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  1. #1
    First I would like to say the information here is amazing and has greatly helped my design and learning for this CNC router build.

    Objectives,

    5 foot by at least 10 ft of machining area
    Z height high enough for paddleboard foam blanks ~ need roughly 12 inches under the tool
    ability to machine wood, aluminum, foam
    good accuracy/precision (still trying to figure out where I want/need to be)
    Vacuum hold down


    Parts I already have
    Linear rails - INA 25mm 4 row linear rails - I have enough to do all axis's and enough bearings
    Y axis ballscrew - 10mm/rev rolled ballscrew
    1850 oz/in stepper motors - 2 for X (long axis) and 1 for Y
    2 4hp regenerative vacuum blowers
    Colombo 10hp spindle with ISO30 ATC

    I will start out where I am now and then go into some questions I have.

    The gantry legs mock-up 4 x6 x 1/4wall box tubing, 1/2 inch plate for the feet.
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    Gantry partially welded up, Gantry is built from 4in x 6in x 1/4in wall box tubing and will get blocking in between the 2 tubing with some vertical bracing on the back. I machined the ends of the gantry before welding them up so I can put an e-stop on each end. The ballscrew is laying ontop of the gantry and will live between the 2 box tubing when complete.

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    Here is the plan for the Z axis, made from 3in x 6in x 1/4wall box as a starting point. I plan to make an A axis and have mounted the motor up and off to the side. Although this could still get in the way. Should I put the motor for the A axis above the spindle motor? This will make the HTD belt 20 inches center to center. If I did that would I be looking for trouble as far as belt stretch is concerned?

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    Heres what I was thinking for A axis


    A few questions,
    Gantry and Z axis is going to be ~550lbs (~250kg), am I shooting myself in the foot using steppers for this weight? I would like to get decent speed out of the thing without the risk of missing steps. When I purchased the steppers I was trying to balance cost but now im worried I will have trouble with it when im done.

    What pitch should I shoot for on the Z axis screw? I was planning on using the stepper motor with a ~4:1 reduction. Total travel as it stands right now will be 16 inches. Weight of Z with Spindle will be around 100lbs should I add spring assist to this? or air springs etc?

    Next steps for me,

    I am working on mounting the rails on the Y Axis and getting prepped for pouring epoxy as soon as the temp rises a bit. Here is the plan for the pour and looking for any insight.

    Lay gantry on its back
    Level with starrett precision level as close as I can in both planes
    pour epoxy for Y axis linear slides
    at the same time pour the mount pads for the Y Axis ballscrew, in my mind this gets the ballscrew on the same plane (albeit at a different height) as the linear rails
    Paint Gantry
    Mount the lower linear rail for the Y Axis
    Flip gantry upside down
    Use precision level on the linear rail and set rail level and also use a precision square and the level to level in the other plane
    Pour expoxy on gantry feet (my thinking here is that I can then get the gantry feet 90 deg to the Y axis linear rails and also on the same plane as the linear rails) I would assume there may be some slight shimming still but the epoxy will be close.


    Thanks
    Scott

  2. #2
    Some updates on the gantry

    All of the bracing clamped in place ready for spot welding. The ballscrew is in place to set the distance between mounts.
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    Here is one of ballscrew mounts
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    this is the end of the gantry showing the space for the estop
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    This is one of the longer braces that connect to the ballscrew mount block

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    Here is the backside with all the bracing welded up
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    And the front side, notice I drilled some 1/2 in holes on the wrong side. My linear rails are threaded from the backside so I have to through drill from the back. The good news is I am welding on 3/8 plate (I drilled the holes to the correct spacing on the mill first and used the 3/8 plates as templates) on the front side where the linear rails are going to mount.
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  3. #3
    Very impressed, with a lot of things. Very excited about your A-axis, sometimes one should just go to ahead and build it instead of pondering if it will work or not :D I have not attempted to build it yet, as I dont even have an idea of how I would use it. I really have no clue how one would incorporate 4 axis programming.

    I would probably fit the widest possible belt there, if I were to use belt, you want the spindle to be rigid enough. What kind of bearings, if that is how you are pivoting the A-axis? Got any detailed view of it?

    Nice work so far.

  4. #4
    Quote Originally Posted by sinnsvak View Post
    What kind of bearings, if that is how you are pivoting the A-axis? Got any detailed view of it?

    Nice work so far.
    Thanks for the comments

    Heres a view of the bottom of the Z axis and a section cut into it.

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    **sorry the drawings are upside down**

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    Here is the box tubing removed

    The bearings are roller bearings that I can get from McMaster Carr easily. 1 1/4 diameter shaft. Bearings are designed to be held into aluminum housings bolted into the 3 x6 steel tubing. The shaft is a 6 inch threaded on both ends. Again something I can just order from McMaster. The bolts into the shaft allow me to put preload into the bearings. I was thinking of bolting the pulley hub (pulley is not pictured) to the spindle mount.

    Open to thoughts on this design. I think it will work....

  5. #5
    A couple more updates sorry for the bad pictures
    Drilled backside holes out to 1/2 inch to allow bolt and ratchet to be put through from the back. Im thinking I will just order a bunch of plastic plugs to put into these holes once I am done.
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    I threw a couple bolts into one of the linear rails just to see how things were coming together.
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    So far I am pretty happy with how the build is coming together. Time will tell if I have some precision/accuracy when im done...

    Here is a ~bad video of me test running the used colombo 10hp ATC spindle that I got. Running it at ~18,000rpm after running at ~8,000rpm for 10 mins to get the grease moving in the bearings.

  6. #6
    Very ambitious for a first build.

    Some thoughts:

    -the gantry legs dont seem adequate for the rest of the parts you will use on your machine

    -the A may work for foam but i dont see it serious for anything more than wood

    -the stepper motors , ok- the huge stepper motors, what drives will power them? 230VAC?

    -that bracing may be was totally unnecessary. I dont see how that will strengthen anything. It could even make things worse, strengthening one point too much and not allowing the forces to spread uniformly and creating pressure points. So later all rings.


    What will you be using this machine for? Remember- the weakest point is the criteria for how strong your machine would be. Again-the gantry legs.


    PS:
    That gantry legs will greatly benefit from bolting or welding on them 10mm steel plates in both directions, 2 per leg in total
    Last edited by Boyan Silyavski; 05-03-2016 at 08:58 AM.
    project 1 , 2,Dust Shoe ...

  7. The Following User Says Thank You to Boyan Silyavski For This Useful Post:


  8. #7
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 19 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 5-6 years. Has a total post count of 5,723. Received thanks 892 times, giving thanks to others 35 times.
    Hi Scott,

    This is how I see couple of not so little things.

    Steppers:
    Really Cannot comment if they will be good enough because you haven't said anything about what your using for linear motion on the X axis. I assume Rack n pinion but what ratio etc.? . . . But let me put it this way 550lbs or put anohter way 1/4 Ton is lot of Mass to Accel and stop so better get this correct or you'll seriously regret using steppers.


    A Axis: You need to think again on this I'm afraid NO WAY will Stepper with such small ratio hold that Big spindle at angle without moving or vibrating.
    Remember the Z axis is the MOST important area on machine so weaken this and all that OTT work you have done on the frame is pointless.

  9. #8
    Quote Originally Posted by Boyan Silyavski View Post
    Very ambitious for a first build.

    Some thoughts:

    -the gantry legs dont seem adequate for the rest of the parts you will use on your machine

    -the A may work for foam but i dont see it serious for anything more than wood

    -the stepper motors , ok- the huge stepper motors, what drives will power them? 230VAC?

    -that bracing may be was totally unnecessary. I dont see how that will strengthen anything. It could even make things worse, strengthening one point too much and not allowing the forces to spread uniformly and creating pressure points. So later all rings.


    What will you be using this machine for? Remember- the weakest point is the criteria for how strong your machine would be. Again-the gantry legs.


    PS:
    That gantry legs will greatly benefit from bolting or welding on them 10mm steel plates in both directions, 2 per leg in total
    Hi Scott,

    This is how I see couple of not so little things.

    Steppers:
    Really Cannot comment if they will be good enough because you haven't said anything about what your using for linear motion on the X axis. I assume Rack n pinion but what ratio etc.? . . . But let me put it this way 550lbs or put anohter way 1/4 Ton is lot of Mass to Accel and stop so better get this correct or you'll seriously regret using steppers.


    A Axis: You need to think again on this I'm afraid NO WAY will Stepper with such small ratio hold that Big spindle at angle without moving or vibrating.
    Remember the Z axis is the MOST important area on machine so weaken this and all that OTT work you have done on the frame is pointless.
    I think you are talking something along these lines for the sides of the gantry legs? I was wanting to do FEA on these legs but never got around to it, I did however do calculations (free body diagram) to try to calculate total deflection based on 1000lb force at the bit and keeping the total deflection ~3 thou at full load.

    I could go higher with the bracing as well this is just a quick drawing.
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    The thinking behind the bracing was to connect the upper and lower gantry beams. I used box tubing between the beams. Now the rear bracing, the thought there was to reduce the twist in the gantry. Hopefully it doesnt cause issues...

    So the A axis, this is exactly what I am worried about, holding it in place when at angle and also moving it. The A axis would really only be used when machining foam blanks for paddle boards. However since I want to be able to machine wood, and aluminum as well then I really need to make sure this thing is right.

    Couple things I am thinking thoughts are greatly appreciated.
    - Eliminate A Axis...
    - greatly increase the belt ratio
    - keep A Axis but have an air operated taper pin that holds it at 0 when machining wood/alum
    - look into a harmonic drive rather than belt drive

    X drive

    I was planning on using rack and pinion with a pinion of 1 inch I was going for 4:1 ratio to the pinion.
    so 3.14 inches per revolution of the pinion, 0.785 inches per motor revolution, works out to 0.0039 inches per step. I was thinking of micro stepping them x10 = 0.000395inch per micro step.

    I am brand new to this and trying to learn what feed and rapid movements I need to shoot for to cut wood/aluminum properly. I know it depends on the number of flutes on the bit etc. Am I crazy to think I should shoot for 1000ipm?

    The motors I have are chinese 1841 oz/in with MA860H drivers along with 60V drives. Based on the questions it sounds like these are not adequate?

    Servos
    So if scrap the steppers for X axis then im looking at servos. Something I am even more NEW to than steppers. I need to do more learning on how to size them please correct where I have errors!

    Things to keep in mind when sizing?
    Gear ratio - want to keep the servo motor spinning at higher speed to stay in its power range - unlike steppers which have the most power at 0 speed
    Load to motor inertia, this one I have seen 10:1 ratio but I dont really understand how to use that

    One thing I dont understand, when X is not moving what is holding if from moving? I had assumed that the steppers hold the load from moving at 0 speed (is this the case with steppers?). If that is the case what is doing the holding when using servos?

    Can my router have both steppers and servo motors? I think the stepper would still be adequate for the Y Axis and could use one for the Z axis (as Im sure I can not send them back)... I plan to use ethernet smooth stepper with mach4.

    Got the X axis steel drilled these needed to be through drilled as well since the linear rails are bolted from the back. 244 holes!!!!
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    Any help with servos for this size of gantry is greatly appreciated.

  10. Hi Scott
    I don't have any experience of the 4/5 axis machines but i would imagine that the "A" axis you are trying to emulate would be a wheel & pinion mechanism.
    Regards
    Mike

  11. #10
    Ok, lets start from the beginning. I will try to resume some things, you just need to further research the topics:

    1. You should absolutely know what weight your gantry is with all things mounted. Knowing the mass of the gantry will be decisive on what motors, what size ball screw, rotating nut, Rack and pinion, etc..

    2. Be realistic about the feeds and speeds. And what you really need the machine for. All in one would be usually a disaster in some area.

    3. Motor sizing. People drive 3nm nema 23 motors at 70VDC. And we are talking low inductance motors. Expected reliable performance from such motors coupled with xx10 ball screws is 10000mm/min. The motors you have are high inductance motors. I am not a specialist here but there are a lot of knowledgeable people here that will tell you at what voltage, but i am sure that it must be more than 110VDC. Do your research and find at what voltage these motors perform well. And if these drives will be ok.

    4.Without knowing the total weight of the gantry... but i see you start ambitious, so yes, you will need servos to drive the gantry reliably fast if you aim at 25000mm/min. And you will need rotating ball nut or rack and pinion

    5. There is a very well made calculator at the forum here, search for it, and i am sure that the gantry legs deflection will not be as you say...but may be i am wrong




    I dont want to discourage you, but i am having the feeling that if you continue without thinking it too much, there will be disappointments on the way. WHY JUST DONT YOU SLOW A BIT AND READ MORE BUILD LOGS. All the info is there.

    And by the way it seems the american thing is to desire rapids of 1000ipm. And make rack and pinion machines. We here in EU prefer precise ball screw machines and rotating ball nuts for big machines and heavy gantries.
    project 1 , 2,Dust Shoe ...

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