Endmill or Slotmill?

[02jcole]

Hello,

I am in the process of making a steam manifold for my 4" tasker T/E. I have machined the radius on the lathe faceplate for clamping to the boiler and next was going to machine the rest of it on the rotary table so I looked in the catologue for a long series 1/4" cutter and found that an endmill was about £3 cheaper than a slotmill so purchased a dormer one at £9.

I then set the rotary table up and start to mill away, it took a couple of cuts then the milling cutter snatched pulling the brass block out from under its clamp, so I thought perhaps it wasn't held don't tight enough so I set it up again but this time tightened it up more only to do the same again but instead of it slipping it snapped the cutter....I wasn't amused at £9

What am I doing wrong? There is a bit of backlash in the rotary table but I lightly applied the clamps to try to combat this. Should I be using an endmill or a slotmill for side milling??

Any thoughts please.

James.

[jackrae]

Providing you're not plunging the cutter into solid metal then it shouldn't matter. A wlot drill can "drill" into metal because atleast one of the cutting faces exceeds half the diameter. An end mill has a blind centre and therefore can only be plunged into a pre-drilled hole.
I suspect your problem is a result of too slow a speed for the amount of feed you're applying. For a 1/4" mill I'd suggest at least 1000 RPM.
By any chance does your table have a lot of backlash. If so then you might try nipping up the gib strips to prevent cutter snatch pulling the work into the cutter.
regards jack

[SteveW]

James,

Sound more like you are 'climb' cutting. If you first visualise of the cutter and job as being a couple of meshed gears then:

If the rotation and the feed operate cooperatively you are are climb cutting.

If the rotations oppose you're not.

The effect of climb cutting is to pull the job into the cutter. You start by pushing the job into the cutter and it grabs it and drags it further in. The very heavy cut either pulling it from the clamps or braking the tool. The tool grabs the job and eats up the backlash in the system and ends up taking too big a cut.

You need to think about the rotation and feed directions so that they oppose each other. In this mode you have to always push the job into the tool and it will always want to push it away. Any backlash is taken up by you pushing.

An end mill will only allow to plunge into material for a short distance because it doesn't cut in the middle. A slot drill as a bit of cutting edge that extends across the centre and allows it to cut (but not a lot).

If the cut is from the side (transverse) then there is very little in it between using either one (providing the tool rotation and feed oppose).

[02jcole]

Hello Steve,

I made sure that I was conventional milling rather than climb milling, but the cutter grabs when I start the cut pulling itself around the corner.

I shall try to add a picture tomorrow to explain it a bit more.

James.

[S.D.L.]

Had you locked the X and Y axis on the mill slides. the backlash in the feed nuts or slop in the gibbs can cause a snatch like you describe.

Steve Larner

[pcplod]

As well as the above comments, spin the mill a good deal faster - 1500 rpm for a 1/4" mill and brass would be reasonable, and take smaller cuts. Don't try to cut the whole length of the side of the cutter in one go, do it in small steps. A long series 1/4" cutter will flex a bit, probably sufficiently to produce the "grab" you're referring to.

Despite what the purists say, I also use a very thin cutting oil with brass as some "brasses" chew a bit and clog up the flutes of the cutter.

Plod

[digbylix]

Hi
Just to give my opinion, as I suppose you cutter is new and as sharp as can be expected and you are not climb-cutting and the work is clamped sufficiently and you have locked off both X & Y axiis and are not trying to take off more stock than say .010"(.25 mm) you should have no problem runnning a 4 flute end mill at between 500 & 800 rpm,but just remember all copper alloys work harden and trying to take too little off with too high a speed will work harden it . Sometimes it's just a case of a sense touch and everyone get that wrong now and again. hope this helps
Paul