Multi-spindle CNC



  • Hi, i am designing a modified Workbee CNC. It will become a small production machine that requires some form of automatic tool changing.

    Since toolchangers are difficult to and expensive, i want to mount six spindles on a wide x-axis plate. Each spindle can move vertically with its own z-axis stepper. So all spindles will move x-y at the same time, but only one is 'down' and actually milling.

    The software has to maintain a table of spindles/tools with x-y offsets and tool heights. When it executes a toolchange, it should raise the current spindle to a safe height and lower the new spindle while adjusting to its offsets.

    For this machine I could use a duet with expansion board to drive the 10 stepper motors.

    Has anyone ever built a CNC like this? And would the firmware support it?



  • have u thought of a small turret kind of system like on emco vmc 100 turret?


  • administrators

    @maukvdlaan said in Multi-spindle CNC:

    would the firmware support it?

    Tools can have individual offsets in X Y and Z - see the G10 command.
    Tool change macros (Tpre,Tpost,Tfree) allow you to configure any action thqat you can control through gcode so you can raise the tool when it is freed and lower a tool when it is selected. using these macros.

    You might want to drive the X and Y axis of a CNC machine from external drivers depending on mass, speed, acceleration and force required for milling. As far as I know @Catalin_RO is using Duet on Workbee so can advise.

    This sounds like it would be heavy to move with 6 stepper motors for each Z adjustment, along with 6 spindle motors!



  • @chris Yes nice! But difficult to build i guess. I really like the openbuilds system and i guess it would be easy to adapt.



  • @t3p3tony Thanks. Would switching stepper drivers while the others keep their hold current be possible as well?

    About the mass - I plan two 500W's for milling POM and aluminium. The others would be lighter motors for drilling, chamfering and tapping and an edge finder. So i guess 5kg would be a reasonable guess for the total weight.

    I have experience with a MiniMill with DRV8825's and it looks strong enough to me. But for this new design i will use heavier steppers and i hope that the trinamics will work out better. Can anyone confirm that?

    I also plan to mount this machine vertically on the wall. The weight of the x-axis would be on the Y steppers and the Workbee has two of them, sharing the load. Not only does it take less space that way, but i like it that the chips will just fall on the ground.



  • @maukvdlaan I am building a multitool CNC just now also. But I use a fixed gantry and the table moves the one direction. Then the tools can move individually. I will build the sides of the gantry open, so I can exchange the tools if necessary. I will use servobelt with T5 belts for moving the tools.


  • administrators

    @maukvdlaan said in Multi-spindle CNC:

    @t3p3tony Thanks. Would switching stepper drivers while the others keep their hold current be possible as well?

    Yes you can configure the idle hold % and timeout

    About the mass - I plan two 500W's for milling POM and aluminium. The others would be lighter motors for drilling, chamfering and tapping and an edge finder. So i guess 5kg would be a reasonable guess for the total weight.

    I have experience with a MiniMill with DRV8825's and it looks strong enough to me. But for this new design i will use heavier steppers and i hope that the trinamics will work out better. Can anyone confirm that?

    TMC2660s can handle up to 2.4A if the board is cooled appropriately (Fan blowing across both back and front of the board). They are more powerfull then DRV8825s.

    I also plan to mount this machine vertically on the wall. The weight of the x-axis would be on the Y steppers and the Workbee has two of them, sharing the load. Not only does it take less space that way, but i like it that the chips will just fall on the ground.

    I have no experience of this - interesting idea!



  • @joergs5 Yes that is another approach of course, with less moving mass. And it could even have two x-axis. Are you using duet electronics?



  • @maukvdlaan Yes I use the Duet. For the stronger steppers I use a temporary solution until the Duet 3 is available.

    The T5 servobelt has the disadvantage of backlash, I am interested in backlash compensation in the firmware.



  • @joergs5 I just read about the duet 3... it would be a waste to buy a v2 now, especially since i need an expansion board as well. @duet people: do you need a beta tester? i am a seasoned embedded developer and electronics guy.


  • administrators

    @maukvdlaan the Duet 3 is still.a concept - we won't be releasing it until the end of the first quarter on 2019 at the earliest. Also we won't be retiring Duet 2 anytime soon as we expect Duet 3 to be more expensive as it has the CAN FD functionality.



  • @maukvdlaan
    I am considering a similar project, for a CNC specialized in the machining of Hylite composite plates, including both milling cutters and saw cutters.
    I need 5 Z axes carried by the same Y slide. I think I will limit the Z stroke to about ten mm, and I hope to keep the moving masses reasonable.
    I think I can handle all this with MachineKit, unless the Duet 3 option comes up fast enough: my project is not immediate.



  • @maukvdlaan I have used my WorkBee for some serious work, including milling 40mm thick POM (but just 0.5-0.7mm on each pass!). Although I have it for about 8 months, it starts showing problems with the wheels on X and Z axis. In my setup, I have started with a Kress FME-P 1050 (left over from an eShapeOko) and GRBL. When Duet firmware had minimal "must have" support for CNC I moved away from GRBL and then I also changed to an 800W air cooled Chinese spindle with VFD.

    You mention "10 stepper motors". Considering the default 4 used in WorkBee, I guess you intend to have up to 7 spindles. My spindle with its mounting adapter weighs about 2.5kg. Your solution will be way over 5kg because for each spindle you will actually need a fully blown Z axis in order to be able to move it up and down, my bet being over 10kg. The C-Beam X axis will not be able to cope with such weight, showing significant deflection and allowing the Z axis to incline from vertical!

    A much better solution to your problem is to simply bite the bullet and go for a spindle with ATC. There is a 800W one made in France, if I properly recall, water cooled, weighing about 2.5-3kg, for about 2000EUR, or as a complete kit (including VFD, water pump, tool holders etc.) for about 3000EUR. Considering all steppers needed for your setup, V-Wheels, V-Slot profiles, nuts&bots, mounting plates and whatever, your final bill will be significantly higher!

    That being said, with Duet you can accomplish your current target rather easily because of the tool changing macros. Just make a general macro that homes all Z axis one after the other by simply homing the first Z axis, replacing the driver for the Z axis and repeat for all. Then make tool specific macros that call the general macro and then force the Z axis driver again and apply the tool offsets. When you change the Z axis you must also remember to change the spindle control pin(s).

    For homing all those Z axis, just connect all home switches in series (NC switches!). It is easier than having 7 separate wires to the Duet.



  • @catalin_ro Thanks for the replies everyone! I will give it a try with the duet. I will strenghten the x-axis with small steel strips for more rigidity. But i will have to test it of course, i will keep you informed about the results.



  • @maukvdlaan I have done a more in-depth analysis of the problem (I want to find a solution myself for the Z-axis). As you want to have 6-7 spindles, you will clearly need a custom X axis. In this case you might be better with a C-Beam Machine solution, with the profile screwed to the X axis plate and the spindle plate vertically sliding on it (the WorkBee has a Z plate screwed to the X axis plate and sliding profile with spindle installed on it!). This should reduce a lot the problems with the Z axis rotating around the X axis, while not braking the bank (it reduces a lot the stress in one of the critical points).

    Your problem with that weight of the Z axis will not be the X axis bending, but the V-Slot wheels literally "exploding". The heaviest gantry installed on machines in this class, based on messages on various forums and some "inside knowledge", is 2.2kW water/air cooled spindle, about 5kg. With over twice the weight, the X axis V-Slot wheels are literally doomed. You need to properly consider the setup scenarios for all the machines in this range (OX, C-Beam Machine, WorkBee, Sphinx) - most of them are shown with standard routers (not very heavy). HF spindles are something extra, not very often, but going beyond a 65mm one (2.5-3kg) is on the "too much" side for sure!

    The WorkBee is a far cry from the initial eShapeOko that I have used, no doubt. Also, it has its uses and a rather well defined users base. But, even so, it can't really be the answer to any CNC related problem. In your specific situation, I would personally chose a different path: CNCs with several identical spindles, executing the same program, are not unheard of, but trying to replace a proper ATC (adequate spindle, tools holder, air compressor, valves etc.) with a multi-spindle Z-azis is on the "strange side" (clearly too heavy and potentially more expensive).

    P.S. While I discuss occasionally with Ryan at Ooznest, I'm in no way related to them. The above is just my honest opinion, based on my own experience and the information I could find on the Internet on this matter.


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