I think I did a square build because it made all the tubes the same length. It is also easier to rip sheet stock down to squares. Only have to set up one dimension on the table saw… Rip, turn, rip, repeat.
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Hi David,
thank you for your reply. The easeness of cutting is a good advice!
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I think I heard Jeff say his lowrider is set up for cutting 2X4 sheets of plywood because that fits in his car, and they sell that size already at lowes and home depot. If you built a 5 foot by 3 foot table, you could easily do that with the lowrider.
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It is a great size for me. I think it is about 28"x48". I prefer the baltic birch sheets, which come in 60"x60". I have them cut it down the middle to fit in my car. 30"x60" fits fine in the table, even though I can’t quite cut the whole thing at once.
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This is the size I’m considering. I was going to do a 4’x4’, but I’m wanting more floor space.
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Can’t decide on a 610x610 mm MPCNC or a small Lowrider 3? I was going full sheet but I still don’t have the space. The lowrider 3 would be 610x610mm working area?
What to do?
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Personally, I have a MPCNC that I originally started building long before the LowRider existed. I built it at 600x600 and haven’t found that much use for outside a few specific scenarios like cutting holes in things like ABS or fibreglass electrical enclosures and certainly nothing remotely close to its maximum footprint. It was rigid enough to cut aluminium if I stayed near the corners but gets noticeably less rigid towards the center. To be fair, this is more an issue with my personal build as it’s built with thick-walled aluminium tube (all that was available in 25mm here at the time) and I also had a cheap and terrible spindle on it which completely soured me on using the whole machine because I was always aware of how hamstrung it was by the crappy spindle.
I’m in the process of building it into a Primo with 300x300 working area and adding a Makita RT0702C as the spindle. Hopefully that should alleviate some of the mistakes I made with the original build.
I’m also printing/cutting some parts for an LR3 for a build that my Dad is going to do.
For me, the extra height was convenient for what I wanted it for, but not much else. It needing a space to stay set up was fine but not ideal. I never figured out a storage solution that would allow it to be put away and eventually it got buried as I needed to store stuff around it. I also ended up with other ways of doing the same things I was originally planning to do with the MPCNC.
Looking at it now, an LR3 with a similar size would still do everything I have needed the MPCNC to do, while also being much easier to share space with, either by removing the LR3 and putting it away, or just having it moved to one end of its travel.
I think ultimately the answer comes down to what you’d be doing with it. If you’re mostly planning to cut/carve sheet goods then I’d probably build an LR3 and spend the effort on making it usable on a general purpose workbench. Especially if you’re planning to build a larger LR3 at some point. In theory it should be pretty easy to swap out the gantry tubes for longer ones to expand the LR3 which would give you a large-format version of a machine you’re already familiar with and hopefully have dialed in somewhat.
I don’t have any experience running an LR3 and wouldn’t say I’ve ever run my MPCNC anywhere close to its capabilities, so take all of this with a decent pinch of salt. This may also just be ‘the grass is greener’ talking here, so hopefully some others with more experience will set me straight if I’m off in the weeds.
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This. 
I questioned the Primo before, because the LowRider is, in my eyes, the more versatile machine. What I did like with the Primo was that it can’t lift off the rails. Also, if you want to cut higher stock the Primo might be for you, but it’s really hard to find endmills that can cut deeper than 4cm. 3cm was the deepest I ever went. You could also add a drop table to achieve this. I also don’t like that the LowRider can’t touch the spoilboard with the collet, I had to rethink carvings in thin materials and the short V endmill. If you never had a Primo this might not be a problem though.
I’d love a LowRider with trucks like the Primo. 
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I still haven’t had time to finish this build.
I am looking at the docs and the size page, when it says outer dimensions, is that of the workspace or total machine footprint?
EDIT: I (finally) have a use case for the MPCNC and I want to mill aluminium at 15mm height and about 110x110mm.
With this size in mind, what size would you make the MPCNC?
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The Primo is more rigid when the Z is up and the LR3 is more rigid when the Z is down. I just am building a new, smaller LR3 for this kind of work.
Mike
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One of the nice things about the MPCNC is that you can always use longer rods for the frame than you need, which makes it trivial to re-size the whole thing.
In your case there, I’d probably try to make it somewhere in the 120x120 to 150x150 range to give you as much rigidity as possible and keep the Z height as low as possible, especially considering that you’re trying to mill to quite a significant depth in aluminium.
I made mine 600x600 originally and shrunk it to 300x300 by just sliding everything inwards on the rods. It looks a bit weird but ‘feels’ a lot more rigid, at least. Tough to tell for sure because I also replaced the spindle but it’s a noticeably different machine after that.
Edit: So you could cut the rods for 300x300 and do the initial build for 150x150, for instance. If you’re making things that are 110x110 then make sure you’ve got at least an extra cutter width so you can profile the entire outside of the part. That and making sure you’ve got enough Z height to clear whatever cutter, as well. Later if you find that you need something larger or have plenty enough performance for your needs, you can just loosen all the clamps, slide the thing out and you’ve got a larger machine.
Hi Jono, thank you for the good advice.
I am thinking about going smaller but also non square, perhaps 150x250mm.
Is there any difference in rigidity on the X- and Y-axis?
Also, do you have a picture on everything slided inwards? Not sure if I follow on how you mean.
There will be lower rigidity in one direction, but I’m nowhere near experienced enough with this to be able to guess at how much of an issue that is. My understanding is that you’ll need some basic level of ridigity to actually even cut the parts at a speed that lets the cutter engage with the work and cut effectively and then anything beyond that is just speed.
I was successful cutting 3mm aluminium with my 600x600 aluminium tube design but needed to go relatively slowly with shallow depth of cut, small stepovers and trochoidal milling. Those things all compound because shallower depth means more passes, small stepovers mean more passes, trochoidal milling means more material removed and more movement for a given cutting path, so the combination of all of those might be the difference between a job taking 10 minutes on a dedicated aluminium-focused machine and several hours on a less rigid machine. There was no chance I would have been able to cut out a 100x100 part in a reasonable timeframe, let alone in 15mm.
I think that’s why I’m so keen on the idea of being able to adjust the size if needed. If the big one isn’t working, shrink it for the specific job. If you know you’re going to be pushing the envelope, capability wise, build it as small as possible and then expand later. If it’s as small as possible, you know you’re giving it the best chance for success.
I’ll have a hunt for some photos but if you look at the MPCNC photos, you can see the exposed ends of all the tubes. There’s nothing stopping those tubes sticking out further than the working area of the machine.
Ah, I have a couple of photos in the last post in my build thread:
You should be able to see the excess tube sticking out towards the back and right hand sides in the last photo. I decided to keep all the excess sticking out on 2 sides so it can still be slid hard into a corner when not being used. I’m also still using the same piece of 40mm Triboard as a work surface, which has been great. That means the overall footprint of the router is still the same as it was when 600x600 but it’s noticeably stiffer in the smaller size and with the Primo parts instead of the previous Burly parts.
If I wanted to increase the size of the machine, I could loosen the truck clamps on the back and right trucks, loosen all the corner clamps other than the front-left one and remove the screws holding them to the bed, take the belts off and then slide it all out to its new size. Because I made the cables the same length as the tubes, nothing even needs to change length. I can re-use the belts because they’re way longer than needed and the excess is just wrapped around the legs and cable tied.
In the process of shrinking my mpcnc. Originally built it with a 24" x 36" working area, but now it is reduced to 18" x 18" working area. Moral of the story is, if you are going to build bigger than the recommended size, do not use 3/4" emt or you will see significant flex mid span. This is not the fault of the design, but my fault for building too big.
Haven’t cut the tubes down yet…
My buddy with an mpcnc now has similar aluminum/metal cutting needs and ended up going with GitHub - MillenniumMachines/Milo-v1.5 (build in progress)
It’s a different beast altogether. (240v 2.5 kW spindle, more $$$$, etc)
I can’t decide on a work area, it feels like I want to be able to do small alumium milling but also larger wood/mdf.
At what size does the alumium milling become less rigid/stable??
You’re heading down the same path that I did and, unfortunately, I never really got an answer because there kinda isn’t one. Everyone’s machines will be slightly different, as will everyone’s requirements leading to there being no ‘one true answer’.
The closest you’ll get is that any increase in size will reduce rigidity which will in turn slow down the maximum speed that the machine can mill material at. It may not be linear, but larger will always be less rigid. Deflection in the middle of the span is related to the length of the span to the power of 3, so a machine that’s twice as large will have 8x more flex in the middle of the bed. The difference will be less pronounced in the corners, but still always worse than if the machine were smaller.
That deflection under load is the main thing you’ll have issues with. A certain amount of force is needed to keep the tool loaded. You can lower that force by moving slower, but then you’re cutting smaller and smaller slivers until eventually the tool won’t cut cleanly and instead just rubs across the surface every 2nd or 3rd rotation. That causes the tool to heat from friction and because cutting away material keeps it cool. You can solve that by slowing the tool down and taking thicker cuts again, but that needs a spindle that can operate more slowly and slows the entire machine down heaps. This all gets massively exaggerated with longer tools because it’s not just stiffness in X and Y, the stiffness in X and Y also translates to rotational stiffness in the core. Longer tools mean more leverage on the core meaning more deflection for a given machine size, etc.
I was able to mill aluminium with a 600x600 working area and using my thick-walled aluminium tubes, but it never worked ‘well’. I’d have said good enough for a few holes or slots for connectors in 2-3mm aluminium, decently fast enough to route pieces out of thin sheet, probably not fast enough to consider using for thick sheet as anything other than a 1-off. Maybe 2-3 hours kinda range? At which point I’d be concerned that a cutter wouldn’t last that timeframe so would also need to plan cutter changes which means keeping tool height consistent etc.
So yeah, I’m not sure I can really help, other than to suggest brainstorming a list of things you want to do and then considering each one vs what other tools you have to do it. If you’ve got a heap of projects in wood that would be ideal for a CNC and one replacement part in aluminium plate that you want to make, maybe it makes sense to build a larger machine and break out a coping saw and some files to do the aluminium part. If you’ve got a bunch of parts you want to make accurately and repeatably in aluminium but also a general desire to do more woodworking stuff without any specific ideas, maybe make a smaller machine and consider using it to make templates for specific tricky features with a palm router.
I’ve come to the conclusion that for my purposes I’m probably better off with something smaller that works well for a more limited selection of tasks than a bigger ‘does everything but poorly/slowly’ type machine. It’s easier to find creative approaches to making big stuff on a small machine than it is to make the big machine work better, if that makes sense.
Worst case, use the MPCNC to make the flat parts for an LR3. That seems to be a common pathway…
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I’ve cut more aluminum on my full sheet LR3 than I have on my smaller 3’x5’ one. Both are extremely capable. The key is Throchiodal Milling
A big part of this difference in rigidity is due to the “webbing” on the gantry of the LowRider.
To get a feel for this, think of any time your car was parked on a bridge and a big truck came onto the bridge, and you felt the bridge flexing.
MPCNC
LowRider
The MPCNC has “single” bars (tubes) covering the spans.
The LowRider gantry has “double” bars (tubes) PLUS the braces and struts, the latter of which form the webbing.