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milling 3/32 slot

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  • milling 3/32 slot

    Trying to mill 3/32 slots 3/8 deep in some brass stock. Even trying to do this in 3 passes I am breaking the tool (ruined 1 double ender so I quit). Would solid carbide handle this any better? Help and tks.

  • #2
    Have you tried useing a slitting saw?


    • #3
      Only 3 passes? You should try to cut no deeper than half the diameter of your endmill, which means you should make at least 8 cuts. Also, try using 2 flute endmill. Since this is brass, HSS should be fine although carbide will provide greater rigidity. Try using one of those inexpensive carbide endmills used for PCB. They work great with brass and even if you break one of two, it will only cost you few dollars.



      • #4
        Yeah, I'd have thought eight or ten passes at the very least. Heck, I can even do it on the home made vertical mill - light cuts, plenty of spindle speed. Do it quite often for inlet ports in model steam engines.

        [This message has been edited by Tel (edited 03-10-2003).]


        • #5
          As others said: patience! More passes. Also, a jet of air to keep the chips blown out can help in a narrow/deep slot.

          Or, as yf suggests, a slitting saw if appropriate for the kind of cut you're making.
          Try to make a living, not a killing. -- Utah Phillips
          Don't believe everything you know. -- Bumper sticker
          Everybody is ignorant, only on different subjects. -- Will Rogers
          There are lots of people who mistake their imagination for their memory. - Josh Billings
          Law of Logical Argument - Anything is possible if you don't know what you are talking about.
          Don't own anything you have to feed or paint. - Hood River Blackie


          • #6
            I needed to make a slot today, 1/16 in. wide, 1/4 deep. I took a 1/16 drill bit, ground a 'd bit' on the shank end of it, and chucked it up short in the milling chuck. I drilled it into the material at the ends of the required slot, to depth, and along the slot as well. At this point, I had a series of holes inline, all drilled to depth, using the 'd bit'. I then milled out the remaining material in multiple passes. This has worked better for me than any other method so far, for these small diameters. I do not have a stock of small diameter milling cutters, so I just make my own from drill bits. In the past, I have used the existing flutes to turn the drill into a 2 flute milling cutter, but that approach leaves the cutter weak, even if I cut most of the length of the flutes off. The 'd bit' idea leaves the most metal behind the single cutting edge, so gives the best rigidity, and it will drill a hole just fine, as long as it isn't extended far from the chuck jaws. If it's extended too far, it will just walk around in circles, bend, break, and piss me off. Another option I've used is to start with a larger diameter bit, then grind down a short section at the end, just long enough to turn into a 'd bit' of the needed diameter. It can extend further from the chuck jaws before it loses rigidity.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


            • #7
              The method of drilling succesive holes and then removing the material out between the holes is called "Chain Drilling" - was used to cut out large holes in thick plates and what not.

              [This message has been edited by Thrud (edited 03-10-2003).]


              • #8
                Thanks, Thrud, for giving the process a name. I would never have thought to call it chain drilling. I was thinking today that I tend to use my own names for things that I don't have the proper name for, and that may be confusing to some. It's interesting to go into a machine shop, asking for something, and get looked at like I just stepped out of a time machine or something, until they put their own name to it, then the lights go on.
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                • #9
                  Thanks for the replies. Didn't use slitting saw because I was slotting to a 1/4 inch hole. Sounds like patience is a virtue on this one.


                  • #10
                    Tedn332, I was doing the same thing, slotting to a hole. I ended up grinding a special cutter, mounted in the mill, and without power, cranking the table back and forth, while taking a deeper cut each time essentially using the mill as a shaper. Talk about patience, that took a long time. Definitely not the way in a production shop. We've talked about adapting a high speed spindle to the mill for small endmills. I've just completed a right-angle, geared up drive that takes 1/4 inch shanks, that clamps to the quill, and is driven by the spindle. It works ok, is a bit noisy though. Uses gears salvaged from an angle grinder. My next high-speed spindle will be essentially a flex-shaft, ball bearing handle, adapted to fit in the #3 taper on the mill, and driven with a separate high speed motor. My thinking here is I'll get the best rigidity and accuracy with it mounted right into the spindle(which won't be turning while the accessory is mounted). I can't wait to get an endmill turning at 5k+ rpm, (up to 30krpm) and see the results.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                    • #11
                      If I had to do more than a very few, I think I would try to use a small radius slitting saw that's about .01" narrower than the slot. The narrow radius would allow the slot to be cut close to full depth to about 3/8" from the hole. Just stop before the saw reaches the other side of the hole. Then you can finish them off with an end mill much quicker and with less danger of breakage.

                      A quick CAD drawing shows that a 1.25" diameter saw would allow cutting to full depth to within 3/8" of the hole and at the hole it's depth would be 1/4", leaving only a 3/8' x 1/8" "wedge" that is not pre cut. I suspect that the top 1/4" of the slot could be finished in two passes (removing .005" on the sides only) and the bottom 1/8" in just two or three more.

                      This requires two different setups but if you are doing any quantity it could save time overall.
                      Paul A.
                      Golden Triangle, SE Texas

                      And if you look REAL close at an analog signal,
                      You will find that it has discrete steps.