Saturday, June 24, 2017

Improved Toolrest for Deep Hollowing

by Wes Jones
(download this article in Office 'doc' format)

(See Woodturning Design Magazine, Spring 2009 for pictures)

I’ve wanted an easily adjustable toolrest to use with my captured boring bar for a long time now. One of the most frustrating problems in hollowing a deep vessel is getting rid of the little nubbin that develops right in the center of the bottom. To remove it or keep it from developing, you have to be cutting on the exact center of rotation. And trying to adjust your toolrest up and down very precisely is almost impossible.

This improved toolrest has a threaded shaft with part of the threads machined down to fit into the banjo. A matching threaded nut on the upper portion of the toolrest shaft rests on the banjo and supports the toolrest. The height of the toolrest can now be adjusted very precisely by rotating the nut slightly before clamping the toolrest in place. I also added a short rod sticking out of the side of the adjustment nut. This ‘handle’ makes it easy to adjust the nut and it gives a good visual reference for the amount you have rotated it.

Making The Toolrest

I selected a 1 ¼ - 7 threaded rod to use for the toolrest post. This size is readily available in short lengths and can be turned down to 1” or 1 1/8” diameter as required to fit your banjo. I needed 1 1/8” diameter for my lathe and you will notice in the pictures that a portion of the threads remain at this diameter. These partial threads do not cause any problem and in fact allow the banjo to clamp the post better. The length of undisturbed thread at the top of the post must be calculated carefully. Set up your boring bar and your old toolrest and adjust it so that your cutter is as close to the center of rotation as possible. Measure from the bottom of your boring bar to the top of the banjo. From this dimension subtract the diameter of your new toolrest bar and another 1/8”. This resulting dimension is the amount of undisturbed thread you want to leave on your new toolrest post. Note: The 1/8” is so that the adjustment nut can provide some plus and minus vertical adjustment.

I selected a 1” diameter rod to make the toolrest bar. I used a piece of 1018 alloy low carbon steel I found at a place that sells steel cutoffs. I cut it to 14” long, but this length is not critical. I welded it to the toolrest post offcenter with about 9” projecting from the center of the post. It is important that the bar be welded at exactly 90º to the post. Be sure the weld is very competent and completely fills the area where the round bar sits on top of the toolrest post. If you are not confident in your welding ability, for the sake of safety take the parts to a welder you trust.

A short length of ¼” diameter steel or aluminum rod can be inserted into a drilled hole in the side of the adjustment nut to create a handle. The rod can be pressed into place or held with thick superglue or epoxy. Be sure to deburr or chamfer all sharp edges of the metal parts before assembly. A light coating of oil or wax will keep the steel parts from rusting.

Parts List [MSC Industrial Supply Co. (800) 645-7270]

(all dimensions in inches)

1 ¼ - 7 threaded steel rod MSC part no. 04352977
1 ¼ - 7 hex jam nut MSC part no. 07479162
1” diameter steel rod MSC part no. 72982291 (alloy 4140, 12” long)
1” diameter steel rod MSC part no. 66102104 (tool steel, 12” long)
¼” dia. x 1” steel or alum. rod (Can be made from a bolt)

This project can be made very easily if you have access to a metal lathe and a welder. The cost to buy all the parts is less than $30. With the investment of a couple of hours of your time, this handy little toolrest will make your deep hollowing much more enjoyable.

Acknowledgement: I want to thank my friend, Jack Morse, for his help in building this project. Jack, in addition to being an artist and woodturner, is also an excellent metalworker.