Hey, with a drop table or raised runners you could get something to work out if you can adapt this to your tool mount. If you only need 8" it is doable
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I’m glad Cesar posted that - reminded me of a HowToMechatronics build. It was a 2.5D hot wire foam cutter. Have you looked at those? I bet for sure you’d be able to build a hot wire machine that would work for blanks.
I get that with the lowrider you’d be able to do the full shaping though. The stickler seems to be the 8" bit required. I’m about to direct you to a handful of 8" offerings but assume no responsibility or liability whatsoever against bodily injury or harms to your wallet. 
The catch here is that you need to be able to run a 1/2" shank which means a different tool than the trim router. I think to run 1/2" shank your only option is a spindle and a bigger one than we usually use on these machines but poke around, I do recall reading something on this forum about a bigger spindle.
FWIW I’d still say you’re best off with a 3 to 4" bit with a 1/4" shank that will run in the trim router and then an open rail build or a “bedless” table build like my extrusion build, and then mastery of the flip job. Flip jobs aren’t that tricky - you just need to be certain your registration pins/dowels are set up perfectly and then included in every job you run. I ran with just two pins, centered on each end of the work piece and then flipped the artwork on that axis. Harder to do with 3d sculpting but not impossible.
With that said hide your wallet…
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Actually…this post shows it all. Run back through and find out what you can about that build and where he got the cutters.
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Never tried anything like this myself. Just a thought would you be able to cut 2” foam in pieces and glue them together after everything is cut? I don’t recall his name however there is a gentleman on here that has built a lot of theater props using that method. I guess you would have to divide your design into sections.
Cutters were from Ali express:
on the lowrider I used 150mm x 6mm flat end 4 flutes upcut bit and 100mm x 6mm corn end (those are total length, cutting length were 100 and 60 respectively)
on the MPCNC I switched to a ER16 collet and increase diameter of the bits to 10mm, they felt more stable … still scary though 
If I can’t figure out the 8" depth it is possibility as my foam comes in 2" thickness already. I would just slice the model and then glue it after.
Since he will using foam he could also use a chuck extender, there are some that can convert to a 1/2 inch
Are you suggesting I switch tools mid-process—use one bit for the top layers and then swap in a longer bit to reach deeper sections?
Why not just redesign the core to be more like the MPCNC?
Or better yet, why not adapt the entire X and Z axis assembly from the MPCNC?
Sure, it would require a different logic to control the motion, but why is everyone so opposed to this idea?
I don’t think anyone is necessarily opposed to it. But I think you’re drastically underestimating the effort to make that happen.
Besides the physical mechanical change, what would be the software change? Is it just software or would I need a different reprogrammed motherboard.
At least on a Jackpot, it’s just changing and uploading a config file. I don’t think it’s a big deal on the software side.
Have a go at it, no one is stopping you.
Because then it is like every other CNC. The LowRider is the most stable at the bottom, that’s why it can be mostly 3D printed…
Have a go. But aiming for a stock lr4 with raised runners/or a lowered bed and a chuck/collet extender with your long bit should work, that way you use the machine as lower as you can and dont suffer from rigidity.
Brilliant!
Eli - my apologies if this was already stated above but are you just hoping to use the LR to cut out the shape or are you hoping to carve/contour with it? I ask because in all my time down the foam slab efoil board building rabbit holes you need to contour both the top and the bottom which you will not be able to do with a LowRider unless you flip the foam (you can’t reach ‘under’ the rails with a straight bit on a fixed Z path). In which case you don’t need to ensure your bit can cut all the way through - just halfway.
The one thing keeping me from grabbing some foam is past life experience carving it…without question the messiest material I’ve ever carved.
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It it possible to put both sides of the y xis on a rail by switching the the bearings from flat to same as the right side?
My thought is, we this can be done easily, the y clips that hold the rail together and the belt tensioners can all be raised by 2 inches, extending the z axis range by 2" giving it a full range of motion. It also can all be mounted on the same flat surface.
That’s a really fantastic introduction. Thank you, and welcome to our community.
This comes up now and then. You’re a mechanical engineer, so you could do this modification.
It’s your machine, you could try it. I still think build it stock first and mod it from there.
That said, there’s a brilliant reason that Ryan has the machine designed the way it is. There’s a single Y rail, and that defines the Y axis. Motion on the dual Y drives is managed by the stepper/belt.
By doing it this way, the machine is not overconstrained. Most folks see that as a weakness thinking that the rails are doing work that they really are not on this machine.
During last years’ RMRRF, I met a visitor who works with a giant CNC sail cutting machine that is built in a similar manner. There’s a massive single rail on one wall of a warehouse wall, and then the opposite side has a much simpler motion system. That person had never considered how much this simplifies the process of designing, building, and maintaining the machine. They recognized that the machine worked better in practice and was less expensive to buy and install than the past system, but they never connected that the reason the old machine was so problematic and the new so much better was: it isn’t overconstrained.
For your purposes, you’re seeing ths as a chance to mirror the axis and modify to add Z. +1 for thought process, but there are other aspects of the machine that usually get in the way.
The entire geometry of the machine is brilliantly designed around that asymmetry- so it would have to be a mirror and fiddle.
Tell me again why you’re so opposed to a drop table and having spacers to position your work piece for successive machining operations? This seems simple, repeatable, and low cost, leaving you with a machine that can do other workflows.
My immediate reaction to this is that it is also easy to raise a flat piece for the Xmin wheels to roll on, which serves the exact same purpose, requires zero modifications and preserves machine rigidity.