Oh no, more experimenting ahead.....

[Reed Gray]

I got to see Eric Lofstrom on Thursday night up in Salem, OR. Looks like an entire different set of experiments in NRSs' (negative rake scrapers). Eric's NRSs all have burnished hooks on them rather than the standard grinder burr. He can rough turn with them, and his burr leaves a surface that pretty much doesn't need sanding.... I have to check back with him about his angles, but most appear to be in the 70 bottom/20 top, but some are more like 50 bottom and 20 top. His burnishing tool is wood handle with about a 1/8 inch carbide rod inserted into it. I took a piece of drill rod, drilled a hole in the end, and put a small carbide drill bit into it. Tried it first on my 30/30 NRS, and just now on my 70/20 NRS. I did a small spindle, then a small madrone bowl. It leaves about a 320 to 400 grit surface. Really! The trick seems to be the small diameter carbide rod. I may have been burnishing wrong all these years.... Anything to cut down on sanding time.

There is a picture of his tool at the bottom of the file on sharpening:

http://www.ericlofstrom.com/resources/

robo hippy

[Ted Calver]

Thanks, Reed. I'd like to give it a try. Now to find a source for those rods.

[Tim Tibbetts]

Got mine via Amazon, unfortunately, price has nearly tripled since I got it in 2015. https://www.amazon.com/gp/product/B007001F52 Eric is a fantastic demonstrator, we are very lucky to have him in our local club. I've seen him several times on multiple topics, always learn something new. And doubly glad we have teachers like him in our local school system!

[Mark Greenbaum]

I've used carbide rods from welding supply house for burnishing platinum jewelry for many years. I believe they're 1/8" diameter carbide for TIG welding.

[John K Jordan]

Thanks for the link to Eric's resources - what I've looked at so far have been good.

As we discussed before, I burnish the scrapers with a carbide rod which gives an edge I think lasts longer and cuts better than the grinder burr. I use a polished 1/4" rod - I never thought of using a smaller diameter. I wonder if the smaller diameter would deform metal with less force. I've been pretty happy with the 1/4" rod.

I would want a polished rod for burnishing.

I see Amazon sells polished carbide rods in various sizes including 1/8" for not too much money. Here is enough to share with friends.

https://www.amazon.com/Diameter-Carbide-Precision-Polished-Chamfer/dp/B01EBC5YBM

JKJ

[Reed Gray]

I am thinking that the diameter has some thing to do with psi pounds/square inch. I notices a long time ago that I got a better burr with my triangle burnishing tool than I did with my round burnishing tool, so now I am thinking square stock or triangle stock if it is available. The difference in psi would be little, but no idea how to measure it. Beyond my abilities. Also, I am wondering if I can polish the carbide, given all the different types and nano grain stuff on the market...

robo hippy

[John K Jordan]

Also, I am wondering if I can polish the carbide, given all the different types and nano grain stuff on the market...

I know you can polish carbide with diamond. It shouldn't be impossible to round over a corner of a square carbide stick with some diamond stones/hones. I've polished a little carbide with some diamond compound pastes.

Hey, I saw diamond-coated sandpaper the other day. That's a new one on me.

JKJ

[David C. Roseman]

I am thinking that the diameter has some thing to do with psi pounds/square inch. I notices a long time ago that I got a better burr with my triangle burnishing tool than I did with my round burnishing tool, so now I am thinking square stock or triangle stock if it is available. The difference in psi would be little, but no idea how to measure it. [snip]

I'm thinking one of our resident engineers will weigh in with the answer. :) In the meantime, I'm willing to bet that the difference in psi is simply the difference in surface contact area of the burnisher at the edge, hence directly proportional to the difference in the diameters of the two rods. :cool:

[Jay Mullins]

Thanks Robo for sharing Eric LofstrJay Mullinson's site, lots of good ingormation there.

Jay Mullins

[Ryan Mooney]

I wonder if the smaller diameter would deform metal with less force. I've been pretty happy with the 1/4" rod.

I would want a polished rod for burnishing.

I see Amazon sells polished carbide rods in various sizes including 1/8" for not too much money. Here is enough to share with friends.

https://www.amazon.com/Diameter-Carbide-Precision-Polished-Chamfer/dp/B01EBC5YBM

Same force over a smaller area means higher pressure. I'm not sure on the actual contact space because I think the metal being deformed probably changes it a bit so it starts getting outside of my ken pretty quickly, a 1/8 would be slightly more than 1/2 the average contact area than 1/4 though (maybe 3/4 the contact area?)... if I'm reckoning about right.

Reeds idea of square or other stock with a slight aris on it is intriguing. Even an old router bit with a slight round over polished on it might work.. Hmmm...

[John K Jordan]

I'm not sure on the actual contact space because I think the metal being deformed probably changes it a bit so it starts getting outside of my ken pretty quickly

Yes, I spent some time reading technical papers and articles on deformation of metals from pressure contact, mostly from theoretically undeformable spheres (apparently a favorite physical construct on which to base equations) and quickly reached the limit of my working understanding math, physics, and material science, reinforcing my feeling that yes, given a constant force the diameter will definitely make a difference, buy no, other than to say it would I could not understand the details and predict just how it might apply to the cutting edge of scrapers without a great deal of study. (and probably with consultation with some friends) By the time I can get to analyzing this I'll probably be to old and senile to do it (or care!)

JKJ

[John Grace]

I spent some time over the weekend reviewing this site and there's a wealth of information there. I think his diagrams would be useful to any woodturner...some of the most clear depictions I've found to date.

[Reed Gray]

I think today's project will be to try the triangle burnisher and see if there is a difference. Eric uses the carbide because he said that is best for raising a burr on M42HSS, and looks like he uses D Way tools from the profiles. I have 2 standard HSS NRSs' and one V10 which is a 70/30 now, wanted to see if the more acute angles made a burr difference.

robo hippy