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Bridgeport DRO X-axis Scale Question

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  • Bridgeport DRO X-axis Scale Question

    What's better, mounting it to the front or the back of the table? I'm wondering if losing the ability to mount something off the front of the table is a bigger deal than losing some Y-axis travel.

    I'm replacing the DRO on my old Bridgeport J-head Mill (42" table, long travel knee) because the PO disabled the power feed stops and had the x axis mounted offset to one side and when I fed the table to one side the reader head crashed into the end of the scale destroying it (and a whole new DRO assembly was cheaper than just replacing the broken vintage Mitutoyo parts).

    The original X axis scale was mounted in brackets made to fit the table front T-slot, I didn't even know there was a slot under them and there were a few times I would have used it- the one that comes to mind was when I was machining the throttle body mount on the front of an intake manifold plenum and it was just too long to mount on top of the table, hanging it off the front of the table would have been REALLY nice (I did something somewhat sketchy with some angle plates hanging it off the back of the table). I'm not sure if it was more convenient or in the way on the front of the table- it got in the way, but it was nice to have a flat surface in front of the table to set stuff on that was not using up table realestate. I'm also not sure if I can use the brackets that were there, all the original hardware is much larger than what came with the new scales (mostly 1/4-20 vs M4 and M5), and I'm not sure if I can drill out the mounting holes in the scale's reader head large enough to use them (the spacing appears to be standard).

    Mounting it on the back appears to be a piece of cake, just locate and drill 4 holes, maybe a few more if I mount the supplied guard. OTOH, right now the y axis can travel till the table is against the column. The scale use up over an inch of space, and If I mount the guard it will use up close to 1-1/2" of the Y-axis travel.

    Thoughts? Anything I'm overlooking?

  • #2
    I put it on the back. Much easier mounting and the lost travel is better than having too much junk hanging out front.
    Definitely mount the shield. Don't know how many times the shield saved me from cranking the table too far back.
    Next time I mount one I will make a stronger guard so it acts as a stop block.


    • #3
      Originally posted by Silverback View Post
      The scale use up over an inch of space, and If I mount the guard it will use up close to 1-1/2" of the Y-axis travel.

      Thoughts? Anything I'm overlooking?
      If possible, I would try to mount a hard stop on the saddle. That way the guard could be smaller since it doesn't need to protect the scale from
      the column.
      Location: Long Island, N.Y.


      • #4
        I put mine on the back also.


        • #5
          Mount on the back, and as per RichR suggestion, a hard stop on the saddle for protection. And while you're mounting and protecting things back there, and loosing a small amount of travel in the process, might as well hang a way cover that protects the knee and column ways too. Depending on the style, the way covers might even double as a travel stop for the scale.


          • #6
            I put mine on the front. Loss of Y can be a problem, but if it is truly a Bridgeport, rigidity is not the best from the factory, and compensating for that loss in Y is compounded when one extends the ram to make up for it.

            Arguments abound for both arrangements. Just my 2ยข.

            Dan L
            Salem, Oregon


            • #7
              On a 12" knee (Y) , I would go in the back
              On a 9 " knee , I would go on the front as Y travel is more critical
              Use a piece of 1-1/2 Aluminum Angle to mount the scale on and the leg of the angle will shield the top of the scale from chips

              Green Bay, WI


              • #8
                I mounted mine on the back. While you do loose a couple inches of travel the head can be brought forward enough to compensate for any loss. I have also installed a hard stop to prevent damaging the scale and/or shield. By leaving the slot on the front of the table available you can clamp down large or odd shaped parts. I have found over the years I often use the front slot to mount a support for oversized pieces.


                • #9
                  I mounted my scale on the back. Out of sight out of mind. The mounting kit also came with two 1 in round dead stops.



                  • #10
                    Sounds like everyone says back... and yes, I have a 12" knee which actually has about 13" travel. The loss of travel bothers me a little since my ram is stuck (I bought it that way) and I haven't taken the time to figure out why and because this whole exercise is because I ran out of X Axis travel and broke the scale.

                    I might have a picture of it with the X scale on the front... the mitutoyo scales are pretty beefy and it really was like someone put a rail across the front of the table.


                    • #11
                      Anyone have pictures of their hard stop? I'm curious what you did.

                      If I don't do something I'm sure at some point I'll run it into the column and smash it, that's just how I roll... "huh, why doesn't this thing want to move any farther, there's still a couple of inches till the table is against the column... grrrr (cranks harder)" :-/