Hand scraper geometry for brass

[Richard King 2]

The secret to scraping soft material like brass, bronze, Rulon /Turcite is a Biax 1/2 moon flaker blade ground at a neg 10 to 20 deg depending on the material. I discovered this technique years ago and have been telling my students like Ulma. The tip radius is 60 R as the bottom is also a 60 R.
If you do not have a Biax 1/2 moon blade, use a 1/2" wide carbide insert ground to a 20 radius and a neg 10 to 30 neg rake. You have to experiment on the material . The softer the more neg rake. Also when scraping the softer materials, use about 2 to 4 pounds pressure down. You can use a bathroom scale to measure it. Cast iron is about 8 pound pressure. You lay a thingpeice of plywood on the scale and hold the hand scraper on the wood like your going to scrape and press down.

 

[AndySomogyi]

The secret to scraping soft material like brass, bronze, Rulon /Turcite is a Biax 1/2 moon flaker blade ground at a neg 10 to 20 deg depending on the material. I discovered this technique years ago and have been telling my students like Ulma. The tip radius is 60 R as the bottom is also a 60 R.
If you do not have a Biax 1/2 moon blade, use a 1/2" wide carbide insert ground to a 20 radius and a neg 10 to 30 neg rake. You have to experiment on the material . The softer the more neg rake. Also when scraping the softer materials, use about 2 to 4 pounds pressure down. You can use a bathroom scale to measure it. Cast iron is about 8 pound pressure. You lay a thingpeice of plywood on the scale and hold the hand scraper on the wood like your going to scrape and press down.

Interesting...

What is it about the material properties of brass that make it cut better with a neg rake?

As I understand it, the logic behind a zero or neg rake hand scraper is greater control, and it will not dig in on it's one, in that it requires constant force from both hands to make a cut, and letting off the pressure hand instantly allows the scraper to lift out of the cut, so it's safer and more controllable.

I know cast iron doesn't work harden, not sure, but I think brass also does not work harden.

I'm trying to better understand why scraping brass is better with a more negative rake.

 

[Richard King 2]

I think your making a speech.

Cast Iron does work harden. Most soft materials are not. The scrape of your describing is what "WE PRO'S" call SCOOP scraping. I push and lift at the end of the scrape. This is why Body push scraping is better then pushing arm pushing which many rookies do. One pulls the scraper into the body with your arms and push with the body. Lifting at the end of the stroke does not leave and abrupt burr if you don't scoop lift it. Soft materials need a neg rake or you dig in to deep and get chatter. I teach the same pressure push down all the time and change the tip radius and rake to get the same results. Many rookies lighten their pressure down when scraping different materials by using the same blade rake for all materials. Seeing I have been teaching "all" types of scraping for over 40 years I have developed all the best and fastest techniques in my opinion. Pic's are scraping Rulon 142 (same as Turcite B) using flaker blade on hand scraper 60 radius front and bottom with neg 12 deg's