turn it is 5 pounds. The force times the distance is 5lb * 10 * 1ft * 2Pi = 314 food-pounds of work. For comparison, suppose you drive in a pin all the way by dropping a 20-lb sledge hammer from a height of 2 feet onto the pin. If you assume all the "potential energy" of the lifted hammer goes into driving the pin, then the "work" is 20lb * 2ft = 40 foot-pounds.

Must be Texas sized "pi" to come out to 314 food pounds!

Doesn’t that sentence suggest you’re overthinking this whole thing?

You could of course do a combination too such as when using a sciortino insta-coiler. Pound it in most of the way and then wind the coil on in place, then pound to proper height.

Pwg

don't pounding on a pin!
screw in the old "native" pin + corrugated cardboard shim. Do this as slowly as possible. Temperature will be minimized here. A wood materials structure will lose few its technical characteristics but it's on level theorethics. In this case, the friction will be restored now.

Yup!

AWilley,
Thanks for doing the math! Great as usual you are.