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  1. #61
    I have spent an enjoyable afternoon staring at the screen. My problem was enough strength to overcome rorational deflection and keeping everything close. I think I may have cracked it using 100 x 50 x 6.35 al channel. Although I have shown a single section it would be no problem to bolt another piece back to back if it was required on building. The rails are close and the leadscrew is also very close. Tidy.Okay comments please.Bruce

    I changed the design slightly for the assy and put channel at the top to support the motor mount.
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    The more I know, I know, I know the less. (John Owen)

  2. #62
    C section also does not have very good rotational stiffness. If you added another bit on the back that would make an I, better but still adding some rectangular on the back (100*50, or over 100) would make a big difference. 1/4" looks a bit thin to be mounting the rails on.

    Two pieces of box section wide enough for the rails on a flat aluminium plate with the rails facing outwards is probably the simplest.

  3. Bruce,

    Another option you could look at with that build is two section of rectangular box section and bolt a backing plate or wings to them and bolt that to the gantry uprights as well as the box sections themselves. This will give a good bit more rigidity and either the wings or the backing plate could be indexed to help keep it all true and proper. Drop me a message and I can send you a few files in a format that you can use of ideas Jazz and I worked on that will work. Also take a look at my build log as there are some ideas in there you might be able to use. The following might help:

    If you scroll down you will see one model with sections lifted off to show an idea for the Y axis. That might be a good place to start from and change the solid rail to box or rectangular section extruded aluminium or steel and you would have something that would be a good bit more rigid then the channel. Just trying to help and hope not to offend.


  4. #64
    I may be sulking but I am not offended.
    Just kidding. I know that you guys just want me to be succesful and I really am happy to be guided. I am enjoying this part of the work and I know that I have to get this right now or spend more later.

    Big Thanks
    The more I know, I know, I know the less. (John Owen)

  5. #65
    Quote Originally Posted by motoxy View Post
    I may be sulking but I am not offended.
    Well let me have ago.!!. . . It's my special talent offending!!. . . . Ask my parole officer:whistling:. . . . . Only on both accounts.

    Bruce I'd be very weary with both the Channel and the angle they could both give you more trouble than they are worth.?
    Angle and channel are very rarely 90deg or very flat.! If the angle for the bearings hisn't perfectly 90deg and flat it will cause binding in the bearings. If compounded with the channel the rails are sat on not being square or flat then you'll have a bear of a time with sticking.!
    Both the Angle and channel will need bracing to fight flex and resonance, esp where the angle meets the channel used for gantry sides.

    Can I just ask why you are using channel,angle and 10mm plate in all your designs.? Do you have the material or a cheap source.?

    If you have the 10mm plate then why not build using a bolted and braced design which incorparates the gantry sides to increase strength and ridgidty. If braced enough even 9.5mm plate can make a very stiff gantry and Z axis.

  6. #66
    If it's any help here is a link to the stiffness calculation spreadsheet I posted some time ago.

    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  7. #67
    Mr Routercnc That is an amazing spread sheet. okay I can now see box rules!! This was a previous design. I had the plate on which i mounted the rails and this was bolted to the box. The angle at the top and bottom get bolted to the plate and box as strengtheners. Is the angle more trouble that its worth? I cannot find where this was slated before so here is your opportunity. Piccy below.

    Jazz i have a limited supply of 10mm plate, 50mm x 6mm angle and a length of 75 x 3.2 box. When i started I was going to make one of those plywood cnc m/c's. Wood I have plenty of. Trouble is you guys have shown me the error of my ways and I know that you are all prodding me in the right direction. Also As I said before this is a bench construction as I do not have access to a mill or c/lathe at the moment.

    I can only ask you all to be patient. when you get close to 60 the old marbles fall away a bit.

    Edit - Talked about in a pm but not actually slated..

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    The more I know, I know, I know the less. (John Owen)

  8. #68
    Just got another computer. Has seperate video card and plenty of memory. Came without a drive so I am just doing a clean install with xp. I will need to study the board and cards and get some drivers.

    Ever noticed how confusing it is to be using 2 computers at the same time. Keep using the wrong keyboard and wondering why nothings happening. Oh well.

    The more I know, I know, I know the less. (John Owen)

  9. #69
    The last drawing looks good to me so long as you bolt both the plate and box section to the gantry sides.
    That spreadsheet is rather good. Same formulas I used earlier in this thread.

  10. #70
    Thanks Jonathan. I feel that at last I am getting close to re-starting this project. How heavy 4 core do you recommend for the spindle?

    The more I know, I know, I know the less. (John Owen)

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