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  • How to cut a rack

    I want to cut a rack about two feet long on the side of some ally tube. I'd probably use thick walled 1 1/2" OD tube, and something like a 1 mod/24 DP rack.

    I have a horizontal/vertical mill, but the x travel is only 9", and that reduces to about 3" if I have the vertical head horizontal. And of course the horizontal arbour is at right angles to the direction I'd need to cut a rack.

    I have a lathe with 20" between centres, so I could think of mounting a cutter on a toolpost spindle and anchoring the workpiece between centres. Still not satisfactory.

    So, I'm prepared to make up some fixtures, but I can't work out the most sensible way to proceed. Any ideas ?
    Richard - SW London, UK, EU.

  • #2
    With out a rack cutting attachment for a horizontal mill, about the only other way is a shaper Slow but does work . One tooth at a time.
    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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    • #3
      Modify your tube to allow a stock rack to be mounted, it will be well worth the amount of time saved. Rack gear goes for just about cost of materials.
      James Kilroy

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      • #4
        Might be a good excuse to build a right angle attachment for the mills vertical spindle.
        I just need one more tool,just one!

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        • #5
          A simple V shaped D bit could be used seeing as it's on alloy.
          OK you only have 9" of travel but you could cut the 9", move the tube and cut again.

          This is what i did doing something very similar only I cut 1 and a half metres.



          And,

          .

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



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          • #6
            Ah yes, John. I remember seeing your video of cutting brass gears with a similar bit. I might take that route.

            Sorry to have missed you at Sandown.

            What kind of rpm do you use for a cutter like that, with say a 1mm width of nose ?
            Richard - SW London, UK, EU.

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            • #7
              Probably about 3,000, the machine will run at 4,400 max but it's like a banshee so i tend to limit speed to 3K max and adjust feed to suit.

              A bit gutted about Sandown, free ticket and free lift down and back but the local airport had booked a full day on the Thursday to modify a powered roller off a conveyor system, Total down time was meant to be 8 hours but instead of it hitting the floor at 8:00am it never arrived until 12:00 noon.

              That meant working late and then instead of it being fitted that evening as planned they decided to fit it Friday and I knew they would need help so stayed here to answer the phone.

              If I had done Sandown I know they would have stuffed the fitting up enough to require me to have to go on site.
              As it was it took 3 phone calls.

              Oh well next show - Harrogate next May
              .

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



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              • #8
                I do not know the purpose of the rack or if about 2 feet long is the same a about 20 inches or if a slight helix angle would be acceptable. One way may be to mount the tube in the lathe but offset and then use normal screw-cutting methods to make a thread on one side of the tube. The chuck end could be easily offset in a four jaw chuck but you would have to make an insert plug with an offset centre to support the far end of the tube.
                Mike

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                • #9
                  Mike.
                  That is workable. Taig cut the racks for their lathes this way, large circular jig that holds 12 - 16 ? racks and it's then screwcut.
                  .

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



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                  • #10
                    Originally posted by John Stevenson View Post
                    That meant working late and then instead of it being fitted that evening as planned they decided to fit it Friday and I knew they would need help so stayed here to answer the phone.

                    If I had done Sandown I know they would have stuffed the fitting up enough to require me to have to go on site.
                    As it was it took 3 phone calls.

                    Oh well next show - Harrogate next May
                    I have a YAC free number I give out to people in the uk to call me on when they insist, I can go on their website and change which number it rings at the click of a mouse, and when it calls me I get a option to send them to voicemail instead of answering them, which I get attached as a .wav or .mp3 on a email.
                    Person ringing you has to pay a higher call cost to use it tho, no free lunch...

                    That way don't have to worry about which number they have etc, only personal callers get my actual home phone.
                    http://yac.com/

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                    • #11
                      I would use the vertical head turned horizontal with a single point cutter. Clamp two vee blocks down so you can move the work indendently, then cut as many teeth as you can. Rig an indexer that will sit into the first tooth cut, then move the work so your indexer drops into the last tooth cut, clamp, and cut the next batch of teeth. You could use a piece of precision ground round stock to drop into the cut for indexing. Hope that makes sense.

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                      • #12
                        Forest - Once I've turned the vertical head to horizontal there's so little x-axis left above the table that that method isn't really viable.

                        Mike - I don't want a helix angle, but... That would be an excellent way to gash before I use John's method. I like it. The milling will get rid of almost all of the helix angle, but I should think that gashing like that should take out over half of material.

                        Ah ! Thinks ! I could gash both right hand and left hand to leave the narrowest part of the gash in the middle of the width. That would sort out any end force on the cutter when I start to mill it too. Just got to set the threading position correctly, but I know what I'm doing there. I've often had to restart a threading operation after a minor crash.

                        Tiff - it's a gravity application, so extra clearance is not a problem. I'm making a copier table, rinning a camera mounting up and down the rack.
                        Richard - SW London, UK, EU.

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                        • #13
                          Just do it on the vertical mill using a suitable vertical cutter. You can grind your own surely.

                          Once you run out of X axis travel simply move the part and start again. You could indicate off a tooth each time to "pick up" properly, there's numerous methods, e.g. by clamping a dowel pin down on a tooth and then finding the center of the overhanging portion of the dowel pin.

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                          • #14
                            Originally posted by loply View Post
                            Just do it on the vertical mill using a suitable vertical cutter. You can grind your own surely.

                            Once you run out of X axis travel simply move the part and start again. You could indicate off a tooth each time to "pick up" properly, there's numerous methods, e.g. by clamping a dowel pin down on a tooth and then finding the center of the overhanging portion of the dowel pin.
                            That's what I was suggesting. Maybe a bit wordey. With a 24DP he could probably cut at least 20 teeth in the 3" of travel before repositioning. The repositioning won't be a timesink considering how many teeth he needs to cut.

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                            • #15
                              Forest, I thought you were suggesting I turn my vertical head horizontal. I was saying that if I did that, I'd lose too much x-axis travel - or table space under the cutter. I'd only get a couple of inches before having to reposition.

                              JS suggested I make a milling type cutter and keep the vertical vertical. That gives me nine inches of x-axis. It's quite a small mill with quite a tall vertical head.

                              The gashing idea is a one set up proposition. A few passes, but safe. The vertical milling with a home made cutter with a max of about 1000rpm with my mill struggling means manually advancing say 200 cuts. Reducing the amount of material each of those 200 cuts has to deal with is well worth a couple of gashing passes in the lathe.

                              At least, that's the way I look at it.
                              Richard - SW London, UK, EU.

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