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Strategy for Project Bigger than Machine..??

Discussion in 'CNC Mills/Routers' started by JWhitten, Mar 24, 2015.

  1. JWhitten

    JWhitten Well-Known

    Sep 16, 2014
    Likes Received:

    I've been mulling over a new project I want to undertake which is going to be larger (longer) than my CNC router. I've been giving it some thought and have realized that I *could* fit the workpiece into the machine from the side and work it in sections. But I'm wondering about the particulars for doing that. My first thought is that I would want to do something like "pin register" it so that I would load the workpiece into the machine to a known starting location and then have it drill registration holes at specific points along the workpiece. Then as each section is completed, I can push the workpiece further into the machine, pin it in place, and continue the job.

    So my issues are at least two-fold, one is devising some method to support the workpiece as it enters / exits the machine. This one is probably not that hard to figure out. But the other issue has me scatching my head a bit and is the basis for my question here:

    Is it possible for Mach3 to somehow alert me that the current section is done and it's ready to reposition the workpiece? Maybe by popping up a dialog box or something? Ideally I'd like to leave the router idling off to the side while I reposition the piece and then just hit "Enter" (or something) to continue the job.

    Does anybody here have any experience in doing such a thing and could offer me some guidance?

    Thanks for your assistance!

    BTW, in case you're curious, I'm interested in building a vertical CNC machine to put into my garage to permit me to be able to work with full-size (4x8) plywood sheets. I don't really have the room to build a horizontal table and leave it set up, nor anyplace to really store it when not using it, so going vertical seems like a reasonable solution.

    #1 JWhitten, Mar 24, 2015
    Last edited: Mar 24, 2015
  2. dddman

    dddman Journeyman

    Mar 2, 2014
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    I don't really no how, but what you need here is a tool change
  3. Rick 2.0

    Rick 2.0 OpenBuilds Team
    Staff Member Moderator Builder Resident Builder

    Dec 20, 2013
    Likes Received:
    What you are referring to in regards to breaking up large works into sections is called toolpath tiling. A brief discussion on the subject is provided here. With this you can work entire sheets of 4x8 plywood on something like a 4x2 machine.
  4. Hytech2k

    Hytech2k Veteran

    May 6, 2014
    Likes Received:
    Here's a video that may be helpful..

    and an article I found on another forum, might give you some ideas... I haven't needed to cut anything longer than my bed yet but the way I understand just setup your DXF in different parts and use index pins to accurately move the project. Use separate toolpaths and Mach will stop and wait for you to move the board and load the next toolpath...

    "We built the Joes2006 model using a Techno Table Top CNC router with a cutting area of 24" X 29".
    Instead of indexing the parts, we made an indexing fixture out MDF. This fixture is 48" long with 3 indexing positions located 12" apart. Therefore I separate the file into 12" or 24" segments depending on the overall length needed. Once the part is clamped in the fixture, I cut the first half, (more or less) of the file. With the part still clamped in the fixture, I lift the fixture off of the indexing pins and move it 12" to 24' inches depending on the size of the part. It's worked great and I've used it for various items other than the 2006 model. With this setup, I regularly cut 48" long parts with no issues on a machine that has only a 29" max cut length.

    On the Techno aluminum bed I attached 3/4" MDF that would normally be the spoil board. I then had the Router drill and pocket 6 holes along the MDF that are separated 13.75" along the Y axis and every 12" along the X. By using the same DXF file to drill and pocket the corresponding holes on the bottom of the fixture, you ensure perfect matching for the fixture pins. The files and JPG attached below will show you this.

    For the indexing pins I used 1/4" dia steel pins bought at Ace Hardware that are 1" long. For the indexing holes in the MDF table top and the MDF fixture, I installed 1/2" long bronze flanged bushings that have 1/4" ID. These were also purchased at ACE Hardware. These bushings look like a top-hat shape which explains the double hole positions on the DXF file attached below. The outer circle/ring is to pocket the flange. However you can choose what you like for the bushings. The holes in in the MDF were cut to match this OD and shape. All the bushings were epoxied in place. Some have slid out, however the epoxy coating in the hole has kept them to a snug fit. Since the indexing holes are just over 1/2" deep, the indexing pins stick up just under a 1/2". In order to assist the moving of the fixture, which can be a little cumbersome, I lift one side and slip a stick of 3/4" MDF under it and then do the same for the other side. This supports the fixture bottom above the pins and allows me to easily slide the fixture and part down the bed to the next set of indexing pins. I marked the outside of the bed and the fixture where the pin positions are located to help line them up during the move. I also clamp the fixture in place as shown in the photo below. The clamps are supported on the outside with the sticks of 3/4" MDF that I use to slide under the fixture for movement.

    I made the fixture from 3/4 MDF with clamp bolts along the side inserted from the bottom up, counter bored in for head clearance, and held in place with blind nuts. I also added 3/4" MDF rails on the top and sides of the fixture to help support the actual clamps. On top of the MDF fixture, between the clamp bolts I screwed down a layer of MDF as a spoil board which also helps to firm up the fixture for flatness, as well as the side clamp rails.

    In the photo below you can see the fixture in place and indexed down 24" inches to finish the cut of the 34.5" piece for the Y Axis, which is also shown in the photo. You can see the forward most indexing pins in position The key is to divide up your file into 12", 24" or 36" segments. I place a 1/4" circle on my part drawings as my X and Y zero positions at every 12" where I may divide up the drawing file. This helps for reference and keeping it straight in my not so straight head.

    I hope I did not over explain this and cause confusion, as I'm trying help you see how versatile your smaller machine can be with this setup. This design could be used on a larger machine, but the longer you go, you may need external support such as used with chop saws. Just my thoughts and ideas.
    I hope this helps."


    Indexing Fixture
    Techvette and thingswelike like this.

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