LowRider v4 Rebuild – From Full Sheet to Quarter Sheet
After living with my full-sheet LowRider v4 for quite a while, I’ve started seriously considering rebuilding it around a quarter-sheet (24" × 48" usable) work area instead of a full sheet.
This isn’t because the LR4 has been disappointing—quite the opposite. It’s because actually using the machine has taught me where my priorities really are.
Why I’m Considering Rebuilding
When I originally built the machine, I assumed I would regularly put full sheets of plywood on the CNC.
That hasn’t happened.
The only time I’ve actually machined a full sheet was when I cut the strut plates used to build the machine itself.
Everything else starts the same way:
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Buy a full sheet.
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Break it down with a track saw.
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Put manageable pieces on the CNC.
The track saw has essentially replaced the need for a full-sheet CNC in my workflow. It’s faster, safer, and easier than wrestling a 4×8 sheet around the table.
Meanwhile, the machine occupies roughly a 5’ × 10’ footprint in an already crowded shop.
The LowRider was designed so the machine can be removed from the table and stored when not in use, but my build doesn’t really work that way. Early on, I designed and published a full Unistrut table system for the LR4, and that’s the direction I chose for my machine. It has proven to be extremely rigid, but it’s also a permanent installation. Between the Unistrut skeleton and the 3/4" MDF spoilboard, the table is a two-person lift, so the original “store it against the wall” concept no longer applies. Here is the link to where I started designing the Unistrut adapters:
Credit Where It’s Due
I also want to give credit where it’s deserved.
The more I’ve thought through this rebuild, the more I’ve come to appreciate just how well Ryan optimized the LR4 for its intended audience.
There are countless little engineering decisions throughout the design that don’t immediately stand out until you’ve built and lived with the machine for a while.
The printed parts are a great example. The internal load paths, hidden geometry, wire routing, and thoughtful nut and bolt placement make the machine remarkably easy to assemble and maintain while remaining surprisingly strong.
The moving gantry design is another one. By raising and lowering the entire gantry instead of building a tall Z-axis, the cutter stays close to its support structure, keeping the Z assembly simple, compact, and rigid.
Even the removable machine concept deserves recognition. I completely ignored that design feature by building an oversized Unistrut table that weighs a ton, but that’s on me—not the design. If I had built a lighter table like Ryan intended, I could simply lift the entire machine off and store it on a shelf when it wasn’t needed.
None of the ideas in this thread are meant as criticism of the LR4.
They’re simply an attempt to adapt an already excellent design to my own shop, my own workflow, and the tools I now have available after several years of using the machine.
I think that’s actually a testament to the design. The LR4 has given me a platform that has been reliable enough to make me think carefully about where my compromises should be, rather than where the machine’s compromises are.
Why Quarter Sheet Makes Sense
Reducing the machine to quarter-sheet size solves several problems simultaneously.
First, it dramatically reduces the amount of floor space dedicated to the CNC.
Second, it shortens the gantry considerably.
That matters because the gantry is the largest structural member in the machine and therefore the largest source of deflection and torsional twist.
Shortening the span improves stiffness before changing a single material. That single change is what made me step back and rethink the entire machine. Once the gantry became shorter, several ideas that weren’t practical on a full-sheet machine suddenly became realistic.
My goal is also shifting toward aluminum machining. Every increase in rigidity directly improves surface finish, depth consistency, and chatter resistance.
The only capability I would lose is slab flattening or occasionally machining long stock.
Fortunately, my existing table construction already suggests a solution.
Unlike the standard LR4 table, my machine references everything from the Unistrut frame. The Y rails are located from the frame itself rather than the spoilboard. That means if I keep those mounting locations fixed, the frame becomes the machine’s permanent datum. The spoilboard can be replaced, and a bolt-on extension can be added, without disturbing the primary alignment of the machine.
My current thinking is to build the quarter-sheet machine first, then create a bolt-on extension that allows the machine to return to roughly a 24" × 98" work area when needed. Alignment features between the Unistrut sections would ensure repeatable assembly while allowing the everyday machine to remain compact, rigid, and optimized for the work I actually do.
Even if I ultimately decide not to build the extension, I don’t consider that a failure. The goal of this rebuild is to make the machine better for the work I do every week, not preserve a capability I rarely use.
Hidden Belts
The table redesign also gives me the opportunity to incorporate the hidden belt modification.
Since I’m rebuilding the frame anyway, I can position the Unistrut specifically around the belt path instead of designing around the original exposed layout.
Beyond simply protecting the belts from dust, chips, and accidental damage, routing them inside the structure cleans up the machine considerably and removes one more exposed component from the work area. It feels like one of those improvements that makes sense to include while everything is already apart instead of treating it as a future retrofit.
Rethinking the Gantry
The standard LR4 relies on printed triangular strut braces connected by front and bottom strut plates.
Those plates are more important than they first appear. Together with the braces they create a deep structural section that resists gantry twist.
The EMT tubes provide both the bearing surface for the bearings and part of the structural beam.
For most builders, I think Ryan found an excellent balance between cost, simplicity, and performance.
My situation is a little different.
I already own a plasma cutter, drill press, welder, and enough 1/8" × 3" steel flat stock to fabricate replacement strut plates.
Rather than asking the CNC to machine replacement parts, I can use my existing MDF strut plates as precision templates.
My fabrication plan is:
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Cut the steel into two matching blanks.
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Tack weld them together.
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Transfer punch the first pair of locating holes.
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Drill those holes through both plates.
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Bolt the MDF template to the steel using those holes.
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Continue transferring and drilling the remaining holes while the template is positively located.
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Plasma cut the outside profile.
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Finish to the line with grinders.
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Separate the finished plates.
The hole locations are the critical dimensions. Everything else can be fit and finished from there.
The outside profile simply needs to provide proper clearance and enough material around the mounting holes.
Steel also changes how the assembly carries load.
Instead of relying primarily on plate geometry, the plates themselves become significant structural members capable of carrying much more of the load.
Tube Selection
Forum testing has shown that thicker-wall tubing is noticeably stiffer than standard EMT, particularly on longer machines.
Because this rebuild shortens the gantry so dramatically, the economics change.
Instead of needing roughly ten feet of tubing, I only need enough for two rails around 30.6" long.
That suddenly makes higher quality tubing much more practical.
At the moment I’m leaning toward staying with the standard two-tube design while sourcing the straightest, roundest, thickest-wall tubing I can reasonably find, whether that’s DOM or another suitable mechanical tube.
I’ve also looked into the three-tube modification discussed on the forum. Based on what I’ve read, and Ryan’s comments over the years, I don’t think it’s worth adding the extra complexity for this build. On a much shorter gantry, I think better tubes combined with stiffer plates is probably the cleaner solution.
Why I’m Chasing Rigidity
One thing that often comes up in CNC discussions is diminishing returns.
I think CNC machines are a little different.
The controller only knows how many steps it commanded.
It has no knowledge of structural deflection.
It doesn’t know if the gantry twisted.
It doesn’t know if the belts stretched.
It doesn’t know if the frame moved.
Every source of mechanical error increases the difference between commanded position and actual cutter position.
None of those errors exist in isolation.
A couple thousandths of frame movement combined with a few thousandths of gantry twist, belt stretch, spindle runout, and cutter deflection become one larger positioning error.
Reducing any one contributor reduces the total accumulated error.
I’m not trying to build a machining center out of a 3D printed CNC.
I’m simply trying to remove as many unnecessary sources of error as practical while staying within the spirit of the machine.
Current Direction
At this point my plan is to:
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Rebuild around a quarter-sheet working area.
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Retain the Unistrut frame concept while making it modular.
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Incorporate the hidden belt modification as part of the table redesign.
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Keep the machine optimized for daily use rather than occasional large jobs.
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Fabricate new 1/8" steel strut plates.
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Source higher quality tubing if reasonably priced.
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Improve rigidity wherever practical without adding unnecessary complexity.
Looking for Real-World Experience
Before I start cutting steel, I’d appreciate feedback from anyone who’s gone down a similar path.
I’m particularly interested in:
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Quarter-sheet LR4 builds
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Steel or aluminum strut plates
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Better tubing on short gantries
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Modular tables
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Hidden belt implementations
If you’ve tried something similar—or decided not to—I’d like to hear why.
I’m not trying to redesign the LowRider from scratch. I’m trying to build the version that best fits the way I actually use the machine.