Funny Endmill

[Rotate]

Just bought couple of new 1/2" M42 endmills from a local machine supplier and this is what I got!



More pictures

Oblique View

Side View

I call the supplier and they agreed to replace them, and told me to keep the defective ones Except for plunge cutting, I think they will work fine for light work.

Albert

P.S. I'm normally impressed with stuff made in Poland, but I guess this one slipped through QA.

[Al Messer]

Albert, I'm assuming that you are talking about the rough surfaces??

[Al Messer]

If it's because the cutting edges are of different lengths, it's probably because it's a "slotting drill."

[Treven Baker]

Al, please explain. I have never seen an endmill like that either. It looks like it has different sized flutes.

[John Stevenson]

Albert,
Nothing wrong with it at all.
Let me try to expain about end mills and slot drills. Many people have their own description of these but I'm afraid no one is right any longer - even me !!!
First off lets go back in history and see what we had. There were 4 flute end mills and 2 flute end mills. Some could plunge some couldn't. Confused? well you will be.
The two flute ones were called slot drills in the UK and were ground with one cutting edge over centre so they can plunge cut vertically down and then traverse, hence the name. These are the ones in Alberts picture.
The 4 flute end mills usually had a hole in the centre for clearance when grinding and so can only cut on the sides of the tool. Trying to plunge with one of these will leave a central pip that will break the cutter when you try to traverse.
Now when we got towards the end of the 20th century things started changing. We had better methods of producing cutters with fancy 5 and 6 axis CNC grinders. We started to see 3 flute cutters getting popular as a compromise between rapid metal removal and chip clearance. We also started to get the 3 and 4 flute cutters with one lip ground over centre like the two flute Albert has. This means that these can also plunge.
To cap it all the manufacturers put paid to any standards by calling their cutters all sorts of different names. Where a 4 flute cutter was called an end mill it can now be centre cutting and be called a 4 flute slot drill.
If you look in any cutter catalogue nowdays you will find that they call a certain type of cutter by one name on one page and another manufacturer calls it by a different name on another page! The manufacturers have moved the goalposts. The cutter descriptions we all grew up with in Chapmans and Moultreich <sp> has gone out the window with the advent of grinding techniques.
I took a 20mm solid carbide 4 flute end mill [ non centre cutting ] in for regrind last month and when it came back it was 4 flute over centre slot cutting cutter. What do I call this now?
The main thing to look for when buying cutters is the number of flutes you require and whether they are centre cutting or not.
I can see the time when the old 4 flute centre pipped type will become obsolete as most cutters are ground up from blank material nowdays.
I had a load of cam track slots to do the other week at 7.2mm wide. I had a choice of doing two passes with an undersized cutter or having a cutter ground down to 7.2mm
I decided to go with the special cutter and asked the local T&C grinders to supply and regrind an 8mm cutter down. Instead they just ground the new cutter straight onto a 8mm solid blank, 3 flute centre cutting. It was on the machine for all of 3 minutes.

John S.

[Al Messer]

I agree with what John said!!

[Al Messer]

Now I'm confused, I think I thought that a "Slot Drill" would cut to its exact diameter but an "End Mill" would veer off and cut an over sized slot. Example from the books: To cut a 1/4" wide slot with an "end mill" use a 3/16" dia. mill and make two passes, one a roughing pass and the other to finish to dimension. To cut a 1/4" slot with a "slot drill", use a "slot drill" and make only one pass. Am I correct, or am I confused??

[Rotate]

This very very strange, because I've never seen an endmill that was not symetrical (this doesn't mean much since I have not seen more than perhaps a hundred in my life), but even the supplier agreed that they are bad (this too doesn't mean much because often they don't know what they are selling). The only authoritative source are my textbooks and none of them, including books on cutting tools mention anything about asymetrical cutting edge on endmills.

I would think that if I tried to plunge cut using this, then I wouldn't get a round hole since the side with the longer web will keep pulling. May be round but definitely oversized.

More explanation please

Albert

[Thrud]

Albert
John is right. Every manufacturer seems to have their own quirks as to how they grind a center cutting endmill. Some are very complex and some are simple. Next time you are in a machinery store look at different brands of solid carbide endmills...

The grind you have is the fastest to do - cheapest to make. Osborne has been making theirs like that for 20 years or more (I have lots older than that). This grind is similar to standard 118* drill points - simple. The 135* split point drills are more like a high end carbide mill - true center cutting.

So don't sweat it, they will work just fine. The symetrical ground endmills are required for good balance on high speed spindles but of little consequence at less than 7,000 rpm.

[Paul Alciatore]

AI would like to see someone say more about the question of oversized slots. I know a standard twist drill will wander and produce a slightly oversized hole. For an accurate hole you must use a reamer.

But what, if anything, is the essential difference between an end mill and a slot cutter? Why would the end mill make an oversized slot and the slot cutter not? At first glance, it seems to me that if the length and diameter are the same and they are made of the same alloy (same stiffness) then either cutter would produce similar results. Again, at first glance, I would think that a two flute design would be more flexible and produce a larger slot than a four flute design.

[Thrud]

Paul
Slot drills (endmills) are two flute, as such only one flute is in the cut at one time, so it is a bit more accurate and chatters less.

For really accurate slots (or holes) extra work is always required. A horizonntal will with a side cutting slitting saw can cut an accurate width slot. Endmills require a center hogging (roughing) pass and two finish cuts to produce an accurate slot. If modest accuracy is allowed - one pass may be sufficient.

Accurate holes require Jig boring. Some holes ae "ballized" with a carbide ball pushed through to burnish the hole to a high finish and very accurate diameter.

[C. Tate]

That type of grind also aides in helical entry. It was probably intended for AL use judging by the tight spiral on the flutes.