Cutting a blind keyway

[Pete O]

Something I read that made sense was that the force acting on the cutter as it cuts into the leading edge of the slot, i.e. the direction of feed, causes it to flex to the side. This is apparently one more reason that a 2-flute cutter is better for slotting than, say, a four-flute cutter. Apart from the fact that a 2-flute cutter is more inherently rigid.
I read that on the internet 2 days ago so now I'm some kind of expert.

[Highpower]

(09-18-2015, 07:51 AM)EdK Wrote: Chip clearance, possibly.  

Ed

I should have thought of that.  Probably has something to do with re-cutting chips as well? Wow. So many little details that make such a big difference. I have learned to keep the chips cleared out as much as possible though.

[Highpower]

(09-18-2015, 07:55 AM)Pete O Wrote: Apart from the fact that a 2-flute cutter is more inherently rigid.

Excellent point Pete. Threading taps are a good example of that having larger "cores", but it just hasn't sunk in yet that I should be thinking of end mills in the same way.  

[PixMan]

The rigidity of any end mill isn't a matter of how many flutes it has. Rather it is the "core diameter" that affects its rigidity. Another big factor is flute length and how much of it is used. Another factor is the material it's made from. A HSS end mill will not be as rigid as a solid carbide end mill. The O.D. minus the flute depth is how you determine core depth.

The flute depth of an end mill, along with grinding angles and finish also affect how it performs in various materials. A lot of end mills are considered "general purpose", which is always a compromise on design. I have some three flute HSS-PM TiAlN-coated end mills designed for aluminum and they work exceptionally well for that material. I would never use them on anything except non-ferrous metals or plastics. I have other general purpose HSS uncoated end mills I use on a wide variety of materials, and some TiAlN coated solid carbide end mills I use on steels, stainless steels and other ferritic/martensitic materials. They all have various core diameters and I can see the differences based upon how I use them.

I still have much to learn!

[DaveH]

I think whether one calls them end mills, slot mills, or slot drills is dependent on how old one is.  
I was brought up on end mills and slot mills. End mills where always 4 flutes and slot mills 2 flutes further slot mills could drill holes - hence slot drills. Another point to note they were made to different tolerances, end mills nominal dia minus zero, plus (a bit) whereas slot mills were nominal dia plus zero, minus (a bit).
Of course someone comes along with a 3 flute and centre cutting and that's that
Things always change over time and what is a fact to day doesn't mean it will always be.  
 
DaveH

[Vinny]

I did a 6mm keyway last week with a 4 flute carbide end mill and it came out just fine.

Pete, since you read that on the internet it must be true 'cuze I read on the internet that they can't put anything on the internet that isn't true!

[TomG]

Pete,

Actually, four flute end mills are more rigid than two flutes. As an end mill feeds, the side force created by the teeth is perpendicular to them and right through the weakest section of the end mill, the web. With a four flute, that weak section is braced by the other web. If I'm milling a slot with a width close to the diameter of the end mill, I'll always opt for a four flute over a two flute.

I have access to a force gauge at work. It might be fun to see how much these end mills do deflect relative to each other.

Tom

[Highpower]

(09-19-2015, 08:46 AM)TomG Wrote: Pete,

Actually, four flute end mills are more rigid than two flutes.

I have access to a force gauge at work. It might be fun to see how much these end mills do deflect relative to each other.

Tom

Just when you think it is safe to go back into the water.....  

I can provide a cross section of a 2-flute. Anybody else want to volunteer to do a 4-flute?  

[Vinny]

I have a few around here, unfortunately the cutting end was tossed.