I picked up a MPCNC off FB Marketplace recently–the seller had everything all set up, but wanted more room in his shop.
It’s clearly been used on several jobs–several marks in the table from contours he cut out.
That said, when I put a 1/8" bit in the Dewalk 660 spindle, I can bring the Z axis all the way down and still be about an inch or two above the table.
This makes me think that the legs are too long–the pipe for the legs is about 6.5". If I poke around with Ryan’s build/cut calculator to get values that match my Z axis rail length (about 11.5"), the calculator tells me that the legs should be about 3.5".
My first inclination is that my legs are about 3" too long–generally that seems right. But if I bring the legs down 3", I’ll bottom out against the table way before I reach my Z limit–I could probably sink 2" of the bit into the table at that point, which seems excessive.
Which brings me to my question: should I do a bit of math to figure out what my leg height should be, based on how far I’d like to be able to cut into the table?
Or are there good reasons for the recommended 3.5" length?
Shorter legs make for more capable machines. You can cut faster with less deflection issues and the it will work better in hard materials. The real performance issue is how much of the Z axis is below the core when cutting, which for most machines is defined by the leg length, but there are designs like raised spoil boards and drop tables where the legs are only part of the equation.
If you want the official calculations, then use the cut calculator to determine the leg length for whatever working height you want. It is okay to leave the Z axis taller than needed in case you want to raise your working height back up at some point. Note that the stock material, the exposed portion of the router bit, and any clamp clearance must fit in the working height. In other words, working height is not the height of the stock you can cut.
Perfect–thanks! I’ve made a few cuts with it so far–it’s an AMAZING upgrade compared to the 3018 I’ve been using.
Once I figure out the leg height, in a bizarre (?) shift, my plan is actually to shrink it down, so the Y axis is about half as big–then I’ll be able to get it on the countertop in the shop, rather than taking up a collosal amount of room by the door.
I figure I can do that AND the legs all in one go.
Ah, that calculator still says 3.5" (which is 3" smaller than my current leg length).
The plan for the new smaller table involves a piece of MDF sitting on top of the table so I might go a bit longer to make up for it. But I figure I’ll save the longer legs so I can swap them in later in case I need to mill something ginormous, so I don’t have too much to lose!
Before you cut the legs down, consider whether you might someday want to carve on the top of something tall. Lots of folks have built “drop tables” so the can work on the surface of larger objects. You might want to just prop up your work on a an extra layer or two of filler that gets it close enough to the tool. As stated in the earlier reply the extension of the Z below the center carrier is the biggest contributor to loss of rigidity (unless your legs are ridiculously long).
Once you’ve gotten some time on the machine and projects under your belt you can make a better informed decision. Conventional wisdom says build it “stock” then mod once you’ve learned your machine. The difference here is you’ve already got an operational setup so why not see how it goes as-is?
Alternatively, the conduit for the legs is cheap so you might want a couple of sets of legs, one tall and one short. Just be sure you’ve got a good method for getting the corners to the same height when you change them. I use mass produced commodity objects (like soup or tomato paste cans) as a gauge for that sort of stuff on the assumption that they’ll be close enough to the same size and I can always grab one from the kitchen when I need it. If you’re changing the Y dimension anyway changing the legs is almost no additional work.
That sounds like a good plan. I’m planning on buying some conduit anyway: the Y axis runs will become my x axis and I’ll have a significantly shorter Y axis so it’ll fit on the countertop that runs along the back of the shop.
I need to do the math, but as short as that Y axis will be, I should have enough left over for a set of 3.5" legs. The current short legs will get taped to the long X railsand stashed somewhere when the mythical Big Job comes along.
It’s hard to tell from the pictures but it looks like there is not a lot of spoilboard above the aluminum clamping slots. If it were me, I would plan on almost always adding an additional board between my work material and that clamp board. Because of that I would add 3/4" to the standard leg height (to help make sure the bit can’t plung to far into that clamp board and collide with one of those aluminum clamping rails, because that would make for a bad day).
Not sure if anyone mentioned it, but at the standard leg hight the z axis will lower enough to put the collet level with the feet.
Ah–“the collet level with the feet”. That makes sense–and explains the difference I’ve been wrestling with (namely, the length of the bit extending out of the collet).
And you’re totally right–there’s basically no meat at all between the top of the current table top and the aluminum rails, which has me concerned for exactly the reasons you laid out–sure enough I’m going to screw something up and drive the side of a 1/8" smack into the side of a rail eventually.
Yeah, I know I would. Since you already have it, maybe you should measure the distance between the bottom of the bit and the table and just shorten the legs by that amount?
