Cutter Radius Matters
I've been using my newly-shaped/sharpened carbide scrapers on my not-so-good surface gauge and noticed something. I have three scrapers, ranging in width from 3/4" down to 1/2". I made three different brass inserts for my sharpening fixture with radii decreasing from 4-1/2" down to 1-1/2". The thought was that the smaller scrapers would be good for more-detailed work & would work better with a smaller radius on the cutting edge.
Problem was, the 3/4" tool with the 4.5" radius on the end was very hard to use. It would skid unless I used a very high angle, and even then it was difficult to control. The problem was not caused by a dull scraper because I re-honed it with my 14,000 grit lapping wheel and did not find any improvement. I then tried the 3/8" scraper and observed that it was much easier to use, so decided to make another brass insert with a smaller 3-3/8" radius. The reason I chose that radius is because it's the same as the Dapra "standard" carbide insert. This was a good decision -- the scraper now works much better. The width of the cut is still pretty wide so it is good for rough work.
It is possible that the 4.5" radius brought too much material into play, making it difficult to get enough power into the scraping stroke to be effective. A smaller radius (& therefore smaller work volume) would reduce the power requirement. In terms of HP needed for milling/lathe work, there's a definite relationship between horsepower and material removal rate -- and the HP requirement goes up considerably as the material removal rate increases. People power can't compete with machine power, so I guess the lesson here is that scraping should be a finishing job not a forming job.
