Homemade Scraper

[jr45acp]

I'm making a home made scraper, as I'm sure many others are too! I've read the book relative to sharpening, but the question is simply; how sharp is sharp enough? any thoughts are greatly appreciated!

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John B

[Forrest Addy]

Carbide scraper I presume.

A scraper used for precision scraping should be dead keen. You can rough with a scraper ground with a 220 grit diamond wheel but finishing where consistant action is essential requires a diamond lapped edge using the green (9 micron) diamond lapping compound.

You can lap the edge free hand on most any piece of soft metal on which is applied a coat of the diamond lapping compound. Cast iron is best as a lap but aluminum and brass and mild steel work too. Find a convenient smooth piece about the size of a bench stone and use it the same way.

When sharp, the mirror bright edge should "catch" when lightly tried on a thumbnail. Go for an included edge angle of 93 to 98 degrees.

Green silicon carbide wheels are utterly unsuited for sharpening fine edges on carbide. They chip and flake the edge so that under magnification it looks like the jagged edges of broken concrete.

[Al Messer]

O.K. No argument, but how did they do it 100 years ago before carbide and diamond laps? Really, I'd like to know how Pratt & Whitney and others did it with what they had to work.

[jr45acp]

Mr.Forest, actually it's an old file being converted into a scraper! No carbide, no nothing! I'm like Al, in that I want to learn how it was done before all the bells and whistles. No disrespect intended, just a very uneducated individual trying to learn something

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John B

[This message has been edited by jr45acp (edited 01-18-2003).]

[Forrest Addy]

Why, heck. Why didn't you say so?

Sharpening carbon steel and HSS scrapers is easy. Simple grind a radius (in plan view) in the end about the same as a 1 lb coffee can, touch it up with an oil stone. Be ready to touch it up every ten minutes or so.

That's how they did it in the olden days too. The scraper hands kept their oil stones with them as they worked. Can't have the boss see his help traipsing back and forth 20 ft to the workbench when they can have the means on hand.

The aroma of the fine cigar the boss later smoked after a sumptuous dinner on his private railroad car might be sulleyed as he contemplated this significant loss of productive time.

[jr45acp]

Mr. Forrest, you make a point in that I left out some critical info. I got the "file" hardened and then dropped it and as you might suspect, it snapped like a glass rod. Welded it back up, ground it down enough to work, annealed it and stoned the cutting surfaces until they dragged over my nail. I think I'm there, but I'll have a better idea later. I'm awaiting some machined angle plates that I plan on turning into true reference surfaces. If you don't try, you probably won't learn!

Fondest Regards!

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John B

[This message has been edited by jr45acp (edited 01-19-2003).]

[Al Messer]

I think I hit the wrong button awhile ago and erased the message I was posting to you. Ian Bradley mentions in his little booklet on "Hints" that the people with whom he worked preferred to make their scrappers out of old files, and the only thing they did was to grind off the teeth and then carefully grind and hone the edges as you have done. Please keep us posted as to your progress.

[Thrud]

jr45acp:
That is the only way you are going to learn is to actually get to it and practice. You could also do your angle plates for milling while you are at it. Don't get discouraged, everything is difficult to do really well the first bunch of times, but sooner or later you will become as good as you strive to be - that is, if you try to do better work, that is what you will end up with eventually.

[jr45acp]

Mr. Thrud, I didn't follow what you meant about the angle plates for milling. could you elaborate for a dummy? BTW I love meatloaf. Send me your sister's recipie!

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John B

[Martin]

Well guys,
After some scrounging and searching, I believe I may have found a suitable scraper tool. AND it's not a file.
Gather close and listen / read carefully....
I have found a piece of 1/4" thich X 1" wide tool steel. They are called spade drill bits and they are cheap and interchangable. If you locate a 1" dia. spade drill bit, you will notice that it has a stepped notch and a hole at the rear of the blade. This makes for a perfect locator into a homemade handle.
A handle can be easily fashioned from aluminum or even CRS. It doesn't take much grinding to remove the shallow point and hone.

Hope this helps.
Martin

[This message has been edited by Martin (edited 01-20-2003).]

[Thrud]

John
Yes, you know those cast iron Right angle doo-dads for bolting to the bed and then bolting fixtures or workpieces to it for milling? Or the adjustable angle models? They are sort of handy for milling, line boring, and bunch of other fun machining operations.

By scraping them you can correct any error they have in their (normally right angle) fixed angles so they can be used as references. Also by scraping the surfaces flat and in proper geometry to the other working surfaces you will be able to produce better work from the better tools that you would then have. Simple.



[This message has been edited by Thrud (edited 01-21-2003).]

[jr45acp]

Thank Thrud! That's what I thought you meant, but seems as though when I don't get confirmation, I end up screwing something up!

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John B

[Thrud]

John

If you scrape them true, you can also use them on your granite plate if you have one. A thick piece of float glass can sub for a plate, BTW. It is not as good as a Granite flat, but pretty close.

[Forrest Addy]

Sorry Thrud. I have to disgree. Even a thick piece of float glass is MILES away from a good granite flat.

For one thing glass is much softer and scratches and chips easily - something you don't want when sliding a height gage across it.

For another, unless a surface I want to use as a reference has a certification sticker and a set of certs from a qualified calibration lab, I'll never know it it's flat, not for work where I have to certify accuracy.

For another unless the glass is several inches thick it will deflect if significant weights are placed on it like a cylinder square, a height checker, or an indexing head - items that practically live on a granite flat whenever the covers are off. Who wants to do inspection on a surface shaped like a hammock?

There's a dozen more reasons but these are plenty for me.

[jr45acp]

Thrud, Forrest; I have a pink granite plate that was destined for the dumpster when a local tool and die company closed it's doors! When I got it, it had a certification sticker for 2002. After I got all the crude off it, and I do mean crud, discovered it was pink granite. This will do just fine for me as I have no need to certify anything! Stand by for update on making scraper as I talked with an old German trained tool and die maker and he provided some excellent pointers on scraper radiu, and sharpening! slightly different rom the "book", particularly with reference to sharpening! I'm goin to try to create a new post with some pix if I can figure out how to get them onto the bbs!

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John B