Hollow form and steady rest

[Peter Jacobson]

I am curious about people's experiences with larger hollow forms. I am contemplating a piece of wood in my shed that is about 15" diameter and 20" long (it might end up a little smaller than that by the time it is trued up and shaped). I do not have a steady rest. I generally use the Trent Bosch hollowing system for my hollow forms. Am I biting off more than I ought to chew? What's the largest piece you've hollowed without a steady rest of some sort? Thanks for any advice.

 

[Richard Coers]

The Bosch hollower is definitely not going to do well going 18-20" deep. That's going to be an expensive hollow form, probably around the neighborhood of $2,000 for a Steve Sinner hollowing system and steady rest. I bring up a steady rest when I go deeper than 6". Not completely needed at that depth, but much less vibration.

 

[Lyle Jamieson]

I am curious about people's experiences with larger hollow forms. I am contemplating a piece of wood in my shed that is about 15" diameter and 20" long (it might end up a little smaller than that by the time it is trued up and shaped). I do not have a steady rest. I generally use the Trent Bosch hollowing system for my hollow forms. Am I biting off more than I ought to chew? What's the largest piece you've hollowed without a steady rest of some sort? Thanks for any advice.

Hi Peter,
A hollow form the size you are talking about will exceed the limits of any hollowing system with a 3/4" boring bar.
I don't use a steady rest, because the methods, techniques, and tools that I have developed, prevent the vibration to begin with...and are safer. To do a 15" diameter hollow form you would also need a more versatile system that can reach a more bulbous shape... I can explain the pros and cons in more detail if you would like....call me anytime!
You can get my number from my website.

 

[Randy Anderson]

My experience is that over about 12" you'll need more than a 3/4" bar and a steady rest. Even then it can be no fun and a tough slog for the last few inches. I've gone to about 18" with a 3/4" bar (won't do it again) but also have a tool rest that can extend into the piece that provides a bit more support. I now use a 1.25" captured bar setup to go that deep or deeper and use a steady rest. It's a very tough job to hollow that deep without more robust equipment and a steady rest.

 

[DON FRANK]

If you are a member of a local club reach out to other members to see if you can borrow a bigger system or go to a friends place after you have it turned and hollow it there. Also, I like Lyles method of using a faceplate instead of a tennon and chuck on most hollow forms. The extra couple inches of wood that you waste is well worth it.

 

[Leo Van Der Loo]

I have a 15 inch hollow form. turned it about 15 years ago, I made it in two pieces, it has sat in my shop and I just now made a picture of it.

It is one way to turn a larger piece without hurting anything, like you or your machinery, and a lot less costly, all held on a faceplate.

 

[hughie]

For me if the opening is big enough I can use it to push the toolrest in. But much of what I do this doesn't suit. So I use 20mm 316 stainless for my main bar 316 is food grade, but it is also one of the stiffest steels around and so value for money, you can go out and purchase very high tensile steels such as 4140 and so and pay a premium. Alternately if you have any access at to Pneumatics or hydraulics the piston rod of say a 3-4" or 75-1--mm cylinder has some super fancy and very steel along with the fact it will be hard chromed. I have a couple, and they are the best by far. Perhaps more importantly is what you use as a cutter, as this will have a direct bearing on vibration and catches. I use the shielded variety of tungsten cup cutters such as the Woodcut Pro-Forme and Rolly Munro Wunderkut 10, plus a couple of shop made shielded cutters. If you're just getting into it drop your speed down low as this will give time to react if needs be and also the slower speed give better control. I find some sort of light [Cindy Drozda sells one] helps greatly. I tend to use the Pro-Forme for bulk removal and the Wunderkut for finishing.

 

[Peter Jacobson]

Thanks, guys. I'm rethinking my approach to this project...

 

[John Tisdale]

Peter,
As to your steady rest question, take a look at Keith Clark's - you'll be hugging yourself for a long time if you go that direction.
I looked at your website - you're clearly no beginner.
While there are several much more talented than I that will take issue, my approach is "size matters". A 20"-dia piece gets attention, and a much much higher price, than a small piece.
So instead of "rethinking", put it on the lathe and solve the inevitable problems as they come up.
If your opening sentence said 24"-dia, the issues and the learning curve would be the same. Assuming you have a big-boy lathe and a place to work, go for it - moderation is for monks.
John

 

[John Tisdale]

To Don Frank's comments: When doing a radial-grain (elliptical or globe} a faceplate is all you need - no need for a steady-rest. But on a tall axial-grain of any size, it's hard to beat the chuck / steady-rest combination.

To Hughie's comments above: Your quest for the stiffest steel is interesting - I've been pursuing the opposite thinking the "deader" the steel, the better. Then again, my toolrest goes inside the piece - I'm usually under 8" over - use a standard Rolle Munro 3/4" and can do a 22"-dia elliptical with no issue. The tall designs over 26" are a bit tasking requiring a longer internal rest - working on that now.
I do a lot of mesquite which is one of the, if not the, hardest in N. America Sometimes when 10" and more over the internal rest, I can get a chatter - drives me nuts. Best solution I've found is a pristine cutter, set to super fine, and speeds between 250 and 350-rpm - if the last several inches take over a 6-pack, so be it.

 

[Peter Jacobson]

Peter,
As to your steady rest question, take a look at Keith Clark's - you'll be hugging yourself for a long time if you go that direction.
I looked at your website - you're clearly no beginner.
While there are several much more talented than I that will take issue, my approach is "size matters". A 20"-dia piece gets attention, and a much much higher price, than a small piece.
So instead of "rethinking", put it on the lathe and solve the inevitable problems as they come up.
If your opening sentence said 24"-dia, the issues and the learning curve would be the same. Assuming you have a big-boy lathe and a place to work, go for it - moderation is for monks.
John

John,
Thanks for sharing your thoughts -- I like your approach.
Peter

 

[Doug Freeman]

FYI - for tool rests or boring bars (that hold cutters), the grade of steel is irrelevant. Stiffness (not strength) is a function of the base material (steel) and heat treatment, minor alloy amounts, etc does not affect it. Mild steel will dent easier (hardness related), but the amount a load at the end of a bar will deflect the bar will be the same regardless of the grade of steel. Yield and ultimate tensile strength are affected but not stiffness, and stiffness is the concern with “structural” components that bend like tool rests and boring bars. If you want dent or scratch resistance, harder grades do help.

 

[Darryn Achall]

My experience is that over about 12" you'll need more than a 3/4" bar and a steady rest. Even then it can be no fun and a tough slog for the last few inches. I've gone to about 18" with a 3/4" bar (won't do it again) but also have a tool rest that can extend into the piece that provides a bit more support. I now use a 1.25" captured bar setup to go that deep or deeper and use a steady rest. It's a very tough job to hollow that deep without more robust equipment and a steady rest.

Agree with this. I can go about 11" deep comfortably with the Bosch 3/4 arm and 3/4" bar. A bit more uncomfortably! I made an 1 1/4" bar that has a 3/4 tang to fit into the Bosch arm. I can get about 18" from that using light cuts. I use the steady rest when my piece is more than 8" tall or so depending also on the diameter.

 

[Thomas Kila]

This is a great thread! Giving me lots to think about before trying a large hollow form.