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Sharpening/shaping carbide scrapers

homebrewed

Active Member
Active Member
#1
This post is about a carbide shaping and sharpening system I came up with for my carbide hand scrapers. The motivation: I found a source of inexpensive carbide scrapers, but they had the wrong bevel for metal scraping.

My setup is a low speed wheel driven by a stepper motor. "sharpen#1" shows the arrangement. It uses a disposable aluminum-foil tray to hold water for lubricating the diamond lapping disks, and a simple tool support to set the bevel angle. The photo also shows one of the scrapers and the tool holder that the scraper is installed into while being shaped/sharpened.

Not so obvious is the scheme I came up with to get a specific radius on the carbide. If you look closely at the end of the support you will see a fence that is parallel to the lapping disk. The tool holder has a brass insert that has been cut with a specific radius (drawn with a compass & cut out with metal snips). In use, the scraper is run up to the lapping disk and clamped into place on the holder. The brass insert is held against the fence and the tool is rotated around that radius while the lapping disk is rotating. I made a number of brass inserts with different radii.

I start with a 600 grit disk to shape the carbide, move up to 1200 and finish with the 3000 grit powder. For the 3,000 grit I charged the back of the 150-grit disk using the diamond powder and a home-made charging wheel made from a 1/2" bearing mounted on a handle. I've also got 14,000 grit diamond powder but that would be total overkill for this kind of tool. While I use water lube for the 600 and 1200 disks, the 3000 grit is used dry. I get a pretty nice finish on the carbide. To re-sharpen I do a few passes with the 3,000 grit wheel.

I used the stepper motor because I had it on hand (I temporarily retasked part of my X2 CNC upgrade kit I'm slowly building up). The advantage there: I can adjust the RPMs to whatever I like. I'm currently using about 100RPM's. Faster than that and the water tends to fly off the wheel.

I also got a 6" diamond saw so I can -- at some point -- use the setup for a low-speed saw to cut my own carbide. All the diamond items were bought from an online lapidary supply outfit and were quite reasonable in price.
 

Attachments

mikey

Active User
H-M Supporter-Premium
#2
A lot cheaper than an Accu-finish, especially if it works well for you. Good thinking on the angle and radius adjustment, too. Love it when I see a vision realized!
 

homebrewed

Active Member
Active Member
#3
One of the advantages of my sharpening setup is that I can easily change the wheel's direction of rotation. When I made the clock generator (to generate the step commands to my stepper driver) I included a toggle switch to control the direction of rotation.

I became curious on how the direction of rotation would affect the cutting edge of my scrapers, so I did a quick experiment. I sharpened a scraper with the wheel rotating into the edge, examined it with my USB microscope, then reversed the rotation and reexamined the edge. Photos are attached. I included a photo of a machinist's ruler to provide a sense of scale. Each division is .01"

It looks to me like the edge produced by the "away" direction is slightly sharper (more abrupt) than the "into" direction. "Away" means the wheel rotation is such that the wheel rotates away from the edge. But in both cases the edge is not smooth -- apparently the carbide still chips with the 3,000 grit diamond (but the chips are very small).
scraper edge away.jpg scraper edge into.jpg Scraper photos magnification.jpg
 

benmychree

John York
H-M Supporter-Premium
#4
It is not obvious in your pictures, but the way I was taught to sharpen carbide scrapers, emulating the original grind used on hand and machine scrapers Sandvik brand is a double bevel grind of several degrees with a peak in the center of end of the insert; this is ground with the wheel turning downwards and the handle held elevated above center so that the wheel does not tend to chip the edge. This method is also taught at Richard King's scraping classes. I also grind a little bevel on the very corners of the insert to make it less likely for them to gouge into the scraped surface.
 

homebrewed

Active Member
Active Member
#5
It's not shown in the photos, but I did relieve the corners to reduce the chances of a gouge. I've seen the double bevel mentioned but am trying the KISS method to see if I can get decent results w/o that additional step. It is possible that's the only way to minimize the small-scale chipping I am seeing. Or maybe I should try an even finer diamond grit (I have 14,000 grit available).
 

benmychree

John York
H-M Supporter-Premium
#6
Unless you do the double bevel, at least one of the edges produced will have chipping. I do not have a slow speed diamond lapper as is most used, that is what RK recommends, all I use is a 150 grit (I think) diamond wheel on a regular carbide grinder, and seem to do an adequate job with it.