Turning Archive 2006
>There seems to be some mis-conceptions about negative rake scrapers. Several days ago I responded to a post on the subject and will now augment that with information directly from Stuart Batty’s own writing, which is as follows ad covers regular scrapers and negative rake scrapers.
“Regular Scraper – with Burr: Usable angles 65-degrees ofter woods up to 80-degrees medium woods – common angle 70-degrees. Suited to soft or medium woods. Extremely aggressive on exotic end grain.”
“Regular Scrapers – without Burr: Usable angle 70-degrees medium woods up to 80-degrees dense woods, with the burr honed off – common angle 70degrees. No burr means it is less aggressive but not usually good on softer woods. Best suited to medium and harder woods, can still be aggressive on exotic end grain but can be excellent on exotic side grain.”
“Negative Rake Scraper – Always with a Burr: Included angle 50-degrees to 75-degrees – best angle 60-degrees. Best suited to dense woods, it will cut some soft woods. Not suited for bulk removal of wood or rough turning, too slow. Excellent for final cuts – requires a lot of resharpening.”
“What is negative rake scraping? It is when the blade is ground on the top at an angle nd then ground fro beneath to produce a burr on the upward edge – it is only the burr that does the work. It is an excellent way to refine shape and take out small tool marks – it is an easy technique to learn and a great way to get accurate shapes or thickness.”
“What’s the down side? Negative rake relies on the burr and so the life of the cutting edge is very short and the tool will need to be sharpened a lot. Once the burr has been won away you must re-sharpen immediately. Life of a negative rake scraper is very short – approx. 15-20 seconds per 3/8 inch wide cutting surface for M2 steel.”
That is a portion of Stuart’s write-up. I also use an oval skew chisel as a negative rake scraper (no you do not ride the bevel, but us it as a scraper), since I don’t like an oval skew. It has worked very well in doing the finish smoothing cut on thin wings of coolibah and red mallee bowls. As Stuart says, the cutting is with the burr, which does not last very long and you must re-grind often. I use a 46 grit blue SC wheel for grinding the burr. A course grit produces a burr with less grinding than the finer grits.
Stuart’s email is: email@example.com and his address is 1437 N. Studebaker Road, Long Beach, CA 90815