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Jon Heron
01-10-2013, 09:34 AM
Excuse my scraping ignorance! Just trying to figure out what its all about...
As the vid starts a guy is sharpening his scraper, is that a chip of carbide for the blade or HSS?
At about the 8min mark the guy is beating on the scraper and putting U shaped scratches into the surface, what is the purpose of that?
Its not really explained in the video... Perhaps for oil grooves?
At the 12min mark they are using an electric scraper that is made from a sawzall, is that an attachment you can get for a sawzall or is it manufactured that way?
http://www.youtube.com/watch?v=btybtxImkAE
Cheers,
Jon

rowbare
01-10-2013, 11:37 AM
The U shaped marks are called flaking, they are for oil retention. Search for flaking and you will find a lot of information.

The sawzall was modified probably based on one of these threads:
http://www.practicalmachinist.com/vb/general/power-scraping-anyone-tried-convert-makita-hk0500-metal-161099/
http://www.practicalmachinist.com/vb/general/my-home-made-power-scraper-236293/

bob

Dave S.
01-10-2013, 11:44 AM
Generally scrapers have carbide blades silver soldered to the steel shank. At the 8 min mark he is producing a flaking pattern that holds oil. It produces a half moon shape and is an art in its self. What you are seeing at the 12 min mark is a sawsall that has been moded for scraping. Laying on the bench is also a Biax power scraper. It has variable speed and stroke. Hand scraping is very time consuming. the power scraper speeds it up a lot.

Dave

TGTool
01-10-2013, 01:29 PM
The tool he's sharpening at the start of the video holds an insert that's clamped towards the end and it can be either HSS or carbide. Later in the video there's a few seconds of a double ended motor with plates on both ends that are cast iron diamond charged laps for sharpening carbide inserts or brazed carbide ends. The supports just outboard of the lapping plates are set at the right (negative) angles for the carbide sharpening. The preferred practice is to grind away from the cutting edge so you don't get micro chips flaked away since carbide is very strong in compression but not so good in tension. For most purposes scrapers are sharpened with negative cutting angles.

dian
01-10-2013, 02:10 PM
i wonder why in the whole video they never stone the surfaces.

Void
01-10-2013, 03:05 PM
dian,
You missed it... at about 02:10 one person stones his work. He is not doing it quite right with 5-6 strokes. Briefly is correct... two swipes with a clean flat stone should be enough.
Earlier at about 01:40 there is a person bluing up their work. That is incorrect technique... just a little shift about an inch or two in two directions is all that is needed.

One other thing I noticed was there was, apparently, not a single shop vac in the entire shop. Scraping is a very dirty business and dirt, even a tiny speck, is the enemy of good clean spotting. When I attended a scraping class with Forrest Addy back in 2007 we had about one small shop vac for ever two students and we sucked up all the scraping dust off our work and work area after ever scrape. Not after each stroke of the scraper ;) but after scraping a single surface and certainly just before spotting. Compressed air blow guns are NOT the way to do it. It just spreads the grit all over the shop. Shop towels are OK if you have an almost endless supply of lint-free towels to use.

All the mistakes I noted are ones we all made in the class I attended. We were corrected several times by Forrest until we got the right habits. He also explained the whys and wherefores for each technique.

-DU-

Jon Heron
01-10-2013, 04:01 PM
Good to know! I have heard the term flaking tossed about but I had no idea what it meant, I thought it meant the flaky look of a scraped surface :o
Thanks guys!
Jon