Saturday, August 15, 2009

Turn and Learn Session

On Thursday I went around to Nelson's shop to use his "Mustard Monster" (Powermatic 20) lathe. The picture is of Nelson showing Robert how to do a honey dipper on a general lathe.
I used the big lathe to turn some elm that has been freshly felled (see previous post).
Here are some observations about turning on a Powermatic. Its nice to have the extra horsepower as my General lathe has 1 HP while the Powermatic has 3 HP. However I did not feel like I could really use the full potential of the lathe because I was unsure of the holding power of Nelson's Nova chuck with dovetail jaws. It seemed to work loose rather frequently whereas my Oneway Stronghold with large jaws has never let me down. Unfortunately the clamping mechanism on the Powermatic lathe also worked loose causing some very unsettling vibration. It took a while to figure out what was happening as I am not that familiar with the lathe of course.
However I did get two bowls turned and I think in the process convinced Nelson that he needs a way to contain the shavings as his shop was pretty well covered.
Some issues with Powermatic which I will raise here:
The design of the banjo is a cause for problems as the off center hole is off center the wrong way in my opinion. (Should be to the right not the left) Since the banjo is so wide it requires the tailstock spindle to be extended way out to allow room for the banjo when turning a bowl blank between centers. Also the banjo is very heavy which requires one to use two hands to move it. Heavy is good but clumsy is how I would best describe the set up.
The clamping mechanism for the headstock coming loose is a problem that I would want to address as soon as I had a lathe like that.
Nelson phoned me up after I turned on his lathe and complained that he could not get the live center out of the tailstock spindle. This I feel a bit guilty about as it is probably my large bowl turning that has jambed it in there.

1 comment:

  1. In defense of the Mustard Monster. The banjo problem is easily solved by steel wool on the ways, followed by WD40 and a coat of paste wax on the bottom of the banjo, tool rest, tailstock, and ways. The banjo weight is an excellent safety feature. The centering pin is fine where it is since clothes can not get caught on the protrusion and adjustment is not required very often. The Nova chuck works perfectly well with large pieces as long as one is careful to turn the tenon with a square shoulder and dovetail. As you saw, the second bowl was no problem with a "Nelson-made" tenon. Moreover, dovetail jaws work fine with cross grain turning as they hold not by crushing fibers but by friction agains the circular jaws and shoulder.
    The "clumsy" excessive vibration could have been avoided by balancing the blank first between centers and taking less agressive cuts consistent with the speed of the lathe and the size of the blank. There were lots of 3/8 in shavings which was unnecessary. Any other lathe would have bogged down. As to the live center problem, that would not have happened had the One-Way live center that comes with the lathe been used. Finally, in two years of using the lathe, the headstock has never come loose from excessive vibration because it has never been subjected to it. Now we know the headstock has to be held tighter in those instances.