I bought all the parts for a MPCNC an embarrassingly long time ago… almost exactly three years ago! Lot of life has happened since then, but I’m excited to finally build this thing. A couple questions before I get underway:
Have there been any really cool new bits of wisdom / upgrades that I should consider implementing right now? 3 years is a long time! Looks like the Primo is still the current version, but I’m just wondering if there’s been any QOL mods/upgrades that have become common practice. For example, I know some people have done clever cable management with tape measures - not sure if I should do that out of the gates.
For the table / bed - I see that Ryan suggests mounting a tabletop then cutting out the center to be a replaceable spoil board. Is pretty standard, or do people just hard mount a tabletop and call it a day?
My first version of the Primo hat the spoilboard as the table, that wasn’t good, the second version had raised feet and then a board in the middle. For the latest version I just milled out a square, it’s just a plotter after all now.
I would seriously consider building a LowRider 4 instead. In my opinion, it has only advantages over the MPCNC. You can reuse almost all the parts you already bought for the MPCNC, and you’ll only need to add the tubes, aluminum plates, and linear rails. Plus, of course, the printed parts—about 2 kg of filament if you have your own printer. That’s maybe $100–120 USD, and in my view, it’s absolutely worth it.
For as much as I like the LR4, there is ONE advantage of the Primo that the LR machines cannot match, and that is some of the hold-down options that exist.
On the LR, hold downs cannot extend more than a few mm above the top surface of the work, since the X gantry rides low. (Imagine that.) Using things like T track clamps, or (As I use) threaded inserts to hold threaded rod and have clamps down to the surface don’t work well on the LR style configuration, and they invariably collide with the gantry.
Of course one still has to be careful with the Primo to ensure that those clamps stay out of the way of the core when it is extended downwards, but I find this method of hold-down to be easier to use, and is the reason why my Primo stayed in service through the LR2, LR3 and now LR4.
I do like the fully captured rails of the Primo as well, which also make it capable of operating at an angle. This could have other implications which I haven’t fully explored, but certainly exist. Also the Primo has easier capacity for increased Z movement, which could be an issue.
That said… The LR4 is certainly capable of everything that the Primo can do from a machining standpoint. More in terms of rigidity. The limiting factor on cutting power for the LR is the lateral capacity of the Y rail to restrict movement of the machine in the X dimension. (Which is within the capacity of the X stepper motor to overcome.) If you might want more cutting area than the Primo can optimally provide, then a LowRider is definitely recommended.
No worries about the timeline, I printed what was I think the original version of the MPCNC, then some upgraded parts then reprinted it all as a Burly, used it for 3-4 jobs, then eventually tore it all down and upgraded it to a Primo, which is where it is currently.
Thinking about MPCNC vs LR4:
The advice I always give is to think about your goals with brutal honesty. Do you have something specific you want to do with it right now? Do you have something you imagine yourself doing in the future? Is it just to have a cool toy to play with? All of those are equally good reasons, but they might point you in different directions. If the MPCNC works for what you want to do, or you don’t have a specific goal, go nuts, build it, make some stuff. If you’re anything like me then by the time you’re done making your 2nd or 3rd item with the MPCNC, even if they’re just ‘for the sake of it’ kinda things, you’ll have a much clearer idea of what you actually want. If you’ve got all the bits, I’d strongly recommend just making the MPCNC and going from there. It’s relatively easy to pull it apart and turn it into an LR4 later…
Some MPCNC thoughts:
I used multi-core cable for each axis and didn’t really need to use anything like the tape measure trick, but it looks good.
I used a length of flexible fibreglass rod and some 3D printed clamps to make a cable ‘arch’ between the core and one of the corners for the Z cabling and router power.
I didn’t worry about a table or spoilboard, I just got a big sheet of triboard and screwed it down. If it gets damaged I’ll unscrew it and mount it somewhere else. If I know I’m doing a lot of through cuts, I’ll tape another piece under the work or mount it elevated to a temporary spoil board. The table and spoilboard are where I think people can get overly carried away. I’d rather use it, make some problems, then fix the problems I know I have than spend the time solving problems I might not ever get to.
I never got a satisfactory dust extraction/dust shoe setup working for the MPCNC.
I originally built my MPCNC too big at 600mm x 600mm using aluminium tubes, but it’s very easy to shrink without cutting any of the tubes, they just stick out a bit.
Regarding LR4 vs MPCNC: I was planning on making a 18” x 26” workspace MPCNC when I first decided to do this project. I figured that was plenty fine for the MPCNC rigidity.
@Tokoloshe thanks for linking a good cable management example, I’ll take a look!
@SupraGuy My default hold-down approach was going to be Intertape 591, which I’ve used as my default fixturing method when using my Shaper Origin. Good point about clamp clearance, though!
and a separate post since you can only tag 3 users in one reply!
@jono035 I appreciate the encouragement to just build the thing and learn from the result. Great advice, especially since I’m somebody that tends to flail in analysis paralysis for quite a long time. Leaning towards following your suggestion
Right there with you. Setting an aggressive goal of ‘get it to cut something, anything, regardless of how good’ and then improving from there is how I got mine across the line.
I’d say that’s a slightly aggressive size. Like I said above, though, it’s very easy to make them smaller so feel free to build it that size then slide it down the tubes to shrink it until you’re happy with the performance.
And also don’t forget to look at it from the other perspective: What do you actually need, realistically? If you want to make cabinets, that’s gonna be rough. If you want to surface a cutting board, maybe 15" by 12" is plenty?
Thanks Jono. I was hoping that since I was <1m in both dimensions I’d be ok. I think I picked that envelope based on some furniture I was designing at the time, and perhaps also because that would comfortably allow me to process quarter sheets of ply.
At that size I’d say you’re unfortunately heading into territory that the LR4 is likely better suited to.
At 300x300 I’ve had good luck with my MPCNC, but you can definitely go beyond that.
The good thing is that the LR4 works extremely well in small sizes, as well, I think a 1/4 sheet size would be amazing for one. From memory that’s what Ryan has built most often and used for cutting aluminium. I personally think the full-sheet format is somewhat of a compromise for a capability that I don’t think ‘that’ many people will make good use of.
There’s a lot of good to say about just assembling the MPCNC anyway, just run it and see how it performs, shrink the working envelope if it doesn’t meet your goals in terms of cutting speed/accuracy and then if after all that you decide you still want bigger, building the LR4 will be with a lot of tricks learned along the way from building the MPCNC so it’ll go way
Good call Jono. I’ll just build what I have in mind and choke up on the rails if needed. That’s definitely the shortest path to a working machine for me at this point!
also, re: table - sounds like I shouldn’t worry too much about making a cute torsion box right now - although my buddy could probably route an interlocking one on his full sheet router if needed…
I definitely wouldn’t worry at all, especially not in that size.
I have a 40mm thick sheet of triboard that just sits up on a workbench and its fine. The great thing about the MPCNC is you can just undo all the screws holding the feet down, lift it up and plonk it on something else. I always thought lifting it and directly attaching it to a workpiece like some kind of weird frankenstein shaper origin would be hilarious.
Glue a couple of scraps of 1/2" or whatever ply together and sit it on an existing table - That’s an awesome MPCNC solution.
I suppose I can also use the machine to deck the top surface after the fact, can’t I… I have some 2x0.75 ply I glued together for a workbench and never built. It’s crappy ply though, so the top surface isn’t that smooth at the moment. But I can fix that with the machine…
love the ‘sit it on a table’ approach. To be honest, that’s been my plan. I’m out of floor space in the studio - but I do have some good workbenches that hold the MPCNC when needed!
Yeah, you absolutely can. As long as the table is stable, you can mount the machine on a pretzel and level it, then use the machine to flatten the table.
The other thing is that a flat table often isn’t ‘that’ useful. If you’re cutting things out, as long as the bit goes all the way through, the flatness just determines how much extra you need to cut. If your table varies by +/- 2mm then you need to cut 4mm deeper than you would if it was dead-nuts on. That’s only one extra pass, really.
If you’re doing anything carving then regardless of flatness I’d be surfacing the stock with the router first.
Also, if you know the table isn’t flat, you don’t even need to surface it, depending on what you’re doing, you can just glue down some shims, put down some XPS foam and cut that (I do all my track-saw cutting on a huge sheet of foam and it’s awesome), all sorts of options.
I think that’s the key: Just crack into it, choose whatever path gets you to functionality soonest, then solve the problems that actually affect you. Tons to learn along the way and solving those problems may lead to a much better solution for your personal situation than whatever someone else does.
