View Full Version : End or Slot

02-26-2008, 07:15 AM
Hi All,
I have some more questions to the knowledgeable on this site.
I am having a bit of difficulty in understanding the separate uses of mill cutters which is probably the reason I end up with chipped carbide cutters.
So just what are the different end mill type cutters used for, I thought that end mills do not cut vertically as they have no cutter in the middle but I have seen some that state that they do cut in the middle and slot cutters can cut vertically.
So questions –
Can you cut horizontally with either cutter.
Is it better to take small cuts until depth is reached or just plunge as per a drill.
Just when is a roughing mill used.
Any help or web site greatly appreciated as the pile of roughed up cutters is growing!!


02-26-2008, 07:33 AM
There are center cutting and non-center cutting end mills. Check the description before you buy them.

02-26-2008, 07:55 AM
Slot Drills (End cutting Endmills) are for cutting slots with no open end where you have to plunge down as in drilling, they used to be 2 flute but you see 3 and 4 flute end cutting now days.

RPM is the same for 2 or 4 flute as the peripheral speed is the same but the federate is lower to allow for the reduced number of teeth or the tooh loading would increase.

The feed rates in most books are normally for rigid machines in good condition. At least halve feedrate for old or hobby type machines. Bridgeport type mills are good universal tools but wouldn’t be considered rigid as say a Knee mill with no quill feed.

Roughing cutters are for removing lots of metal quickly then finish of wit a fine one or std end mill.

What Mill have you got?Steve larner.

John Stevenson
02-26-2008, 07:57 AM
Read this post from an earlier reply on the same question.

There are some references to some pictures but ignore these as the text is out of context to the rest of the thread the pics were in


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 on the right in JCHannum's 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 in the picture. 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.


02-26-2008, 07:58 AM
Peter.. I'm still learning this also. I've found that good quality roughers are "magic". With a regular endmill, when I need to cut a slot, it's usually a bunch of passes with my (light) macine. Not so with roughers.
I've found that I can either plunge right through a lot of work and do a full depth slot in one pass with them. They do leave a bit of a rough finish (duh) but for a lot of the things I build this is good enough.
I use the roughers whenever I can. Use an undersize for "hogging" then a four flute for final size.
I have some slot drills and while they do punch a pretty hole... I don't like milling (steel) with them. The higher R's required with the two flutes seems to burn the things up. Of course if I had coolant on my mill it would prolly help that.