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Rack cutting on a POS Bridgeport

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  • Rack cutting on a POS Bridgeport

    Post to be done over two days as it's half past dark here and knocked off for the day.
    Don't like staying in the shop after dark because it's haunted !

    Making a centring jig up, it's basically a very crude 3 jaw chuck that uses pegs instead of jaws. You drop pegs in to suit the job and tighten the bars up using a pinion then lock them off.

    They fit on a 40" round Phenolic [ Tufnol ] plate 2" thick which goes inside a crack detection machine under water for testing aero engine parts.

    These are normally 36" diameter but a job has arisen that calls for the 40" plate and longer arms.



    Problem with rack cutting on a Bridgy or similar is that the cutters are never big enough to clear the spindle or drive attachment.

    In this case I have the horizontal head fitted but spun round 90 degrees sideways. I can't run this the normal way because the stainless arms are too long to fit front to rear without clouting the support bracket so it has to stick out sideways with no overarm support.





    Closer shot of the setup plus one of the smaller bars as a pattern.

    I'm hoping this works out OK as the stainless is horrible stuff, it's harder than a witch's tit and wants to work harden as soon as looking at it.

    Follow up post tomorrow.
    .

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




  • #2
    Ah Ha! I knew that shop was haunted! That explains why there's no floor, ghosts don't need no steenk'n floor.

    Where's the 3jaw w/pegs fixture? Am I overlooking that, or is it yet to be shown? ....ahhh, I bet the ghosts took it.

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    • #3
      Originally posted by lynnl

      Where's the 3jaw w/pegs fixture? Am I overlooking that, or is it yet to be shown? ....ahhh, I bet the ghosts took it.
      It's three of those bars fastened to a spigot in the middle of the plate.

      Pic tomorrow if you insist.
      .

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



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      • #4
        John,
        Your shop is haunted by all the ill feeling caused by the POS Bridgy.
        Dave

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        • #5
          Originally posted by John Stevenson
          It's three of those bars fastened to a spigot in the middle of the plate.

          Pic tomorrow if you insist.
          I don't see what you're talking about either John?

          The pins are radially spaced, right?
          "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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          • #6
            Sorry it's a bit vague, picture tomorrow will help but the post is more about cutting the rack [ or hopefully cutting the rack ]

            You are right though about the radial pins, the pins fit in the holes on the bars, tighten one bar and the others spin on the offset centre boss and all tighten up together.

            The chuck or centring device is very crude and only good for location, definitely not suitable for holding anything for machining as crack testing is a non contact sport
            .

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



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            • #7
              First thing that jumped out at me was the cutter overhang (unavoidable) and the lack of outboard support for the arbor (PITA to set up.)

              And stainless. Rack take lots of push to make the cutter chop. Stainless take about double the push.

              How about a three legged strut attaching to the column and having a bushing in a block? Three legged fixes a point in space and the block if cleverly attached will give good support to the arbor and take the cutting moment off the quill key. You'll have to drill and tap some holes in the column but yours is a POS Bridgy so you shouldn't mind defiling it.
              Last edited by Forrest Addy; 07-28-2011, 08:35 PM.

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              • #8
                Buy a bigger gear cutter?
                Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                • #9
                  Hard to tell if this will work from the posted info, but if you only need to cut teeth at the end of the bars as shown by the sample, wouldn't it be better to swivel the head 90 degrees toward the back so the usual support that attaches to the underside of the ram can be used to support the free end? Or will this rear support not clear the bar?
                  TexasTurnado

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                  • #10
                    BM,
                    Gear cutters, at least affordable ones seem fixed at 3" or so OD.

                    TT
                    Bar is too long to go front to back and fouls the support arm.
                    .

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



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                    • #11
                      Just a idea like Forrest said.take a piece of 1 1/2 - 2 inch key stock cut a dove tail in it to fit the dove tail on the column . Lock in place with grub screw. tap a fair size hole in the other end . Make a plate with a block and bushing welded on to fit the arbor. Slot the other end of plate to bolt the the clamped bar . Should be plenty solid then and mill away.
                      Every Mans Work Is A Portrait of Him Self
                      http://sites.google.com/site/machinistsite/TWO-BUDDIES
                      http://s178.photobucket.com/user/lan...?sort=3&page=1

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                      • #12
                        What about a single flute cutter

                        It appears as if the form on your rack cutter has straight sides or close to it.If this is the case, maybe you could use a home made single flute cutter such as I have used on a deckel copy mill in the olden days.Of course it would be nice if you had the deckel cutter grinder . However, I have made single flute cutters with a cheapo spin grinder on a surface grinder. Also ,my shop is haunted as is yours, but as the song says ''Aint no haint gonna run me out''Good luck, Edwin.

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                        • #13
                          Originally posted by John Stevenson

                          TT
                          Bar is too long to go front to back and fouls the support arm.
                          Too bad they are too long - otherwise I would suggest making a new support to clear the bar or just a semicircle on the top half of one of the spacers. It's not likely the cutter is going to try to go too deep....

                          What about using a small carbide endmill in your CNC setup? Or maybe a carbide em to remove most of the metal and then finish up with your current setup? I haven't seen a carbide em with that much taper, but it could probably be ground for a single pass solution.....
                          TexasTurnado

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                          • #14
                            John,
                            I'm agreeing with Edwin. As the rack has straight sides, why not make up a cutter? No fancy involute form to grind up. Either a single point (slow but simple) or a multiple arrangement from some gauge plate. Might have to be properly heat treated but I think you were saying you had a friendly H/T across the road. If you had a T&C grinder buried in your shop somewhere you could even braze on some carbide and grind the form you need.

                            Michael

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                            • #15
                              I had thought of that, using end mills but they would have to be carbide, a small HSS one won't last on this stuff.

                              I have done them this way before, funnily enough for the same job / customer. A 1.2 metre length of curved back rack to bolt to a round column.






                              I do have a Deckel clone grinder so that's no problem but seeing as this is setup and the CNC is busy on a long running job I'll give this a try.
                              .

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



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