Thread: The Burr

Hi David


The smell like dry rot, old atmosphere thats been trapped for long time- a bit like drilling a pearl and smelling a tiny bit of seawater that was trapped in there - not a great smell




Effectively the blades I ground and polished the lead are like the sketch. I have not noticed any deterioration in durability. Looking at exaggerating further and seeing if there's an effect.


Lets see sketch clarifies

toothed bevel side.png

Hmm - I've placed the smell of the old beech , it smells like an anaerobic digester - gee I really have hung around all the good places...

Cheers M

Sheoak is like that. The stuff grows like gangbusters on a beach coast or at the edge of a costal estuary. The lumber off of trees growing along the ocean dunes smells like ocean. The stuff growing along coastal estuaries smells like rotting seaweed and dead fish in hot weather.

Wouldn't surprise me to find similar with other trees. Wouldn't surprise me to learn that the stuff smelling like an anaerobic digester came from a tree growing on a hog farm... Beech nuts featured as a prominent
source of animal feed back in Ye Olde Days.

Originally Posted by MartinCH

Hmm - I've placed the smell of the old beech , it smells like an anaerobic digester - gee I really have hung around all the good places...

Cheers M

The only place I've been around an anaerobic digester is a relatively progressive backwards conservative set of brothers where I grew up - who realized in the mid 1970s they could capture the methane off of cow manure and find an out of service group of rural electric cooperative gen sets and then make electricity.

They did that starting around 1977 - not because they were green, but because they were cheap, and very kind of old timey american independent.

Or put differently, poop. poop digester.

I have planed the transition line in limba where it goes from light to dark and whatever the wood picks up and stores there, it definitely smells like a poop digester, too.

Originally Posted by IanW

"Sharp" is such a relative concept....

And, a good thing to be reminded of here amongst the gathered sharpologists, Ian.

As always, I have enjoyed the input and discussion.

I have nothing of value to add myself, but will ponder the input here as I go off to do further testing of the comparative 'sharpness' and edge durability of bowl gouges made of submicron grade Tungsten Carbide, V10 and M42 HSS when used for turning our toughest woods down this way.

Sharp for carbide and HSS turning tools seems to be a different question, as the cutting action is considerably different. Mostly scraping vs slicing. The power input is also tremendously higher, which results in massive tool overheating problems that are simply not seen on hand tools. Horses for courses.

There is probably some benefit to dressing HSS turning tools used for finishing work to a finer finish than the typical rough off an 80-grit wheel. The thing is, now you're talking diamond plates (which everybody owns these days vs 20-years ago when I got my first ones. They were expensive and you had to order them.) Even then, it's slow going.

Originally Posted by truckjohn

Sharp for carbide and HSS turning tools seems to be a different question, as the cutting action is considerably different. Mostly scraping vs slicing. The power input is also tremendously higher, which results in massive tool overheating problems that are simply not seen on hand tools. Horses for courses.

John

In the project I'm currently working on the TC and HSS are both cutting with a slicing action in the way that bowl turning gouges are most typically used.

The submicron TC has been sharpened to #1,000 on diamond.

Most HSS grades benefit from going up to at least #600 that is now available in CBN.

Initially the TC may not seem to slice quite as readily as the HSS, but the HSS quickly loses its cutting performance and the TC continues cutting on in a similar fashion long after the HSS has stopped cutting altogether. I'm talking here about lathe woodturning and not hand tools.

There are issues with TC, including its brittleness and cost, but its edge durability saves much time on sharpening. It has particular benefits with the very tough and gritty woods that we often get down our way.

99% of my turning is spindle work, and that is done 99% by slicing cuts if you have learnt to use your skew & spindle gouges properly. You can certainly scrape your way to a final shape, but with most woods I know you'll be in for a devilish amount of sanding, which is something I detest above all else.

I've turned very few bowls, and there was plenty of slicing cuts involved in those too, but not being very experienced at it, I found I had to finish any surfaces perpendicular to the grain by scraping. That's difficult for me to do neatly, I'm so used to controlling the tool by "riding the bevel" but you've got no 'riding surface' to work from when scraping, so it requires a very steady hand (or maybe just a lot more practice!)....

Cheers,

Originally Posted by IanW

I've turned very few bowls, and there was plenty of slicing cuts involved in those too, but not being very experienced at it, I found I had to finish any surfaces perpendicular to the grain by scraping. That's difficult for me to do neatly, I'm so used to controlling the tool by "riding the bevel" but you've got no 'riding surface' to work from when scraping, so it requires a very steady hand (or maybe just a lot more practice!)....

Cheers,

You can also do a 'shear scrape', which is a cut where the scraping edge is presented at an angle to the rotating wood and is in effect a slicing cut when it comes off the burr. It is used as a fine finishing cut to eliminate any endgrain tear out. The shavings produced by shear scraping are typically gossamer thin.

Originally Posted by NeilS

...... The shavings produced by shear scraping are typically gossamer thin.....

Neil, I guess a sharp edge & a fine shaving are a good recipe for minimising tear-out in any situation, whether you're using a plane or a chisel or any cutting tool. My problem with "face-plate" turning & that sort of scraping is not so much getting a fine, clean shaving (to start with), it's that I struggle to keep the scraper taking that fine cut evenly across the bottom of the bowl. For a practiced bowl turner like yourself it's probably easy, but for someone like me who turns a bowl maybe once in 3 years, it's certainly not easy!

After posting, I was thinking about the difference between a 'shear' cut and a 'scraping' cut (in turning) & when it comes down to it, there is no difference in the process, both involve a sharp edge cutting wood fibres cleanly. The main difference, it seems to me, is that with a scraper you are presenting only the cutting edge to the work & you have to mainatin the optimum cutting angle whilst sliding the tool across the tool-rest evenly to get those continuous shavings and a flat surface. 'Shearing' cuts are more easily controlled because you can 'ride the bevel' with either skew or gouge, and tilt the edge into the cut to maintain a smooth, continuous slicing action.

It's all about practice & persistence, of course....

Cheers,

Originally Posted by IanW

After posting, I was thinking about the difference between a 'shear' cut and a 'scraping' cut (in turning) & when it comes down to it, there is no difference in the process, both involve a sharp edge cutting wood fibres cleanly. The main difference, it seems to me, is that with a scraper you are presenting only the cutting edge to the work & you have to mainatin the optimum cutting angle whilst sliding the tool across the tool-rest evenly to get those continuous shavings and a flat surface. 'Shearing' cuts are more easily controlled because you can 'ride the bevel' with either skew or gouge, and tilt the edge into the cut to maintain a smooth, continuous slicing action.

There is a lot of similarities between the bevel rubbing cut made with a gouge and the cut made with a hand plane in which the sole of the plane is doing the rubbing. Both benefit from having the burr substantially removed.

There are also similarities between the scrapers used by woodturners and the card scrapers used by cabinet makers. Most woodturners retain the burr that is formed when a scraper is sharpened on the grinder and cabinet makers deliberately form a burr on their scrapers, which they usually form with a hard burnishing rod.

You know you are doing a scraping cut when the scraper face is at less than 90° to the surface being cut.

It is the burr that is doing the cutting work if it is retained on a scraper and, although not immediately obvious, there is a micro-bevel rubbing...

Scraper action.jpg

The same applies in woodturning if the burr is retained on a scraper. David Weaver's unicorn method is a very quick way to raise and refresh the burr on a woodturning scraper. It makes a very finely polished and firm burr...

Polish from buffer on top bevel.JPG

If the woodturning scraper has a neutral rake (ie, flat on the top) then the scraper tip is dropped below centreline so that the face if the scraper is at less than 90° to the wood. That is not necessary if it is a negative rake scraper (bevels on both top and bottom) is being used .