Help decide best method for the cut

[Cadillac]

So I have a chunk of cast iron I'm turning into a dovetail straight edge. Piece is 13" long 2" wide and just short of a 1" thick. I've ruff machined to those dimensions and scraped in the bottom surface flat. Now I need to cut the 45* angle. I set up a angle plate on the Bridgeport have it trammed in along with the piece. My question is what tool would induce the least amount of stress on the part slitting saw, or just common endmill? I have clearance for a slitting saw and thought that might be the way to go and the quickest and cleanest. Machining to ruff dimensions was a dream bandsaw went through it like butter no hard spots at all,and when machining it was throwing nice curl chips minimum dust. I was very surprise some of my past cast iron experiences had been disappointing this stuff acts like aluminum when machining. The part hasn't moved any and I don't want to induce any more stress than I have to so what do you all think would me the best method to cut this 45* on this bar a slitting saw or endmill ?I don't have a shaper as a option either so don't remind me please. Here's a pic of the bar in question.

 

[benmychree]

You should have roughed it out all over before doing any scraping at all, if it distorts when roughing the angle, it will be time wasted. Probably best (safer) to just use the end mill. When you start scraping again, alternate scrapes on both surfaces, and "ring" the casting after scrapes to relieve stresses.

 

[bhigdog]

Cut or mill makes no difference. Any warpage will be from internal stress not induced stress...............Bob

 

[Cadillac]

You should have roughed it out all over before doing any scraping at all, if it distorts when roughing the angle, it will be time wasted. Probably best (safer) to just use the end mill. When you start scraping again, alternate scrapes on both surfaces, and "ring" the casting after scrapes to relieve stresses.

The reason for scraping the surface was it wasn't flat was bellied .002 so I scraped it out. I didn't want to cut the angle already wonky. So 1 for a endmill of course I was leaning on the slitting saw. I do see the endmill having less forces on the set-up.

 

[benmychree]

There is less chance of the end mill breaking or losing a tooth (or so) than the slitting saw. My point on the scraping was that when you cut the angle, distortion may make some of your scraping labor wasted. When attending a Rich King class, I had a 24" straightedge much like yours, I had machined the flat and tapered sides many years ago, and decided to scrape the angled side; when I did so, it distorted the flat side, making a rescrape of it necessary also, although a certain amount of it was relieved by ringing it at Rich's suggestion, it became a class demonsration and lesson.

 

[Cadillac]

I gather it will move too I was also farting around getting a feel for it. Surprisingly when cutting the piece out my cut line didn't pinch or pull away which to me was a clue that it doesn't have a lot of stress in it. I've cut pieces where the cut closes up from the material pushing and pulling. The cast iron part I got the material from is well seasoned. 30 yr old bed knife bar from a gang mower that's been sitting in a junk pile at my shop. It's whole life had been outside getting banged around. Thanks for the thoughts.

 

[Bob Korves]

John York gave you the accepted method of scraping in multiple surfaces. Long and slender work like straightedges are all the more fussy, and much time and effort can be wasted by the metal moving around. Ringing it definitely helps to let the stresses settle out.

 

[Cadillac]

Had alittle time to get it cut. I took John recommendation and used a endmill. Took .050 cuts with a 3/4" 4flute and it cut like butter. Set-up was solid but I need to make a permanent adj. table supports which was on the list already. Yes the cast moved a touch. Prior too I scraped it flat hinged nicely. Now it spins like a top it curl up on the ends. Checking the angle for flatness it touches on the ends its smiling at me.
Which brings my next question should I scrape the angle then go back to the flat? Or do the flat then the angle? I would think the first.