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  1. #1
    Join Date
    Jul 2013
    Posts
    85

    DIY Hobby Size 5-axis mill

    Hey guys. I'm in the process of getting parts together for a diy 5 axis cnc.

    Lets not talk about the g-code or cam software. I'm only interested in talking about the electronics. (which im not an expert with) and the trunnion table rotary bed build.

    I'm not concerned about head clearances either. This can be changed. The rotary bed on the trunion table will be 6" and will hold a 5" chuck.

    I'm going to build it around a 'little machine shop hi-torque mini-mill model 3900'.

    I spent some time looking at stepper motor sizes. I got some calculators. It was a decision for me to go with overkill using g203v drivers to allow for upgrading the machine later. (stiffer and better spindle.)
    I decided to go with 381oz/in steppers all around. With g504 4 axis and g251 driver. Smooth stepper. And a C11G breakoutboard for the 5th axis breakout and pump/spindle control. 48VDC 20A power supply

    Heres the current order list for the electronics from AutomationTechnologies.

    Gecko Diver G540 4 Axis Driver, Current Version
    NEMA23 381oz/in 3.5A Single Shaft Stepper Motor KL23H2100-35-4A
    Ethernet SmoothStepper Motion Control Board for Mach3
    Geckodrive G251 50V/3.5A Stepper Motor Driver
    E-stop Switch
    Coupling 1/4" and 1/4 "
    Micro Limit switch
    Ethernet SmoothStepper Cable Combo
    4 conductor 22 GA Shielded Motor wires
    Motor cable connector
    C11G - Multifunction CNC Breakout Board
    Unregulated Linear 960W/ 48 VDC/20A Toroidal PSU (KL-4820)


    I also plan to build an enclosure for it.
    I could use some suggestions on the electronics. I wasn't sure about the C11G breakout board. But it seems like it has a lot of room for expansion.
    Lets hear your thoughts.

    Cheers

  2. #2
    Join Date
    Apr 2005
    Posts
    861
    I can't see any problems with the electronics you have listed. Going with the SS is a good idea, I have built a 5 axis mill and before the SS my rapids were extremely slow. The PC couldn't produce a clean enough pulse stream at the sort of rate needed to move all 5 axes simultaneously.
    You might not get too many replies because 5 axis builds are not common here. There are a couple of reasons for that. Most people doing hobby stuff just don't need it, and ignoring it or not, the software is expensive and can be tricky to learn. Most times it is just more than you would need. I would be interested to hear your intended application for this mill.
    LongRat
    www.fulloption.co.uk

  3. #3
    Join Date
    Jul 2013
    Posts
    85
    Thanks for the reply,
    I've been working on designs of model jets at home. Am interested in producing custom impellers and blisks. Mainly from aluminum. If possible I would chew away at some one off parts in inconel. I believe its possible at much slower speeds. We will find out.

    I will most likely have to put a spacer block under the gantry support to gain some headway for the trunnion table. and add steel tubing support to the top of the collumn, which will also be apart of the enclosure. Which costs me nothing but my time.

    I appreciate the positive feedback!

    Attachment 216060Attachment 216062Attachment 216064Attachment 216066

  4. #4
    Join Date
    Feb 2013
    Posts
    164
    Very neat! That compressor blade looks nice! I'd like to do the same thing at some point, although it will be years before I'm at that point. Once I get my mill running a Wren 54 is on the top of my list of projects. I have too little time to even think about engineering one at this point. As for the Inconel, it may be difficult with a machine that small, especially holding the tolerances necessary for a jet engine. Do you already have the mill?

  5. #5
    Join Date
    Jun 2007
    Posts
    3757
    Without zero backlash, or a way to compensate it (and that will leave marks) what you are trying to achieve will be difficult.
    How are you going to get zero backlash on the tilt table and the rotating parts?
    Harmonic drives, come to mind.
    Servo drives, running against high friction drag brakes, and positional feed back is also an option on any/all axis.
    Double loop servo controls, which are rather difficult to make work with Mach3, if you can make them work at all.
    One loop for the servo control, and an external one to account for position errors in drive (reduction) system.
    Backlash compensation will always make all axis pause for the one changing direction (removing it's backlash).
    Could never get 5 axis compensation on Mach3 working, and then if it did the referencing would not work properly on all axis.
    referencing, or compensation, but not both!! Does anybody know a Mach3 version with NONE of these features broken?
    I have worked on a 5 axis machine, and initial planning to achieve repeatability/reliable zeroing/referencing on the 4th and 5th axis (and other axis) will make or break the project.

  6. #6
    Join Date
    Apr 2005
    Posts
    861
    Are those some of your parts? Very nice work.
    If you build your machine stiff enough and use the right tooling, you will be able to machine inconel. I think you will need to make a lot of the much-documented improvements for that machine, and the size of the rotaries you wish to fit will be tight. You need to know what you are doing but if you are building engines like these already, you do.
    LongRat
    www.fulloption.co.uk

  7. #7
    Join Date
    Jul 2013
    Posts
    85
    Hey all, thanks for the reply's. Happy holidays/new year!

    I'm planning on reinforcing as much as is needed with the machine. I'm not going to spend a fortune on it. I'll do what is necessary. I'll have to find and read up on the improvements that have already been done! The rotating table is 6" but I will be using a 5" chuck making mostly 4" OD diameter parts. The LMS model has 5.1" movement in the Y axis. I've seen a few extended bed mods. We'll see what happens..

    I'm not looking for spaceX quality parts. But getting zero backlash is definitely a concern. I think I'll be using worm gearing on the trunnion/rotary table. I've seen belt drives but im curious what the backlash with a belt would be like. The current engine plans available, such as a KJ-66, suggests accuracy within +/- 0.05 mm on some parts.

    Then again I've seen running inconel turbine's been made from hand. So even if I was able to get an accurate rough cut. I could finish the blades by hand.

    The parts in the photo's I've posted are done by hand. Based upon a lot of math! Its all experimental stuff still. I have a manual 7 x 12 lathe at home. It takes patients. But I have no time limit. And one of the best tips/sayings I've read on the dedicated machining forums is 'you cant rush art'.

  8. #8
    Join Date
    Apr 2006
    Posts
    3498
    You are a real craftman. Are you from USA ? USA workmanship is well reknowned in the world. Love the parts so neat and fine that i wonder how long it would have taken to complete them by hand. Sorry for my fractured english
    http://free3dscans.blogspot.com/ http://my-woodcarving.blogspot.com/
    http://my-diysolarwind.blogspot.com/

  9. #9
    Join Date
    Jul 2013
    Posts
    85
    Khalid, I hadn't noticed. Your English is great.

    All the parts are made in Canada!

  10. #10
    Join Date
    Jan 2011
    Posts
    385
    I think that .005mm accuracy might not be achievable with a worm gear drive. I would think it could on a belt drive with a lot of reduction like 5:1 to give you maximum holding torque. I also like the idea of duel closed loop servo system to ensure positional accuracy. LinuxCNC will definitely be better suited for control until Mach4 comes out.

    Sent from my KFTHWI using Tapatalk
    Jeremiah
    PM45 CNC Build in Progress

  11. #11
    Join Date
    Jul 2013
    Posts
    85
    Oops! Typo there. I meant 0.05 mm.. And its referring mainly to the rotating parts and spacers.

    But anything needing to be concentric/round and accurate, such as a turbine would first be done as a blank on the lathe.

    The ballscrews for the x and y will give me .001 " increments per step. Actually 200 steps per complete revolution. So I would assume to try and have similar increments for the rest.

    Thanks for the input. I think I will definitely be going with closed loop servo's once everything is said and done. But for prototyping I'll be using the steppers. It will be a while.

  12. #12
    Join Date
    Nov 2009
    Posts
    4415
    Quote Originally Posted by MichaelGolden View Post
    Oops! Typo there. I meant 0.05 mm.. And its referring mainly to the rotating parts and spacers.

    But anything needing to be concentric/round and accurate, such as a turbine would first be done as a blank on the lathe.

    The ballscrews for the x and y will give me .001 " increments per step. Actually 200 steps per complete revolution. So I would assume to try and have similar increments for the rest.

    Thanks for the input. I think I will definitely be going with closed loop servo's once everything is said and done. But for prototyping I'll be using the steppers. It will be a while.
    If you are using a G540, it is configured to have 10x microstepping (it is not adjustable as some controllers are). You will have 2000 steps per revolution instead of 200. If theoretically you were at .001 per step prior, you will now be .0001. In actuality it wont be that accurate.

  13. #13
    Join Date
    Feb 2006
    Posts
    7063
    Quote Originally Posted by Fastest1 View Post
    If you are using a G540, it is configured to have 10x microstepping (it is not adjustable as some controllers are). You will have 2000 steps per revolution instead of 200. If theoretically you were at .001 per step prior, you will now be .0001. In actuality it wont be that accurate.
    And, in actuality, MANY other factors will will much more significantly limit the achievable, real-world accuracy....

    Regards,
    Ray L.

  14. #14
    Join Date
    Jul 2013
    Posts
    85
    Quote Originally Posted by Fastest1 View Post
    If you are using a G540, it is configured to have 10x microstepping (it is not adjustable as some controllers are). You will have 2000 steps per revolution instead of 200. If theoretically you were at .001 per step prior, you will now be .0001. In actuality it wont be that accurate.
    Yeah I see what your saying. But can we tell it to move just 1 microstep at a time? I thought it was just a way to smooth out the signal for a full step.

    The x and y kit is coming from cncfusion.

  15. #15
    Join Date
    Apr 2005
    Posts
    861
    Yes, the microsteps are the smallest movable increment. You have to treat the motors on a G540 as being 2000 steps/rev.
    Although many will point out that this resolution in no way represents the true ACCURACY you will be able to achieve, if you don't have high resolution you will never be able to get good accuracy, even with the best mechanical components on the planet. For a true 5-axis system, especially one with quite large rotaries, you will find high resolution is actually quite important, because a tiny rotary increment will lead to a somewhat large linear move when at a significant radius from the rotation centre. This is where I found the Smoothstepper so important. On my benchtop 5 axis I wanted a linear effective resolution of <10µm on the table, which meant quite fine encoders on my rotaries. This led to the requirement for VERY high step rates to achieve a decent speed which isn't a problem for the SS, but you'll not get good performance from the parallel port.
    I would also add the the trunnion table I was using was equipped with two harmonic drives. I think you may find it difficult to get low backlash with normal worm-drive rotary tables, but you might get lucky with good quality units.
    LongRat
    www.fulloption.co.uk

  16. #16
    Join Date
    Jul 2013
    Posts
    85
    LongRat, thanks for your experienced input. Do you have a link to a build thread of your own? Would be very interested in seeing your machine.

  17. #17
    Join Date
    Apr 2005
    Posts
    861
    Sorry, I didn't do a thread as it was a machine I built for work. Not exactly a hobby set up, so not relevant to most on here. I used a Wabeco F1410LF High Speed as the base machine and used some DC brushed servos to drive it. FYI, this mill is a good starting point with linear guides on all axes. For the rotary system I spoke to MDA Precision and bought a TN4 trunnion with custom specced servos for my requirements. They are good to deal with. This set up got me a machine with a small working envelope but high accuracy which is exactly what we needed at the time. Because it wasn't a complete scratch build it treads the mid-ground between expensive industrial machine (£120k-plus) and home-made hobby set up, and ended up costing us about £15k. That's a lot of money for most benchtops but you couldn't get a 5 axis machine accurate to ±15 microns in a 100mm spherical volume for anything like that if you went off-the-shelf.
    LongRat
    www.fulloption.co.uk

  18. #18
    Join Date
    Jul 2013
    Posts
    85
    Accuracy is definitely costly!

    I'm thinking about using the 90:1 worm gearing from a 6" rotary table.
    With 2000 microsteps that would be 90 x 2000 = 180,000 steps per revolution of the table.. 360 degree / 180,000 = 0.002 degree per microstep

    For the trunion mount I would use a 72:1 worm gear from a 4" rotary table.
    With 2000 microsteps that would be 72 x 2000 = 144,000 steps per revolution of the clamping surface.. 360 degree / 144,000 = 0.0025 degree per microstep


    With the trunion table surface widest point at 3" radius from the center.
    3.1416 x 6 = 18.8496" perimeter... 18.8496" / 144,000 steps = 0.0001309" movement around 3" radius from the center
    At 0.5" radius. 3.1416" perimeter... 3.1416" / 144,000 steps = 0.00002181666" movement per microstep

    So I would assume put the chucks center as close to the pivot point, in order to keep the movement of the workpiece very small. But if I was to use the table without the chuck my step movements should still be manageable.

    Any thoughts?

  19. #19
    Join Date
    Feb 2009
    Posts
    2143
    But your "accuracy" is calculated not taking any backlash in to account. Any worm driven rotary WILL have backlash, or it will be bound up and not be able to be turned. You should consider a different technology for the rotary if precision is important to you. As suggested earlier, I would look at Harmonic Drive components...
    CAD, CAM, Scanning, Modelling, Machining and more. http://www.mcpii.com/3dservices.html

  20. #20
    Join Date
    Jul 2013
    Posts
    85
    I understand. And I began looking into harmonic drives. Not sure where I would get them and at what cost. I did a search and they seem very costly. Anyone know of a distributor for this application?

    But realistically, I dont need +-15 microns and wouldnt expect it. Especially without going with a heavier machine to begin with.

    I've read some success with cnc converted worm gears. You have to adjust them. And binding would be the biggest concern.

    Some people have said to have about 0.002-0.005" of backlash with the same gearing. And they say it can be adjusted and mostly eliminated. Lapping the gears is also an option. I think its worth a try for the cost.

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