How to build a 2 spindle diy CNC machine?


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    Default How to build a 2 spindle diy CNC machine?

    Has anyone here built a 2 spindle (or more) CNC machine?

    I saw a custom machine for sale on eBay which had both a high speed CNC router spindle and a seperate belt-driven low speed / high torque milling head:

    https://www.ebay.com/itm/CNC-All-Bal...8AAOSwX61ZCfsI

    The listing states that the machine is capable of cutting both hard metals like steel and titanium or high speed routing of wood, plastic, soft alloys etc. It seemed like a good idea and I was wondering why we don't see more like it here on the diy end of the market?

    I have seen others that seem to have 3 or 4 identical spindles on their gantry. Can machines be set up to cut 3 or 4 (or more) identical mold cavities (or other parts) at the same time? Or can multiple spindles be used as a cheaper ATC alternative? You could buy 5 or 6 Chinese spindles for less than buying a single Chinese ATC spindle without a carosel or air source.....

    I like the idea of having one machine with multiple capabilities. Many people have space and budget limitations. CNC routers, mills, 3d printers, CNC plasma cutters etc are all based on an XYZ computer controlled moving frame. It seems like a no-brainer to build one machine with two spindles, or one spindle and a 3d print head etc over the alternatives.

    Is there some limitation in software like Mach3 or some other limitation that prevents people building multi-use diy machines or machines capable of making multiple parts simultaneously? Or is it just a case of making sure your steppers are powerful enough to move two spindles and making a wider Z plate to accommodate them?

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    Default Re: How to build a 2 spindle diy CNC machine?

    Some people have done it.

    Linux_fan did it on his build, but I believe he is reverting to a single ATC spindle.

    Ger21 is doing it on his current build I believe.

    I don't actually know how to control more than one Z axis in generating the G-code or running the machine software, I just know it's possible.

    If I was going to do it, I'd probably ask Ger21 how he's doing it and go with that.



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    Default Re: How to build a 2 spindle diy CNC machine?

    With his setup both spindles are attached to the same plate, so you cannot do an operation with one and finish with another, in one shot. Unless the part was very small. You'd have to slide the high speed spindle up. Also Mach3 does not natively support multiple spindles if I recall. You can "trick" it potentially by using relays. I think Gerry's large wood machine is multiple spindles on multiple axes so maybe you should check out his build thread.



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    Default Re: How to build a 2 spindle diy CNC machine?

    Is there some limitation in software like Mach3 or some other limitation that prevents people building multi-use diy machines or machines capable of making multiple parts simultaneously?
    It's up to you to write the code to deal with them, depending on what exactly you want to do. Mach3 (or UCCNC) doesn't have any built in support for multiple spindles, but it can be done.

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    Default Re: How to build a 2 spindle diy CNC machine?

    Having multiple spindles on a machine is nothing new! On a router though you cant assume that you will be getting a huge benefit from a low speed spindle. Further a low speed spindle by itself doesn't mean you will be able too machine steel well. Of course machining steel covers a broad area but you don't want to be expecting milling machine like operation.


    So in simple terms you need to consider factors out side of the spindle to consider if this approach is worthwhile. The big one is this: is the machine going to be stiff enough to even bother with a low speed spindle and to consider machining steel.

    On the flip side there are good reasons to consider a low speed spindle even if steel isn't the goal. Possibilities here include drilling operations, and running large fly cutters. With fly cutters though you still need a stiff machine to get good results.

    What it comes down too is the idea cant be dismissed but at the same time the potential user has too understand all the issues involved. Note that we haven't even mentioned software yet. I certainly wouldn't bother on a light weight machine.

    One issue with this implementation is tool interference that was mentioned above. You need a way to clear one spindle while the other is in use. This can lead to one huge Y axis saddle trying to implement various solutions on a single saddle. It might be easier to consider mounting two saddles on the Y axis and driving them separately, thus one has a high speed spindle and the other a low. Another option would be mounting the spindles on a turret of some sort, this would be engineering intensive. Either of these options requires that one can manage the required software. Another option would simply be to buy a two speed spindle.

    Beyond a two speed spindle many ideas become design intensive. Having two saddles on the Y axes probably being the simplest to building a spindle turret as possibly the most complex.

    Another consideration that might work in limited use cases would be a self contained spindle that also supplies a stroking mechanism. These would be compact solutions but are more limited in capability. ARO use too make one example of these.



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    Default Re: How to build a 2 spindle diy CNC machine?

    For a wood router, I've thought of putting two spindles back-to-back on a rotary table; one for roughing and one for finishing. When the roughing operation was done, it would retract to a safe height, spin 180, and go back to work with a tool pre-set for the finishing operation. It would be cheaper than a ATC, and a lot easier to implement. It would require an extra channel on the control box, though, and since my current concept is already using six, it might be one too many. And I haven't figured out how to switch the control signals over from one VFD to another, or, alternatively, how to share a VFD between 2 spindles, although I suppose it's possible.

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    Default Re: How to build a 2 spindle diy CNC machine?

    And I haven't figured out how to switch the control signals over from one VFD to another, or, alternatively, how to share a VFD between 2 spindles, although I suppose it's possible.
    I have my VFD feeding two contactors with an interlock, so only one can be active at a time.. My tool change macro will wait for the spindle to stop, then turn off one contactor, and turn on the other.
    You just have to make sure that the active contactor doesn't disengage while the spindle is running, when an Estop or limit hit occurs.

    Gerry

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    Default Re: How to build a 2 spindle diy CNC machine?

    I knew you guys would know about this. You guys are so much more knowledgeable and helpful than the Practical Machinist crowd!

    It sounds like getting two spindles to act independently and consecutively without manual intervention is going to be limited to users with highly developed g-code skills (or equivalent) unless someone develops a more advanced piece of software than Mach3.

    On the other hand, it sounds like running two spindles on one machine is fairly easy / simple if they are either running one at a time (e.g. Milling head for steel, router for woodwork) or, if both spindles are doing the same thing with the same tool in a different space.

    Aside from expanding the capability to cut steel with a milling head, the area I could see it being most useful is milling two or three (identicle) mold cavities in a single mold blank. Similarly, I saw an awesome CNC design a while ago where the machine was cutting 4 wood rifle stocks at the same time except it used one spindle with 4 independent rotary axis. 4 rotary axis with 4 spindles wouldn't require any special G code right?

    I was assuming that each spindle needed it's own VFD. For Ger21, do you need to double the VFD specs for 2 spindles? I.e. Do you need a 6kw VFD for two 3kw spindles, or with your solution, can you use a 3kw VFD for two 3kw spindles?



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    Default Re: How to build a 2 spindle diy CNC machine?

    Quote Originally Posted by awerby View Post
    For a wood router, I've thought of putting two spindles back-to-back on a rotary table; one for roughing and one for finishing. When the roughing operation was done, it would retract to a safe height, spin 180, and go back to work with a tool pre-set for the finishing operation. It would be cheaper than a ATC, and a lot easier to implement. It would require an extra channel on the control box, though, and since my current concept is already using six, it might be one too many. And I haven't figured out how to switch the control signals over from one VFD to another, or, alternatively, how to share a VFD between 2 spindles, although I suppose it's possible.

    I assumed that this was the point of those double head spindles that Colombo sells. I.e. You would need to be able to rotate the spindle 180 degrees to use the other side. If it isn't a cheaper tool change function, I can't think what they are for.

    It seems like it would be fairly easy to install a motorized rotary table to switch between 4 or 8 spindles but making the machine do it as an ATC function sounds complimicated. Then again, a regular ATC spindle with a motorized carosel sounds complicated to me... it might work as a fast tool change instead of auto for the right type of user.



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    Default Re: How to build a 2 spindle diy CNC machine?

    Quote Originally Posted by Goemon View Post
    I assumed that this was the point of those double head spindles that Colombo sells. I.e. You would need to be able to rotate the spindle 180 degrees to use the other side. If it isn't a cheaper tool change function, I can't think what they are for.
    Many uses in a factory setting with specialized machines. One use I know of is in a certain guitar factory, where a machine aligns the neck and body on two separate carriaiges, then pulls them to the double spindle for precise alignment of body and neck later on. Another use would be as a grinding machine. You'd need tooling with a left-hand twist for the other side, if you use it to mill.

    It seems like it would be fairly easy to install a motorized rotary table to switch between 4 or 8 spindles but making the machine do it as an ATC function sounds complimicated. Then again, a regular ATC spindle with a motorized carosel sounds complicated to me... it might work as a fast tool change instead of auto for the right type of user.
    The big turning stations have a large turret that has live tooling, in addition to a main mill head and two lathe spindles. If your gantry was stationary you could conceivably make a vertical turret.



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    Default Re: How to build a 2 spindle diy CNC machine?

    It sounds like getting two spindles to act independently and consecutively without manual intervention is going to be limited to users with highly developed g-code skills (or equivalent)
    There are a million different ways to do multiple spindles, but you also have to consider that you may have more than one Z axis. On my router, each spindle is on it's own Z axis. I'm using two spindles to minimize tool changes, and have no intention of using them at the same time.



    I was assuming that each spindle needed it's own VFD. For Ger21, do you need to double the VFD specs for 2 spindles?
    I'm only running one spindle at a time, so only one spindle will be connected at any given time.

    Gerry

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    if you really want to get into a complicated machine build im going to suggest that you look at the various open source G-Code interpreter solutions out. The old stand by here is LinuxCNC but you may want to look at GRBL. Then you have derivatives that are slowly coming along like the various attempts to get GRBL running on ARM and things like Machine Kit.

    I mention this because at some point you will need to become a programer if you want to implement something that hasn't been done before. As mentioned above there has to be a million ways to do dual spindles but not one of them already implemented may be suitable for your specific solution. For example right off the top of my head i cant remember anybody doing a dual Z axis machine off one Y axis saddle, if you did something like this you would need a G-Code interpreter modified to be aware of the two axis. This likely isn't a trivial programming job to get to a technically correct and bug free solution. Im sure the community would love to see such a solution though.




    Quote Originally Posted by Goemon View Post
    I assumed that this was the point of those double head spindles that Colombo sells. I.e. You would need to be able to rotate the spindle 180 degrees to use the other side. If it isn't a cheaper tool change function, I can't think what they are for.

    It seems like it would be fairly easy to install a motorized rotary table to switch between 4 or 8 spindles but making the machine do it as an ATC function sounds complimicated.
    Actually many G-code interpreters out there can already handle tool changes and the associated offsets. From the software standpoint much of the work is done. It would be a lot like a tool changing carousel, but you rotate spindles instead. The real trick is in doing that carousel in a mechanically sound way. You would likely need to consider various machines like lathes with live spindles and some of the CNC drilling machines out there.

    Then again, a regular ATC spindle with a motorized carosel sounds complicated to me... it might work as a fast tool change instead of auto for the right type of user.
    An ATC might be a better choice than going dual spindle in your case. Im not convinced that a high torque spindle supplementing the high speed spindle makes sense. Sure it can be done but I'm not convinced of a pay off for the types of molds you are talking about. It really comes down to the number of expected tool changes per run.



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    Default Re: How to build a 2 spindle diy CNC machine?

    For example right off the top of my head i cant remember anybody doing a dual Z axis machine off one Y axis saddle
    That's what I'm doing. I just haven't had the time to put it all together.

    http://www.cnczone.com/forums/attach...5&d=1346115527

    if you did something like this you would need a G-Code interpreter modified to be aware of the two axis. This likely isn't a trivial programming job to get to a technically correct and bug free solution.
    It's actually much simpler than that, but some programming is required.
    Both Mach3 and UCCNC have a "swap axis" function available in their tool change macros. So you set up one axis as the Z axis, and one as the B or C axis. When you want to switch spindles, you just call the Swap Axis funcxtion, and the Z is now the C, and the C is now the Z.

    No special g-code is required.

    Here's the rough plan of how my machine will operate.
    Each spindle will have a range of tool numbers assigned to it. Say tools 1-100 for spindle #1, and tools 101-200 for spindle #2.
    If both the current tool and new tool are in the same range, then the same spindle is used, and nothing changes.
    If the new tool and current tool are assigned to different spindles, then the swap axis command is called, and second spindle becomes the current Z axis.
    When the axis are swapped, relays are used to transfer the connection from the VFD from one spindle to the other.
    I'll be doing some custom screen work so that the screen has info on which spindle is active, and which tool is in each spindle.

    It's really not a lot different, and no more difficult, than writing an ATC macro for Mach3 or UCCNC.

    Gerry

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    Default Re: How to build a 2 spindle diy CNC machine?

    Here's a more updated rendering from Fusion 360.

    But I think I'm going to redesign the Y axis carriage, and change the design to use helical rack an pinion. This will be the 4th drive system I've changed to since I started designing this 10 years ago.
    And it should be the final one, as I've almost finished gathering components. All I need is two more AC servos, and the rack and pinion.

    Attached Thumbnails Attached Thumbnails How to build a 2 spindle diy CNC machine?-2_spindles-jpg  
    Gerry

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    Default Re: How to build a 2 spindle diy CNC machine?

    Here's a single Z axis, 3 spindle machine.



    Gerry

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    Default Re: How to build a 2 spindle diy CNC machine?

    "OK, Ivan, the boss would not pay for an ATC spindle, but we have a few regular spindles laying around. Can we figure something out?"



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    Default Re: How to build a 2 spindle diy CNC machine?

    Goemon... if you don't mind redoing your gantry, the easiest solution would be to make a gantry that extends well past the upright on each side, and have two spindles on two carriages, mounted independently, using a dedicated ballscrew for each spindle. One spindle would be "parked" to one side while the second spindle ran. Or you can "slave" the other spindle and run them in tandem.



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    Nice find! This just highlights that there are many ways to approach the problem.

    Quote Originally Posted by ger21 View Post
    Here's a single Z axis, 3 spindle machine.





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    Default Re: How to build a 2 spindle diy CNC machine?

    Quote Originally Posted by ger21 View Post
    Here's a more updated rendering from Fusion 360.

    But I think I'm going to redesign the Y axis carriage, and change the design to use helical rack an pinion. This will be the 4th drive system I've changed to since I started designing this 10 years ago.
    And it should be the final one, as I've almost finished gathering components. All I need is two more AC servos, and the rack and pinion.
    Youre going to have to update your user avatar now



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    Default Re: How to build a 2 spindle diy CNC machine?

    The G code can be very simple. With Linuxcnc, and I would guess Mach3 also.

    The G code does not need to know you have multiple spindles, they are just multiple "tools".

    The Gcode just calls tool 1 or 2 or 3 etc - so no change to gcode or post processor.

    In LinuxCNC it's easy to have a custom approach to a toolchanger. You can use a C program (referred to as a 'component') or a classic ladder program. This program can then handle the spindle switch pretty much however you want.

    No fancy G code needed necessarily.



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