I’m hoping to start my Primo build shortly, but was wondering what the Z height you enter into the “Workspace” area of the calculator actually measures?
My initial thought was that is the distance that the Z can move? But it also seems to control the length of the legs, so, is it the distance from the bottom of the empty collet to the top of the table?
How does the length of a bit in the collet affect it? Is the usable amount of Z height equal to the specified amount minus the distance that the bit protrudes?
I’m wanting to have a max cut depth of about 3 1/4 inches on a workpiece. So do I need to specify 3.25 + allowance for bit height + allowance for a spoil board?
Thanks! I hadn’t seen the graphic/diagram. That makes it clear what the distance is…its the distance from the bottom of the tool mounting plate(?) to the top of the table.
I’ll investigate to see if I can determine how much of that space is used by the various mounting options, but in general I’m going to assume that the tool holder, and thus the tool itself, hangs below the mounting plate…using some of the available space.
Ideally, it would mount where the collet just clears the bottom of the tubes. You don’t need it to poke out further than that.
I will tell you this, the Z is very sensitive to making it too long. If you double the size of the Z, it will deflect 4x more. I don’t think you’ll lose any sleep over 3.5", but 6" is too big. Think carefully about how much room you actually need, and consider solutions where you install the spoil board below the feet, or if you really need to mill a work piece that is large (like engraving the top of a log) then consider building a drop table that can lower the work piece down enough to fit under the bit, instead of having the bit reaching down away from the gantry to reach your thin work pieces.
Don’t forget the bit either. You won’t be able to find any 3" bits. And if you are using a 3/4" long bit, and trying to mill the top of a 3.25" board, you will need to raise the top of the bit at least to 4" to clear the work for travel moves.
Lastly, remember you can always change the size later. The electronics, motors, wires, etc. are all fine on a different table, and some new pipes can increase the size.
I always viewed Z height as the maximum depth I’d ever need to cut. So I chose 4". This allows me to mill the top of a 3" piece using a 3/4" bit with .25" leftover
Z Height is the distance from the bottom of the Z carriage to the of the bottom of the feet on the frame. Typical builds have the feet mounted at the same height as the top of the spoil board, and most tool mounts align the bottom of the nut on the router/spindle with the bottom of the Z carriage. So as a result, Z height (or working height) becomes the distance from the top of the spoil board to the bottom of the nut on the router. In that space must fit A) the stock material, B) the exposed portion of the router bit, and C) any clearance for material clamps.
And this spacing calculation can be difficult for more complex cutting. For example, if doing two-sided milling using the pin method, the bit must be somewhat longer than the material is thick, and many people don’t want to mess up the spoil board with lots of holes and add a protection board above the spoil board. Or take David Walling’s post. He has the height to face and do surface carving on 3" stock, but he couldn’t carve a box out of 3" stock since at most he can only carve down 1". So a person has be explicit about what kind of carving they will (and won’t) be doing with the machine, design accordingly, and live with the limitations of those choices.
Or there are more complex approaches that have variable Z height like drop tables, replaceable leg sets, adjustable leg height designs, and replaceable spoil boards of different heights.