Feed Rate Question

[Derek13]

I'm curious why i'm coming up with this crazy number when i use the feed per tooth X number of teeth X rpm equation to figure out feed.

for instance i was running a horizontal mill, with a 3.5 inch face mill. not sure on the number of teeth, but i think it was 6, at about 1200 rpm (top speed) and a feed of 22in per minute. Now i was looking through a machining book and it said the feed per tooth for aluminum with carbide inserts has a feed rate of .020in per tooth. So if i put that into the equation of .020X6X1200 it comes out as 144 inches per minute! now i know that that is wayyyy too fast (i don't even think the rapid on the machine goes that fast).

So now i'm curious... if i were to have put in a stainless steel block, and having not milled any stainless in my short career thus far, i would HAVE to start with the suggested feed/spindle rates in teh book and tweak from there... BUT what if the feed rate was that far off (proportionatlely) like it is when i try to figure out the 'textbook' speeds for aluminum? I know for a fact if i tried to run at 144 ipm at a decent doc, there would be hell to pay :P. BUT if someone had never milled aluminum before and tried that equation... they would have started off there. So i'm curious if the same problem will occur for me (proportionately) when i try to figure out speeds/feeds for other metals? Or is aluminum just suggested at insanely high speeds/feeds and the rest are alright?

[This message has been edited by Derek13 (edited 06-07-2004).]

[Dave Opincarne]

Aluminun is just insanely high IMHO, I've always had good luck with the suggested speeds and feeds from M.H. but you have to factor/guess about the type of setup and machine they're basing their starting points on. It sounds like they're basing .02" per tooth on a lot of hp and chip clearance and roughing on a BIG machine.

Dave

[mochinist]

First of all what book suggested .020 per tooth? In my chart I have at work I believe it says .002 per tooth for finish and .006 for rough. One thing to remember with those charts also is they dont take into account the rigidness or horspower of your machine. Use your ears and eyes and learn to read the chips, the only time I use any charts is when I am progamming the cnc or if I get some exotic metal that I have not machined before. When manual machining you will soon learn what speeds and feeds work for the type of metal and type of tool you are using.

[Dave Opincarne]

Oops.. misread your post as saying you were working out of Machinery Handbook. I'd take other books with a grain of salt.

Dave

[ibewgypsie]

I just finished some cuts on my bridgeport Series 2 cnc. I lay my hand on the head, my machine has a adjustable range, angle and depth and tilt. ANY overfeed makes the head move slightly. ANY blue chips and I slow it way down.
I just drilled some 1" holes in a tractor Bushhog's yoke. GEEZE I said what is that stuff.. talk about spring steel. I set the downfeed at 3ipm, then had to slow it down and turn up the coolmist even more, then do it manually on the downfeed.. geeze...

I usually use the suggested feed / 2 and speed it up as possible.

As a mill dulls it won't cut as fast and heats up more. Thus it must run even slower. Most my mills are now junk (dull) and I have to run my machine that slow.

David

[Derek13]

Mochinist or dave, would either of you happen to have a RELIABLE chart you could load up onto here or email to me? I would really like a chart with RELIABLE starting numbers (sfm, inch per tooth) when i have to machine metals i havn't machined before (and with different cutter sizes, teeth etc.). Obviously the one i have (it's a school text book... i forget the name off hand) is not reliable (at least not with the aluminum speeds :P).

Oh my email is [email protected] if you happen to have a chart on the comp.

[Dave Opincarne]

I had one I made and kept in the back of my calculator but it's not there now. I'll look at work. mochinist's advice of .006 to rough and .002 to finish is an excelent starting point. For aluminum the general rule is as fast as the machine will go. Ultimatly you do need to listen to the machine, it will take on a certain sound when you're pushing the feed just right.

Dave

[wierdscience]

Sounds like another screwed up book to me,just think thou,even with round inserts it would leave a p--- poor finish,I think they took a spec for a turning insert and tried mistakenly to use t for milling,seems to me it should be .020" per revolution,not insert.

[Dave Opincarne]

Sorry this took so long, I finaly found the little cheat sheet I made up and kept in the back of my calculator when I was on a mill on a daily basis. For 90%+ of the stuff I did it worked.



Dave