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Dovetail failure

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  • jtveazey
    I am having problems cutting a 60 degree dovetail. First several passes went well, but once 50% finished, I burned up the cutter. Bought a US made replacement
    Message 1 of 7 , Oct 31, 2004
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      I am having problems cutting a 60 degree dovetail. First several
      passes went well, but once 50% finished, I burned up the cutter.
      Bought a US made replacement and knocked the corners off it in short
      order. Material is CRS, cutting 0.005 to 0.015 per pass, feed is
      manual and slow, spindle speed is high, minimal lubricant. Any
      suggestions? Will cross post to 9x20 group also.
    • Chris Baugher
      ... Sounds like the spindle speed is too high. Usually you cut steel at pretty low RPM s, especially with HSS cutters. Otherwise the cutter burns up. Maybe
      Message 2 of 7 , Oct 31, 2004
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        On Sun, 31 Oct 2004, jtveazey wrote:

        > I am having problems cutting a 60 degree dovetail. First several
        > passes went well, but once 50% finished, I burned up the cutter.
        > Bought a US made replacement and knocked the corners off it in short
        > order. Material is CRS, cutting 0.005 to 0.015 per pass, feed is
        > manual and slow, spindle speed is high, minimal lubricant. Any
        > suggestions? Will cross post to 9x20 group also.

        Sounds like the spindle speed is too high. Usually you cut steel at
        pretty low RPM's, especially with HSS cutters. Otherwise the cutter
        burns up. Maybe try about 500RPM. Cut depth sounds ok. Feed will
        probably be slow.


        C|
      • mitchell
        ... you are probably using to much spindle rpm . Slow it down . Now all depending on rigidness of you mill,size of cutter and p[art you should try and put as
        Message 3 of 7 , Oct 31, 2004
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          --- In GrizHFMinimill@yahoogroups.com, "jtveazey" <jtveazey@a...> wrote:
          >
          > I am having problems cutting a 60 degree dovetail. First several
          > passes went well, but once 50% finished, I burned up the cutter.
          > Bought a US made replacement and knocked the corners off it in short
          > order. Material is CRS, cutting 0.005 to 0.015 per pass, feed is
          > manual and slow, spindle speed is high, minimal lubricant. Any
          > suggestions? Will cross post to 9x20 group also.
          you are probably using to much spindle rpm . Slow it down . Now all
          depending on rigidness of you mill,size of cutter and p[art you should
          try and put as much load as you can on the cutter each pass . What im
          trying to say is complete the cut in as few passes as needed . Every
          pass you make you put wear and tear on the cutter . Get a good tooth
          load going . Not so much of coarse to break anything but enought your
          not making undue pases . I generaly take alot more then .005 or even
          .015 with my dovetail cutter or any cutter of mine .To shallow a cut
          leads to rubbing which ruins your cutters. I save a shallow cut for
          the final pass to get it to size being doevtails are so sensative to
          size .You might want to try a mister also . This will cool the tool
          and blow the chips out . I get along time out of my dovetail cutters
          doing this (they where all bought used also ) and I dont use carbide
          like others like to do it is also not needed . Another thing to keep
          in mind is dont worry about the inside corner being razor sharp its
          not really needed . The mating part should not be reaching that far in
          . Razor sharp corners only lead to stress risers anyhow.
        • mvcalypso
          The formula for calculating dutter RPM is: RPM = (4 * SFM) / (cutter diameter) where RPM is rev per minute SFM is Surface Feet per Minute and depends on the
          Message 4 of 7 , Oct 31, 2004
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            The formula for calculating dutter RPM is:
            RPM = (4 * SFM) / (cutter diameter)
            where
            RPM is rev per minute
            SFM is Surface Feet per Minute and depends on the material being
            cut (Steel is typically 100 SFM and Al is typically 400 SFM - the
            values for different materials can be looked up in handbooks).
            Cutter diameter is in inches
            The result is for HSS cutters.
            (multiply the answer x 2-4 for Carbide).

            So if your cutter is 1/2" in diameter we have:
            RPM = (4 * 100SFM) / 0.5" = 800 RPM
            If your cutter is 1" then you would get 400 RPM

            These are the starting RPM points (On variable speed Mills one
            adjusts the speeds to impact finish etc.)

            I suspect that using a high spindle speed is buring up the cutter.

            Dave

            --- In GrizHFMinimill@yahoogroups.com, "jtveazey" <jtveazey@a...>
            wrote:
            >
            > I am having problems cutting a 60 degree dovetail. First several
            > passes went well, but once 50% finished, I burned up the cutter.
            > Bought a US made replacement and knocked the corners off it in
            short
            > order. Material is CRS, cutting 0.005 to 0.015 per pass, feed is
            > manual and slow, spindle speed is high, minimal lubricant. Any
            > suggestions? Will cross post to 9x20 group also.
          • Richard Albers
            My experience: I was making a QCTP. (See the dropbox at http://metalworking.com ,2000_retired_files , filenames starting with A6 .) That requires cutting
            Message 5 of 7 , Oct 31, 2004
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              My experience: I was making a QCTP. (See the dropbox at
              http://metalworking.com ,2000_retired_files , filenames starting
              with "A6".) That requires cutting many 60 degree dovetails.

              I started with a female block to be used as a go/no-go guage.
              I began by removing the center portion with a standard, straight
              cutter (3/16" deep), then changed to the 3/4" dovetail cutter.
              I took many shallow cuts, like you did, to cut the first side.
              Then I cranked the table over, counting turns, to start cutting
              the second side. From my experience with the first side, I added
              one turn (1/16" on my mini-mill) for the first cut on the second
              side. I continued, using a *lot* of Tapmatic cutting fluid, low
              RPMs, and a slow manual feed for the first pass. The mini-mill
              made this deeper pass with no complaint, verifying my guess that
              the mill and cutter could handle it.

              Imagine my surprise when I *looked* at the resulting cut and
              found I had cut to the full depth of the dovetail! In *one* pass!
              (I must have miscounted the turns - hindsight/another lesson.)
              Actually, I had cut .002" too deep, but since this was to be my
              guage for the entire dovetail system, I just changed the drawing.
              ;-) (Its my system, and doesn't need to fit anyone elses'...)

              Needless to say, the rest of my dovetail cutting went *much*
              faster than I had anticipated! And I am now the happy owner/user
              of a custom (!) QCTP that works very well on my 7x12. :-)

              Some of you may have seen my QCTP at MMM Oct. 23/24, 2004.

              RA

              --- In GrizHFMinimill@yahoogroups.com, "jtveazey" <jtveazey@a...>
              wrote:
              >
              > I am having problems cutting a 60 degree dovetail. First several
              > passes went well, but once 50% finished, I burned up the cutter.
              > Bought a US made replacement and knocked the corners off it in short
              > order. Material is CRS, cutting 0.005 to 0.015 per pass, feed is
              > manual and slow, spindle speed is high, minimal lubricant. Any
              > suggestions? Will cross post to 9x20 group also.
            • ken.mary
              Hi Richard What type, size, and brand cutter were you using? It sound very worthwhile! Bye, Ken in Carmichael ... From: Richard Albers
              Message 6 of 7 , Oct 31, 2004
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                Hi Richard

                What type, size, and brand cutter were you using? It sound very worthwhile!

                Bye, Ken in Carmichael

                --- Original Message -----
                From: "Richard Albers" <rralbers@...>
                To: <GrizHFMinimill@yahoogroups.com>
                Sent: Sunday, October 31, 2004 12:13 PM
                Subject: [GrizHFMinimill] Re: Dovetail failure


                >
                >
                > My experience: I was making a QCTP. (See the dropbox at
                > http://metalworking.com ,2000_retired_files , filenames starting
                > with "A6".) That requires cutting many 60 degree dovetails.
                snip
              • Richard Albers
                Brand: Good question. I can t find it right now - probably put it away. ;-) As I recall, it is a quality import from J&L (they used to have a store just
                Message 7 of 7 , Nov 2, 2004
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                  Brand:
                  Good question. I can't find it right now - probably put it away.
                  ;-) As I recall, it is a "quality import" from J&L (they used to
                  have a store just down the street, closed now). Definitely not
                  USA made. Maybe I was lucky, or maybe J&L's buyer knew his job...
                  I haven't needed to cut more dovetails (yet), but when I do I'll
                  try the cutters I got from HF for $19.99, and report on them.

                  Size: 3/4" x 60 degree

                  Type: Not sure what you're asking. It looks like a "standard"
                  60 degree dovetail cutter. 3/8" shank, ISTR 8 (straight) flutes...
                  Oh, yeah. HSS. (Must be "real" HSS, not "drill bit" HSS. ;-)

                  RA

                  --- In GrizHFMinimill@yahoogroups.com, "ken.mary" <ken.mary@s...>
                  wrote:
                  > Hi Richard
                  >
                  > What type, size, and brand cutter were you using? It sound very
                  worthwhile!
                  >
                  > Bye, Ken in Carmichael
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