Announcement

Collapse
No announcement yet.

Setup on horizontal mill?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Setup on horizontal mill?

    Click image for larger version

Name:	mill setup.jpg
Views:	139
Size:	10.4 KB
ID:	1885209
    The sketch is the end view of a piece of round stock in a vise, with a cutter above. The object was to cut the slot in its center (it's a broach guide).

    I first clamped a piece of flat stock in the vise and touched off the cutter's right side against the stock's left side, to get the cutter zeroed on the vise's left (fixed) jaw.

    Then I advanced the table (in the same direction) such that the right side of the cutter would cut the right side of the slot. I got the advance distance as follows: "rem" is the diameter minus the slot, divided by 2: (0.500 - 0.196)/2 = 0.152. The advance is then "rem" plus the slot: 0.152 + 0.196 = 0.348.

    The cutter is smaller than the slot, so the table was reversed to cut the left side of the slot. I couldn't use the dial because of the reversal, so the distance was determined by measure.

    The slot width came out perfectly, but it wasn't centered! "rem" on the right was 0.020 less than that on the left; the cutter must have been advanced 0.010 too far (?).

    I'm baffled - I can't see anything wrong with the technique or the arithmetic. I'm not a great machinist, but I pretty much always get sizes closer than 0.010. The only idea that I have is that when I aligned the cutter on the jaw, I zeroed the feed dial wrong. I.e, to 90 instead of 0. Anybody have any suggestions?

    Thanks, Bob


  • #2
    I am a little confused by your procedure.

    So let me describe what I would do.

    For your distance REM, that would be the part diameter less half the keyway. Knowing that distance, you would then need to touch off on the part, advance distance REM PLUS the FULL thickness of the cutter. The first advance of REM would put the cutter just "outside" the keyway, and then advancing the cutter thickness would put the cutter "inside" the slot.

    1601

    Keep eye on ball.
    Hashim Khan

    Comment


    • #3
      Sounds like a lot of work where something to go wrong. You just need a centered slot, if im reading that properly, so why not touch off one side of the bar, zero, touch off the other side of the bar, then move to half that measurement. If you need a wider slot than the saw youre using, then take the slot width, subtract the cutter width from that and divide by two. Step that amount to either side of the cut. Long asa you dont twist too far youll get a centered slot the right size with minimal math.

      Course, if youre trying to make an offset slot that doesnt work, but works great for centered ones

      Comment


      • #4
        Originally posted by epicfail48 View Post
        Sounds like a lot of work where something to go wrong. You just need a centered slot, if im reading that properly, so why not touch off one side of the bar, zero, touch off the other side of the bar, then move to half that measurement. If you need a wider slot than the saw youre using, then take the slot width, subtract the cutter width from that and divide by two. Step that amount to either side of the cut. Long asa you dont twist too far youll get a centered slot the right size with minimal math.

        Course, if youre trying to make an offset slot that doesnt work, but works great for centered ones
        That method can be wicked frustrating with a fair bit of backlash. That's 100% the way to do it with a DRO though. However, if OP has a 1 or 2" mag back indicator, that's just as good as a poor man's DRO.
        21" Royersford Excelsior CamelBack Drillpress Restoration
        1943 Sidney 16x54 Lathe Restoration

        Comment


        • #5
          I've not heard of touching off both sides of the bar, why? find one side and go from there, you know the work dia and cutter width presumably. Work like the OP describes has to be diligently done by always moving to a dimensions on the same direction. If you don't backlash will bite you. Shouldn't be an issue with a DRO, but its also not an issue without one if everything is done, insofar as dial readings, in the same direction. i.e. if you have to reverse, go past where you want to be and come back so you always reading the dials after moving in the same direction.



          in Toronto Ontario - where are you?

          Comment


          • #6
            Given D = diameter = 0.500" and S = slot width = 0.196".
            We don't know the width of the cutter, let's call it C.
            The distance "rem" = (D-S)/2 = 0.152" - ok

            Assuming that the right side of the cutter is aligned with the inside of the left jaw (the initial position),
            the move to get the right side of the cutter to the right side of the slot is
            rem + S = (D+S)/2 = 0.348" - ok

            The move from the initial position to get the left side of the cutter to the left side of the slot is rem + C

            I don't understand "the table was reversed to cut the left side of the slot. I couldn't use the dial because of the reversal, so the distance was determined by measure". How was the table reversed, and what measurement was taken? If you measured from the right side of the slot and moved S-C to cut the left side of the slot, the slot would have come out the proper width. However this happened, it appears to have been carried out correctly.

            Since the slot is the proper width but not centered ("rem" on the left is 0.020" more than "rem" on the right), then either -

            (a) the cutter was not aligned and/or zeroed with the inside of the left jaw but was actually aligned/zeroed 0.020" inside of the left jaw. Depending on the flexibility of the cutter and the method of touching off, this might be the source of the error, but it seems like a lot to me. Zeroing a dial on something other than zero might be a possibility.

            or (b) the move to the right side of the slot was 0.020" too much, that is, the move was 0.368" instead of 0.348". On a manual machine, most errors are "even" as we miscount dial revolutions and graduations. If this were me, I'd assume this is where I messed this up.
            Last edited by DrMike; 07-07-2020, 08:43 AM.

            Comment


            • #7
              Thanks for all the replies - I knew I could get help here.

              1. I can't touch off on the part - it's totally within the vise (as shown). But what I did was the same as touching the part on its left side.
              2. The cutter is staggered tooth and measuring its width was too difficult to be accurate enough.
              3. I don't have a DRO, but TMB's suggestion for a dial indicator is a good & something that I didn't think of. Thanks, TMB. When I re-make it, I'll use a DI.
              4. I do have a lot of backlash and I was careful to not reverse until I had located the right side of the slot.

              I thought my procedure was straight forward & simple-easy:
              -touch off
              -do a 2-step calculation
              -advance that distance
              In trying to be very specific, I probably clouded the description. My bad.

              Comment


              • #8
                You did things pretty well right, but I snuck in your shop and reset the dial 10 thou.

                Comment


                • #9
                  Originally posted by Mcgyver View Post
                  I've not heard of touching off both sides of the bar, why? find one side and go from there, you know the work dia and cutter width presumably.
                  Well, cant speak for everybody but my theory is that i like all my measurements being done on the same tool, least for something like getting a feature put in the exact center of something. If i make an error measuring the width of a part with the calipers or micrometer, either through poor technique or a miscalibrated tool, then i try to use that dimension to step off of to get to the center of the part, i wont be in the center of the part. If i do all the measuring with the DRO of the mill, ill be in the center, even if the DRO isnt calibrated. Doesnt matter if the DRO reads 1.5" on a 1" part, long as i split that in half ill be in the center

                  Granted this only works if you want something in the exact center of something

                  Originally posted by Bob Engelhardt View Post
                  1. I can't touch off on the part - it's totally within the vise (as shown). But what I did was the same as touching the part on its left side.
                  2. The cutter is staggered tooth and measuring its width was too difficult to be accurate enough.
                  Well, for #1 you can just touch off the vise jaws instead, long as you dont have anything between the jaws and the part, or as long as whatever you have between the jaws and the part is the same thickness on both sides of the part. Same process applies, touch one side, zero, touch the other, divide by two. Dial indicators make an excellent DRO substitute for this too.For #2, can always run the first cut down the center, then measure the slot width. Same process after that, slot width you want minus slot width you got, divide that by two to get your stepover

                  Comment


                  • #10
                    Well, I remade the part & another one as well, with the same technique and no problems. The inevitable conclusion is that I just plain f---ed up. Clumsy Bastard, it could be said.

                    Comment

                    Working...
                    X