Spinning the tool not the stock to cut tenons
Posted: Sat Apr 26, 2014 3:56 am
In that S. Bang thread SEThile asked about how I cut tenons, since he knew I didn't have a lathe.
I said with a drill press. (DP's are pretty much a requirement in repair work to allow fast centering wherever you want, on any part you want.)
The trade-off is usually a lack of precision, because even small lathes are quite rigid while many surprisingly large DP's are not (small ones are usually hopeless), and cutting truly good tenons is somewhere between difficult and impossible on them. They normally end up grooved and inconsistent in diameter over their entire length.
It can be done, though. I had to design my setup, and find a good machinist to make some one-off components, but it was straightforward since the task is so well defined.
The cutter itself is one that Tim West used to sell (and hopes to again one day), and it's unmodified. The way it is attached to the machine isn't off-the-shelf, though. The mechanism to hold the stem stock (as well as molded & cast stems) is also not something that can be bought but must be made.
Why might you pipe maker dudes be interested in all this? Because it is FAST. A few minutes ago I grabbed a chunk of scrap stock that already had an air hole, chucked it up, centered it, and made a cut to illustrate the result. The total time for everything was under a minute. The cut itself took 8 seconds. Going deeper to make a full length tenon would have taken about 20 seconds.
Accuracy-wise, diameter consistency from end to end exceeds the ability of a high quality dial caliper to resolve. I'd guess it's within a couple of ten thousandths. No finish steps or final tuning is needed---the stems come off the machine ready to use as-is. I usually use both inner and outer chamfering cutters before removing the the stem, though, to give things a finished look.
Anyway, speed is again the reason I'm bringing this up. A high volume producer would probably recover the cost of a dedicated tenon cutting machine fairly quickly, depending on how long he takes with a lathe. Those of you who might have thought that, but decided against one for "quality of cut" reasons, this is for you:
I said with a drill press. (DP's are pretty much a requirement in repair work to allow fast centering wherever you want, on any part you want.)
The trade-off is usually a lack of precision, because even small lathes are quite rigid while many surprisingly large DP's are not (small ones are usually hopeless), and cutting truly good tenons is somewhere between difficult and impossible on them. They normally end up grooved and inconsistent in diameter over their entire length.
It can be done, though. I had to design my setup, and find a good machinist to make some one-off components, but it was straightforward since the task is so well defined.
The cutter itself is one that Tim West used to sell (and hopes to again one day), and it's unmodified. The way it is attached to the machine isn't off-the-shelf, though. The mechanism to hold the stem stock (as well as molded & cast stems) is also not something that can be bought but must be made.
Why might you pipe maker dudes be interested in all this? Because it is FAST. A few minutes ago I grabbed a chunk of scrap stock that already had an air hole, chucked it up, centered it, and made a cut to illustrate the result. The total time for everything was under a minute. The cut itself took 8 seconds. Going deeper to make a full length tenon would have taken about 20 seconds.
Accuracy-wise, diameter consistency from end to end exceeds the ability of a high quality dial caliper to resolve. I'd guess it's within a couple of ten thousandths. No finish steps or final tuning is needed---the stems come off the machine ready to use as-is. I usually use both inner and outer chamfering cutters before removing the the stem, though, to give things a finished look.
Anyway, speed is again the reason I'm bringing this up. A high volume producer would probably recover the cost of a dedicated tenon cutting machine fairly quickly, depending on how long he takes with a lathe. Those of you who might have thought that, but decided against one for "quality of cut" reasons, this is for you:
