No announcement yet.

slot mills end mills

  • Filter
  • Time
  • Show
Clear All
new posts

  • slot mills end mills

    I have a friend who used a slot mill in the lathe to bore a dead end hole in a piece of aluminum (spelled the good old American way)
    Anyway he showed me how to spot the difference between end and spot mills.
    I am none the wiser.Please someone talk me through the differences so that I finally get it at last Alistair
    Please excuse my typing as I have a form of parkinsons disease

  • #2
    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.

    Taken from

    [This message has been edited by John Stevenson (edited 08-17-2005).]

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


    • #3
      Thanks John now you can see whay an amateur like me gets confused I seriously think there will be many amateurs who like me get confused over this one, so this may be a good thread to continue if anyone else is also confused here is your chance to clear it up Alistair
      Please excuse my typing as I have a form of parkinsons disease


      • #4
        There are 2 flute straight sided double end mills shown in the Penn Tool Co. catalog on page 140. Slotting is what it is designed for.

        Is this what is referred to as a slot drill?


        • #5
          Drilling is an operation where the tool is plunged into the work along its axis, and milling is (generally) where the cutter is moved sideways through the work.

          Therefore, shouldn't these little beasties be called either "end drills" or "slot mills", irrespective of the number of flutes, over centre edges etc?

          Often wondered this...

          All of the gear, no idea...


          • #6
            surely the point is that slot mills don't just drill they both drill and mill, as oposed to end mills which can't drill ??Alistair
            Please excuse my typing as I have a form of parkinsons disease


            • #7
              The collection of cutters one has assembled over a period of time since the seventies gives all sorts.
              There are cutters that are all of the above and of course round nosed cutters with four edges. Some with screw threads and some with their own screw on collets which have two lugs in the top for driving I guess. some with flats for holders of various kinds and busted ones. Because I do not use above 1/2"cutters it has been easier to buy a new one when ever the price is right.
              My trouble is sharpening the ones worth saving. I have started on a grinder but it is slow going. There must be a better way than all those ball handles on a quorn.
              Any suggestions.


              • #8
                Yes but it's up for ridicule *AGAIN*

                Posted this a couple of times before to total apathy, derision and hoots of maniacaly laughter but when I get world patents in a few months you twonks are going to laugh on the other side,

                OK staged shot BUT two have been built in the UK and work.

                You need four off the shelf parts.
                A bench grinder
                An import X - Y table
                A Spin Indexer
                and a brick.

                Added to these 4 parts you need a piece of heavy angle or a proper machined adaptor to hold the spin indexer on the X - Y table and a base plate to bolt the X - Y table to.

                The rest is self explanitory.
                The brick goes under the grinder to get the hight up

                The spin indexer and the X - Y table will give you all the moves needed for sharpening cutters.
                The rest is up to your imagination.

                Now laugh away.

                Sir John.

                [This message has been edited by John Stevenson (edited 08-18-2005).]

                Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


                • #9
                  John S, Looks great but dummies like me need more detail: What angle do I present the mill to the wheel? Am I grinding the inside edge of the flute or the outside? How do I advance the mill along its spiral?

                  Sorry to be dim. John C
                  John C


                  • #10
                    One additional point worth mentioning in the 2-flute / 4-flute discussion is the effect of cutting forces in a slot. If you plan on cutting a slot the exact width of the cutter you want a 2-flute (or maybe 3) rather than a 4-flute. With a 4-flute, as the cutter feeds forward, the sidways deflection from the cutting tooth will deflect the left side tooth into the sidewall. The 2 or 3 flute cutters don't have a tooth at that position to dig into the sidewall. Thus, in this situation a 2 or 3 flute will indeed be a better slotting tool than the 4-flute. (And it took me 25 years to realize this.)

                    "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill


                    • #11
                      These little indexers are brilliant they have come down in price quiote a bit they can be bought for around آ£30 now I see some joker on ebay trying to sell a second hand one for buy it now of آ£70 I suppose some poor soul might bite.Alistair
                      Please excuse my typing as I have a form of parkinsons disease


                      • #12
                        Sir John,
                        That looks as if it could be made to work. The angle of the grind should not be a problem as long as sufficient clearance to avoid rubbing is given. It takes so long to get a clearance for a patent these days that I can probably sort it out and grind a little cutter before you tie up the loose ends. love the brick. much more accurate than the roadside rock.
                        my little 5"shopmate might be up to the job but I think I will have to spend some hard earned and get a 6".
                        I have this ex-food blender motor and I think I can get sufficient speed with pulleys and I was on the lookout for a cup wheel. one of those white ones.
                        We will see .
                        thank you,


                        • #13

                          Sir John,
                          On another posting, i have just posted a very similar idea to yours.

                          Sorry, no attempt to steal your thunder.
                          Just great minds thinking alike.
                          Question- did this come from Tony Jeffree?
                          I mentioned this at a ME Exhibition to him.

                          Your loyal Page



                          • #14
                            Baron Norman,

                            No the idea for the T&C grinder came off the top of my head.
                            I did mention it to Tony as we often meet at shows.

                            Sir John

                            Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


                            • #15
                              Sir John, wouldn't you have to levitate that puppy horizontal so as to NOT get a concave grind on the face?

                              Thanks for the explanation on the cutters. I'm still a little confused but I can refer my inquires to Alistair for clarification!
                              - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
                              Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

                              It is true, there is nothing free about freedom, don't be so quick to give it away.