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XLarge C-Beam Gantry Plate V10 Dimensions

Discussion in 'CNC Mills/Routers' started by cncbeagle, Jan 2, 2019.

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  1. cncbeagle

    cncbeagle New
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    I recently ordered 7 of the XLarge C-Beam gantry plates and C-Beams to upgrade my existing router to something like the new LEAD Machine. I have assembled two gantrys and the wheels are too tight with the eccentrics in the full out position. As I obtained the eccentrics and wheels from other sources I assumed that was the source of my problem. Careful measurements compared to the drawings suggest the V10 plates do not match the drawings. I am comparing the plates to the STEP parts Library 1.5. The attached drawing shows the dimensions from the Xlarge plate in that library. It is difficult to accurately measure the center to center distance to verify the 100.6mm spacing. However, I am able to measure the distance from outside to outside of these holes. This distance should be 106.75mm according to the drawing. This matches the calculated distance as well (5.1 + 7.2)/2 + 100.6 = 106.75). This dimension on the plates I received measures between 105.5mm to 106.1mm depending on which of three calipers I used. The Starrett mechanical calipers measured the shortest distance. Given the +/-0.528mm adjustment range of the eccentrics (again from the drawings) I can understand why the gantry is wheels are tight. In addition the two C-Beams I recently ordered measure 0.2mm larger (outside to outside) than one I purchased earlier.

    Measuring the distance from outside to outside of the 9mm spacers with the eccentrics in the full out position should yield about 111.1mm (100.6 + 0.528 + 10). All my measurements average about 110.6mm. Similarly the inside to inside dimension of the 9mm spacers is 90.70 +/-0.05mm vs. the calculated 91.3mm (100.6 + 0.528 -10). Every measurement I can take suggests the 100.6 dimension on these plates is more like 100mm.

    The alternate sourced wheels measure 0mm to 0.15mm larger than an Openbuilds Xtreme wheel purchased earlier. I used the wheels toward the smaller end of the range to build the gantrys. The eccentrics are as close to identical as I can measure to those purchased from Openbuilds earlier.

    Are my measurements in error or do the plates not match the drawing? Any suggestions how I can use these plates?

    John
     

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  2. cncbeagle

    cncbeagle New
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    I found a V-Slot Gantry Plate 20-80mm in my parts bin left over from a previous project. The STEP 1.5 Drawing for this plate shows the dimension for an 80mm V-Slot as 99.70mm (see attached). The spacing between the eccentric and fixed holes on this plate exactly matches the XLarge C-Beam plate. Either one of these drawings is incorrect or the XL Gantry V10 plates have a 99.7mm spacing vs the 100.6mm on the drawing. The second attached drawing shows an assembled double XL gantry using drawings from the STEP 1.5 library. With the eccentrics in their mid position the wheels are spaced 100.6mm apart. That allows the full range of the eccentrics to make up for tolerances.

    With the eccentrics in their full out position the 99.7mm spacing the wheels will only be about 100.23mm (99.7 + 0.528mm ~= 100.23mm). Based on the drawings this spacing would likely result in tight wheels on a C-Beam.

    I'm left to conclude the V10 XLarge C-Beam Plates I received are not manufactured to the dimensions represented by the STEP 1.5 drawings.

    Beware!

    John
     

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  3. Christian James

    Christian James Well-Known
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    V wheels sourced from China can vary as much as a 20 thou diameter difference between smallest and largest. While this can present a major problem, I think the plate design could be altered such that either the eccentrics are made with a larger "sweep" or (preferably) vertical slots are machined in the plate (where the bottom eccentrics would have been) with an adjusting setscrew to take up the slack - something I intend to do.
     
  4. cncbeagle

    cncbeagle New
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    My measurements of the wheels I have are well within the 0.02" (0.5mm) range you mentioned, more like 0.01" (0.25mm). With the size and tolerance of the wheels I have there would be no problem building gantries if the hole spacing was 100.6mm as shown on the drawing. I measured each wheel the best I could and matched like sizes on each double wheel. So at least the wheels are universally tight.
     
  5. Christian James

    Christian James Well-Known
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    Problem is, its not just the wheels, the C beam itself has to be dead on spec which is why I would prefer a greater adjustment envelope.
     

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