Is there a good resource for a 101 level course on reamers? Carbide vs HSS, spiral vs straight flutes, even vs odd number of flutes, pilots, ect?
Interesting topic.
I'll take a cracked at it. First what is a reamer? For this application it's more form tool than ream. Although it shares some commonality.
reams are generally made to qualify a hole. Chip evacuation generally sucks because your making little marbles instead of ribbons or curls .
adding complex features like tapers only complicates the matter further because now you have distinct pressure zones. HSS tooling is a bit more sensitive to the torsional forces. I've watched reamers "load" and twist up an alarming amount. Go to far and it'll break.
bad day.
carbide is much more resistant because it's hard as wood pecker lips. That said it's easier to break as its much less forgiving to loading in torsion than speed steel.
work holding, tool rigidity, and speeds n feeds all make this a variable that has to be sorted out. That's largely dependent upon experience. The most efficient than path involves wrecked barrels and broken tools. It's an expensive education.
flutes help to stabilize the tool. However this is where I personally move away from St practices. Figure a 6 flute reamer. If I want a chip load of .002 per rev which is pretty standard stuff for reaming heat treated ss- I have to move the tool .012 per rev to get it.
Now take a long hard look at a 223 reamer. Cut one in half and look at the base circle of the tool. (Largest circle formed at the root of all the flutes) now look at the height and width of the chip gullets. Not a great deal of room for swarf to pass through.
compound this with a pilot that effectively serves as a wine cork and you've got a setup begging for failure. Which happens with alarming frequency.
so what to do?
Common sense dictates a reduction of feed rate. BUT you really want the .002 to .0035 per flute per rev chip load on heat treated ss because of its temptation to work harden. You need to keep the tools cutting edge ahead of the thermal wave created by the friction. One reason why peck cycle drilling with carbide in steels is bad ju ju. The material work hardens and now the drills cutting surface has to chip through a hard candy shell. Carbide hates this. Premature drill failure to follow.
tool vendors will love your VISA...
you could ignore it. Your tool will cut well for awhile, then the edges will break down and tool pressure will go up and up will it's ring welding chips to your flutes and eating barrels. Most then start mofoin the tool maker and or the barrel.
neither are at fault. You just cooked it.
speeds and feed are critical fundamental machining formalities that command respect.
so again what to do?
You can bump pressure up to encourage more fluid transfer but in all my efforts I hit a brick wall. I Built a positive displacement pump last summer that made over 2k psi.
just made a mess and a ton of noise. Didn't make chambering any better.
Cutting fluid will also start to play big on this. Oil is a nightmare of a mess. Stinks, ruins your clothes, and is a horrible heat exchanger. Water is in car engines for a reason...
But it's what most have to work with so yer stuck.
till you discover something....
crank up the work holding ability of your tool. Make it rigid and start getting rid of flutes. 3x flute tool on reams are prone to chatter. Once it starts it behaves like a Wankel engine. A triangle banging around a hole. Gotta get it solid. Carbide helps and the higher speeds get the shear action going, but it's gotta be solid. The wider chip gullets promote exchange and give coolant a broad Creek bed to travel.
but the work holding has to be Johnny On the spot to make it work.
rigidity is everything...
hope this spawns creative tinkering late into the wee hours...
fun stuff.
c.
not a whole lot of
