View Full Version : Six Flutes on a Bridgeport/RF45 mill?

10-16-2007, 01:43 PM

I just bought some six flute end mills at a scrap yard. They range in size from 1/2" to 15/16". They are nice quality and still sharp. I used them to cut some mystery steel that I am making a glorified nut out of to hold my tool post on my compound rest.

I just read in the machinery book by Frank Marlow, that you should never use more than a four flute end mill on a Bridgeport mill because it is not rigid enough for the cutting forces. I have an RF45 Benchtop mill and did not notice any problems cutting ?

Is anyone else using these type of end mills on their benchtop mills ?

Should I be concerned about the this ?


10-16-2007, 04:39 PM
Well, I know that I wouldn't worry about it....

10-16-2007, 04:46 PM
First off, I think it would not be useful for anything other than steel or CI. Aluminum or anything at all soft/gummy would pack it solid before you even got started. Then there is the problem with calculating chip load and resulting feed. If they are HSS, and very sharp, it might get by ok. But in order to push a 6 flute fast enough (feed, not rpm) to keep the chip load reasonable, you start running into power/rigidity problems that you mentioned. If they are Carbide, your SOL from the get-go as they will not tolerate light chip loads without rapid edge failure. So I guess, from my limited knowledge, you will probably be ok until they start to dull in the slightest (which won't take long with super light chip loads even on HSS), then you'll start getting major chatter I think, or possibly breakage...

Bill Pace
10-16-2007, 05:12 PM
I've picked up many an unknown cutter off ebay.....I just chuck the boys up and see what happens, and its rare that one wont at least do a reasonable job. On those rare occasions one dont act right, I just take it out and pitch it --- though I have not run across any 6 fluters,.... like dog says, I bet Al would jam em up.

10-16-2007, 05:28 PM
I have used six flute endmills on a Bridgeport W/O incident. Had a job where I had to make several pyramids from aluminum and delrin. The only way I was going to get the LOC that I needed was with a 3/4" x 4" LOC six flute single endmill.

Just took light cuts. No problems.

Almost everything I make is from aluminum or plastics. I use four fluters as often as I use two fluters in the Bridgeport. Just keep an eye on it.

10-16-2007, 06:33 PM
I just read in the machinery book by Frank Marlow, that you should never use more than a four flute end mill on a Bridgeport mill because it is not rigid enough for the cutting forces.

strikes me as a load of crap. cutting forces result from removal rates, cubic inches/time. its chip loading, feed rate, depth of cut, material etc that determine the loads on the machine. He might have meant that with a given chip per tooth, the 6's generate more force, but this is just another way of saying if the removal rate increase force increases.

for any cutter, adjust depth of cut, speed and feed rate to suit what the machine can handle. not surprisingly, I've found the 6 flutes cut much more smoothly than 2 or 4's. i'll take your dull ones :D

10-16-2007, 06:42 PM
Makes sense. If you reduce the DOC, you reduce the power/rigidity requirement, and can still keep the feed high enough to keep the feed/chip load high enough to avoid scraping.

But I can't imagine running a 6 flute in aluminum. I've had problems with 4 flutes in slots or pockets, or even when burried on a surface cut. Then again, maybe I just don't know how to run it...

10-16-2007, 06:56 PM
being ever the frugal sort, I usually maximize depth of cut if i can (an inch or more sometimes) and slow down the cutting speed and obviously the feed goes way down. my theory is that the overall removal rate probably hasn't changed but by slowing down I've reduced tool wear rates. I know with a smaller chip I'm not maximizing tool wear, but I am wearing out the entire cutter rather than just the bottom 1/2" or so.