Another Hollowing Tool Question

[Shaun Tyler]

Are there any recommendations for how deep a particular tool can safely go? Stuart Batty has some recommended ratios of overhang vs handle lengths but as far as I’ve found he doesn’t mention hollowing tools. I just finished my second hollowing project and it was definitely pushing things so I have some empirical data ;-) But it would be nice to go into future attempts with better planning.

 

[Dave Landers]

It's more about bar size/diameter than the handle. Trent Bosch has some recommendations on his site, on the FAQ page:

The 1/2” Hollowing tools can hollow approximately 6” deep. The 5/8” Hollowing tools can hollow approximately 8” deep, the 3/4” Hollowing tools can hollow approximately 12” deep and the 1″ Hollowing tools can hollow approximately 14″ deep.

Your mileage may vary depending on mainly experience and aggressiveness of your cuts. Be gentle and take small cuts and you can push these a bit. Be aggressive and you'll not get close to that deep.

 

[hockenbery]

Are there any recommendations for how deep a particular tool can safely go?

Safely is 99% on your skill level and hollowing method.
You can get a catastrophic catch a 1/4” deep.

If you want to know about hollowing effectively - the working overhang distance depends on the bar diameter, skill, and hollowing method.

A 3/16 hollowing bar works great ornament balls 4” overhang. Longer overhang the bar vibrates too much to be effective.
Lighter cuts can compensate but eventually you get to a depth where the cut has to be so light that you are barely removing any material.

What I do for general depth guidelines for myself
1/2” bar 7” deep
3/4” bar 9” deep
1.5” bar 18” deep. - I’ve not done anything deeper.

I could maybe hollow 12” deep with a 3/4” bar but it might take an hour to go the last 3” that i can hollow in 5-10 minutes with my 1.5” bar ( chip removal can take more time than cutting at depth)

 

[Shaun Tyler]

I'm thinking my problem has a lot to do with technique – or lack thereof. I’m using a carbide goose neck and I’m finding it “grabby” as I go further out (6 inches max). That’s why I was thinking it a leverage thing.

 

[William Rogers]

I would suggest that you set up a bowl blank and use your hollowing tools. That way you can see what is going on. I have carbide hollowing tools (cup type) but rarely use them. I think they take some getting use to to get past the “grabby” point. I almost always use my Jordan or Bosch tools with HSS cutters. I’m sure I could get use to carbide, but just like the feel of the HSS cutters better than carbide.

 

[Shaun Tyler]

I would suggest that you set up a bowl blank and use your hollowing tools. That way you can see what is going on. I have carbide hollowing tools (cup type) but rarely use them. I think they take some getting use to to get past the “grabby” point. I almost always use my Jordan or Bosch tools with HSS cutters. I’m sure I could get use to carbide, but just like the feel of the HSS cutters better than carbide.

I think stepping back and practicing on a bowl is a really good idea. And this is also my first time using carbide. I bought a set when I was getting started but then decided to stick with conventional tools but it had the hollowing tool so I thought I'd try it. I'll have to look into the HSS types to see what I like better.

 

[hockenbery]

I think stepping back and practicing on a bowl is a really good idea

You can see what happens when you set the tool rest close at the beginning of the straight bar and back at the 6” overhang depth.

Check how it cuts at a bit above center, at center, a bit below center.

If you tool lets you roll it (some have flats for one cut angle). Generally level or rolled down slightly work best
You can put a reference line on the tool,so you can check the roll angle when the curve is all the way in the form.

 

[Mark Jundanian]

You may already know this, but I'll just mention that no part of the "swan's neck" of a swan neck tool should be on the tool rest. So there is a minimum overhang.

I'm thinking my problem has a lot to do with technique – or lack thereof. I’m using a carbide goose neck and I’m finding it “grabby” as I go further out (6 inches max). That’s why I was thinking it a leverage thing.

I am assuming that you're carbide tools are flat top scrapers as opposed to cupped cutters. The two types require very different techniques.

 

[John K Jordan]

Are there any recommendations for how deep a particular tool can safely go? ...

I think the depth depends on the wood, the particular tool (and sharpness), the length of the handle, and the experience and skill (and maybe a tiny bit the strength) of the turner. Pushing things can be dangerous!

This is a bit sideways from the original question, but have you looked at a "captive" hollowing system like the Jamiesson?


I have this and it is allows more depth than most hand-held tools. The design of the system restrains the tool from twisting.

Mine has been converted to replace the laser with a camera - using an overlay on a monitor lets you easily see the wall thickness all the way down the sides. Works with small hollowing projects too. Makes life easier. There are several companies that make similar systems, but they are not cheap. But if handy at metal working, you can easily make a similar system for cheap.

Did you ever see David Marks' big hollowing project? Amazing!



He used a similar constraint/captive system.



If you've never met David, he's a fantastic, kind, patient, and creative person. I still have a burled blank from him.



JKJ

 

[John K Jordan]

Oh, here's the final result of David's big vase. I like the stand he made!



JKJ

 

[Doug Freeman]

Cutter type and size have a lot to do with how deep a given bar dia can go. The chip load (how much edge is cutting and depth of cut) is the major factor. Sharp hss can go deeper vs carbide - the sharper edge creates less load.

There’s also hogging vs finishing - initially you want material out, best accomplished with small cutters. I use 3/16” square hss tool bits or 8.9mm carbide flat top. These can be difficult to het a smooth surface, if desired. I’ll use teardrop scrapers to clean up the id if needed.

If you enjoy hollowing and want to go more than 5-6” overhang, I recommend a captive or articulated system, sized for depth. After you have a few catches and possibly blow up a few projects, you’ll understand why. As projects get larger, and hollowing takes longer, it’s a chore to keep your concentration. A hollowing system is a lot less stressful.