Supported boring bar setup for hollow forms

by Steven Antonucci

I have been hollowing for many years, and I have always hollowed with handheld tools. I am familiiar with the variety of hollowing systems on the market, and the high prices associated with them, and an engineer by nature. I took a long, hard look at the problems that are solved by hollwoing systems, and I boiled it down to two simple things: keeping the cutter level and on centerline and measuring.

I think that most of the systems are pretty overpriced for the problems they solve, so I set out to make a DIY version of a hollowing system. I added the extra contraint that I could not buy anything to support this project. Phase I is complete and I have met the stated goal. I now have a setup that overcomes keeping the cutter level and on centerline (measurement is still manually done, laser forthcoming in Ver 2)

Anyone with the usual workshop equipment can make this project, and it will only take about 1 hr. The supplies needed were in my case offcuts and leftovers from 15 years of shop time, but if you didn’t have anything, I suspect you could make this for $20.

I will start with the easy stuff. The handle for the setup is a piece of quartersawn white oak. I had slabbed the pith out of a piece that I turned many years ago. The center slab contains 2 quartersawn sections on either side of the pith that I always remove and stack for handle material, since the quartersawn lumber is the most stable. This piece was a shelf support in my firewood pile for at least 5 years, and air dried enough that I thought it would do the job. Surfaced on a 6” jointer on two sides, and planed parallel then ripped on the tablesaw- all that remained was the hole for the boring bar. I’ll come back to that in a bit.

I chose MDF for the support, frankly, because I had it. With the handle being about 1.5” thick, I needed to put the hole at 8” above the ways (swing of the lathe), which meant my platform needed to be 7.25”. A sheet of MDF is .75”, one top and bottom equals 1.5”. That makes the ribs 5.75” If I wanted to do it from scratch, I would double up the top and bottom of the box, and triple the ribs. If you are going to build something, why not overbuild it? Oh, yeah, cause I didn’t want to spend any $$$...

Glue and screw the box together. It is no mystery how this is done, but you do have to countersink the screws through the top and bottom so that everything will slide nicely. The box is about 9”x 24” across the top, which is plenty big enough for most sized forms. I cut the corner off of it because it was poking me in the ribs. If I was doing it again, I’d mount the outer rib flush.

Attaching the box to the lathe is simple. There is a runner that I made from a scrap of white oak that you can see in one of the pictures. It is about 6” long and fits in the channel on the lathes ways. You need to make the upper part of the T sllgthly (1/16”-1/8”) lower than the lathe bed surface so that it can clamp on the ways when the bolts are tightened. I drilled 2 holes through the box and the runner in the center and on the left section of the box. The runner holes have also been countersunk to make sure that the bolts clear the ribbing. A stack of washers and a nut hold everything together. Everything gets tightened to the lathe with a ratchet, and you don’t have to go much past snug because there is so much surface area.

I put a drill chuck in the headstock of the lathe with a bit that matches the diameter of the boring bar I want to insert into the handle. Using a piece of MDF standing on edge against the side ot the drill bit, I establish a parallel line on the support box. I clamp a temporary fence to drill my hole in the handle by slowly pushing the flat oak board against the spinning drill bit. My hole is now parallel to the support table and the edge of the board. I hand drill a set screw hole in the top by eyeball, and tap it with a standard bolt. I will likely replace this with a wing nut bolt so that I don’t need tools to remove the bar.

In addition to this bar set-up, I will be drilling other holes for other diameter bars shortly. Simply by removing the set screw and replacing it in the right spot, I should be able to accomodate 4 different sized bars with one setup. A lathe innovation was the plane handle, which gave me a comfortable grip to maneuver. As mentioned earlier, a laser measurement system isn’t going to be far behind. Having a wooden handle to mount it on will make it pretty easy.

First test drive is also shown. In one of the pictures, you will notice that the lathe is running at 1000 RPM while I stood back and took the picture. It’s a little bit slower to cut a vessel because a lot more gotes into switching tools and cutters than handheld, but the cutting is done withoutany stress or concern. There is almost no feedback at all from the tool, so I think you almost need the laser to measure or risk cutting more vessels in two pieces. The vessel in the pictures was 2.6 ozs finished, and was probably not any different than what I could have done by hand (very carefully).

Everything you need to build one is sitting in the pictures I’ve attached. It ain’t rocket surgery…

-- Steven


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