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Hollowing deeper than 6 inches

Randy Anderson

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I've been using the DWay hollowing tool for a while now and completed about a dozen small hollow forms with it. It works fine for me so far and feel I've gotten the hang of it. That said, I'm still finding it a challenge to use near the bottom once I get to 6" in depth. Grabby and a bit hard to control. I have to take it very very slow and easy to work the bottom contour. Not sure if anyone else is using this tool but I think it's a typical style - cutter with an outrigger - so wondering if 6" is the max depth I should expect from a tool like this or if there is a technique I need to work on. I've changed the position of the cutter head and doesn't seem to help me much if any. I make sure I have a fresh sharp edge on it when I get to the bottom. Working with green wood, end grain, turning about 500rpm.
 
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Looking at the D Way hollowing tool, it says it's a 5/8" bar. So 6" depth probably it about the limit. I'm not a mathematician but there's probably a formula that predicts when the chatter becomes uncontrollable as the reach over the tool rest increases. The larger the boring bar diameter, the longer the reach. I use 3/4" bars (homemade) and 6" is pushing the limit with them too. In my experience endgrain is a lot harder to hollow as you near the center, especially with those pith centered pieces of wood. So that's straining the capacity of the tool too. Wood variety makes a difference also. I admit I've done a lot of heavy bottomed hollowforms just because I couldn't get as deep as I had hoped. I tell people it makes them more stable. ;-)
 

Randy Anderson

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I’ve done the same. I don’t fret with calipers or lasers on my wall thickness and try best I can on the bottom but at some point I call it a day. I do want it to look reasonably smooth when you peek inside and feel smooth for the depth of my finger. I got a quick reply from DWay and they confirmed 6” is really the max for the tool but said to try grinding one of the cutter heads to be a NR. That should make it easier to control. I agree. It will also let me lightly clean up the inside a bit. Will give it a try.
 
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Looking at the D Way hollowing tool, it says it's a 5/8" bar. So 6" depth probably it about the limit. I'm not a mathematician but there's probably a formula that predicts when the chatter becomes uncontrollable as the reach over the tool rest increases. The larger the boring bar diameter, the longer the reach. I use 3/4" bars (homemade) and 6" is pushing the limit with them too. In my experience endgrain is a lot harder to hollow as you near the center, especially with those pith centered pieces of wood. So that's straining the capacity of the tool too. Wood variety makes a difference also. I admit I've done a lot of heavy bottomed hollowforms just because I couldn't get as deep as I had hoped. I tell people it makes them more stable. ;-)
I think that depends on the boring bar and cutter. I use 3/4 inch boring bars from John Jordan and have had no problems going as deep as 16 inches side grain and end grain. I think alot of it has to do with the 3/16 cutting bit not being as grabby as some of the bigger carbide cutters other brands use.
 

hockenbery

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I think that depends on the boring bar and cutter. I use 3/4 inch boring bars from John Jordan and have had no problems going as deep as 16 inches side grain and end grain. I think alot of it has to do with the 3/16 cutting bit

I’m impressed! I’d say it says more about your skill.

I have a couple of 1.5” bars. I rarely go deeper than 10” with a 3/4 bar. I have done 12 but then even with the 3/16 cutters I use it is slow going because I can’t remove wood as fast that far over the tool rest.

the beef in the larger diameter bars let’s be remove wood at a reasonable pace.
 

john lucas

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I'm with Al. I fight the tool beyond 10" with a 3/4" bar and 3/16" cutter. I use 1/2" bars up to 6" with the small cutter. That's in a Jamieson captured bar.
 

Dennis J Gooding

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There are several factors involved here. First of all, for a given load, the deflection of a tool that is rigidly fixed at the tool rest will increase as the third power of the reach. For example, in this situation, if the reach is increased by 25%, the deflection will double. Furthermore, the tool is not rigidly fixed at the tool rest, but is held down some distance away by the turner's hands so the tool bends still more on that side of the tool rest.

Second, the Dway tool, while controlling torsion of the bar, does not control the vertical aspect. In other words, it cannot be adjusted to maintain a desired vertical base position of the cutter with respect to the center of the turning. In contrast, hollowing systems such as the Jamieson have two tool rests and can be set to maintain a desired vertical position as well as controlling torsion.

Third, as best as I can see from the pictures I can find, the Dway is using rather large cutter so that the turner must contend with rather larger cutting forces. Personally, I use a very small (3/16 inch) scraping bit for most of my hollowing, even with a system such as the Jamieson.

Despite these difficulties, some turners such as John Jordan have done some amazingly large pieces using simple tools. However, my recommendation for any new turner wanting to hollow much beyond 6 inches reliably is to invest in a boring bar system such as the Jamieson. As a bonus, one can add laser or camera position guidance.
 

Randy Anderson

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I see the reference to a 3/16 cutter several times. The cutter in the DWay tool is a slotted mount with a set screw. The actual rounded cutting end is not very wide but bigger than 3/16. I've wondered about fashioning a different cutter or reshaping one of the ones I have for it to use when I get out further from the tool rest. Wouldn't be hard. I have some HSS material I use to make NR scrapers that might work. Going to first try shaping one of my existing cutters to a NR but, that won't remove much material so not sure that gets me to my goal. What shape is the 3/16 cutter? Rounded, point?
 

Dennis J Gooding

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I see the reference to a 3/16 cutter several times. The cutter in the DWay tool is a slotted mount with a set screw. The actual rounded cutting end is not very wide but bigger than 3/16. I've wondered about fashioning a different cutter or reshaping one of the ones I have for it to use when I get out further from the tool rest. Wouldn't be hard. I have some HSS material I use to make NR scrapers that might work. Going to first try shaping one of my existing cutters to a NR but, that won't remove much material so not sure that gets me to my goal. What shape is the 3/16 cutter? Rounded, point?

The ones that I use are bits intended for metal lathes. I grind them to roughly a half circle. I will try to post some example pictures of how they are mounted tomorrow.
 
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I use Trent's tools and his 3/4" stabilizer and once I get over 8" deep you really have to slow down and focus. I have gone almost 12" deep on end grain and ground his cutter a little smaller in size. I made myself a steady rest and found it to be a big help after 6" deep. When I set it up I just have to play around with how much support the wheels supply at a given RPM to get the smoothest ride.
 
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I see the reference to a 3/16 cutter several times. The cutter in the DWay tool is a slotted mount with a set screw. The actual rounded cutting end is not very wide but bigger than 3/16. I've wondered about fashioning a different cutter or reshaping one of the ones I have for it to use when I get out further from the tool rest. Wouldn't be hard. I have some HSS material I use to make NR scrapers that might work. Going to first try shaping one of my existing cutters to a NR but, that won't remove much material so not sure that gets me to my goal. What shape is the 3/16 cutter? Rounded, point?

In deep hollowing, less is more. That is, the smaller the cutter, but not too small, will reduce the chance of vibration. So the 3/16 size was concluded to be the compromising size that could take off a reasonable amount of material with the least amount of vibration and/or stress on the wood. Another reducer of vibration is to be able to shear or slice the wood vs scraping it off. Cutters like the "hunter 3/16" carbide or HSS cutters ground and presented to the wood on an angle were designed to do this. The Hunter cutter is sloped at around 30 degrees.
Here is some info on what the cutter looks like and the presentation of the cutter to the wood.
https://www.yumpu.com/en/document/r...rstanding-all-3-cutting-actions-lyle-jamieson

A third reducer of vibration, is instead of taking one cut that is long in duration, try taking multiple short and lighter cuts.

Sometimes the above 3 make enough of a difference in being able to hollow another few inches of depth or not.

Hope this helps
 
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The earliest arm brace hollowing tool came with a tip that would hold a 3/16" HS steel tool bit and a slotted teardrop scraper. The tool bit is used for rough cuts and works because it puts less strain due to the small cut or should I say scrape. The tear drop scraper is used to smooth over the mess that the tool bit left.
Excuse me if I repeat myself but there are 2 manufactures in NZ that make genuine cutting tips for hollowing plus the Canadian MFR of the termite tool.
 

Dennis J Gooding

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The first figure shows some of the shop-made cutters that I use with my Jamieson boring bar system. Each cutter is a piece of 3/8 " steel rod drilled to accommodate the 3/16 " tool steel bit and bent to the desired shape by heating to red with a torch. The the 3/16 bit can be epoxyed into a slightly oversized hole, or with more effort driven into a 1/4" slightly undersized hole. The kcutter on the far right is a shear scraper used with a light touch to smooth out the tool marks of the smaller bits.

The second figure shows some of the shop-made torque-arresting tools that I use for relatively shallow hollowing tasks.

IMG_6202p.jpg IMG_2748p.jpg
 

Randy Anderson

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Thanks for all the tips. I think I've got a plan for modified/different cutters for the bottom and cleanup that will let me dive a bit deeper next time.

Dennis, cool set of tools. I'm a big fan of making your own stuff.

John, as Russel says if you can steal a set of good roller blade wheels from your kids (that's what I did) they make great rollers. There are plans on youtube for making your own steadyrest. It's a good project and a very handy contraption to have on hand.
 

Dennis J Gooding

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Thanks Randy. I also built a steady rest using skate wheels. Tip: If your are going to be hollowing with laser or camera guidance, try to set the size and wheel orientation of the steady rest so that it does not conflict with these items or the boom that holds them. DAMHIK
 
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I think a teardrop cutter is very versatile and need not be restricted to final smoothing. if you orient the pointy end correctly, it presents the same amount of steel to the wood as a 3/16 inch cutter.
 
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I think a teardrop cutter is very versatile and need not be restricted to final smoothing. if you orient the pointy end correctly, it presents the same amount of steel to the wood as a 3/16 inch cutter.
What you say is correct and keep in mind that the point tapers like a wedge which means that it can't make as deep a cut. The problem with the tool bit is that it can easily dig in then you have to move it out of that narrow slot and feel around for the edge to continue the cut where as the wedge has cutting edges that work to recover from a lesser dig. I have the original arm brace and the tool bit holder but I have not used the tool bit for at least 20 years.
 

John Jordan

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I see the reference to a 3/16 cutter several times. The cutter in the DWay tool is a slotted mount with a set screw. The actual rounded cutting end is not very wide but bigger than 3/16. I've wondered about fashioning a different cutter or reshaping one of the ones I have for it to use when I get out further from the tool rest. Wouldn't be hard. I have some HSS material I use to make NR scrapers that might work. Going to first try shaping one of my existing cutters to a NR but, that won't remove much material so not sure that gets me to my goal. What shape is the 3/16 cutter? Rounded, point?
The trouble is sometimes the teardrop is too large. You can grind the tip a little smaller to be about the same size as a 3/16 tip. I don't see where trying to make a negative rake would help anything. Sharp tools and a lighter touch are what's needed. Dave Ellsworth used to use a 1/8" cutter in some of his very large pieces to reduce the size of the cut.

John
 

John Jordan

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Chris, you're doing well, you must have a light touch. That's not easy, but doable.

John

I think that depends on the boring bar and cutter. I use 3/4 inch boring bars from John Jordan and have had no problems going as deep as 16 inches side grain and end grain. I think alot of it has to do with the 3/16 cutting bit not being as grabby as some of the bigger carbide cutters other brands use.
 

john lucas

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John. I find a negative rake on my ornament hollowing tools makes them a little less grabby. Does not reduce chatter when you get deep. They are round shaft and the tip is ground just like your cutter.
 

Randy Anderson

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I ended up not regrinding one of my cutter heads to be a NR. As I sharpen them I'm gradually making the tip a bit narrower while leaving the teardrop shape. I find that if I orient the cutter outward (more toward center and away from outrigger arm) it only makes it worse re chatter and tendency to grab. Makes sense, the torque gets in line with the tool arm vs the outrigger so less support. For now it's 6" as my target depth and light cuts at the bottom. I may make a few from the HS steel blanks I have to try different shapes and sizes.
 

Dennis J Gooding

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John. I find a negative rake on my ornament hollowing tools makes them a little less grabby. Does not reduce chatter when you get deep. They are round shaft and the tip is ground just like your cutter.

John, I would agree that the NRS may work better when hollowing straight in. However, when cutting cross-wise into the side it yields exactly the same cutting angle to the wood as cutting at an appropriately higher point above center. Dunno what happens between these two extreme positions.
 
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