Question about sharpening/shaping scraping inserts.

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kdtop

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Hey all,

I am wanting to venture into the world of scraping. I have watched many videos about it and am ready to try -- but as a hobbyist am not yet ready to invest the amount needed for Richard King's class (though I would love to). I purchased a Sandvik hand scraper that came with a carbide insert, but it doesn't seem the correct radius.

I read elsewhere Richard King posting that he recommends approximately "coffee can" radius for roughing and "soup can" radius for finishing. My current insert seems more like "dinner plate" radius.

Questions:
  • Do most Sandvik (or other manufacturer) inserts come with a large radius, with the understanding that the user will grind them to desired shape?
  • I don't have access to a diamond lap, but I do have access to a pedestal grinder with a green wheel designed for sharpening carbide bits. Is this usable? Can a whetstone hone a carbide tool after use?
  • Is there supposed to be a rake on the cutting surface, or would it be formed with 90 degree face?
Thanks in advance.

Kevin
 
You can grinder the bit with a green stone, but a diamond hand lap is the minimum needed to finish the cutting edge. It is a lot of work to hand finish, thus the slow power laps people use. lap until there is a mirror finish on the cutting edge. Grid the bit so the included edge is about 85 degrees included angle or -5 degrees cutting edge. This will leave two cutting edges. Don't scimp on the lapping or the cutting edge will leave lots of scratches . I am sure Richard King can explain it better.
 
Nutfarmer said:
You can grinder the bit with a green stone, but a diamond hand lap is the minimum needed to finish the cutting edge. It is a lot of work to hand finish, thus the slow power laps people use. lap until there is a mirror finish on the cutting edge. Grid the bit so the included edge is about 85 degrees included angle or -5 degrees cutting edge. This will leave two cutting edges. Don't scimp on the lapping or the cutting edge will leave lots of scratches . I am sure Richard King can explain it better.
Click to expand...
Thanks for this reply. Dumb question about the rake: With a 5 degree rake, one corner will be sharper (more acute) than the other. Is this sharper corner supposed to be oriented downward, i.e. the cutting edge in contact with the work? (I'm thinking this is correct) Or does it go upward? Thanks again.

Kevin
 
I'm sorry to be dense, but I still don't understand. Are you saying that the face would be ground as below? If so, how would one achieve this??

----------------------- 85 degrees (5 degrees from vertical)
....................../
...................../
..................../
....................\
.....................\
......................\
------------------------ 85 degrees (5 degrees from vertical)

Thanks
Kevin

EDIT: After posting this, I'm guessing it is supposed to be as below. I have a hard time remembering what a (+) vs a (-) rake angle refers to. But if it is as below, it seems that an obtuse angle (> 90 degrees) would cut less well than an acute angle (<90 degrees.

------------------- 95 degrees (5 degrees from vertical)
....................\
.....................\
......................\
....................../
...................../
..................../
-------------------- 95 degrees (5 degrees from vertical)
 
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If you look at this blade it is ground on both sides. A positive angle would look more like a wood chisel blade angle. For scraping steel you would use more of a positive angle. This is what a blade looks like ground on both sides. This blade has been ground on both sides and all four sides so there’s 8 cutting edges. Some put different radius’s on each end so the tool can be used for multiple steps71FC7A9A-2D59-4B6F-9F17-E6548A571428.png
 
Kevin, I'm teaching a class in Fayetteville TN starting Wed - 10 - 14th. I see it is 4 hours from you. That's a bummer... I always say you grind them for scraping regular cast iron to a Neg 5 with a radius of 60 mm or 2.4", if your a rookie, for steel by hand - same . For steel with a Biax use 60 mm rad. but sharpen to a wood chisel positive 20 to 30 rake. For scraping Turcite I use a Biax Flaker blade - 60 radius front and bottom with neg 12 neg rake. You need to buy some diamond wheels. Glendo.com stopped making the Accu-finish lappers . The still make the wheels. I use 3 grits. For roughing a 260, for preparation to finish a 600 grit (but used a 600 for years for all) and a 1200 for fine finish. It really makes scraping much easier to scrape using a lapper machine. I hope this is OK to link. We had a great discussion a few yrs ago on PM. It tells all. I have used a lathe with mounted diamond wheels to sharpen blades. Many make a home made lapper and if you google that, you can make one from a Tread Mill (exercise mill, that people pay to get rid of) motor. You need approx. 300 rpm. I used a Baldor tilt table 3000 RPM grinder with a 300 grit wheel for years before lappers were used, but they are dangerous and the carbide get to hot to hold, so use coolant. I would never use a green wheel as it fractures the carbide and yu have to lap longer to rid the edge of scratches from the fractures. You can Google so much about the Subject. Also BIAX and DAPRA have manuals describing their tool.

Glendo Accu Finish diamond wheel alternatives

Picked up a Accu finish series II which i'm in love with and now I've come to a point where I want to order new wheels but before spending the serious
www.practicalmachinist.com
I would skip through Thermite's rants, I have that dude on ignore.
 
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Richard King 2 said:
Kevin, I'm teaching a class in Fayetteville TN starting Wed - 10 - 14th. I see it is 4 hours from you. That's a bummer... I always say you grind them for scraping regular cast iron to a Neg 5 with a radius of 60 mm or 2.4", if your a rookie, for steel by hand - same . For steel with a Biax use 60 mm rad. but sharpen to a wood chisel positive 20 to 30 rake. For scraping Turcite I use a Biax Flaker blade - 60 radius front and bottom with neg 12 neg rake. You need to buy some diamond wheels. Glendo.com stopped making the Accu-finish lappers . The still make the wheels. I use 3 grits. For roughing a 260, for preparation to finish a 600 grit (but used a 600 for years for all) and a 1200 for fine finish. It really makes scraping much easier to scrape using a lapper machine. I hope this is OK to link. We had a great discussion a few yrs ago on PM. It tells all. I have used a lathe with mounted diamond wheels to sharpen blades. Many make a home made lapper and if you google that, you can make one from a Tread Mill (exercise mill, that people pay to get rid of) motor. You need approx. 300 rpm. I used a Baldor tilt table 3000 RPM grinder with a 300 grit wheel for years before lappers were used, but they are dangerous and the carbide get to hot to hold, so use coolant. I would never use a green wheel as it fractures the carbide and yu have to lap longer to rid the edge of scratches from the fractures. You can Google so much about the Subject. Also BIAX and DAPRA have manuals describing their tool.

Glendo Accu Finish diamond wheel alternatives

Picked up a Accu finish series II which i'm in love with and now I've come to a point where I want to order new wheels but before spending the serious
www.practicalmachinist.com
I would skip through Thermite's rants, I have that dude on ignore.
Click to expand...
Richard,

Thank you for your reply. I would love to take your class. But since I am a hobbyist, I have to keep up with my day job, which interferes with that scheduling. I have watched many of Keith Rutger's and Abom79's videos about your class, and would love to get to one some day.

I'll look into getting diamond wheels. Looks like they are not too expensive on ebay.

Thanks for the like to that other post. One part caught my attention:

Radiocontrolhead: Many people make the mistake in assuming that the Sandvik blades are ready right out of the box. This is not true, since they're ground with an extremely large radius and you need to reshape them to the correct curvature and angle. This translates to a lot of grinding, especially for 60mm and shorter radiuses.

That answers one of my original questions about my Sandvik insert.

Thanks again.

Kevin T
 
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