Has anyone tried milling aluminum sheet on the lowrider?
I’m looking to cut max 1/4" sheet.
I haven’t yet. How big did you build your LowRider?
I haven’t ordered parts to build one yet. I have a mpcnc and its good for small stuff up to 1/2" thick but has a small build area.
I’d like to cut bigger sheets like 4’x8’. Just simple 2d dxf lines.
That will take a very long time. The smaller the machine the faster, even for the LowRider. I know it seems really convenient to drop on a full sheet and cuts parts as you need them but it will be much more efficient to keep the machine as small as your largest part and drop in cut down material.
I am sure it can do the cutting, but 1/4 is pretty thick and a 4’x’8’ cut would take a really really long time.
How does having a smaller machine that you have to cut pieces down for equate to being faster then a machine that you can set with a path to complete the entire print at once?
A smaller machine can cut the paths much faster. Half the size equals, roughly twice as ridged, equals cutting much faster.
And I don’t think you would be cutting an entire sheet worth of parts at once. It would take a crazy amount of time. A water Jet is typically used for large scale 2D cutting, Plasma if it can be rough.
CNC’s are not set it and forget it, you have to be actively monitoring the progress.
Slow is fine, when one part is the size of a sheet it shouldn’t take very long.
I’m mostly concerned about the machine being able to repeatably cut along the same line after travelling to the other side of the table and back. Are the belts able to stay in tension properly over 8ft?
What sort of tolerances are you needing/expecting in Aluminum?
1/16" or less over 8’
Not ever going to promise that. It is technically possible, the resolution is plenty high, steppers and router are plenty strong but to be safe I will say this is definitely not for you.
1/16" is a lot harder than it sounds over 8’ but is doable with a finishing pass for sure if you started perfectly square, but I just don’t think 24’ (minimum) of milling 1/4" aluminum is going to be as fast as you think and some of the fine details could be lost in metal if your CAM isn’t perfect. Heck even making sure you start your machine that square isn’t an easy task, that is 0.037 degrees.
This was built as a full sheet wood router and can handle others materials at a smaller size. Pretty good for $500, next steps are $3200 for a crawlbot but I have no idea how they feel about milling metal, then maybe a few options starting at about 8K, still none really want to promise metal.
A related question (and comment).
Im interesting in building a 4x4 1/2 sheet CNC. Keep debating back and forth between a Low Rider and the MPCNC. I intend to cut 95% wood, and occasionally Aluminum.
Which build would you recommend, a big MPCNC, or a 1/2 sheet Low Rider?
I intend to cut a bunch of the parts out of 1/4 Aluminum on another CNC I have access to.
As for Whole Sheet work. It’s not the speed that I care about (Set it up and forget it). Sometimes it’s a a big sheet with a few small holes, sometimes it’s cutting a lot of small parts, and it’s nice to keep re-running the same Gcode over and over with a different x-y home without having to re-setup the table.
Welcome to the community! Glad to have you! Enjoy your stay, here, have a cookie… 
Now, listen up. CNC is NOT fire and forget. This is not your 3D printer. You need to be within arm’s reach of your e-stop during the entire run, and paying attention. No gaming with the headphones on, or CAD work with Spotify in your noise-cancelling Bose (you bourgeois pig). 
Seriously, the threat of fire (or rapid unplanned disassembly of a rotating cylinder of solid, sharpened carbide) is real and not insignificant. Unless you are willing to risk the loss of your entire workspace and any attached buildings, I’d avoid walking away from a running CNC.
Otherwise, welcome again! Safety is really the only thing that can get people riled up around here. Well, that and charcoal vs wood pellets vs gas… 
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Yes, and I appreciate the warning.
Im very familiar, and have a decent amount of CNC machining under my belt on several different commercial machines, and am decent on Fusion, Mastercam, etc… I have broken my share of bits and learned from every failure. I’d say that I agree, cutting harder materials, I know something is askew more often than not by ear, than before by sight 
More so it’s the “Set it up” and not have to setup repeatedly that I was referring to as “Set it and forget it”. Not the Hey, let’s find out the hard way that I put in feed rates for a 2 flute cutting wood when cutting aluminum.
My CNC will be inside a well contained safety shell with a 2x4 bullet proof glass view panel on the front. Safety and chip control. Even with that, yes I watch like a hawk.
I’ve read a lot on the site before asking, and largely it seems that the Low Rider is the right fit, but I haven’t found the info of 4x4 low rider vs MPCNC on aluminum debate.
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Ah…
“Never miii-iiind…” - Rosanna Rossanadanna 
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Probably because there are few, if any, folks cutting alu at those sizes… A lot would depend on what you’re cutting for. Are they silhouette signage pieces, or are they dimensional/structural pieces that need to have really high precision? Are you doing any surfacing work on them, or are they just cutouts? I would think (and I’d wait for confirmation from those with actual knowledge) that if you’re just doing cutouts for signs, then the low rider is probably your best bet. But if you need better precision and/or repeatability, you may need to push the limits of the MPCNC, which would include mid-span supports on the X and Y rails, etc. And even then, you’d want to keep your work as close to Z 0 as possible.
Mostly Brackets and precision drilling. Basically more concerned with drilling accuracy than contour milling accuracy. Anything that’d need precision contours, I’d probably use another machine, or be OK with the slop.
I’m also figuring on using an 11amp 2.5 horse spindle that I have lying around. I already have a bunch of 1/8 and 1/4 mills and collets that fit it.
I’f it’s for precision drilling, you could probably go either way. I might suggest the LowRider for that workspace size. You’ll have zero load (aside from the spindle/gantry weight) for your X/Y movement. At issue would be if you’re going to be just drilling, or also cutting out larger holes, in which case, my reasoning is off, since you’ll be making helical cuts. Although for larger holes, you can also do finishing passes to help tighten up your tolerances.
How about forget and fire? 
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Thank you all for the feedback, and the Humor.
For Drilling I Require Precision, For Helical Cuts (Contours, Pockets, etc…) Im OK with a lot less precision and accuracy. I think the Low Rider is going to be the way to go, and if down the road I want to make it more precise, I could always add 5 ft Gear Racks for $160 for Y and $80 for X.
Much Thanks!
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