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Bowl From a Board Burning Blues

Joined
May 30, 2022
Messages
32
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46
Location
Camp Verde, AZ
Website
knotonboard.com
Greetings all ,

Getting back into turning after a several decade hiatus. Have progressed lately from twig pots, to segmented, to hollow forms, to hybrid resin, and recently onto Bowl From a Board.

The result of my first attempt (16" diam bowl) turned out OK but getting there was rather frustrating due to massive burning issues when parting off the rings (except the first ring).

I built a tool rest jig to steady the 1/16" Sorby parting tool along with later "sinking" the whole tool into a larger DIY handle. The first ring (at 45 deg. angle) parted off fine. The remaining rings
were a nightmare of burning wood (almost gave up several times). Tried varying lathe speeds, tool rest height, attack angle (45, 50, 55), flipping the tool, all to no avail.
The wood used is cherry, bloodwood, oak and walnut (all dry).

Any advice and/or suggestions (other than scrapping this idea for a bandsaw solution ;-) is most appreciated.

Here's a "project progress" link showing filmstrip of all pics from along the way - Burned Bowl From a Board

Thanks !
Steve
 

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I have yet to do a BFB, but it’s on my list. @Alan Miotke Al gave a really nice demo in Portland on his process. Great visuals—he might be willing to share the presentation file (I also think it’s located on the SWT site, but could be wrong - consider joining if you’re not already a member).

That said, considering your problem, I imagine the burning came about because of two reasons.

1) How often did you sharpen your parting tool? 1:16” doesn’t hold its edge for very long, especially with dry and dense hardwoods (mainly looking at you, Bloodwood).

2) You may be pressing too hard on the wood, especially the smaller rings. Like with gouge, the closer you move to center, the lighter your touch should be.

Aside from these, it may be helpful to use a diamond parting tool for this. The compromise is a wider kerf, but it can be quite helpful for reducing friction (especially when approaching sidegrain).
 
Greetings all ,

Getting back into turning after a several decade hiatus. Have progressed lately from twig pots, to segmented, to hollow forms, to hybrid resin, and recently onto Bowl From a Board.

The result of my first attempt (16" diam bowl) turned out OK but getting there was rather frustrating due to massive burning issues when parting off the rings (except the first ring).

I built a tool rest jig to steady the 1/16" Sorby parting tool along with later "sinking" the whole tool into a larger DIY handle. The first ring (at 45 deg. angle) parted off fine. The remaining rings
were a nightmare of burning wood (almost gave up several times). Tried varying lathe speeds, tool rest height, attack angle (45, 50, 55), flipping the tool, all to no avail.
The wood used is cherry, bloodwood, oak and walnut (all dry).

Any advice and/or suggestions (other than scrapping this idea for a bandsaw solution ;-) is most appreciated.

Here's a "project progress" link showing filmstrip of all pics from along the way - Burned Bowl From a Board

Thanks !
Steve
Sharpening between rings will help. Beeswax on the side of the tool will help.
Using a different tool or wider kerf will solve the problem.

That parting tool is going to rub on the smaller diameter rings unless you cut a wider kerf which you don’t want to do because it reduces the overlap. The binding of the tool is causing the burning. You will get the least binding with the tool above center by 1/2 its height.


If you have a diamond parting tool it will produce much less friction. They are generally less tall. And the wide part at the center line is the only part rubbing on most rings. You still can get a little binding on the smaller rings. A 1/16 extra clearance cut may do it there.
I have a tiny ancient sears parting tool that is about a 1/2” tall. I grind it at an angle so that the right side leads. It’s great for cuttin smaller rings.
 
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Hi,

That parting tool ought to be ok but it needs to be sharp. The other thing I’d recommend is giving it a little wiggle as you cut, your jig will probably prevent that, but a wiggle will slightly open the kerf and release any binding. I usually use an 1/8” diamond parting tool freehand and have never had burning. Looking at your finished bowl, you do need to work on your sharpening as those marks in the bowl’s end grain are from a blunt tool used with a lot of pressure. Try not to bully the work, it needs more finesse than that.

I hope that helps

Richard
 
Agree with Richard, looks like your parting tool is dull, for one thing, you're pushing it in too hard - it should be sharp enough that just touching it to wood it'll peel a whisper thin shaving - I find with mine , I need to resharpen or touch them up about every half inch or so of depth (I need better quality tool steel!) Also I made my own 1/16 parting tool out of an old machine shop hacksaw blade - it is just carbon steel, not HSS so I often have to sharpen that too. I also will swage it a bit before sharpening (This involves a little precision hammering to "squish" the tip wider than the blade - Swaging is one of the ways they'd "set" massive sawmill saw blades way back when) It creates the kerf for the blade to run in , then I resharpen , and it doesn't get stuck.

I want to get a diamond parting tool myself, but can't really justify the cost of a quality tool when my current tooling does fine, if I sharpen often (and considering how little I really use them, I don't mind the extra time spent sharpening) But as mentioned, you're binding the tool, pushing too hard, and IMHO it needs sharpening which might help with the first two issues.
 
You can try using a "cutoff" blade available from industrial supply companies. You would have to come up with a way to mount in a handle or buy a holder used with a machine lathe. I checked some companies just now and can't believe the prices.
You might try Ron Brown's new parting tool (P-type blade) with or without a handle. I might even buy one to replace my old homemade version. He also has his own "BfaB" jig in case you might be interested.

 
...my first attempt (16" diam bowl) turned out OK but getting there was rather frustrating due to massive burning issues when parting off the rings

Sounds like you need more clearance, some how.

I also prefer "diamond" parting tools, but I sharpen them differently than I've ever seen. And, as said, sharp, sharp sharp! Even parting tools should be ground and honed until they are shaving-sharp.

Another great type of parting tool (I don't remember the name of the one I have) is trapezoidal in cross section, i.e., the width at the top is the widest place in the cross section of the tool. Those I have look a bit like the one you are using but are made with a shallow flute ground all the way down the top edge of the tool. These cut very well and don't put friction on the sides of a straight cut, but those I have are fairly tall and might have trouble making the radius of the ring sections. If not afraid to modify one, most of the steel below the wide top could be ground away for a enough distance from the tip to cut through the board at the angle you use; you would lose a bit of stiffness but not much.

Also, if you have extra diamond parting tools and don't mind grinding one into a special shape, you can slim the tool behind the cutting edge for clearance. I keep a box of old cheap or free tools that I often grind to modify into special shapes as needed.

Also, since you are alternating the woods and don't have to keep the figure as close as possible to match, seems like you could simply cut wider grooves - cut a little depth then move over a bit and cut again, repeat. Might result in a slightly smaller diameter bowl if your board size is limited.

JKJ
 
You can try using a "cutoff" blade available from industrial supply companies. You would have to come up with a way to mount in a handle or buy a holder used with a machine lathe. I checked some companies just now and can't believe the prices.
You might try Ron Brown's new parting tool (P-type blade) with or without a handle. I might even buy one to replace my old homemade version. He also has his own "BfaB" jig in case you might be interested.

Tom- I see that Ron has a buy one, get 2nd one 25% off on his parting tool. I'd be happy to in on that with you.
 
As Richard say's you don't have enough clearance on the blade's sides. You should be able to see where it's rubbing and burning.

If you can't see where it's rubbing mark the blade on the sides with a felt tip marker. Do a cut, where the marker is worn off grind some relief.
 
Wow ... very much appreciate all the analysis/opinions/options/suggestions !!

Here's what I think I heard/learned so far -

Sharpening -
I forgot to mention in the orig post that the Sorby 1/16" parting tool I used is fluted
and I only sharpen the "bottom" bevel (back n forth between CBN wheel and diamond cards as I went).
Thought I was sharpening enough but I guess probably not.

Pushing too hard -
The burning definitely happened from side friction on the tool and only got worse as I went ... seemed like I had to keep pushing harder to
get past the pinch point when going back in, during multiple attempts on the same ring, to get to the point where the tip would start cutting again.
I realized pretty quickly I wasn't doing something right with my approach/tooling/technique/etc. but decided to keep slogging through on this one.

Diamond parting tool -
Agree that having the top cutting edge be wider than the "shaft" of the tool, along with a short shaft height, with minimal side tool contact, is key to allow for clearance
and minimize rubbing. The only diamond parting tool I have at the moment is an old school 1/8" kerf Shopsmith (non HSS) from back in the day.
I might experiment with grinding that down. A 1/16" diamond parting tool would be nice but probably to flimsy which is probably why nobody makes/sells one.

Ron Brown tools -
I had looked at Ron's product(s) at one point but didn't want to sink another 100 bucks into this endeavor. On reflection I may
go ahead and order his raw parting tool, make a handle, and give it a try.

Relief cuts -
I had tried this along with wiggling the tool but it wasn't enough to make a diff and was focused on keeping the cut width as small as possible.
Maybe my small mind is too concerned with a 1/16" kerf since I kept thinking using a 1/8" diamond parting tool would cause too much misalignment of
the different boards in the rings.

Ring Master video -
Thanks for posting this as I hadn't ever look closely at how that setup worked. Which led me down a few other YouTube rat holes last night ;-) Especially this one
on a "DIY Ringmaster" setup. Had seen some of Brian Procter's videos in the past ... quite the inventor.
I also dug through a box of old lathe parts someone gave me long ago and finally realized that one of the tools is a Oneway Drill Wizard. May give a friend of mine who's an expert machinist a call to pick his brain on designing a jig/cutters/etc. as more of a longer term project (and/or obsession ;-)

Going forward-
My next planned project is another large BFB using - Zebrawood, Paduk, Sapelle, Maple ... none of which I've ever turned (except maple) so I'm probably just asking for trouble.
-
Thanks again for all the advice from everyone. I'll definitely look at retooling alternatives, sharpening, less pressure, etc.
 
Steven,

If you use a parting tool that is fluted on the angled end, the flute should be down, not up, but you probably know that.

I think I mentioned I grind my diamond parting tools different from any way I've seen, although maybe others do to. After experimenting with some different methods, I think this method cuts best.

The widest part, the cutting edge, is right in the center of the tool. The three 1/2" tools pictured are all 1/8" at the widest point.
The slopes both above and below the center line provide clearance.
If having problems with clearance, I wouldn't hesitate to slope the upper and lower halves with a grinder or belt/disk sander, maybe even grind down the upper and lower edges.

I usually grind the top half to curve down to a point at the center and put a convex radius on the lower half.
Sometimes I grind the top edge so it's almost parallel to the center line at the cutting tip.

I try different grinds and experiment with them - some work better for some woods/situations.
It's important to hold the tool at the right angle. I'd try parting with it freehand with no jig to verify the best angle (the best angle might depend on the specific grind.)

parting_tools_grind_diamond.jpg

I love this type of parting tool - I think I have four or five, some different sizes, one that I made very small and narrow.
My favorites are these old Craftsman HSS tools - wish I could find some more.

Someone said "wiggle" in the cut but I'm not sure what was meant. What I do is keep the handle straight and very slightly (and quickly) rotate the tool left&right around it's long axis while cutting. Maybe that's the wiggle mentioned. The rotational "wiggle" cannot increase the width of the cut. The narrowed upper and lower edges of the diamond shape never contact the wood when wiggling (when parting straight into the wood - I haven't tried precision deep face-parting on thick disks.)

Oh, if I touch up the tool with a hone I only hone the bottom curve, then strop bottom then top for a sharp cutting edge with a leather wheel on a Tormek.
For touching up the edges of straight ground parting tools, all skews, and more I like to use polishing/honing compound rubbed into the rough resawn surface of a piece of MDF. Works better than anything else I've tried.

stropping-board.jpg

BTW, I use the diamond parting tools mostly with spindle turning but it's also great to hollow small end-grain turnings, for example these handbell ornaments.
Incredibly versatile tools!
bells_PC244161es.jpg hollowing_IMG_0426.jpg

Hey, am I the only one who doesn't like paduk? It would be nicer if it held the color longer. Well, I dislike wenge more but for a different reason...

JKJ
 
Al was dead on at the first. Widening the kerf is essential . I have a Ringmaster attachment and it uses a very narrow (height) blade and we crank it thru all at once. Your material looks thicker and you are using a steeper angle . With regular parting tools you can withdraw the tool to cool the wood and the tool as well as to slightly widen the kerf as you go. Remember you have a lot more metal in contact with the kerf than a Ringmaster machine does. SO cool it.
 
Steven,

If you use a parting tool that is fluted on the angled end, the flute should be down, not up, but you probably know that.

I think I mentioned I grind my diamond parting tools different from any way I've seen, although maybe others do to. After experimenting with some different methods, I think this method cuts best.

The widest part, the cutting edge, is right in the center of the tool. The three 1/2" tools pictured are all 1/8" at the widest point.
The slopes both above and below the center line provide clearance.
If having problems with clearance, I wouldn't hesitate to slope the upper and lower halves with a grinder or belt/disk sander, maybe even grind down the upper and lower edges.

I usually grind the top half to curve down to a point at the center and put a convex radius on the lower half.
Sometimes I grind the top edge so it's almost parallel to the center line at the cutting tip.

I try different grinds and experiment with them - some work better for some woods/situations.
It's important to hold the tool at the right angle. I'd try parting with it freehand with no jig to verify the best angle (the best angle might depend on the specific grind.)

View attachment 68579

I love this type of parting tool - I think I have four or five, some different sizes, one that I made very small and narrow.
My favorites are these old Craftsman HSS tools - wish I could find some more.

Someone said "wiggle" in the cut but I'm not sure what was meant. What I do is keep the handle straight and very slightly (and quickly) rotate the tool left&right around it's long axis while cutting. Maybe that's the wiggle mentioned. The rotational "wiggle" cannot increase the width of the cut. The narrowed upper and lower edges of the diamond shape never contact the wood when wiggling (when parting straight into the wood - I haven't tried precision deep face-parting on thick disks.)

Oh, if I touch up the tool with a hone I only hone the bottom curve, then strop bottom then top for a sharp cutting edge with a leather wheel on a Tormek.
For touching up the edges of straight ground parting tools, all skews, and more I like to use polishing/honing compound rubbed into the rough resawn surface of a piece of MDF. Works better than anything else I've tried.

View attachment 68580

BTW, I use the diamond parting tools mostly with spindle turning but it's also great to hollow small end-grain turnings, for example these handbell ornaments.
Incredibly versatile tools!
View attachment 68582 View attachment 68581

Hey, am I the only one who doesn't like paduk? It would be nicer if it held the color longer. Well, I dislike wenge more but for a different reason...

JKJ
John ... thanks for the info on your diamond parting tools and grinds ... I'll experiment with one as a future option ... BTW ... amazing bells.

I originally thought I was on the right track using the 1/16" micro parting tool and diy jig since I'd watched several YouTube videos where they used the exact same parting tool with no burn. Each inner ring started to pinch 1/2 way through no matter how many times I sharpened, how lightly I initially pushed, or "widening" the groove ... (live-n-learn).

Current thinking is to try Tom Gall's suggestion above with using a P-style metal cutoff blade and fab'ing a mount/handle (along with doing relief cuts as necessary) ... pretty much a similar approach as Ron Brown's tool. With the top cutting edge at 3/32" wide and the body at 1/16" should help some with clearance issues ... plan to order this one.

Also took some additional inspiration from this The Hobby Machinist NZ video.

Thanks again.
 
John ... thanks for the info on your diamond parting tools and grinds ... I'll experiment with one as a future option ... BTW ... amazing bells.

I originally thought I was on the right track using the 1/16" micro parting tool and diy jig since I'd watched several YouTube videos where they used the exact same parting tool with no burn. Each inner ring started to pinch 1/2 way through no matter how many times I sharpened, how lightly I initially pushed, or "widening" the groove ... (live-n-learn).

Current thinking is to try Tom Gall's suggestion above with using a P-style metal cutoff blade and fab'ing a mount/handle (along with doing relief cuts as necessary) ... pretty much a similar approach as Ron Brown's tool. With the top cutting edge at 3/32" wide and the body at 1/16" should help some with clearance issues ... plan to order this one.

Also took some additional inspiration from this The Hobby Machinist NZ video.

Thanks again.
Never trust what you see on youtube!
I spoke to a BFB guy at the Portland symposium. He made his parting tool from a table saw blade. Cut out a chunk, keeping just one carbide tooth. The tooth creates the clearance you need.
 
Laying out in CAD it becomes obvious quite a bit of relief is needed on the outside of the tool and just a bit on the inside would be good if the tool tip is on center. The amount of relief needed increases as the diameter decreases and/or the thickness of the workpiece increases. The angle of cut is an issue too.

There is a possibility not too much relief would be needed if the tool could be progressively angled and the tip lowered from center as the diameter decreases.

A machinist's P type cut off blade with relief on both sides could be used by angling the blade and lowering tip center with no grinding needed.

Thinking of this as being somewhat like a bowl saver cutter is shaped may help. The have significant relief under the tip.

bowl board.JPG
 
The thin kerf blades have very little difference between the teeth and saw body which I don't believe would make enough clearance too make a curved cut.
It is a straight in cut no curve. One thing I just thought of is lathe speed. A faster speed will cause more burn.
 
It is a straight in cut no curve. One thing I just thought of is lathe speed. A faster speed will cause more burn.
Better think that again since it is a cut into the face of flat board which makes it a radius cut verses using a parting tool on a spindle turning is straight in. Look at the burn marks on the photos and you will see that the burn starts after a significant amount of the cutter is in the cut.
 
@Don Wattenhofer & @Gerald Lawrence

I think you are talking past each other.

We all know the parting cut is a straight cut/scrape made at an angle to the face of the wood so that the rings will stack.
I suspect what Don is talking about is the fact that the width of the parting tool blade as it goes deeper does not conform to the curvature of the kerf created by said parting tool - as you go closer to center that curvature (Radius) becomes smaller, so as the parting tool goes deeper, more of its width (height if you want to look at it as being up and down direction from user's viewpoint) is touching or binding at top and bottom corners as it cannot conform to the curvature of the kerf being cut - the deeper you go, the tighter it fits - - If the parting tool could be shrunk down to more of a Square-ish dimension (1/16 x 1/4 perhaps) it'd likely have no such problem - but a 1/16" parting tool being what a half inch to 3/4 inch wide when you get deeper into the cut , is gonna bind on smaller radiuses.

At least that's how I'm understanding Don's argument.
 
There was a past thread titled something like this "bowl from a board does not need to be conical" explaining how to vary the angle to produce a non conicl BFOB. I had a parting tool that I had purchased back about 1995 used a machinists cut off blade, so I made a captured holder that could be set for the different angles. The cut off tool has a .06" (1/16" = .0625" wide cutting tip, the bottom of the cutter is about .046" (3/64" = .046875" and the height is about .5" or 1/2". The difference in width of the tool eliminated most of the binding except like BG said above the smaller diameters did cause some heat that shows as discoloring on the tool. Note visualize the face plate as the board being cut into rings.
IMG_1104.jpg
IMG_1105.jpgIMG_1108.jpg
 
is touching or binding at top and bottom corners as it cannot conform

It’s like everyone agrees this is what’s happening but are disagreeing on how to express it.

Yes you cut circles.
The binding will be top a bottom as you say on the left of the tool against the concave side of the ring being cut loose and at center on the right side of the tool against the convex side of the next ring.
Gets worse on the smaller rings - tighter radius.



It’s why the diamond parting tools work better for rings. Especially the ancient smaller Sears parting tool if you can find one - can’t have mine
 
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My point is that the cut (whatever the entry angle is ) will be straight in . As this is in a circular motion of the workpiece does make a curved cut but entry is still straight.. As to the size of the parting tool I also said that a Ringmaster blade is only about 1/4 inch tall. This height of cutter means as you have stated less friction and less burn. Only about 1 to 1.5 inches of the blade needs that reduction in height.
 
In the machining world this operation is called trepanning. It's commonly done to make holes either tapered or straight sided. Sometimes it's done to not waste the valuable core valuable material. A customer job needed expensive titanium tubing which is not readily available in a variety of sizes. Titanium is expensive in traceable certified material (not surplus material without alloy certification) so the cores had value. We precision ground tools by laying out the needed cutter relief as shown in the CAD drawing as in post #20 for short lengths of tubing. Trepanning of any kind needs tools with relief because any rubbing in metal is an immediate disaster. This is not rocket science, it's a simple a matter of laying out the cutter in CAD and using a radial relieving fixture in the tool grinder to create the relief. In this case hand grinding is sufficient because wood is tolerant of a bit of rubbing where metal is not.

All this speculation seems a bit nonsensical. It's obvious what the cutter design needs to be. For multiple diameters as needed for bowls the cutter for the smallest diameter would be used for all cuts.
 
If you need to see where or if the tool is rubbing, just mark it all over in sharpie and make a cut. The marks will be gone where it rubs. That will let you know where the tool shape needs to be changed.
 
Success !! ... I epoxied a machinist cut off blade into a diy handle and cut rings from a new BFaB glue-up (Sapele, Bloodwood, Zebrawood, Purpleheart).

Took many suggestions from above comments into account -

- Machinist cut off tool
- Cutting edge vertical height from center 1/2 of tool width (1/4")
- Slowed down approach and didn't force things
- Pulled out 3-4 times per ring and quenched tool in water each time
- Cleaned off tool and re-honed each time before going back in

Also incorporated a crude backstop to "catch" parted rings (attached to lathe ways via strong magnets).

Still had a little burn but MUCH better than original attempt. All burning constrained to the wider upper 3/32" portion of the cutter and the top (none at all on 1/16" lower part of the cutter)

Now on to ring glue-up, turning and finishing the bowl.

Without a doubt I would have given up had it not been for this great forum and it's generous members.

Thanks again for all the help from everyone !!
 

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What is your lathe speed? From experience too fast (greater than 700) can cause significant burning. There does not seem to be a set speed as diameter and wood species need to be taken into the equation. Possibly try a slower speed and see if that helps. Just a thought.
 
What is your lathe speed? From experience too fast (greater than 700) can cause significant burning. There does not seem to be a set speed as diameter and wood species need to be taken into the equation. Possibly try a slower speed and see if that helps. Just a thought.
Kept lathe speed right around 800 and slowed it a bit for the last "break through" cut. Will try a bit slower on the next one to see if it helps ... thx.
 
Another thing that MIGHT help a little more is to grind the bottom of the blade in a concave curve instead of convex ... and maybe the length of the curve. (your 2nd photo above)
Was wondering about that as well but figured since there didn't appear to be any rubbing/friction on the lower 1/16" section of the cutter (at least no visual burn marks) that
it wouldn't make much of a difference. May try it anyway with keeping in mind not to have too much of the top 3/32" hanging out there "by itself" to avoid it bending/snapping
in the event of a catch ... thx.
 
I made a special tool with good clearance and have never had any burn marks. Cutting time about 1 min/ring, no sharpening for several bowls.
K3_04937LRse.jpgK3_04937LRse.jpg

A good backup when cutting the rings minimises tear out at the break through.

In the below thread there is a description of how I make non-conical bowls from a board:


 
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