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Thread: Checking your PRS for square

  1. #1
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    Default Checking your PRS for square

    Hey all here's a method I use to check my PRS for square.

    https://youtu.be/s2z9tTbTdcY

    It's a quick check I do with some scraps. I so this every time I surface my table to make sure my machine is nice and square.

  2. #2
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    I wanted to thank you for your video, Eric. I did not use your exact method but a variation of it. I nailed a couple of scrap pieces of MDF in each corner with plastic nails and then cut out a large rectangle, approx 94" x 46". Working by myself, it was then pretty simple to hook my tape on the corners and check the diagonals.
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  3. #3
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    I dug this old thread up looking for it so I could share it to someone else and I realized I never posted my updated way that I keep my ShopBot in square:

    https://youtu.be/LrSLWpKjLU8

    This is a method that I use that uses a prox switch on both of my X motors. With a script, I stop one of the X motors, and use the other one to gently (and accurately) bring my gantry into square each time I power up.

    When I first started using my ShopBot, I didn't realize they could get out of square, which is why (after getting burned on running a bunch of MFT tables) I started using my modified squaring method. Now I have it run automatically with this method at powerup. It's very accurate and repeatable. Best of all, if you're into doing a bit of wiring, it can be setup with a relay and some scripts.

  4. #4
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    Once again digging up this old thread... I recently moved my machine across the shop, and naturally I checked everything after the move to make sure it was in spec. Unsurprisingly it got a bit out of square. I used the same method as I did with the dowel pins, but I changed it a bit. I got some flat tape measures and taped them to the table:

    IMG_20191008_101026.jpg

    I used a V Bit to set the the tape measures' origin exactly at X0 Y0 and X0 Y48. Then taped them down and ran them diagonally across the table. From there I used the routine I did in these videos to get my machine perfectly back to square.

    https://www.amazon.com/FastCap-PMS-F...6&sr=8-1-fkmr2

    That's the tape measure I used. Hope this helps someone!

  5. #5
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    Jun 2016
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    Hey Eric

    watched some of your videos and you have done some really cool mods to your shopbot. You may have already done this, but if not - any chance you could put together a step by step tutorial on how to get your auto square of the gantry setup and share the code to do it? I would think every owner and frankly shopbot should implement this into their machines.

    Thanks

  6. #6
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    I haven't put together a tutorial to be honest. It'd be hard to do it because of the differences between each different ShopBot. The concept is pretty simple though:

    Whenever you move your X axis both motors move in unison. This is often controlled by a simple jumper on the ShopBot. Pull that jumper and now when you move on X one stepper motor will turn, and the other one will not.

    So if you move your gantry with that jumper removed you twist your gantry.

    You can very simply wire that jumper into a relay (one that you might already have in your control box, or one that you add). Relays can be controlled by any output in the SB control software. Once you have that setup you have a software switch to shut off one of your X motors. Follow so far?

    Now with this control, you can shut off one motor and move the other motor thereby twisting your gantry to an exact amount of your choosing.

    The next step is to do a measurement. Most ShopBots only have a proximity sensor on one side of the gantry, so how do you measure how far your gantry has twisted? Well, you add another proximity sensor to the other side. This is really simple. Just get the sensor and wire it like the other ones you already have. Use an open input.

    Now you have a way to shut off a motor, twist your gantry and measure the amount of "twist" your gantry has.

    The last part is to tie it all together:

    You write a script that will home your machine and measure the distance between the two sensors. If the distance is what you want, the script moves on. If it's not what you want the script knows how far apart the sensors are, it can shut off one motor, move the gantry the specified amount and then turn that motor back on. Your gantry is now square.

    The script itself is really simple, it's just turning on and off some inputs, and moving tiny amounts, and doing a bit of arithmetic.

    Does that make sense?

  7. #7
    Join Date
    Jan 2004
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    Marietta GA
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    Default

    It all sounds so simple when you put it like that...

    Quote Originally Posted by EricSchimel View Post
    I haven't put together a tutorial to be honest. It'd be hard to do it because of the differences between each different ShopBot. The concept is pretty simple though:

    Whenever you move your X axis both motors move in unison. This is often controlled by a simple jumper on the ShopBot. Pull that jumper and now when you move on X one stepper motor will turn, and the other one will not.

    So if you move your gantry with that jumper removed you twist your gantry.

    You can very simply wire that jumper into a relay (one that you might already have in your control box, or one that you add). Relays can be controlled by any output in the SB control software. Once you have that setup you have a software switch to shut off one of your X motors. Follow so far?

    Now with this control, you can shut off one motor and move the other motor thereby twisting your gantry to an exact amount of your choosing.

    The next step is to do a measurement. Most ShopBots only have a proximity sensor on one side of the gantry, so how do you measure how far your gantry has twisted? Well, you add another proximity sensor to the other side. This is really simple. Just get the sensor and wire it like the other ones you already have. Use an open input.

    Now you have a way to shut off a motor, twist your gantry and measure the amount of "twist" your gantry has.

    The last part is to tie it all together:

    You write a script that will home your machine and measure the distance between the two sensors. If the distance is what you want, the script moves on. If it's not what you want the script knows how far apart the sensors are, it can shut off one motor, move the gantry the specified amount and then turn that motor back on. Your gantry is now square.

    The script itself is really simple, it's just turning on and off some inputs, and moving tiny amounts, and doing a bit of arithmetic.

    Does that make sense?

  8. #8
    Join Date
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    MA
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    Default

    The script I had setup wasn't even that long, 100 lines of code at most, and that included blank lines and comments. I'd share it, but it wouldn't make any sense or be useful to anyone because it was custom to my setup.

    If you just follow the logic and look at the ShopBot programming handbook you can write your own script really easily. I didn't use any fancy commands. The most fancy one I used was the "move until you hit a prox switch" command.

  9. #9
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    Mar 2015
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    Chicago, IL
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    I worked with Eric and Gary Campbell a few years back on this feature and set it up on my control box as well. I used a relay as mentioned above on a separate stand-alone module to interrupt one of the two X motors That's setup on output 5 which then allows me to rack the gantry accordingly. You can do all of this without the second prox switch if you'd like. In that instance, you would test for square, measure, find out if you need to move one side forward or back, make the adjustment, and test again. Either way, setting something like this up is helpful. I'll try to get some photos or a video of the basics for how this is setup on my system.

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