Bore size for rethreading

Michael Webb said:
On the Topic of this Thread wher everyone says..you can do this, this or that.
I'm the guy who wants to know why it originally failed to make you question how to repair it.
Define that, and go from there.
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My observation with wooden threads screwing into a hard big pin getting loose is because the major diameter of the shaft was machined too large to begin with. Wood compresses to a point. You want your threads to compress to that point so there is nowhere left to go later when the shaft is in use. To me this means boring the major diameter of the shaft wood about .005" smaller than the minor diameter contact area of the pin. This is about the right amount to allow the pin to compress the wood for a lasting and snug fit.

Then I seal the threaded hole not with CA but with Zinsser sanding sealer with shellac prior to screwing it on a pin the first time. The sanding sealer penetrates the exposed grains of the wood and hardens but not nearly as hard as CA. And protects against moisture swelling the wood. After drying several hours when you screw the shaft on the first time you may think it's too tight but the hole with the shellac will compress just right to stay put and not get larger. Also the shellac is more a lubricant than CA. After you screw them together a couple of times they usually feel just right at the sweet spot and remain that way for many years.

When I read about people using a .308" hole in a wood threaded shaft for a .308" pin minor diameter thinking they are machining precisely I just shake my head. They are usually proud of their .308 reamers and gauge pins but I know these shafts will get too loose in short order. You have to understand the properties of the material you are dealing with. Whatever it is.

Your mileage may vary.
 
Michael Webb said:
I use Boshield T9. Works great and doesn't leave any residue. I also use it on all my machines with cast iron beds.
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I have a couple questions if you have a minute.
It says it leaves a wax film when it dries. Do you normally let it dry before tapping? Also, do you apply it to the tap every time you use it?
Thanks
 
dendweller said:
I have a couple questions if you have a minute.
It says it leaves a wax film when it dries. Do you normally let it dry before tapping? Also, do you apply it to the tap every time you use it?
Thanks
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I haven't noticed and film left behind. I spray it on the tap when I start, then blow it out afterwards.
After tapping, I use a mixture of blo mixed with zinsser sanding sealer.
Pour it in, wait a few seconds, dump it out and let it dry.
 
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