As topic states, no room for a full sheet Lowrider 3 at the moment.
What is a good size for the MPCNC?
Hi Barry, I have read the docs and they talk about maximal size.
I was thinking more if someone here built a MPCNC and after using it though:
a) It´s too small. I wish I had made it bigger.
b) It´s too large. I wish I had made it smaller.
All the time. 
Generally we suggest the no larger than 2 foot square. Any bigger and you can run into rigidity issues. It’s easier to make it smaller than make it bigger.
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It’s the crazy folks like me that finally got Ryan to design the lowrider. We were making them waaaaaay too big. I made the default size at first, then extended it to 5 foot square. Then went back to stock size and built a lowrider.
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I had a Primo for 2.5 years that was 545x755mm. It had chatter in the middle that I could obviously not get rid of which drove me crazy sometimes. You didn’t really see it in the results (you can find a lot of the things I did in the “Things you’ve made”), even without a finishing pass mostly, but it was annoying.
I switched to a LowRider now, with 1220x880mm workspace (Hornbach in Germany sells small sheets that are 600x1200, that’s what I was aiming for, the rest is bonus) and I am really happy with it, even though I have only cut one project until now.
I, like @azab2c also “rotated” the table so that X, the open side, is facing the user. A lot of setups have Y facing the user since it is the longer side. Not with us though, un-uuuunh! 
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If you would build a Primo today, what measurement would you go for?
Or would you go for a smaller lowrider perhaps? I have very limited space at the moment.
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the lr3 can be as big or small as you want it. The mpcnc and the lr3 are 2 very different machines. If you think the lr3 is what you need, scale it to fit you. It does not need to be 4 x 8
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I am not in this space at all at the moment but I want to learn it.
I am looking at making a copy of an arcade machine that I own.
But I lack the space for a larger lowrider.
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One thing you can do is make the X axis the longer axis. You could do a cutting area of 4 feet X and maybe even as little as 3 feet Y. You would have to index and “tile” the longer pieces to make something long er in the Y dimension.
This is what I did to get a chance to use the old table surface for the LR3.
I had a Primo that had a couple issues relative to the work I do, and it necessitated an overall change in approach which was handled better by a LR3. I will say that the Primo was an easier machine to use and assemble. I ha the normal Z axis length and found that I didn’t need that much for the parts I was making.
Mike
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The workspace to total area of the two machines is about the same. They each lose about a foot in each direction. You can build a 2’x3’ low rider, and it performs great, especially for sheet goods. It will end up being 3’x4’ or so. A primo will be about the same for the same area.
I started with 3’x4’ and I ended up shrinking it. I wouldn’t build a primo over 24"x24" when the low rider works so well at that size.
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What do you think about 50x50 cm?
If you’re talking about the cutting area, that should be a great size for the Primo. Of course, the LR3 can be built to that size too.
Another point to consider is the rigidity you will need for your planned parts: the Primo is less rigid when fully down to the spoil board, while the LR3 is most rigid when all the way down. The total vertical travel for both machines can be whatever you want, within limits.
Mike
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I had a burly that I had cut the pipes at 4 foot. I only lost 3mm of accuracy in the center. But everything I cut didn’t require exactly measurements. There was a little chatter, but that was solved with slower speeds and more passes. The only reason I don’t have it now is I took it apart for parts to make a LR2.
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I’d make a list of projects that you want the cnc for and what their dimensions are and size your cnc to match for 80% of them.
You can always tile pieces in one dimension for the occasional oversized project.
Once you’ve knocked out your 80% you can always rebuild your machine to match the other 20%
I have a 4x6 LR2 and I don’t even have a spoil board on 2/3 of it because everything on my currwnt honey do list is 2x4 or less.
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How does the rigidity work? I hear what you write but what does it mean??
Say I have an MPCNC and a LR3 and I am milling MDF board, how does the difference in rigidity work?
The LR3 can be made small, but scales to larger more easily than the MPCNC. The MPCNC Primo starts to become less rigid because of the nature of the steel tubes used to make the movement rails. the longer it is the less rigid.
Within their sizes though there is a difference between the two types of machines. The Primo is more rigid the higher it is cutting. As it extends downwards towards the table, it becomes less rigid. This is because the core remains in place at the top of the Z travel, and the close to this that the router is at, the less leverage the router bit has to make things bend.
The LowRider on the other hand is most rigid at the bottom of its travel. The higher it goes the more the YZ plates have to support the machine, and the more flex they can introduce, due to higher leverage. This makes the LowRider best at cutting out 2D shapes in sheet goods where it does the most important work at the lowest height.
A Primo for smaller work areas is an excellent machine, and I personally like the design with fully captured rails, so that the machine does not rely on gravity for stability at all.
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Hi Dan,
thanks for a good explanation!
What smaller work area would you say is excellent? (For a Primo)
I believe that 2’ square working area should deliver excellent results. I am rebuilding my 2’ × 3’ Primo now and I am going to go for 25" × 19". That lets me leave my X axis alone (25") but cut the long axis in half. I believe this will make for a strong machine.
In those parameters, I believe that the Primo will be able to work faster than the LowRider can, but my LowRider will have a larger work area.
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At 2x2 it RIPS
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