Scraper blade geometry

KD7SBB · Feb 4, 2018

Hey guys! I'm pretty new to scraping and have been reading and learning all I can. I recently built my own scraper using a junk carbide spade drill insert. I've played around with different edge geometry with varying amounts of success. I'm curious what the general consensus is on proper shape. Any advice and pictures are much appreciated!

dcsipo · Feb 4, 2018

KD7SBB said:
Hey guys! I'm pretty new to scraping and have been reading and learning all I can. I recently built my own scraper using a junk carbide spade drill insert. I've played around with different edge geometry with varying amounts of success. I'm curious what the general consensus is on proper shape. Any advice and pictures are much appreciated!

3[SUP]o[/SUP] to 10[SUP]o[/SUP] negative on both sides and 30 to 90 mm radius...

dee
;-D

otter · Feb 4, 2018

You also want to put a nice round on the corners, to minimize gouging when you tilt over the blade when scraping, not that that ever happens

KD7SBB · Feb 4, 2018

Thanks for the replies! I haven't tried that geometry yet. Currently I've been using an edge like what you would find a gasket scraper but a lot more refined. I've been using a accu finish lapping machine to hone the edge. I did figure out pretty quick to round the corners over, those gouges are ugly! Is there a specific rake angle that seems to work best for cutting cast iron?

JST · Feb 4, 2018

KD7SBB said:
Thanks for the replies! I haven't tried that geometry yet. Currently I've been using an edge like what you would find a gasket scraper but a lot more refined. I've been using a accu finish lapping machine to hone the edge. I did figure out pretty quick to round the corners over, those gouges are ugly! Is there a specific rake angle that seems to work best for cutting cast iron?

You want what Dee said.... NOT a positive rake.

Try it, and you will soon "get it" why that is.

dcsipo · Feb 4, 2018

KD7SBB said:
Thanks for the replies! I haven't tried that geometry yet. Currently I've been using an edge like what you would find a gasket scraper but a lot more refined. I've been using a accu finish lapping machine to hone the edge. I did figure out pretty quick to round the corners over, those gouges are ugly! Is there a specific rake angle that seems to work best for cutting cast iron?

Set your table at 80[SUP]o[/SUP] to 87[SUP]o[/SUP] inclusive and finish on the downward side of the wheel. Use plenty of windex to lube the grind. make sure both sides are about the same, the softer the iron the higher the negative rake should be, or you get chatter. Only use positive angles for scraping steel, Since i have not scraped steel after taking the class, and done no experimentation i cannot give you advice on what angle works for what steel, I have scraped steel with carbide sharpened for CI, it works, it is just not optimal

dee
;-D

dian · Feb 7, 2018

im reading connelly and he says 0-30°, depending on hardness of work and if roughing or pinpointing (larger angle). he also proposes a rounded grind, that makes the blade more universal (as you dig in more, the angle decreases).

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