Looking for build size recommendations

Mostly Printed CNC - MPCNC Troubleshooting
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First, I have to say it: wow, is this project cool. Okay, got that off my chest.

I’ve started building my parts, since they don’t depend on build size, and I’m planning to order a bundle pretty soon. From the “pics or it didn’t happen department”, parts photo attached.

I’m looking for recommendations on build volume. I’d like to attach the Dewalt 660 for routing wood, so I’d think a 24x24" up to 24x48" working area might be nice. But I don’t want to try to build something really big, and be disappointed with poor rigidity. What’s a good place to start?

Similarly, how tall is a good place to start for Z axis? I mean, for wood maybe it’s not even useful to have more Z throw than a drill press? I don’t have even a guess.

Finally, I could imagine someday trying to mill aluminum. On one forum post, I read that 500x500mm was too ambitious for metalwork – and that’s probably kind of small for woodwork. Is it fair to say I shouldn’t even think of trying to work aluminum on a machine sized for wood?

And last question for now: the parts list mentions the “Tool Holder V2”, and links to thing #724999, which I assume refers to Tool_Holder_13mm.STL. But the forums suggest a thing called the “universal tool holder”, and say that works much better with the DW660. Where should I be looking for the universal tool holder STL and the matching adaptor rings for the 660?

Thanks! I’m really looking forward to building this ridiculously cool project.

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Hi Jon, welcome to the forums. Yes, you’re in for a great time working with this machine! So versatile and lots of cool things to try.

Before I continue, is that a Kossel delta in your picture? I’m looking for my next 3D printer and the Kossel XL is on my short list.

As far as tool holders go, the MPCNC is designed to have tools mounted using parts that screw on to the z rails, using nut plates inside the tube. This works very well, except that changing tools can be tricky, or at least time-consuming. This setup is very rigid, and there are mounts already designed for many different types of tools.

Some people, like me, use a lot of different tools and want to be able to change them out more quickly, without having to deal with screwing a new mount to the rails each time. I had been on the lookout for universal mount that was easy to change tools on, but was also rigid enough for running the router. I found one on New Year’s Eve that seems to fit the bill, and immediately adapted a bunch of existing mounts to work with Hicwic’s universal mount. I also came here to the forums and started talking it up, so at least a couple of other folks are using it now, too.

Others can chime in and tell you what they think of the universal mount, but it works fine for what I’ve been doing - laser etching/cutting, foam cutting, and routing in (soft) wood. I have not tried aluminum or very hard woods yet. It’s a bit fiddly to get the various parts to fit right - I usually print the tool mounts in ABS, then sand and use acetone to make them smooth and get them to fit. After that, changing the tools is simple.

One note about changing the tools, for those already using the universal mount: I’ve found that you need to be careful when inserting and removing the tool mounts from the universal mount, especially if they are very tight. I usually brace the z tower against whatever direction I’m applying force - luckily my MPCNC is in an enclosed space, so I can brace the top then needed. The reason for this is I once pulled the Z couple nut out of its holder by pushing down too hard, and pulled the threaded rod out of the rigid coupler by pushing up too hard. I’d like to design some sort of tool that would hook onto the tool mount and maybe part of the middle section, to allow you to apply force without straining those two points I mentioned.

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Welcome and thanks for the compliments!

On the build volume side of things, Z is the most important. You can do you large build for wood and knowing that you will try some aluminum just make the z really short 2"-4".
The Z axis is the “weak” link in that aspect, because it is combination axis. The bits are usually 2" so usually you will never usually mill deeper than that so the added height would be for material thickness. I have about 2’x2’x8" build volume and aluminum works fine. I use the added z height for 3d printing. My next build will probably be even smaller. I want the rigidity so I can increase my cut speed. I have also never cut anything large, but that is just me.

Good luck let us know if you have any issues.

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Dr. Vicious,

Good advice. I think I’ll go for a 2’x2’ or 2’x3’ addressable surface, since it sounds like a long y won’t be too problematic. I’ll keep Z to maybe 4-5". (I know I’d like to carve a 3.5" thick board, so that gives me a lower bound to aim for.) That’ll probably be a useful balance for me, and leave open the option of playing with aluminum.

Karl,

Thanks for the welcome! Is this the mount set I should be building from? http://www.thingiverse.com/thing:1245848/#files
Any particular reason you did the mount in ABS? I just started my first roll of PLA (based on the MPCNC build advice), and I’ve been delighted with how much easier it is to get working well. If ABS is important for strength, I still have plenty to play with.

<em>Before I continue, is that a Kossel delta in your picture? I’m looking for my next 3D printer and the Kossel XL is on my short list.
Why, yes, thank you for noticing! (blush) It's a Kossel 250 from an Ultibots kit. It's an aesthetically gorgeous design, just a pleasure to watch moving around, and the Ultibots kit was really nice to put together. Plus Brad provided really top-shelf support during the build.

However, I wouldn’t actually recommend the delta geometry. Other than the aesthetics, the main advantage of delta is no moving mass – no motors ride on carriages. For a pick and place machine, this is a huge win: low moving mass means a blazingly fast robot. For a 3D printer, it’s totally irrelevant, since the speed bottleneck is extrusion rate and cooling behavior of the printed part.

If that were the whole story, the aesthetics would still win. However, leveling this thing is a dog. On a Cartesian printer, you level it in physical space by turning a couple screws (or so I’ve heard), and you’re done for eternity. On a delta, leveling involves solving some crazy set of trigonometric equations; if any one parameter is off, the z=0 logical plane isn’t even a plane in physical space. I bought FSRs (force-sensitive resistors) with my kit, which lets the firmware probe the bed and then compute the parameters, which sounded great in theory. In practice, the algorithm is very slow – it tweaks one parameter at a time and hill-climbs, re-probing the bed between every adjustment, so “leveling the bed” takes an hour. (In principle, you could probably write a smarter algorithm that approaches the correct solution much more quickly using a multivariable derivative of the geometry, but that’s not what comes with the firmware.) The first few times it seemed to converge pretty well, but then, for reasons I don’t understand, it no longer does, and I can’t level the bed closer than 0.2mm. That’s enough that, on my bigger parts, the skirts don’t smush well enough to stay stuck together. The conclusion of this sad tale is that, as lovely as this printer is to watch, I’d love to be able to level the bed by turning a few screws. My next 3D printer will be Cartesian. (My next 3D printer will probably be a hot-end stuck to my new MPCNC, of course. :v)

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Thanks for the info on your delta, Jon. I’ll definitely keep that in mind. The other option I’m considering is a corexy machine - I need to keep doing research on that. I am looking for speed and accuracy, but ease of use is high on the list, too. Plus I don’t have a lot of money to put toward it, so some machines that have all that engineered in are out for me.

Yes, those are the mounts I made for the universal. I just replaced my DW660 mount with a new one, after discovering some issues with the old. I will post it to thingiverse so you can get the new one.

I used ABS for the tool mounts (not the universal piece mounted on the MPCNC) because it can easily be smoothed with acetone. This is not absolutely necessary - the new DW660 mount I printed in PLA, since that’s what was in the printer. I just had to do a lot more filing/sanding/fitting. The smoothness, particularly on the tool mount side, is important because of the long mating surfaces involved. Because FDM prints have natural ridges running horizontally, you really need to do something to smooth out the surface so it can slide easily, otherwise those ridges tend to lock together and make it hard to slide in and out.

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The newest version of the DW660 universal mount (v5) is up on thingiverse.

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Because FDM prints have natural ridges running horizontally, you really need to do something to smooth out the surface so it can slide easily, otherwise those ridges tend to lock together and make it hard to slide in and out.

Ah, okay, so I can choose between the aggravation of getting ABS to stick, or the aggravation of getting PLA to smooth. Noted. :v)

The newest version of the DW660 universal mount (v5) is up on thingiverse.

Fantastic! Thanks! That v5 looks like the support structure will be … interesting … to build. :v) We’ll see how I do.

Although I printed my MPCNC "Better Middle Z"s yesterday and today, because it looked like the hardest printing challenge, and they came out okay. That’s even with slic3r, which I read here isn’t as good at support as cura (which I haven’t bothered installing yet). I’m 31% through my MPCNC printing right now. Woo! (And thanks to Vicious1 for posting a table with estimated build times!)

The other option I’m considering is a corexy machine

That seems worth a try: it has the same benefit of off-carriage motors, but it still creates its planar surface with rods instead of math.

I am looking for speed and accuracy

What motivates the desire for speed? My delta can fly around the build volume, but who cares? When it’s actually working, it spends all of its time moseying along at modest speeds dictated by the extrusion behavior.

--Jon
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I too have read that Cura is better at support and other things, and is also simpler to use. However, I started with Slic3r, and although I have Cura as well, I’m reluctant to go through all the growing pains I went through with Slic3r all over again with Cura. I probably should, or spend the money for Simplify 3D, which is supposed to be really good.

You have a good point - speed doesn’t necessarily need to be a factor. Accuracy is much more important. I just think it would be nice to print things in less time. I was thinking of getting a volcano or a clone to speed up extrusion. Since you already have a delta, you should look into it.

I should mention that I was attracted to the larger build volume of the XL, but it’s possible to make larger xy-style printers. Hey! I have one in my garage! Maybe I just need to buy the printer head from Ryan or put together my own. There are really only a couple of things I’ve run across that are too big for my current 200x200x200 build area.

LOL but I still want a new printer. In the music biz (another hobby), we call that GAS, for gear acquisition syndrome.

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I just switched to using cura directly instead of inside of repetier host for some of the printers I run. I prefer to use Simplify 3d when I can, but the license I have access to is on a couple of computers in a lab that has classes in it. Cura does the job for most of my prints, but the results of simplify 3d are simply better and support is a breeze to remove.

As far as build volume, something the size of a mpcnc would be a nightmare to try to print ABS reliably, but pla would be super easy. That being said, I saw that someone has recessed a heated build plate into the table of a mpcnc. A well tuned ultimaker can reach about 150mm/s where as my tinyboy can reach about 50, so I can understand the want for faster printing. Someone here has an i3 with an e3d volcano on it for super fast printing. Of course you sacrifice the layer resolution.

I am in a similar boat as Jon. I am almost done printing parts (just the middle z stuff left) and I need to start thinking about build size so I can buy the correct amount of conduit. I think I want 2’x2’, but have no clue on the z. I will be using it with a dw660 for routing, but also want to use it as a printer. I currently feel limited with the 3.1in height on my printer. I think I would like about 5 in of space for printing.

Would having a different set of legs help? So I would have a taller set for 3d printing so that I can get maximum z height, and then have a shorter set so the x and y axis are closer to the work surface thus making the spindle closer to the x and y axis. Actually, it would probably be more like blocks to put under the feet to lift the whole machine up for taller prints. They would have to be secured to the table of course.

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I am always skeptical about those max print speeds. The Stock MPCNC can handle 197mm/s but none of my 6 printers can print parts with any strength over 35mm/s. The prints look good, some of them get ringing worse than others but they all have very poor layer adhesion. The only way I know to truly speed up printing is a larger nozzle.

Yup you can make your legs go into your table to make an adjustable MPCNC. That is why the feet bottoms don’t have bottoms. Give it a try for the best of both worlds.

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Yup you can make your legs go into your table to make an adjustable MPCNC.

Wait, what? That’s interesting! You said earlier in the thread that Z-axis is the critical dimension for a rigid tool. If I understand you correctly, here it sounds like you’re saying that the extra Z is only bad if the tool is hanging down on a long cantilever; if you shorten the legs so the tool is never lowered far from the Z gantry, then you get all the rigidity benefits of a short Z axis?

If my understanding is correct, then it might make sense for me to build a bigger Z (say, 8"), and just stick some short conduit in the machine legs to shorten Z travel to 2" when I want to try milling aluminum.

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karltinsly: Two more questions on hicwic’s universal mount. First, is this the mount I should be building to attach your DW660 parts to?
http://www.thingiverse.com/thing:1234989

Second: if I understand correctly, this universal mount takes the place of the part Tool_Holder_13mm.STL on http://www.thingiverse.com/thing:724999/#files, so I should skip building Tool_Holder_13mm. Is that right?

Thanks many – I’m trying to get as many of the right parts printed as I can so that when I order the bundle, I can minimize delay before gratification. :v)

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That is exactly what I was trying to get at. I don’t think it is quite all the benefit of a shorter z axis, but I think it will certainly help if you want to keep the z axis tall.

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Agree.

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Stick with the recommended build size from the assembly pages to start with. you can always go bigger for another 5 bucks in pipe. The universal tool mount works great even in pla. I had no issues with it seizing or mating too tightly. I used the same 26mm/s 60% infill that used on all the other parts.