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Holding small parts

Discussion in 'CNC Projects' started by Revdjembo, Dec 2, 2020.

  1. Revdjembo

    Revdjembo New
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    Hi,

    I have been asked to make 150 Christmas tree decorations using 75mm x 60mm x 3mm wood slices. My plan was to v carve a Christmas greeting from the customer into one surface. If the blanks could be vacuumed to the table then rather than reset zero for each item I could return the v bit to zero, slide the blank in underneath and turn on the vacuum. cut part. repeat. Unfortunately, I can't get a vacuum fixture to work. I've looked at lots of YouTube videos, experimented with a range of materials and layout but I just can't get enough suck to stop the part moving. The parts are all irregular shapes having been sliced from a branch of a tree.
    Any ideas?
    Am I going about this in the wrong way?
     
  2. Ariel Yahni

    Ariel Yahni OpenBuilds Team
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    Could you post what the stock looks like and what the end result should be?
     
  3. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    What are you using for the vacuum?
     
  4. Revdjembo

    Revdjembo New
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    Hi Thanks for replying.

    I'm using a shop vac for suction. I do have a small fridge compressor that I've been experimenting with too. But again not getting enough suction.

    Attached is a picture of the prototype. Which gives the general idea of what I'm trying to achieve.
     

    Attached Files:

  5. David the swarfer

    David the swarfer OpenBuilds Team
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    masking tape and CA glue.
    and don't do one fixture, do 6, set each of G54 through G59 to the center of a fixture/workpiece, then copy and paste your code 6 times with a G54, then G55, etc till G59.
    Then the same code will run centered on each of the Work Cordinate Systems in turn.

     
  6. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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  7. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Shop vacs are designed to move large volumes of air, pulling dust along in the process. Trying to use one to achieve and hold a true vacuum is an exercise in futility. Get a dedicated vacuum pump.
     
  8. Revdjembo

    Revdjembo New
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    Hi David,

    thank you for this.
    I had considered masking tape and ca glue but discounted it due to the fiddle of setting up each new piece. But the game-changer is doing more than one at a time. Which I didn't think would be possible as they are all irregular sizes. My knowledge of grbl is limited so hadn't come across G54 etc. Could you explain a little more or direct me to a video.
    Many thanks. I was starting to fret at the amount of work that was beginning to pile up.
     
  9. Revdjembo

    Revdjembo New
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    Hi, thanks for the reply. It's on my list of future purchases. I'm trying to do this as inexpensively as possible as it is for a family members restaurant.
    Thanks.
     
  10. Revdjembo

    Revdjembo New
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    This looks spot on! sadly it's out of my price range just now. Something to work towards.

    Thanks for putting me on to them.
     
    Peter Van Der Walt likes this.
  11. Alex Chambers

    Alex Chambers Master
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    What cad/cam software are you using?
    Alex.
     
  12. sharmstr

    sharmstr OpenBuilds Team
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    I had a similar situation. I went the double sided tape route (basically the same as tape and glue but faster.) However, I used the pattern feature in Fusion to do multiple parts. No need to set multiple stock locations. Each part was a bit different in size so I figured out where I wanted the center to be (that's how I CAM'd it. Bottom of stock, center) and where the top and bottom were (12 and 6 o'clock). I drew marks at 12, 3 and 9 o'clock on the part. On my machine bed, I drew multiple crosshairs that were 6 inches apart (yours will be whatever you want it to be). I could easily place my pieces exactly where they needed to go and in the correct orientation by lining up the marks on my parts with the crosshairs on the machine bed. In fusion I set it to pattern 6 inches apart. While the job was running, I could prep (tape and marking) the next set of pieces.

    You can still use this method without fusion patterning, just set your multiple work offsets like others have suggested.
     
  13. Revdjembo

    Revdjembo New
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    Hi,
    Vectric Pro and GRBL on UGS
     
  14. Alex Chambers

    Alex Chambers Master
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    Pity, we have a Fusion post processor that allows you to use multiple work co-ordinate systems, but I don't think you can do that in Vectric. So either you take @sharmstr 's advice and use patterning or you could use a text editor to create one g-code file from several - are your designs all identical or is each one different to the others?
    Alex.
     
  15. David the swarfer

    David the swarfer OpenBuilds Team
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    The machine has a home, this is 0,0,0 and is the Machine Coordinate System (MCS). Everything else happens relative to this.
    GRBL supports 6 Work Coordinate Systems, (WCS) accessed via G54 through G59.
    WCS are offsets from the MCS
    The default is G54, when you click the 'reset' buttons you are setting this offset, unless you have selected a different WCS on purpose.

    Why have offsets? Because generating Gcode (used to be written by hand!) with everything relative to the home is painful and error-prone. Writing it relative to a start position on the workpiece or on the jig/fixture/vice is much easier and is also universal, you can probably run the same code on 2 different machines, or run the same code at 6 positions on the same machine! (industrial controls have many more offsets, so you can fill a fixture with 50 or more parts and do the same code to each of them in turn, using the appropriate WCS offset.

    Looking at the UGS screenshots I see there are no buttons for WCS selection so one would have to use the command panel and enter the one you want, like G56 and press enter. when you do this you should see the offsets change. (and hopefully UGS is aware that the Reset buttons must now operate on the current WCS, I have not run UGS for years)

    How do we use this for 6 cup mats?
    When you generate your Gcode it will have some setup commands at the top, and one of them will be G54. The setup commands are there to make sure the machine is in the state the Gcode expects, otherwise expensive bad things happen, so do not delete anything but the G54.

    If we remove that G54 we now have code that can run under any WCS, it will use whatever WCS is set when it starts. (check the whole file, there may be G54's spread through the code for each operation)

    Way to do it 1:
    given that the gcode file has no G54-9 command in it we can set the WCS we want, and then run the file, and it will cut wherever the WCS has been set.
    1. for each WCS in turn, we must set the 0,0,0 point on the blank bit of wood.
    2. give G54
    3. run the code
    4. give G55
    5. run the code
    6. and so on till G59 has been done
    way to do it 2:
    first (if Vectric can output to multiple offsets then rather do that!)
    1. edit the basic file so there are no G54-59 codes in it
    2. create a new file in notepad
    3. put in six lines, G54, G55, G56, G57,G58,G58
    4. copy and paste the Gcode file after each of the above lines,
    5. save this file as 'alltogether.nc'
    then
    1. for each WCS in turn, we must set the 0,0,0 point on the blank bit of wood.
    2. run this alltogether.nc file and it will do all 6 workpieces in one run
    3. remove the finished pieces, replace with blanks, go back to (1)
     
  16. Revdjembo

    Revdjembo New
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    Hi Dave,

    Wow!

    Thank you for taking the time to explain all this. I have been Googling this too and I think I have a grasp of what I need to do now. I am impressed by your generosity. Thank you.




     
    sharmstr likes this.

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