arranging everything to build an MPCNC, sourcing parts and designing the workbench.
I’m an electric guitar builder and my projects are usually just 2" hardwood, top 3", I’m going with the minimum recommended of 81mm Z workspace, but how much workable area is that?
I’m asking because I want a spoilboard as well and the bit itself will have a length, therefore, the functional Z wokspace would be reduced accordingly?
if I have a 10mm spoilboard, and the cutting bit has a 25mm cutting depth, this means that when the Z axis is at max, the distance between the cutting edge and the spoilboard would be 46mm?
also, when the machine is unloaded, and the Z axis is maxed out into to the bottom, does this mean the router collet is aligned with the bottom of the feets of the machine? and by this same logic, when the Z axis is maxed out at the top, there is a 81mm distance between the router collet and the bottom?
I’m asking because I want a spoilboard as well and the bit itself will have a length, therefore, the functional Z wokspace would be reduced accordingly?
The design of the Primo calculator assumes that the bottom of the feet are at the same level as the top of the spoilboard. If you do an image search for MPCNC Primo builds, or the earlier MPCNC Burly, you will mostly see machines that are built with the feet at the same level as the top of the spoilboard. Additionally, the spoilboard on these machines is typically bigger than the working area.
My Burly was built with the spoilboard bigger than the working area. I ran into a problem in that, when I surfaced my spoilboard, it left a pit in the board since the router cannot reach the entire spoilboard. This pit made it difficult to mount stock that extends outside the working area.
When I upgraded to a Primo, I mounted the feet at the level of the base board, made the spoilboard my working size, and floated the base board on top base board. My spoilboard is a bit smaller than my XY working area so I can surface the entire top. If you go this route, you will need to increase your leg length by the thickness of your spoilboard, or you can put the feed on blocks the same thickness as the spoilboard.
Note the issue of Z height and its impact on cutting has to do with how far the tip of the bit is below the core…how much things are leveraged. If you wanted a taller machine, you can mitigate this impact (mostly) by either making the leg height adjustable, or by making the spoilboard interchangeable with a thicker spoilboard (to bring the thinner stock closer to the bottom of the core). Personally, I do a few cosplay props in 2" foam, so I made my legs adjustable. I drilled holes below the feet (a bit larger than the 1" tubing. Then I 3D printed some spacers that clip on to the tubing to adjust the height.
Since I did not built my machine to “spec,” I cannot answer your question about where the nut is when the Z axis is at its lowest usble position.
I think the max is around 39mm or so. You can put your legs on strips of wood, then you won’t lose depth from your spoilboard.
You can see my spoilboard was level with the rest: MPCNC Primo Schneewittchen Reanimated - Oldenburg, Germany
You could also build a drop table. I always thought about doing that but never got around to it.
