Hollowing speed

[Steve Campbell]

I just got done rough turning a 6 inch by 3 inch birch hollow form. The wood was somewhere between green and dry. The outside went as expected but the inside was kind of a bear. I was using a Sorby swan neck scraper. I just couldn't get it to cut very well. I did manage to get it but it sue was slow. I got a lot more dust than curlies.

My main question is how many RPM's do you guys usually turn something like this?

Thanks guys
Steve

[Reed Gray]

With a piece that size, I would be in the 800 to 1000 range. It depends more on how comfortable you are with whatever speed you are using. As far as a clean cut, grain orientation is important. On the outside, with end grain turning, you cut from the high/wide spot to the low/narrow spot. On the inside, it is the opposite, you cut from the narrow spot to the wide spot. The small square hss cutters don't give a really clean cut, but as with any finish cut, take very light passes with a freshly sharpened tool. I prefer the carbide discs for my finish cuts.
robo hippy

[Allen Neighbors]

Depending on the size of entry hole.... I use an Oland-type tool, swan necked, with a 3/16" HSS cutter, on 5/8" holes. On wider openings I use my Hunter carbide cutter.
If you have room, the Hunter tool is awesome.
Speed? I use from about 1000rpm up to about 1800, depending on the cutter.

[Steve Schlumpf]

Steve - on a hollow form that size I would probably turn it somewhere in the 850-950 rpm range - only because I am comfortable with that range. As far as having problems cutting the inside of the form - make sure that with the tool angled slightly down (handle is raised), that the cutting tip is at or just above the centerline. To far above or below the centerline and the cutter will grab or not even make contract with the burr.

Keep working on it - it gets easier!

[Steve Campbell]

Thanks guys. I should have made it clearer. This is not an endgrain form. I am making a birch potpourri bowl. The opening will be 3 inches when I'm done. I was able to hollow a lot of it out with a bowl gouge.
I was using a sorby swan neck hollowing tool that has kind of a fingernail shaped HSS cutter. I think my biggest thing now is to try and figure out how to sharpen it better.
Thanks again

Steve

[Neal Addy]

I agree on a range of 800ish for that size form. I would rarely go over 1K when hollowing any size. Don't expect curlies like you would with a gouge. Your HF cutting bits don't work that way. But be sure and stop frequently to clear out the dust and chips. They can bind the tool very quickly making cutting difficult.

Just for fun, here's a shot I took the other day just playing around. Don't ya love watching chips fly?

107654

[Steve Schlumpf]

Neal - how do you train your shavings to come out the opening? I always have to stop and dig for awhile! Is that a laser dot I see?

[Neal Addy]

Yeppers, that's me trusty laser. Sure saves a lot of funnels. ;)

[Curt Fuller]

In addition to the advise everyone else has posted, keep in mind that the cutters on the sorby tool are just basically small scrapers. They cut with a burr that doesn't last very long. So in addition to cleaning out the shavings frequently you need to refresh the burr on the cutter also. Each time you put a new edge on the cutter you really feel the difference.

[George Conklin]

Neal - how do you train your shavings to come out the opening? I always have to stop and dig for awhile! Is that a laser dot I see?

Ahh ha!!! I new I was doing something wrong. I didn't know to train my shavings. I've been sucking them out with the shop vac:D.

Nice picture, Neal.

[Wally Dickerman]

I use a Stewart hollowing tool which is the same as the Sorby that you are using. For hollowing on small and medium sized HF's I turn at around 1500 to 1600 RPM. Faster speeds give cleaner, faster and easier cuts. Of course too fast is unsafe. The 3/16 in. cutter must be sharp.

3/16 in. cutters are available at places like Enco with 5 or 10% cobalt. That makes them harder and they will hold a good edge for a lot longer.

When I'm teaching beginning HF's I ask the students to hollow at around 1200 RPM until they gain confidence in handling the tool.

When you're using the armbrace tool, or any other hand-held tool, always tuck the tool against your side and use body motions to control the tool. You'll have better control and is much safer.

Wally

[Steve Schlumpf]

Although I have a number of hollow forms under my belt, I still consider myself a beginner. So, as such, I took Wally's advice and finished hollowing out a green piece of maple at 1200 rpm. I have to admit that I am not used to using that high of a speed for anything other than buffing - so it took a while to get used to it!

I made sure the hollowing bit I was using had a fresh burr on it and then I also made real sure that I took very light cuts. I was actually very surprised at the results! Very smooth interior and it seemed like a lot less effort to get to that point!

It will take me a little time to get used to hollowing at that speed but, for me, the results speak for themselves! Thank you Wally for the suggestion! Once I get a little more used to 1200 rpm, I'll give the higher speeds a try also! Appreciate it!

[Clark Hall]

Wally,

What bit are you using from Enco? The Sorby Hollowmaster uses a 1/2 round bit that is 3/16" across.

Clark