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Thread: Table Top Not Flat

  1. #41
    Join Date
    May 2014
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    MA
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    610

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    I've never owned a PRT, but I know the PRS pulling up against the stop blocks is just part of the start up procedure. Just pull it tight to the blocks with the machine off, hold it there and power on. The motors will hold it square.

  2. #42
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    May 2014
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    Also, you might want to grab a tube of red Locktite and fix those bolts in place.

  3. #43
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    Oct 2009
    Location
    Elgin Illinois
    Posts
    706

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    Hello Eric..... I finally made it out to buy some red Loctite, and on Tuesday I removed each X car gantry bolt, one by one, applied Loctite to each thread and nut, and then torqued appropriately. (Except for the bolts that have a loose flat threaded plate hidden inside of the extruded cross pieces so I could only apply Loctite to the bolts.... Very challenging to re-install those bolts, when the threaded plates can slip and slide all over without any way to see them......)

    And on Tuesday evening I made a magnetic base for my dial indicator. I can continue on with your list on Wednesday afternoon.

    Thanks for the advise on pulling the X-car into square, and then powering up the Bot. I was so hypnotized by my long-time routine of checking the squareness of my gantry with the power off, I just would not have thought outside of my box.

    Mayo,,,,,, any word on the local source for pinions?

    Thanks, Chuck
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

  4. #44
    Join Date
    Apr 2001
    Location
    South Elgin, IL
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    458

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    Chuck, I got pinions from Motion Industries Inc. 786 Church Rd, Elgin IL 60123
    I brought them one of mine so it would be easier to order.
    Looking at the 5 year old receipt, it may be time for me to get them again!
    They didn't have mine in stock so they shipped direct to me from Boston Gear.

  5. #45
    Join Date
    Oct 2009
    Location
    Elgin Illinois
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    Thanks Mayo! I go by Motion Industries once a month when I go to a local auction gallery. Chuck
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

  6. #46
    Join Date
    Oct 2009
    Location
    Elgin Illinois
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    Hello Eric. I have done some testing results. First, I set up my digital height gauge and the dial indicator, both as shown. I used the MZ command to change Z, and see if the dial indicator and height gauge matched the Bot display.
    With the height gauge measuring at the collet: Start at Z=0", MZ .5 -> .498", MZ.75 -> .747", MZ1.00 -> .995", MZ.75 -> .749", MZ.5 -> .501, MZ.25 -> .249", MZ0 -> .002", MZ1 -> .994", MZ0 -> .001", MZ1 -> .993" (IE: entered move z .5, measured .498") I don't know if these readings are acceptable or not. Thanks, Chuck

    With the dial indicator reading on the top of the Z/spindle mounting plate: Start at Z=0", MZ.005 -> .005", MZ.010 -> .009", MZ.050 -> .049", MZ.1 -> .100", MZ.010 -> .011", MZ.005 -> .007", MZ0 -> .002"
    Attached Images Attached Images
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

  7. #47
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    Oct 2009
    Location
    Elgin Illinois
    Posts
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    Hello Eric. With the dial indicator touching on the little bracket, as shown in picture 2 of the previous post, I jogged the spindle all over the table, at Z = 0". I kept the spindle moving around for about 20 minutes. The start of this movement is shown in the attached picture. At the start, z= .000" and at the end of 20 minutes, z was still at .000". But it was interesting, though probably not significant, that the entire time the gantry was moving, the needle on the dial indicator vibrated, almost to the point of being a blur, between the values of +.0005" and -.0005", always centered on zero for the average reading.

    Then I ran the last actual file I had run, where I had to shim up one end of the plaque to get a good V-carving. This was a small file, that only took 10 minutes to run. I ran it as an "air cut". At the start of the test, the dial indicator on top of the spindle attachment plate (shown in middle picture of previous post) was at .000" By the end of the short test, the dial indicator read .002" when the SB3 screen showed it was back at the start value.

    Does any of this suggest anything?????? Thanks, Chuck
    Attached Images Attached Images
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

  8. #48
    Join Date
    Oct 2009
    Location
    Elgin Illinois
    Posts
    706

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    Hello Eric. Here are some pictures of my table. What other pictures would you like to see? (My camera's macro/close focus doesn't seem to work.)

    My bottom two layers are single big sheets of 3/4" Medex (or equal), screwed to the steel frame, with the plenum glued on to the bottom layer with Tite-bond glue. The sacrificial layer is Ultralight, glued on to the plenum with Tite-bond. The inside of the plenum was sealed with shellac, and the outside edges were sealed with shellac, and then painted. I couldn't find any visible evidence of delamination by looking at the edges, except for a short glue gap, of maybe 1" (it's too late to go back down and check), but it is painted over, so it has not moved since I built the table.

    I will try to figure out how to get the Z pinion out, so I can buy a new one at the local source Mayo provided...... I have never had to take apart the Z car, and it didn't look obvious when I looked at it.

    Sorry this has taken me so long....... I have been working on making a strange table for somebody, just using regular tools. I greatly appreciate your input!!!! Thanks, Chuck
    Attached Images Attached Images
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

  9. #49
    Join Date
    May 2014
    Location
    MA
    Posts
    610

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    Ok, here's where I THINK you're at:

    You said that after you ran that file that your dial indicator read .002 instead of 0 like the shopbot display said for Z. You also said that if you push up, and pull down on your Z you can get it to move .001" in either direction. That's where I believe the difference is coming from. Did you tigthten your motor to the gear rack? Did you replace your pinion?

    After you sort that check that your long X rails are prefectly level the long way, and too each other. This will probably require you getting your hands on at least a 6' good quality level. If they aren't level you'll have to adjust the feet on your machine to get them level.

    Do that first.... THEN:

    Zero off of table and surface your entire table. Surface deep enough so that every single square inch of the table is machined so that you can gaurantee that the table is flat. Then try your job again.

  10. #50
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    Oct 2009
    Location
    Elgin Illinois
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    Hello Eric. All the measurements I supplied were made with the old Z pinion, and without having tightened the Z motor (to tighten on the PRT requires disassembly of the Z car, which I didn't want to do,,,, I just wanted to measure one thing at a time).

    I have a 6 foot and 8 foot level, which I bought for my Shopbot assembly, and have never used them for anything else. I measured everything (with a digital angle gage on top of the level for double checking) this morning, and will post pictures later. But everything checked in X and Y, from rail to rail and on the table, at many places was level.

    I just got done removing the spindle and taking out the Z pinion. At that point, I checked the tightness of the Allen head bolts holding the Z motor, and they both snugged up without too much effort, but they were not actually loose.
    I will be going off to the business Mayo told me about shortly to get, or order a new Z pinion. The old one does show some wear, which I think is clear in the photo.

    Thanks, Chuck
    Attached Images Attached Images
    Chuck Keysor (circa 1956)
    PRT Alpha 60" x 144" (circa 2004)
    Columbo 5HP spindle
    Aspire 9.0, Rhino 5

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