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Thread: Rack Cutting

  1. #1
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    Default Rack Cutting

    While I was away Michael G asked me if I had any additional information pertaining to the cutting of racks on a mill. Additional because Michael was pondering the hows a couple of years ago. http://www.woodworkforums.com/showth...23#post1589223

    I had a look and found some information in a Cincinnati milling treatise that may or may not be relevant. A skim through Google Images resulted in the discovery of photos of a Brown and Sharpe rack indexing attachment that may provide MG with some inspiration - http://www.practicalmachinist.com/vb...chment-239525/

    Others may have information or rack cutting experience that they may be able to share. I have yet to cut a gear let alone a rack.

    BT
    Attached Images Attached Images

  2. #2
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    I used my shaper. It was simpler than making a rack cutting attachment. Funnily enough one came up for sale on fleabay recently but I didn't bid on it - I think it was 50 taper and while convertible to 40 taper, too much hassle given I've cut 1 rack in 30+ years. PDW

  3. #3
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    Thanks Bob. Interesting stuff - may still be filed in the too hard basket but currently sitting in the future projects file (why? - because I'd like to see if I can) From your earlier post I printed out the picture of the stack of gears and while in Scotland I tried working out the number of teeth. I got some but some I missed. Most interestingly though only by a few teeth and probably because I assumed that they would be similar gears to those for the D/H, so 48 instead of 49 and so on.

    Michael

  4. #4
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    HI,
    I was actually just wondering today how would you cut a Rack on a Milling Machine, now I know, Thanks Bob. I would think that one of those attachments wouldn't be cheap to buy.
    All The Best steran50 Stewart

    The shortest way to do many things is to do only one thing at once.

  5. #5
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    By coincidence there is one on US ebay at the moment -
    http://www.ebay.com/itm/Brown-and-Sh...item3a87a0ed68
    Looks to run on a 50 taper so no good to me, although the weight is something too.

    As the pictures will eventually disappear, here the main ones for posterity.
    $(KGrHqVHJEIFJbMtiLK!BSdrZb0YS!~~60_57 (Medium).JPG $(KGrHqN,!qsFJgVksmNQBSeBIUWGSQ~~60_57 (Medium).JPG $(KGrHqEOKpgFJjUOhd0cBSdrZfPUPg~~60_57 (Medium).JPG

    Michael

  6. #6
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    I've only ever had cut gears and haven't had a reason to cut a rack, but is there any reason the table isn't simply moved along by the appropriate distance according to the Circular pitch being cut? I have a DRO on my mill, but failing that I would set up a temporary equivalent so any errors weren't cumulative.

  7. #7
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    No, that's how it's done.
    The doosaflicky that Bob posted is the linear version of a dividing head so that the circular pitch movements are more exact and regular (similar to cutting a gear on a rotary table vs. dividing head - they can be done on the RT but requires a more meticulous effort to get it right). A DRO would make things far easier but this is old school pre DRO stuff - black magic to the CNC generation
    The pictures that I posted for the cutting device are because on a normal horizontal mill the cutter is orientated in the wrong direction to cut a rack more than a few inches long (runs into the arbor support or the machine). Strictly speaking you could sharpen an end mill to 29 degrees and use it in a vertical head but that becomes a fraught exercise as the cutter is now long and thin.
    I've used a few horizontal (disc type) cutters lately and they work beautifully for slits and other deep but narrow cuts so much prefer to do it this way.

    Michael

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