Bent McNaughton Coring Blades

[DaveL]

I finally got to use my McNaughton system and during the first bowl the medium blade bent and twisted. This was the first bowl so i was inserting the tool very slowly and the lathe was spinning about 350 rpm when the blade twisted in the gate and the blank wedged on the blade. When i pulled the blade out of the blank it is bent and twisted right where the blade curves.

Are the blades really this fragile?
How does everyone keep the blades from bending?
How do you submit a warranty request?

Any suggestions and or comments are appreciated.

Thank You,
Dave

 

[Greg Kaldor]

Dear Dave,
When I first started using the system I to had diffuculty bending blades. What I did and what worked for me was heat up the blade to red hot and bend back to normal. However care must be taken to keep radius correct. Picture this, when point of entry is started body of blade will clear if blade was bended back to normal shape. Be advised that it will not be perfect. A small amount of error will be allowed and will still core.

Greg

 

[Bill Grumbine]

Hi Dave

I have bent a couple of blades in the past using my KM tool. They usually bend because they are either being forced too hard into the wood, or the blade is not set up properly with respect to the gate. More often than not it is the latter, although I cannot say exactly how you bent yours. The tool needs to be set up so that the tip is right on center, and the blade is up against the top of the gate. This way the tool will not flop around, beating you up while you core, and there is a lot less chance of bending it because the forces on it are constant. I usually core at about 700-800 rpm with a 2 HP 3 phase motor, and since I figured out how to set the tool up, I have not had problems with bending blades, unless I get a little too aggressive, which is how I bent the second one.

If you go to my personal website, www.enter.net/~ultradad, you can see a pictorial tutorial on how I use the tool.

I hope this helps you out some.

Bill

 

[GeeSeaWhy]

I've been using the McNaughton system for a while and, touch wood, have never bent a blade. Torn a few blanks off their tenons, but never damaged a blade. Are you sure you had the blade in the correct slot - the narrowest one the body of the blade will slide in? What lathe do you have? My Nova DVR isn't exactly overpowered for coring and stalls fairly often - that's OK, I'd rather have the motor quit than keep going and bend the blade.

I find that even in the correct slot, the blade sometimes tends to rotate clockwise and that's what jams it. All I can do is try to keep a good grip on the handle to resist the twisting. It may be that keeping the feed rate up also helps by keeping the whole of the cutting edge under pressure. And as Bill noted, setting the tool up correctly is critical.

HTH

Graeme

 

[Mark Mandell]

Dave,

I wonder about your set-up. If you have your guide/holder block set too far away from the wood, you will have a lot of space where the blade is unsupported by either the kerf or the guide. A catch in the situation where the guide block is set back from the face would, I think, put a twisting force on the knife sufficient to bend it; a somewhat loose banjo will amplify that as well. I set my holder up as close as possible to the wood face, usually just enough to allow the blade's flair to clear the wood, and make sure the holder is rock solid. I also make sure to keep the blade up tight against the t-bar in the holder.

Are you allowing the blade to self-guide in the wood? Are you trying to cut a radius that's different from the shape of the knife in use? 1. is good; 2 is not.

Just my thoughts.

Have you contacted Kelton?

Mark

 

[DaveL]

Thank You for your assistance.

Gentlemen,

I appreciate all of the advise. I contacted Greg Jensen, the MN rep here in the US, and as soon as i started to explain what happened he was able to finish the sentence.

He reiterated basically everything that you all stated in your posts and then he also stated that the tool feed rate has a lot to do with bending the blades. While coring the side of the bowl pressure is applied to get knife to cut the grain, but as you make the turn to start across the bottom the knife wants to self feed and if you are still applying pressure it will grab and possibly bend the knife. He said that if the pressure you apply when cutting the side is 10 then the pressure across the bottom should be 1 or 2.

Thanks again for all of the information and guidance.

Dave

 

[Jeff Jilg]

I've also got a new McNaughton (large) coring system. It seemed a shame to see 20 gallons of shavings from large bowls, when those shavings could have been a bowl. There's some good advice in this thread that I've followed. I successfully pulled a 11" core from a 15"x7" ash blank today. The wood was wet.

I went slow mostly thru the whole thing. Also I stalled the motor piece a few times. But the belts are setup loose so that a catch like this is not as harsh. In this piece I kinda went too far, and the core fell out and rolled to the ground. It was only 300 RPM so no real harm done.