Second Momus Build (Pro Version)


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    Default Second Momus Build (Pro Version)

    Been a few months and slowly working on a heavily modified Momus CNC. Will update pics shortly with some detail.

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    Ok, been working slowly on my second machine. I posted some of the carriage pics in another thread I had started but going to gather everything under this thread now. My goal was a larger working area and a more rigid machine along with some design and setup changes. And, quite a few of the parts were machined using my original Momus CNC.

    First, I needed a larger working area, starting with the gantry, I extended it 8 inches to get approx. 24 inches of tool travel. will lengthen the base by 12 inches to get approx 28 inches of tool travel...so 24x28.

    Instead of aluminum I used brass for the gantry tube...more rigid for the added length although maybe overkill and hoping the added weight will cut some vibration out.

    Then, instead of using multiple pieces for each bearing rail, I cut 2 exact pieces from a sold chunk of aluminum that the gantry slides into on each end as well as adding yaw bearings to the left side. Again, going for a rigid design and trying to eliminate as much play from vibration and any flexing at the joints.

    Finally, I removed the belt system. Belt are good for the first build but over time I learned to dislike them No offense to belt lovers. In place of belts I went with a lead screw/anti-backlash nut setup hooked to a 495 oz. in. stepper. My original setup had 270 oz. in. which worked great, 495 is overkill but what the hell. The advantage to the lead screw setup is fewer parts, the disadvantage is everything needs to be squared and aligned or its gonna destroy the anti-backlash nut and bind up the carriage.

    Attached Thumbnails Attached Thumbnails Second Momus Build  (Pro Version)-imag0905-jpg   Second Momus Build  (Pro Version)-imag0906-jpg   Second Momus Build  (Pro Version)-imag0907-jpg   Second Momus Build  (Pro Version)-imag0908-jpg  



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    And here is the carriage that I built months ago, it is only 4 parts instead of 8. Integrated the spacers into the rails. And the opposite rail is keyed to remove the step of having to square the carriage when it is being built as well as eliminates racking. I also used 5/16-18 threaded rod instead of 1/4-20.

    Attached Thumbnails Attached Thumbnails Second Momus Build  (Pro Version)-imag0481-jpg   Second Momus Build  (Pro Version)-imag0483-jpg   Second Momus Build  (Pro Version)-imag0484-jpg  


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    Default Nice anodizing!

    I really like the anodizing on the carriage parts. I thought about trying that also, but I wanted to get things going and that would just be one more thing to set up to do. I have been plating with Caswell's Copy Chrome, but have never done any anodizing. So, I just did a little buffing & polishing. I've got the base completed and the metal is assembled but not yet aligned. I hope to pour the epoxy this weekend and get started on the alignment next week. Then I'll start sourcing out the electronics. Your machine looks good.

    I don't make mistakes ... I make 'unintended engineering design changes'.


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    In place of belts I went with a lead screw/anti-backlash nut setup hooked to a 495 oz. in. stepper. My original setup had 270 oz. in. which worked great, 495 is overkill but what the hell.
    That looks like 1/2-10 acme? If so, you've got a combination of poor choices.
    1) 1/2-10 acme is slow. Most now use 2 start or 5 start to get 4-5 times more speed with no other changes.

    2) A 48" 1/2-10 screw will whip at high speeds. The 2 start and 5 start can minimize this by slowing the rpm of the screw, thus reducing whipping.

    3) The 495oz motors lost torque faster than the smaller ones, so it's possible that the 270oz motor will spin much faster. Combine this with 1/2-10 acme, which requires higher rpm for higher speeds, and you may find that the 495oz motor will perform worse than the 270oz motor.

    On my 30x45 machine, I use 1/2-8 2 start acme with a Xylotex and 250oz motors. I can get 190ipm reliable on my 40" Y axis screw, but my 60" X axis screws whip badly at high speeds, which limits me to 150ipm on the X. That's 600rpm, which would be 60ipm with 1/2-10 acme.

    Gerry

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    Where in Chandler are you? I'm down near Cooper Rd and Chandler Blvd. I'd like to come see your new machine as I'm thinking of some of the same things to upgrade mine or build a bigger one.



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    you are absolutely correct ger21. But, longest lead screw is 36", shortest is 32". I'm using 1/2-10 because that is what I had on hand to build with, later will change to a 2 or 5 start depending on performance. As stated, 495 oz in is overkill. I'm also not feeding anything near 190 ipm or higher. I'm mostly focused on getting it built, lead screw/motor combinations are worhtless if I don't have a machine to use it with It may be better using a 5/8 lead screw to further reduce whipping...will see when the time comes.

    billj



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    Quote Originally Posted by SpeedyDad View Post
    Where in Chandler are you? I'm down near Cooper Rd and Chandler Blvd. I'd like to come see your new machine as I'm thinking of some of the same things to upgrade mine or build a bigger one.
    You can walk over anytime! Ray and McQueen Warning though, preggo wife with child number 4. My house is always in chaos. So visit at your own risk

    My parents also run the mini storage about 2000 feet from my house which is where I do all my machining and building so either place works for me. They have a machine shop setup there!

    Billj



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    A little chaos is good for you. Keeps things fresh.

    Yeah, I'd like to see it and your machine shop



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    Quote Originally Posted by ger21 View Post
    That looks like 1/2-10 acme? If so, you've got a combination of poor choices.
    1) 1/2-10 acme is slow. Most now use 2 start or 5 start to get 4-5 times more speed with no other changes.

    2) A 48" 1/2-10 screw will whip at high speeds. The 2 start and 5 start can minimize this by slowing the rpm of the screw, thus reducing whipping.

    3) The 495oz motors lost torque faster than the smaller ones, so it's possible that the 270oz motor will spin much faster. Combine this with 1/2-10 acme, which requires higher rpm for higher speeds, and you may find that the 495oz motor will perform worse than the 270oz motor.

    On my 30x45 machine, I use 1/2-8 2 start acme with a Xylotex and 250oz motors. I can get 190ipm reliable on my 40" Y axis screw, but my 60" X axis screws whip badly at high speeds, which limits me to 150ipm on the X. That's 600rpm, which would be 60ipm with 1/2-10 acme.
    I'd have to agree. You have to work from what max cutting speed you need. The torque on a typical stepper will drop drastically past say 250-400 rpm depending on size. So for example, I cut wood at about 120ipm with a 1/2" bit at about 3/8" doc. So I'd probably use 5-start (2tpi) ACME, and that would give me comfortable headroom, and fast rapids, since I don't need a lot of torque to rapid. THEN I can size a motor for the amount of torque I expect to need at that speed,a nd the manufacturer's torque charts will show that. Even if you COULD spin your leadscrew at 1000rpm (and I'd like to see that!) you'd only rapid at 100ipm, with very little torque to even push your gantry or z carriage!

    Having to spin your ACME screw excessively will also wear your AB nuts faster. Gerry also mentions whip. Not having a fixed end bearing block at the motor end will exasterbate this, as well as lead to premature wear on you stepper bearings since it will be taking radial loads from the whipping which it will at anything above 400rpm at that length. At the very least, a way of tensioning the leadscrew to make it axially and radially stiff would help.

    Oversizing your motors means you're just generating excess heat and wasting electricity! I actually use dual 8-start leadscrews on my machine (1tpi) synched with a timing belt, run by one 425in-oz stepper with only 24v, pushing an over 70lb gantry, and still get 250ipm rapids! (I get 450 on the y) If you feel you need to 'push' your tool through your stock, then it's the spindle that's underpowered, not the stepper!



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    I would see it looks like a great start and keep the pics coming.



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    My enlarged Momus gives me a cutting area of 26(X) x 22(Y). I kept the belts. At this size the problem that I'm noticing is that the left hand or non driven end of the Y-axis deflects. The two solutions that occur to me to correct this are to use a second slaved stepper and belt drive on the left hand side or spread the bearings on the right hand side and add a gusset between the gantry beam and the drive side bearing blocks (in other words make a stiffer T-square with a wider bearing base). You've done some nice machine work but I don't see where you may have incorporated either of these modifications so I'm very inclined to think that you will be seeing the deflection that I'm seeing. Looking forward to further posts.

    Chris



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    Quote Originally Posted by OCNC View Post
    My enlarged Momus gives me a cutting area of 26(X) x 22(Y). I kept the belts. At this size the problem that I'm noticing is that the left hand or non driven end of the Y-axis deflects. The two solutions that occur to me to correct this are to use a second slaved stepper and belt drive on the left hand side or spread the bearings on the right hand side and add a gusset between the gantry beam and the drive side bearing blocks (in other words make a stiffer T-square with a wider bearing base). You've done some nice machine work but I don't see where you may have incorporated either of these modifications so I'm very inclined to think that you will be seeing the deflection that I'm seeing. Looking forward to further posts.

    Chris
    Using steppers in parallel would be extremely risky. The amount of precision alone to do that is a little high granted the belt system would be a bit forgiving. All it would take is one stepper to miss a pulse and you would rack your gantry. I actually did incorporate something to remedy the deflection. The left and right sides are now identical...* beraings per side, the four vertical and four horizontal. Refer to your Momus plans, I have added parts 10,11, and 12 to the left side. Should eliminate the left side deflecting.

    Billj



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    Quote Originally Posted by louieatienza View Post
    Having to spin your ACME screw excessively will also wear your AB nuts faster. Gerry also mentions whip. Not having a fixed end bearing block at the motor end will exasterbate this, as well as lead to premature wear on you stepper bearings since it will be taking radial loads from the whipping which it will at anything above 400rpm at that length. At the very least, a way of tensioning the leadscrew to make it axially and radially stiff would help.
    !
    I really like the suggestion of a bearing block on the motor side, will probably try it with and without just to get an idea of how much whipping it will do.
    Thanks again for the lead screw comments all...I'm still in the mock-up stage so I may use the 270 oz or I may use the 495 oz I just dont know until I can run electricity to them. The beauty of using NEMA 23 motors, they all fit the same mounting hole patern

    One thing I am wondering about whipping though, the AB nut, unless driving the carriage to the extreme ends would also counteract whip wouldn't it? Maybe you guys with larger lead screw drivin machines can answer.

    PLEASE keep the constructive criticism coming, it's nice to hear from people running larger machines with different setups and may resolve any future headaches before I run into them.

    Thanks again!

    Billj



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    One thing I am wondering about whipping though, the AB nut, unless driving the carriage to the extreme ends would also counteract whip wouldn't it?
    I have about 46" of travel, and it whips the most when its within about 12" of each end.
    There isn't any whipping when in the center.


    Using steppers in parallel would be extremely risky. ................................ All it would take is one stepper to miss a pulse and you would rack your gantry.
    Most of us with lager machines are driving the gantry with 2 motors, slaved in Mach3, without any problems. You just need to not try to move faster than the motors' capability.

    Gerry

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    When the AB nut is at center there should be no whip... On my long axis, it would whip, but only on one side, if I got over 300ipm. Possibly because it's not perfectly straight, despite my best efforts.

    You can actually square your gantry using Mach 3 and two steppers. Another solution would be to run the second screw via a timing belt. I haven't started mine yet, but my thought was to run two belts via a jack shaft.

    Another nice thing about making a fixed end bearing block is that you can use a flex coupler between the screw end and motor; this will compensate for any minute misalignment. And makes it easier to swap out motors.



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    Quote Originally Posted by ger21 View Post
    I have about 46" of travel, and it whips the most when its within about 12" of each end.
    There isn't any whipping when in the center.




    Most of us with lager machines are driving the gantry with 2 motors, slaved in Mach3, without any problems. You just need to not try to move faster than the motors' capability.
    Thanks Gerry,

    never knew Mach had anything like that built into it but really never had a reason to look into it. Is your machine home built? was it derived from Momus plans in some form?

    Billj



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    Quote Originally Posted by louieatienza View Post
    When the AB nut is at center there should be no whip... On my long axis, it would whip, but only on one side, if I got over 300ipm. Possibly because it's not perfectly straight, despite my best efforts.

    You can actually square your gantry using Mach 3 and two steppers. Another solution would be to run the second screw via a timing belt. I haven't started mine yet, but my thought was to run two belts via a jack shaft.

    Another nice thing about making a fixed end bearing block is that you can use a flex coupler between the screw end and motor; this will compensate for any minute misalignment. And makes it easier to swap out motors.
    I'm definitiely going to add a bearing on the motor side, I can see where it would be stressful to the motor without one and it is an easy addition...cut piece, machine adjustment slots in it, press bearing in, and bolt on. Maybe an hour to do it.

    billj



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    I actually did incorporate something to remedy the deflection. The left and right sides are now identical...* beraings per side, the four vertical and four horizontal. Refer to your Momus plans, I have added parts 10,11, and 12 to the left side. Should eliminate the left side deflecting.
    I thought about that also but wasn't sure if binding would be an issue. Have you set your gantry on the X-rails yet to test for binding?

    Chris



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    Quote Originally Posted by bjesson View Post
    Thanks Gerry,

    never knew Mach had anything like that built into it but really never had a reason to look into it. Is your machine home built? was it derived from Momus plans in some form?

    Billj
    I'm sure that Gerry will answer for himself but if you haven't yet seen what he's been up to check out his thread when you get a chance.

    Chris



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