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View Poll Results: Time to pull the trigger?

Voters
9. You may not vote on this poll
  • Do it! You can always buy more parts.

    5 55.56%
  • Hold off. Parts cost money.

    4 44.44%
Results 1 to 17 of 17
  1. #1
    Join Date
    Nov 2009
    Posts
    4

    Question First Build: Looking for comments on my design

    After drooling over this forum for weeks, I have decided it is time to start my own build. This will be my first CNC project and I'm starting from scratch in
    order to learn as much as possible during the process. I'm looking for guidance from folks who have been down this road. Any help or comments (good or bad; I can take it) would be greatly appreciated!

    The basics of my design are as follows:

    The base frame will be 2" square welded steel tubing. The rest of the structure will be constructed from 3/4" MDF. The rails are 1/4"x2" aluminum sheet. All rails overhang 1/2" from the edge. Sitting on the rails are linear carriages from cncrouterparts.com. The gantry rides on the extended linear carriages.

    I will be using 5 start 1/2"-10 precision threaded rod and anti-backlash nuts from cncrouterparts.com. I will be placing thrust washers at each end to bear the axial (correct?) loads. I plan to use 380oz-in steppers with a Gecko G540 and 48V 12.5A power supply. I'm also planning to use a Makita RF1101 2.25HP router due to its built in speed controller and reported low noise.

    When all is said and done, I should end up with a cutting area in the neighborhood of a 45.5" x 31" x 8.5".

    I have modeled the machine I intend to build in Inventor. I have posted the designs here:



    You can view the model with Autodesk Design Review or eDrawings Viewer (both free).

    I have also put together a BOM with price, quantity, and source.

    So, what do you all think? Did I make all of the newbie mistakes at once, or could this actually function? Thanks in advance!

    -Brian
    Attached Thumbnails Attached Thumbnails Gantry Side.jpg   ISO Bottom.jpg   Iso.jpg   Rear Bottom Perspective.jpg  

    Rear Gantry Back Removed.jpg   Rear Perspective.jpg  

  2. #2
    Join Date
    Mar 2009
    Posts
    106

    I approve!

    I just completed a router using Ahren's parts and I'm completely satisfied with the results. I don't think you can go wrong with his approach.

  3. #3
    Join Date
    Mar 2009
    Posts
    106

    Unhappy oops

    I accidently sent that post before I was finished. The only advice I would give you is to use something a bit stiffer than MDF for your gantry. I used a laminated wood structure but if I was doing it again I would definitely go with the 80/20 extrusion for the y-axis beam. I did use the 80/20 for my Z and I was able to assemble it in less than an hour.

  4. #4
    Join Date
    Feb 2004
    Posts
    1086
    Looks good! I would second the comments by Marzetti than an MDF gantry could be problematic. Unless you drive it from both sides, this material just isn't stiff enough to resist racking and torsion problems. I'd get a piece of extrusion or steel in there.

    Best regards,

    Ahren
    www.cncrouterparts.com

  5. #5
    Join Date
    Mar 2003
    Posts
    35538
    Yes, everywhere you have a single layer of MDF, it won't be stiff enough. At a minimum, I'd say either laminate 3 pieces of 1/2" MDF into a solid 1-1/2" piece, or build torsion boxes. 3 pcs of 1/2" will be stronger than 2 pcs of 3/4".

    You're going to be spending a lot of money, and you won't be happy with the results from that design.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  6. #6
    Join Date
    Mar 2009
    Posts
    106

    one other thing....

    I hadn't noticed the other day that you were planning on aluminum for your rails. While this would certainly work short term, it would wear very quickly. Cold rolled steel is cheap, I'd stick with that.

  7. #7
    Join Date
    Feb 2004
    Posts
    1086
    Marzetti, that's a good point on the aluminum rails -- I admit I went straight to the pictures . Another thing to keep in mind is the tolerances held on CRS is much better than aluminum. So if you want a nice flat rail of uniform thickness, you'll be much better off with the cold rolled steel. Additionally, the piece you use for the gantry rail will add substantial stiffness to the system if it's steel.

    Ahren
    www.cncrouterparts.com

  8. #8
    Join Date
    Nov 2009
    Posts
    4

    Updated Drawings

    First, I'd like to thank you for the feedback. You have already saved me hours of building and rebuilding.

    I've made some updates to the design according to some of your advice. I already have some steel laying around the garage. This seemed like an ideal home for it.

    I have reinforced the gantry vertical members with 1" square steel tubing (welded). Also, I have sandwiched a piece of .13" thick steel between two 3/4" sheets of MDF for the main gantry cross member. These reinforcements should make the gantry a bit more rigid. Another option would be to put a 1" square steel tubing frame on the back of the gantry cross member. Do you think these additions will be enough?

    On the Z axis, I realized that I had no material to "close the box" around the rails. I added an aluminum back plate to ensure the bearings stay snug against the rails.

    I've also decided to use cold rolled steel for the rails. I'd rather spend a little extra and only have to do it once. Thanks for the tip!

    I've attached updated drawings. Thanks again for the thoughtful commentary!

    -Brian
    Attached Thumbnails Attached Thumbnails Image.jpg   Image2.jpg   Image3.jpg  

  9. #9
    Join Date
    Nov 2009
    Posts
    4

    More updates

    After some doing some simulation in Inventor, I have decided to to use torsion boxes for the gantry verticals and horizontal to reduce flex.

    I've also decided to mount the Y and Z bearings back to back and place rails on the Z axis.

    I think the motor pushing the gantry is the biggest weakness with the current design. Ideally I'd go with a rack and pinion drive for the X and Y axis, but budget is starting to get tight and I can't make the numbers work. For now I think I'll stick with one motor driving the gantry and upgrade to 2 if it becomes a problem down the road.

    I'm feeling much better about this design. Do you see any new major flaws? Thanks!

    -Brian
    Attached Thumbnails Attached Thumbnails Image.jpg  
    Attached Files Attached Files

  10. #10
    Join Date
    May 2009
    Posts
    264
    I don't think you are going to be happy with the Y drive nut up on top like that. You may get binding due to the offset forces.

    If you have not re-thought the use of aluminum rails.....you should.

  11. #11
    Join Date
    Feb 2004
    Posts
    1086
    The offset screw will actually work OK, although it's not ideal. These carriages are rolling element, and would take a significant offset moment to bind. I agree on the rails however -- definitely CRS and not aluminum.

    Other than that, I think your design is looking pretty good!

    Ahren
    www.cncrouterparts.com

  12. #12
    Join Date
    Apr 2007
    Posts
    8082
    I'm in agreement with Ahren and mlabruyere. I think that your previous design is the better one due to placement of the Y axis lead screw and as Ahren indicates, the CRS rails are more precise will last much longer than aluminum. If this machine is not intended for long term use then aluminum will work ok. The CRS flat stock rail is probably less expensive than the aluminum anyway.

    CarveOne
    CarveOne
    http://www.carveonecncwoodcraft.com

  13. #13
    Join Date
    May 2009
    Posts
    264
    A not about CRS:

    I got my CRS pretty cheap by calling the metal shop and asking for "DROP" pieces that are close to the length I need. They cut them down to size for me at no charge as well. I saved a lot of cash over getting a virgin plate.

  14. #14
    Join Date
    Nov 2009
    Posts
    4
    Putting the Y screw up top was certainly a bit of a convenience trade-off. I'll try it out and see how it goes. I've seen other designs that place the drive screw in similar locations, so hopefully it won't be too much of an issue.

    I took the leap yesterday and ordered all the mechanical parts! I did decide to go with CRS rails after marzetti and ahren's suggestions late last month. (thanks!) I also ordered the router (Makita RF1101).

    I will begin documenting the build as soon as things start arriving. I expect to order the motors and controller later this month if things go well.


    Thanks for the tip on "DROP" CRS, mlabruyere. I wish I had waited one more day to order it, now! I'll keep that in mind for the next round.

  15. #15
    Join Date
    Jan 2010
    Posts
    2

    y screw placement

    the ideal vertical position of the y screw in order to have the least binding forces. would that be in the middle between the 2 horizontal rails or below that point, closer to the router bit?
    i am trying to picture how these offset forces work.

  16. #16
    Join Date
    Nov 2005
    Posts
    103
    For your first router, 'just do it' comes to mind. This one is an educational experience, and I am sure won't be your last.

    The guy at buildyourcnc.com suggests 'build ugly' so you can 'build pretty'. Just use this one as a working experience so you can re-design to rebuild your machine to be nicer. His free design is an 'ugly build' of a 2'x4' cutting bed machine. He really built it so he could design and build nicer ones like he is selling.

    The things I would buy 'to big' to start with are the steppers and drivers. If you don't want to DIY your drivers, consider the GeckoDrivers.com g540 (it drives up to 4 steppers at once). Also get you an old 'beater' (almost trash) PC with a real parallel port, or if you insist on using usb or a laptop, consider getting something like flashcutcnc.com as it seems to be a good USB interface and the laptop parallel ports are often just not up to the task (also, turn off ALL power saving features while you are on AC power!). If you use flashcutcnc.com device you will use MACH3 as the driver software, or if you use a parallel port typically MACH3 if you want to use windows, or use EMC2 if you are OK with running Linux (my personal preferance, but pick your poison -- both work well).

    If your are designing your own, go review the free plans at www.mechmate.com (you must register and agree to their conditions, but the plans are free for personal use or even commercial use ... check the agreement for details, just not true open source. They will negotiate royalties if you want to make their stuff for sale). Anyway, I like their rails and rack/pinion drive methodology. Just my thoughts.

    I hope there are a few jewels you can use. ... Let us know, and post LOTS OF PICTURES!

  17. #17
    Join Date
    Mar 2009
    Posts
    178
    nice design...hows it coming? i would move that y-screw

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