• February Turning Challenge: Choose Your Box! (click here for details)
  • Congratulations to Isaac Litster winner of the January 2025 Turning Challenge (click here for details)
  • Congratulations to Jim Grieco for "Southwest Diamonds" being selected as Turning of the Week for February 3, 2025 (click here for details)
  • Welcome new registering member. Your username must be your real First and Last name (for example: John Doe). "Screen names" and "handles" are not allowed and your registration will be deleted if you don't use your real name. Also, do not use all caps nor all lower case.

3' hollowing tools? And steel types

Joined
Aug 29, 2023
Messages
24
Likes
5
Location
Bemidji, MN
What type of steel might work best for a free hand hollowing tool with roughly a 36" shank?

So I've made a handle and actually an entire tool with swan neck with a 36" bar and a 50" handle and it works but the chatters not great I was able to make roughly a 6" tall 4" wide bowl with it at its maximum overhang with a relatively thin wall..can't find the photo of the turning on my new phone but I was able to recover a photo of the tool. The shank is 1" 1\8th diameter rod mild steel with a maybe 10" long swan neck made from stainless I bent. Now there's a man named Benjamin pnalitzer(I think) who has made some 3' and apparently 4' forms with what looks like a similar tool but with the chatter I saw, roughly 1\5" flex in my bar I can't imagine just how.

Now I've seen I think Steve sinners set up and such and that suggested one needs a 2.25" bar diameter but my experience and seeing Benjamin's work and tool I know this is not likely the case so I have a suspicions that steel type is a factor, and after seeing some of ed moulthrops tools I feel like I may just be missing something small.

Photos of Benjamin and then my tool. I hollowed that blank on the lathe with that tool with the rest in its photographed location.
 

Attachments

  • Screenshot_20250201-202537.png
    Screenshot_20250201-202537.png
    1.8 MB · Views: 95
  • FB_IMG_1738461978002.jpg
    FB_IMG_1738461978002.jpg
    103.8 KB · Views: 95
Steel type (chemistry) does not affect the stiffness of steel for all practical purposes. The modulus is the same regardless of steel type. Steel chemistry and heat treat hardness affects the yield point of steel, not its stiffness (modulus). It is section size (diameter in the case of round rod or tubing) that affects stiffness. More diameter = more stiffness. Chatter is the result of too much overhung length relative to the stiffness of the tool coupled with excessive load (force) on the cutting tool.
 
Steel type (chemistry) does not affect the stiffness of steel for all practical purposes. The modulus is the same regardless of steel type. Steel chemistry and heat treat hardness affects the yield point of steel, not its stiffness (modulus). It is section size (diameter in the case of round rod or tubing) that affects stiffness. More diameter = more stiffness. Chatter is the result of too much overhung length relative to the stiffness of the tool coupled with excessive load (force) on the cutting tool.
Well this response does give me some terminology I've been looking for. I did look into tubing vs rod and what I found there was mass effects the stiffness, as in a tube of the same mass will have the same rigidity, but I've also read counter information that the diameter of tubing is what effects it's stiffness. My conclusion there was. I want the smallest diameter and therefore if mass is the major contributing factor I'd want rod over tube.

I forget the exact answer I got on the point of inertia on tubing vs rod. I can say after using the pictured tool that the 2" white oak handle has greater rigidity than the 1 1\8th rod and that the not quite 2:1 ratio of handle to shank was enough with the handle in the armpit as far as the lever.

So tempering or steel type shouldn't effect this in any other way than tempering will make the steel more prone to breakage?

But this begs the question here, the man with the tool in the photo is using the same type of cutter on a longer rod of what appears to be a similar diameter and has been successful so what is the missing variable
 
Choice of steel will affect it. I have a 20mm high tensile pneumatic cylinder rod that works just fine to around 4-500mm and the type of turning tip or head has a part to play as well. Another example is 316 stainless it is very hard to bend even at red hot temps, 304 stainless on the other hand will bend cold easily..
The hardening and tempering is about 'how hard' it ends up as to whether it cracks/break etc if done right it shouldnt, its a fit for purpose thing.. Its hard to say if the tips are the same and the first image looks like it has the potential to have a greater over hang and that will be a contributing factor
 
I agree with the comments about steel type. I admit I’ve only seen a few deep hollowing systems online but the rig pictured in the OP is without doubt one of the longest and skinniest I’ve ever seen. I’d say you’d need to increase the diameter quite a bit to reduce vibration. Just my thoughts.
 
The cutter used will also affect chatter. A scraper type of cutter will always have chatter to a certain amount whereas if you used a Hunter carbide cutter which cuts not scrape you will see much less chatter.
 
Cross-sectional geometry of the bar is more important than steel type since the elastic modulus of most steels is very similar (around 29 million psi). This is a commonly misunderstood aspect of solid mechanics.

Tim
 
I’ve seen square bar hollowing tools in smaller sizes. Is there any reason not to use it for deep hollowing tools, or someone just not thought of it?
I’m thinking increased mass and stability. The business end of the tool could still be round if needed.
For gated systems it would be a trade off between extra stability versus increased friction but perhaps this could be mitigated with careful adjustment of the gate? Just a thought.
 
I agree with Bill Dwayne and Tim. Diameter is your solution. Going to tube from solid, you would need bigger diameter yet. Tube is only used to reduce weight and material for a given stiffness, but diameter would need to go up. Square cross section at the same size, I think would give you slightly higher stiffness.
The small hunter tools will help to reduce the load at the point of cutting which will be better over a large scraper tip.
 
I’ve seen square bar hollowing tools in smaller sizes. Is there any reason not to use it for deep hollowing tools, or someone just not thought of it?
I’m thinking increased mass and stability. The business end of the tool could still be round if needed.
For gated systems it would be a trade off between extra stability versus increased friction but perhaps this could be mitigated with careful adjustment of the gate? Just a thought.

Or maybe an added "rail" that it slides on? A square tube could have a smaller round (hardened?) rod attached to the underside to reduce the contact surface. Or maybe just use a square profile, but turn it up onto a corner. Or use a hexagon bar.
 
Or maybe an added "rail" that it slides on? A square tube could have a smaller round (hardened?) rod attached to the underside to reduce the contact surface. Or maybe just use a square profile, but turn it up onto a corner. Or use a hexagon bar.
I’ve seen lots of hollowing tools, some square some round, with a second rail, but these are to stop the tool rotating.
I was thinking more about the added mass of a square bar. A bit of added stability being just a small bonus?
Maybe some have tried square bars for larger hollowing tools though and it didn’t work out for some reason? I’m guessing it’s easier to buy round bar with a decent surface finish. Probably not so much for square?
 
You should talk to John Tisdale. Planet Mesquite I believe he uses a large diameter titanium bar with a custom toolrest extending into the neck of his large forms. Here Brian McEvoy uses a 2" steel bar to go 48" deep. Most deep hollowing is done with captured systems, both for safety and to support the heavy bars required.
 
Square cross section at the same size, I think would give you slightly higher stiffness.

Depends how you look at it. A 1" square bar is stiffer than a 1" diameter round rod. But they are not really the same size.

The maximum dimension on the 1" square bar is the diagonal (corner to opposite corner) at 1.41". That's what would determine how small of a hole you could enter on a hollow form. And if you compare it to a round rod with 1.41" diameter, the round rod would be stiffer. So I'd say stick to round bars if you want to work with small openings.

I guess with 36" deep hollowing, no one would have the patience to remove shavings through a small opening, so it's probably a moot point.
 
Depends how you look at it. A 1" square bar is stiffer than a 1" diameter round rod. But they are not really the same size.

The maximum dimension on the 1" square bar is the diagonal (corner to opposite corner) at 1.41". That's what would determine how small of a hole you could enter on a hollow form. And if you compare it to a round rod with 1.41" diameter, the round rod would be stiffer. So I'd say stick to round bars if you want to work with small openings.

I guess with 36" deep hollowing, no one would have the patience to remove shavings through a small opening, so it's probably a moot point.
As I mentioned earlier, there’s no reason not to put a smaller rod on the business end.
Then again there’s the twin welded rod option shown on this page.

 
Last edited:
As @Dave Bunge explained, a round rod is the stiffest shape to pass through a given opening, and as discussed, for a given size, solid bar is much stiffer than a tube, and type of steel is irrelevant for stiffness.

Using a tool rest that extends through the opening, to reduce overhang, works well. That can be done, but will require a larger opening bs a larger bar dia.

The amount of force applied to the end of the bar, determined by the cut depth and amount of cutting edge engaged, is the force driving the chatter. Surface cutting speed plays a role in resonance (as do all the previous mentioned factors). Its a design compromise of all of these factors.

I disagree that a cupped carbide cutter produces less chatter vs a scraper. I have Lyle Jamieson’s captive system, including the hunter 6mm carbide cutter that is angled at ~45deg. I can hollow deeper (maybe a few inches) with a sharp hss 3/16” square cutter vs the carbide. The hss cuts easier when sharp, producing less load. I mainly use the carbide cutter to clean up the inside.
 
Doug of course you disagree, what don't you? There is absolutely no doubt that the Hunter carbide cuts smoother with less chatter than a scraper. What you may also find is that the scraper leaves sawdust where the hunter leaves curls which might be harder to evacuate. I have never ever used a square or round HSS or other type steel scraper that does not chatter. With the big Hunter boring bar I can go about 18" with the hunter hollowers with the only sound is the slicing through the wood quickly and cleanly with very very little chatter. Here are a couple photos I took for an article.
 

Attachments

  • Fig4.jpg
    Fig4.jpg
    272.1 KB · Views: 20
  • Fig33.JPG
    Fig33.JPG
    348.5 KB · Views: 21
Doug of course you disagree, what don't you? There is absolutely no doubt that the Hunter carbide cuts smoother with less chatter than a scraper. What you may also find is that the scraper leaves sawdust where the hunter leaves curls which might be harder to evacuate. I have never ever used a square or round HSS or other type steel scraper that does not chatter. With the big Hunter boring bar I can go about 18" with the hunter hollowers with the only sound is the slicing through the wood quickly and cleanly with very very little chatter. Here are a couple photos I took for an article.
Hey Bill, I just believe my own eyes and experience more than anything else. After many comparisons of the cupped carbide vs a 3/16” hss bit in my shop on my equipment, the hss goes deeper before chatter brings an end to things. Yes the carbide cuts and leaves a smoother surface , but time and again I have been stopped by chatter using the carbide tool, and been able to change to a hss bit and get that last inch or 2 that I could not get with the carbide.
 
Doug I have been doing hollow forms (My favorite form) since I started turning almost 25 years ago. I have used every type of cutter imaginable so the only thing that I can think of that you are getting chatter with a Hunter carbide is that you are doing it wrong.
 
Choice of steel will affect it. I have a 20mm high tensile pneumatic cylinder rod that works just fine to around 4-500mm and the type of turning tip or head has a part to play as well. Another example is 316 stainless it is very hard to bend even at red hot temps, 304 stainless on the other hand will bend cold easily..
The hardening and tempering is about 'how hard' it ends up as to whether it cracks/break etc if done right it shouldnt, its a fit for purpose thing.. Its hard to say if the tips are the same and the first image looks like it has the potential to have a greater over hang and that will be a contributing factor
That was my instinct from working with metals in the past. As far as the first photo. I can tell it's a home made pro forme cutter with a depth limiter, Wich is what I use, as far as overhang, it does have greater potential overhang but we still need some leverage

Thanks for the reply
 
Depends how you look at it. A 1" square bar is stiffer than a 1" diameter round rod. But they are not really the same size.

The maximum dimension on the 1" square bar is the diagonal (corner to opposite corner) at 1.41". That's what would determine how small of a hole you could enter on a hollow form. And if you compare it to a round rod with 1.41" diameter, the round rod would be stiffer. So I'd say stick to round bars if you want to work with small openings.

I guess with 36" deep hollowing, no one would have the patience to remove shavings through a small opening, so it's probably a moot point.
I've already made a system for removing shavings while turning I use it for light bulbs just need to scale it.
 

Attachments

  • FB_IMG_1738190771306.jpg
    FB_IMG_1738190771306.jpg
    72.3 KB · Views: 12
As @Dave Bunge explained, a round rod is the stiffest shape to pass through a given opening, and as discussed, for a given size, solid bar is much stiffer than a tube, and type of steel is irrelevant for stiffness.

Using a tool rest that extends through the opening, to reduce overhang, works well. That can be done, but will require a larger opening bs a larger bar dia.

The amount of force applied to the end of the bar, determined by the cut depth and amount of cutting edge engaged, is the force driving the chatter. Surface cutting speed plays a role in resonance (as do all the previous mentioned factors). Its a design compromise of all of these factors.

I disagree that a cupped carbide cutter produces less chatter vs a scraper. I have Lyle Jamieson’s captive system, including the hunter 6mm carbide cutter that is angled at ~45deg. I can hollow deeper (maybe a few inches) with a sharp hss 3/16” square cutter vs the carbide. The hss cuts easier when sharp, producing less load. I mainly use the carbide cutter to clean up the inside.
Carbide is never sharp..it's always jagged, and a cupped cutter adds resistance as the shaving has to bounce off the cutter, I use a hook tool where shavings pass through and there's far less resistance, I found a way to cut with this thing at the over hang with the tool moving .5" Wich honestly would be fine for clean up but not hogging out the interior. What I did with the tool stabilized the bar.
 
As I mentioned earlier, there’s no reason not to put a smaller rod on the business end.
Then again there’s the twin welded rod option shown on this page.

The reason I want need round stock is how I manipulate the tool, I also cannot use a captured system for the same reason. If I can stabilize this tool I have the potential ability to make a 4' tall 1mm wall form, I've done it with 17" just trying to scale up
 
I don't know what steel or cutter he uses for his hollowing tools but Lyndal Anthony has hollowed over 4ft. He may have some insight for you. A couple photos of his homemade system are on his website. http://www.midwestwoodart.com/
Funny my dad invented the same tennon turning tool.

His bar seems overkill to me, there's a guy who makes 6' turnings that uses a bar the same size, but as discussed above choice of cutter is a huge factor.

Thanks for the link, honestly this was one of the most useful replies to this post
 

Attachments

  • 3e3d9be43ea45d95951ce007c31cb0d2.jpeg
    3e3d9be43ea45d95951ce007c31cb0d2.jpeg
    21.1 KB · Views: 26
As the owner of two Pro-Frome hollowers I have found that there is a bit of a learning curve that can be steep for some. But my advice would be to buy only the heads and then fit them to your own shaft and handle as I have done, my big rig shaft or bar is around 750x20mm or so it telescopes into the handle of similar length. As hollow vessels are my main thing the shop is set for that almost exclusively, short bed lathe with a big swing, lathe is set to my height and then some. I have the lathe set up with the center height so I can tuck the hollower into my arm pit and most of my hollowing is free hand. Although I have a couple of captured hollowers with lasers attached. I'm thinking of building another suitably tailored to my requirements, its just a matter of getting around to it.
 

Attachments

  • IMG_3167.JPG
    IMG_3167.JPG
    387.8 KB · Views: 13
As the owner of two Pro-Frome hollowers I have found that there is a bit of a learning curve that can be steep for some. But my advice would be to buy only the heads and then fit them to your own shaft and handle as I have done, my big rig shaft or bar is around 750x20mm or so it telescopes into the handle of similar length. As hollow vessels are my main thing the shop is set for that almost exclusively, short bed lathe with a big swing, lathe is set to my height and then some. I have the lathe set up with the center height so I can tuck the hollower into my arm pit and most of my hollowing is free hand. Although I have a couple of captured hollowers with lasers attached. I'm thinking of building another suitably tailored to my requirements, its just a matter of getting around to it.
Profomes just a hook tool for dummies lmfao. Anyway I've already built a similar size tool to yours, that was the first I did when I bought the thing because the retail handle was way to spendy for what it is. I'm just trying to scale it and determine what I need for a shank
 
Carbide is never sharp..it's always jagged, and a cupped cutter adds resistance as the shaving has to bounce off the cutter, I use a hook tool where shavings pass through and there's far less resistance, I found a way to cut with this thing at the over hang with the tool moving .5" Wich honestly would be fine for clean up but not hogging out the interior. What I did with the tool stabilized the bar.
"Carbide is never sharp etc" todays fine grained carbide is capable of taking a fine edge, check here.
 
Carbide is never sharp..it's always jagged...

Austin

That depends on the carbide grade and how you sharpen it.

TC that is not 'sub-micron' grade, where the carbide size is above 1μm, and you grind with diamond that is too coarse, like with <#1,000, then the larger carbide particles can be pulled out of the matrix at the cutting edge. However, it is best to use sub-micron or nano grade TC as that has been shown to give the best results for working with wood. I expect that most TC tips that are now supplied for woodworking are in that sub-micron or nano grades, but best to check on that if you are getting carbides breaking out of the edge...

Combinations-of-WC-grain-size-and-cobalt-content - cropped.jpg

I found that grinding with #1,000 diamond greatly increased the edge integrity and durability of YG6X TC, with 3x longer durability compared to sharpening with #120 grind and twice as long compared to a #800 grind. The improvement between #120 and #800 was only gradual, but significant when going up to #1,000.

Improvement in performance with #1,000 over #120.png
Sharpening/polishing with fine diamond grit can then take you down closer to the sub-micron size of the carbides. Of course, diamond is really the only option for sharpening/polishing TC. You can get a quite a high polish on TC with fine diamond grits and it is quite economical to buy now in both a paste or loose grit...

TC tip after polishing flute with diamond.jpg
I rarely ever use carbide inserts myself, but if I did I would keep them sharp by polishing then on a firm powered hone/strop (sharp edge trailing) with diamond paste and it is only takes seconds to do that. The grind that comes on many carbide insets is quite coarse when looked at under magnification. Here is one with the original grind on most of the bevel and the very tip that has been honed with diamond paste on a power strop... apologies for the extraneous fluff!

20241128_170539.jpg

But, if your TC grade and sharpening methods are quite different from this you results might also be quite different... :)
 
Profomes just a hook tool for dummies lmfao.

I'm not sure what the acronym 'IMFAO' means, but I'm among the dummies who use the Woodcut Proforme cutter head. I've used every style of hollowing tip that has become available on the market over the last thirty years or so, starting with the shephid loop cutter, and before that I used the hook tools that I forged myself and along the way the HSS Oland style scraper tips. Of those, dummy that I am, the Proforme cutter head and its swivelling scraper tip, which allows for inside shear scraping, is one of my favourites.

I'm not a hollow form specialist and only turn at most half a dozen of those a year, so can't speak with the same depth of experience as some others on this forum, like @hughie, but I have been doing it for a long time and well before any of those hollowing rig contraptions came along. If you couldn't do it 'free hand' it just didn't happen, so I'm a bit amused by those, but then the deepest I have hollowed is not much more than 12", so nothing like 36" deep. But then, in my market, very large pieces don't sell very quickly and take up a lot of gallery shelf space where two or three smaller pieces of the same collective value would have sold several times over.

Besides that, I'm also well past needing to make any statements with grandiose pieces. That's not to say that I don't admire large beautifully formed pieces made by others, although it is my general observation (albeit not universally applicable to the worthy members of this forum) that the aesthetic appeal can be in inverse proportions to the size of the piece.
 
Back
Top