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loply
07-23-2012, 11:37 AM
Hi folks,

Thinking of making some hand scraping tools for various purposes - mainly tuning on my mill and lathe (after learning the art, of course!).

First thing's first I was trying to figure out where to get the carbide from, then I was going to knock up a holder/scraper or two.

Do people use carbide turning/milling inserts for this? If so, which designation? I'm having trouble figuring out what type of insert offers the largest size piece of carbide.

Cheers,
Rich

Mcgyver
07-23-2012, 12:37 PM
I suppose you could use an insert, but they're small and awkward shapes.....go to msc industrial, page 678....this is what you use, carbide blanks. Pick something the width and thickness you like...say 1" x 1/8"...just notice you're in the UK; there has to be someone local that stocks carbide blanks. Anyway, thats what to search for

Fasttrack
07-23-2012, 01:56 PM
Even Enco used to sell carbide blanks, although not sure about shipping to the UK.


For instance: http://www.use-enco.com/CGI/INSRIT?PARTPG=INSRAR2&PMAKA=619-1252&PMPXNO=16719001

You should be able to make many scrapers from that one 6" piece... it'd take an awful long time to use up 6" in a hand scraper... :)

Forrest Addy
07-23-2012, 02:24 PM
Old insrts, don't work very well unless they are C-2 carbide.

I made a couple hundred carbide scrapers for my scraping classes over several years. They were not perfect but they were simple, strong, easily maintained, low in cost, and very effective. For the shanks, I used 1/4 x 1 cold rolled flat bar 14" long. I machined a file tang on one end and on the other I milled a shallow taper one side only from 1/4" to 3/32" in 5". The taper curled a little because of the rolled-in stresses. I hammer straightened them on the anvil and tweaked the taper a little to make it symmetrical. Deburr and buff for smoothness and ease of handling..

I used MSC supplied 1/4" x 3/32" carbide rectangles 1" long for the tips. The carbide comes looking like it was sandblasted, too rough for a scraper as is. The faces form one plane of the cutting edge; they have to be smooth. Grind or lap the faces mirror smooth before brazing the tips on the shank.

Attach the carbide to the shank by silver brazing as a butt joint. If you've never silver brazed before look up the how-to. Emphasize joint cleanliness and careful heat control. Surfaces to be brazed HAVE to be clean, bright, grease-free metal, not even a finger print. I use Harris 56 silver and their white flux. You can get a little blister pack kit for about $20 from a welding supply house and sometimes Home Depot.

Butter silver solder on one edge of the carbide tip being careful not to slop over the edge onto the face. PITA. Then silver braze the tips on the tapered end of the shank. Use plenty of flux. Remove the crusted flux with a soak in boiling water for a few minutes

Install a standard file handle.

Grind, lap the end radius.

You can not satisfactorily sharpen a carbide scraper suited for precision hand scraping on a green silicon carbide grinding wheel. The edge microfractures; under magnefication, it looks like the corner of broken concrete. Make a home brew diamond lap from a small induction motor and a disk on a hub. A diamond lapped edge on cabide done well is dead keen.

Look at the second image down in this link:

http://prowave.blogspot.com/2007/05/scraping-class.html

Yes it's as cheap built and crude as it looks. The tool rest angle on the wood block is 5 degrees.

Use the Green 9 - 12 micron diamond lapping paste. It comes in a srynge for $5 to $45 depending on source and quality. The cheap stuff works pretty good. The expensive stuff not much better.

dp
07-23-2012, 03:04 PM
There are several examples of Forrest's shop-made scrapers in this link. The photos are quite large but unfortunately none show a close view of the scrapers. I took these at the Newport, Oregon scraping class that Jay (RIP) in coveralls and Forrest (in suspenders) put on a few years back.

http://thevirtualbarandgrill.com/machinery/scraping/

I've used mine for many hours and it does a good job.

Forrest Addy
07-23-2012, 03:39 PM
I looked at dp's images - which are very sharp and detailed, by the way. 6th image down shows one of the scrapers I provided in the hands of one of the students. The angle could have been better but the details are there if you study a little.

Isn't my belly photogenic?