hollowing tools

[Kevin Jenness]

I have made a few dozen small hollow forms, the largest about 9" diameter x 7" tall, using a homemade "snake" articulating setup and a JT Tools Transformer bar with an 8 mm carbide cup shaped tip. I have been wanting to do larger pieces but found I was reaching the limits of my gear. After a long wait I finally received and set up a new Clark hollowing system and tested it out with some different tooling on some small green end grain cherry blanks.

I got a short holder from Keith Clark for the ProForme shielded cutter that fits in his 1 1/4" boring bar. It cuts very fast and clean, but I realized that the steep bevel and the overall size prevents it from boring in at less than about 5/8" from center. I was able to bore in leaving a core and then nibble away back to center. Do folks using the ProForme typically bore a center hole with another tool? Also, the tool tended to clog with fibers between the cap and cutting edge. How can that best be avoided?

The Transformer bar worked well in the new setup. It cuts almost as cleanly as the ProForme though slower and is small enough to be easily controllable, plus the bar and cutter can work through about a 1" minimum hole, depending on the vessel shape. I may have a shorter bar made to connect the cutterhead and the Clark bar for deeper forms with larger openings. The Transformer has several hinged links that allow for swiveling the cutter to reach areas that a straight bar won't touch.

I found a reference in an old thread here to modifying a twist drill bit for hollowing, so I had a go at it. I had a dull 1/2" two flute end mill in the rack which I ground back to a swept-back gouge shape to the left of one flute and a small round tip in the front with a 40 degree bevel. The right side is simply ground away for clearance. It's quite aggressive and fast cutting but surprisingly controllable with clean results. I can bore straight in at center as far as the cutter projection, about 1 1/2". I resharpen it on a platform just like a bowl gouge.

I had started hollowing an old dry gnarly maple burl about 9" deep but set it aside as it was too much for my original setup. It has some major interior voids, plus it is quite unbalanced as I wanted to leave the exterior natural, so I can run it at only about 200 rpm- kachunk, kachunk. The ProForme cut fairly well initially but the vibration loosened up the shield and allowed too big of a cut for comfort. The Transformer cut reasonably well but at the end of a 10" long 5/8" square bar it was hard to take much of a cut without major vibration. I wound up using the modified end mill for the roughout and am using the Transformer for cleanup. It's challenging because of the voids, but it's working.

The Clark system is impressive, very solid and smooth. It has the ability to rotate the boring bar to change the cutter attack angle which can be helpful.

I have some John Jordan cutters as well and like them for forms with small entry holes, but they don't cut near as fast or clean as those I mentioned above.

I'm eager to hear any suggestions on improvements and alternatives.

 

[Bill Blasic]

Mike Hunter has two different Boring bars used in conjunction with his carbide tool that work really well. One is a 3/4" bar which easily gets me down 9" or better and the other is a 1" bar with which I easily get 12" or better. Do a search at Hunter Tool Systems for boring bar and you will find them.

 

[john lucas]

If your getting a cone in the center your setup is not dead center or not parallel to the lathe bed. The cutter tip should hit dead center when you get to the bottom of the vessel. When I first started using a captured bar system I set the cutter up so it was the exact height as my drive center point. I was till getting a cone. What I found was my secondary tool rest and my main tool rest were not set the exact same height from the bed so the cutter was actually going down hill as it got deeper into the vessel.
My experience is a little different than Bill. I can go about 10" with a 3/4" bar. I've gone as deep as 14 but you have to take really light cuts beyond 10. when I get that deep I do all my cuts as a sort of pull cut so the cutter is cutting downhill with the grain. If I cut straight left it cuts across the grain and chatters badly. I'm using the Hunter #1 carbide cutter in my bar.

 

[Clifton C]

Using the Rolly Munro hollowing tool (a shielded cutter), I found the smallest opening helps prevent the clog. Notice I said "helps"... There is alway the errant splinter... I understand what you are saying about the cone, the Rolly will do it but it takes time, I bore in with a spindle gouge in steps, or use a drill bit depending on how I feel.

 

[Don Wattenhofer]

https://www.aawforum.org/community/index.php?threads/hollowing-tool-question-scorp-termite.16548/
This link to a previous thread shows a standard ring tool compared to my home made mount and the proform tool standard mount compared to my home made mount. The homemade mounts are made from 1" drill rod tapered down to the size of the cutter. The handles are extended with iron pipe to about 4' OA.