It’s almost spring time so that must mean Kelly the Carver has time on his hands again while ice carving season ends and wood carving season waits to get going. Hahaha
It’s true! One more ice job tomorrow, Friday and Saturday and then it’s “annoy everyone at V1” again. The portable LR3 is still on the “to-do” list but a new, more critical need has surfaced. I’ve got a fully printed set of Primo parts collecting dust and have a need for a new dedicated MPCNC so it’s time to build it up! This bad boy will do nothing but make custom engraved ice cubes. Just a 10x10 work area and 3” thick slabs of ice. And this one will live in a freezer so hopefully the PLA doesn’t shrink too much on me.
I need a hand determining the z height to enter into the tubing calculator. Is the height required the max thickness of material I need or the max depth of cut I’d need?
As Philipp indicated, the working height needs to include all the space needed to get the job done including the stock thickness, the endmill length, and any clearance needed for the clamps. If you wanted to cut completely through 3" of material and clamped the ice from the side, you would need 6+" of Z working space. This is a huge amount of space for the Primo, and you likely will suffer from some deflection and perhaps other issues.
The issue is the leverage on the tip of the bit. The further the bit is below the bottom of the core, the more leverage, and therefore the more deflection with the same force. If you don’t have cut through the entire block but are instead engraving on the surface, the strategy is to keep the carving as close to the core as possible. If this is the case, and if the ice will always be the same thickness, then just calculate your size as:
Max ice thickness + exposed endmill length + clearance height
If the ice varies in height, you will want to look at other approaches. One solution is a “drop table” where the center of the table is lower to accommodate the stock. Personally, I wanted to cut 2" foam with my machine (cosplay props), so I drilled holes in the table below each of the legs. I use 3-D printed spacers of different heights so I can raise and lower my machine for different thicknesses of material.
I think it’s the maximum depth of cut, plus the endmill length, then if the cut isn’t all the way through, you can drop the bottom of the bed.
I’m picturing the CNC around the outside of the freezer with a tray under it into which you pour water, then carve when it freezes. Presumably you need to be able to remove the tray from under the machine, so it may be that the 3" defat height would be fine if you set up the MPCNC to pull up and out of the freezer, so that the 3" Z height can have the top of travel be at the top of the ice. If the machine sits on a rectangular frame that fits into the freezer compartment, this could work very efficiently.
If the desired effect is a snow filled logo/letter etc then you don’t really need to worry about the “chips”…on the last pass that is. I found that if I didn’t clear the snow between passes it would pack in tight enough to cause the steppers to skip. So I use an airhose (manually for now) to blast puffs as it cuts. This clears the snow. But it gets the snow EVERYWHERE so I have to protect the important bits like the stepper motors and I keep an eye on any buildup around the core bearings. If the end result will be refilled with colour then the snow needs to be cleared throughout the cut.
My current setup is indeed a drop table. I’ll work that (sort of) into the new dedicated machine. The new machine won’t use the crazy 3" long 3/8" endmill - just little 1" long, 1/8" and 1/4" mills so I don’t need anywhere near the same amount of clearance or z travel as my current machine.
Some pretty big developments coming…I’ll be sharing the progress on V1 all summer long. I’m super SUPER excited about what’s coming. And part of it involves meeting Heffe in person! I still can’t believe it.