Hollow Tool Sharpening

[LANKFORD]

I purchased some hollow tools and don't think the cutters are ground properly. As for the 1/8" tool bit cutter, it has a shape (top view) that looks like a bowl side scraper. Ground flat on the end and rounded on the left side. The bevel is about 70 degrees, very steep. From videos I have seen the top shape should look like a fingernail gouge, nice radius on the end and both right and left side ground. Correct? Also, I believe the bevel would be better at 45 degrees. My thinking is based on Jordens video and his cutting procedure.

The tool also has a roundish finishing disc. It has no bevel at all, just a flat piece of steel. The only way it will cut is to tilt the tool over about 45 degrees, but wouldn't a 45 degree bevel on this cutter also be better?

None of the videos (or books)I have on hollow turning say diddly about proper sharpening the bits. They spend the time telling you whos tool they are using.

 

[Andy Coates]

bevels

I suppose it depends on which hollow tools you have bought, and what was intended for them...but all mine, which are from Sorby RS2000 set, I grind (when a regrind is needed) at about 60, hone the top face, and use at about 45 degrees to the side walls.

I think the difference in ground angles stems from the fact that most (if not all) are intended to be used at an angle, so any ground angle is probably best when it is ground for durability rather than keeness of edge. Your working angle giving you the actual cutting angle.

I struggled for a while when I first started hollowing with what are essentialy scrapers, but after working at it I now find I get a very good finish...which I'm certain has more to do with the tool than my application of it!

My circular dished cutters are ground at about 45 but I still present them at an angle of 45...now I'm wondering if that makes sense at all, but it seems to work very well so I'll leave it alone until somebody advises otherwise...which they probably will!

Andy

 

[LANKFORD]

One other thing I observed from videos and books. Presenting the tool at 45 degrees is recommended but they say to then rotate the tool upward into a cutting angle where you definitely would need a bevel. Also, a lot of the tools have a flat on the bottom side of the tool so that would assume you use the tool flat on the tool rest. So again a bevel on the cutter seems essential.

 

[Steve Worcester]

Whose tools are they?

If it is an insert tool, like Ellsworth's (or what Trent Bosch or Jordan use in their hollowing tools), where they round out a shank and insert it in a rod, yes, it gets a steep bevel all around the sides and flat on the top.
The shallower that bevel, say from 70 to 45, the more grabby (technical term) it will get.

 

[hockenbery]

Never ride the bevel with a scraper

Most hollowing tools are scrapers.

It is important to keep clearance between the wood and the bevel of any scraper or the wood will drive onto the tool until something gives (usually the work)

I sharpen all my hollowing tools down the sides a bit. The hook tools usually does more work on the leading side edge and the straight tool is often swept side to side.

Stop by a Capitol Area Woodturner help session: they will take all the mystery out of it in a few minutes.
CA Savoy is often there and he has made many of my Hollowing tools and he is wonderful teacher and delightful guy.

Happy turning,
AL

 

[CA Savoy]

LANKFORD--

As Al sez Hollow turning tool tips are scrapers. No bevel rubbing required, tip turned slightly down when cutting. Hollow turning is not a difficult task, just a dirty job. Come see me at Capital Area Woodturners, will be glad to work out your problems.

CA