Bowl Coring ?

[Brian Grenia]

Using the One Way bowl coring system. Having all kinds of problems advancing the support finger on the #3 knife. When I turn off lathe to advance the support it binds. I can't get it to follow the knife curve further into the cut. (or else the cut is closing?)

After enough STRUGGLE I can advance it a little but it rubs a lot creating heat (think steam literally). I think that heat then exacerbates the problem.

Also my cutters don't stay sharp. it takes 3 or 4 to core the big bowl. I wonder if that's from the heat too? Anyway it's too much work to fight the support and remove-sharpen-replace cutters that much. Last night did a big ole maple bowl set. Little bowl popped out. Second bowl popped out. But the third (and resulting big 4th bowl) took over an 90 minutes!!!!! There has to be a solution or this thing is going in the trash. Ironically, it's the big bowl and the second bowl concept that led me to buy the coring system. I didn't buy it to save a bunch of 4 inch bowls I want it to save a bunch of 12 inch bowls and some time. Right now it's doing neither.

Anyone else have this issue and solve it?

Thanks.

 

[jschnell1203]

I would call Oneway. Also I would check the setup with them just to make sure.

 

[Owen Lowe]

Brian,

I'm going to ask the really obvious questions to make sure the basics are in place before anything else:

1) Are you sure you're using the matching support arm with the #3 cutter?
2) Is the cutting tip aligned with the center height of the lathe?
3) Is the support arm touching the underside of the cutter arm after ensuring item #2 is set?

I found on a set of mine (don't recall the knife size) that the support arm and knife arm are not parallel through the horizontal swing of the knife. In that case, I set the support height so that the cutting tip is supported at the end of the stroke regardless of the support at the beginning.

Steam will absolutely swell the wood fibers enough to bind everything up tight! Can you examine the 4th bowl wood piece on the lathe with the coring setup to see where the support is binding as well as examine how the cutter is traveling through the cut? If everything is still on the lathe this is easy to do but hard to recreate if the base of posts have been moved from the final position.

4) Are you using a relatively slow speed (500-800ish rpm) so that the friction is kept to a minimum and the shavings can clear the kerf?
5) Are you backing out the knife to clear shavings once you progress 1/2 way or so into the knife depth? I do this every 15-20 seconds as the knife approaches full depth.

You should be able to get at least one large bowl per cutter sharpening.

6) Are you sharpening with the same geometry that Oneway uses?
7) Is it possible the cutter is not hardened adequately from the factory? Will a metal file skate across top surface or does it leave file marks? You want the skating action.

That's the basics as I can think of them. I'll ponder some more.

 

[Bill Boehme]

Is there any chance that the blade is bent slightly? It needs to be a perfectly circular arc or else it will bind.

 

[Brian Grenia]

I think the cutters are good. Not having issues with smaller cores and the first part of the big bowl cut. But once it starts turning the corner then everything binds.

I'm clearing the chips often. Under 500 rpms. I'll check height again

It is almost as if the finger itself-as it enters the bowl- is too tall (not talking post height- talking the metal on the finger before the taper) As the bowl comes around it is hitting the finger at 7-7:30. If it was a wide kerf (say 5/8) it would clear but as it is the top left edge is binding at 9:00 and the bottom right edge at 7ish.

 

[Brian Grenia]

I'm using the oneway jig to sharpen
It doesn't look bent in the last inch before the post there is a little separation but I'm no where near this deep before the issues start.

 

[Owen Lowe]

I'm using the oneway jig to sharpen
It doesn't look bent in the last inch before the post there is a little separation but I'm no where near this deep before the issues start.

Maybe it's just the angle of the photo, but it appears the cutter is sitting on a pile of shavings and is canting downward and sorta to the right as well. I think this would cause some pretty tough coring. Make sure the grooves of both the knife arm and the cutter are mating cleanly and securely.

 

[Bill Boehme]

Rubbing could be caused by several things. A dull or worn out cutter is the most likely. The cutter should be making a 3/8" wide kerf. Other problems could include setting the coring system at the wrong height or not having the pivot point distance set correctly for the cutter being used. You can check that the coring system is following a circular arc.I believe that for the large cutter that the radius is supposed to be 18 inches. There is a small amount of latitude on making the cut, but not much.

The first paragraph of these sharpening instructions is very important and might be the cause of your problem. Here is the first paragraph:

Successful coring with the Oneway Easy-Core system is very dependent on a sharp cutter. If the cutter is dull you will need to use excessive pressure on the handle, causing the knife to be forced off-line in the cut. As the cut goes deeper the groove will get more off-line and the cutter will widen the groove when you retract and re-insert the knife. If the groove gets too wide the knife will fall off the support causing a jam, and possible tool damage or breakage. Keeping the cutter sharp is the easiest way to avoid this.
​

Whether the cutter is sharp or dull, if you apply too much force, it will flex the cutter arm away from its correct circular path and cause the support arm to bind. The cutter arm will also likely bind. If it will not cut unless you apply lots of force then the cutter is either dull or worn out. Don't forget to sharpen the top of the cutter as well as the sides.

You mentioned that the support arm does not follow the cutter, but it is really supposed to be viewed from the perspective that the cutter arm must follow the support arm path. When it doesn't, something is wrong with the set up, technique (too much force), or the cutter is dull.

Here is some additional information from the Oneway site. You may already know this, but just in case:

When the entry cut is made, the support finger is positioned at the face of the bowl supporting the cutter blade.

The cutter is on a fixed arc and it becomes a simple matter of deepening the cut by exerting pressure with the handle. After progressing 2 - 3 inches into the groove, the cutter should be removed and the lathe stopped to re-position the support finger by introducing it into the groove. This procedure is continued until the knife reaches maximum depth. Tapping the edges of the core will break it lose, or it can be pried out with a minimal amount of force. Cores produced will have a smooth surface and be symmetrical.


Successful coring with the Oneway Easy-Core system is very dependent on a sharp cutter. If the cutter is dull you will need to use excessive pressure on the handle, causing the knife to be forced off-line in the cut. As the cut goes deeper the groove will get more off-line and the cutter will widen the groove when you retract and re-insert the knife. If the groove gets too wide the knife will fall off the support causing a jam, and possible tool damage or breakage. Keeping the cutter sharp is the easiest way to avoid this.
​

 

[John King]

The Video

Brian - I routinely core 12" to 15" bowls in mesquite and oak without the problems you are describing.

Watch the Oneway DVD titled "Easy-Core Coring System." If you setup and use the coring tools as described in the DVD, you should not have any problem with achieving great results.

Good luck! - John

 

[robo hippy]

The only time I have seen the Oneway bind is when the pivot point is not centered in the ways of the lathe. Because of the huge height of the entire cutting system, if you are wide by much on either side of the center, then the blade becomes kind of a square peg in a round hole as the two arcs (blade and kerf/cut) are different. You can have an 8 inch bowl arc, and a 7 inch blade arc. This is when you may have to move the center a bit to open up the kerf.

As for the cutter going dull, either you are not sharpening it properly, or you got a bad cutter. You should not have to sharpen more than once every couple of bowls.

I did have some cherry once that was incredibly stringy, and all I got from the cutting, no matter how sharp the tip, was a lot of smoke and steam. It cut the same way with my gouges.

robo hippy

 

[Brian Grenia]

Thanks for the replies. Here's what I've found. I was a little above center. The posts filled with some chips and raised about 3/16 above center. Don't know if that's enough to bind it up or not. We'll see. Also maybe the bowl was too small. It (second bowl) was 13 1/4. The #3 is for 13 inches so I thought but now I don't know. Oneway's website says plus or minus an inch. The training video ( Dave Lancaster) says #3 is for 13.5 to 15 inch. The website where I bought it says 14.5 to 16.5. It seems to me that bigger bowls allow more room in the arc to accommodate all the metal. I can see this being the fix.

Using the sharpening jig. watched Glenn Lucas and Lancaster both today. Seems pretty straightforward so I think the cutters are sharp. Same technique and cutters as use on the #1 And #2 knife without issue. I just can't advance the finger on the larger #3 knife. I thought the kerf was closing up b/c if heat but maybe the bowl was just too small and the arc started arcing not leaving enough room for the "tall" end of the tapered finger

 

[John Giem]

The excessive height of the cutter can cause the cutting edge to be above the contact point with the wood. This is similar to bevel rubbing without the cutting edge touching the wood. I always instruct turners that the first thing to do is verify the position of the cutter tip when the cutter bar is fully extended.
Your photo may be deceiving but it looks like the curvature of the cutter bar and the support finger do not match. They should align exactly. If they don't then either they have been damaged or you are mixing different sizes. Both the cutter bar and the support finger are curved along the vertical dimension to fit within the kerf and avoid binding.
The pivot point can be anywhere as long as it can be bolted down. The pivot point must be moved around to place the cutter tip at the correct starting point and to control the thickness at the bottom of the bowl blank. The position of the pivot should/cannot cause binding.
This may make more sense when you read the article 'Bowl Saver Systems' coming up in the February 2013 issue of the American Woodturner. (Yes, I did write it.)
I hope this helps.
John Giem

 

[Bill Boehme]

.... Your photo may be deceiving but it looks like the curvature of the cutter bar and the support finger do not match. They should align exactly. If they don't then either they have been damaged or you are mixing different sizes......

I sort of had the same impression from the images that things did not look like they fit together as well as they should. I am looking forward to the February issue.