Use the calculator to get your Z rails length but ignore the leg lengths, that should clear it up. If you think about it though, you can not go any deeper than your longest bit…3/4"-1.25" or you will hit the floor/surface.
What if you put angle or square on the outside of the legs?maybe with printed brackets.and have clamps on permanent table for quick mounting?
What legs do you mean? Could you draw a quick picture to help me understand your idea?
We’re definitely going to build a permanent table with a quick mounting solution, which should be very doable due to the versatile nature of the extrusions / rails.
You could look into magnesium Mason screed. Lots of sizes, light weight, but very strong and rigid.
I saw this and have been thinking about doing the same sort of thing with mine. But I was wondering if it were a good idea to just use conduit for the bottom frame instead? Maybe rather than have the feet, print more of the corner pieces and mount them similar to the main frame? Has anyone tried this, and does it seem like there would be some stability or squaring issues?
Similar looking to this design: https://www.thingiverse.com/thing:3002700
yes thats about what was thinking,easy to bolt to permanent table. not sure for floor .some sort of weight maybe
I think there is indeed someone who tried; came across this a while back: Mostly Printed CNC (IE) -Add On- foot by Arcade_Machine - Thingiverse
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I’ve designed some feet to easily mount the Bottom_Corner to the frame, and give the roller a bit more clearance: https://www.thingiverse.com/thing:3036995
They fit a slide nut:
Nice!
I love this route. I’m still trying to figure out how it would work with the Z axis clearance though. Is this only for shorter Z axis builds?
Z axis really only gives you your maximum material depth once you start cutting. If the MPCNC is clamped onto your work-piece short or tall Z height shouldn’t affect you other than the normal rigidity stuff.
Still going to figure this out as well. Might have to make these mounts a bit higher or add in some conduit legs after all. However, I will be using it mainly for milling, so don’t need that much height. Also, less height equals more rigidity / accuracy is what I read in most discussions here.
Most builds have a table, with the Foot+conduit+Lock_Corner legs and have their spoil board bolted on top of the table. I will have the 4040 extrusion + the above Frame_Corner part and my spoil board will be mounted below the frame. Using the conduit size calculator, I’ve determined this is the same as having 72mm conduit legs, which translates to a 85mm work height. Seems a fair amount?
Here is my calculation for this:
Normal build - standard legs - 72mm conduit - Lock_Corner (adds 7mm on top of conduit, before connecting to Bottom_Corner) - 20mm spoil boardDistance top of the spoil board to bottom of Bottom_Corner = 72 + 7 - 20 = 59mm
4040 build
- Aluminium extrusion (40mm high)
- Frame_Corner (19mm high)
- Spoil board mounted below the frame, thickness irrelevant
Distance top of the spoil board to bottom of Bottom_Corner = 40 + 19 = 59mm
Conclusion
4040 build == normal build with 72mm legs (which means 85mm work height)
Created some mid span supports as well: https://www.thingiverse.com/thing:3040712
Almost done printing, going to build this one soon!
Looks pretty fancy
What you’ve done here looks good.
How much flex is there in your frame? If you throw this in the back of a car and drive for a couple of hours, will the frame still be square, or will it have slightly shifted? If you pick this up, how careful do you have to be when moving it so that you don’t put it out-of-square?
Not sure how to quantify it, but it feels extremely sturdy. Of course, most of the time it will be either on a flat table or mounted on a flat piece of spoilboard. Should it ever get out of shape in the upward (Z) direction, you’ll notice it when you put it on a flat surface. If this happens it can probably be fixed by loosening and re-tightening the 16 bolts in the corners.
I don’t think the aluminium extrusions will bend easily. There are even stronger 4040 extrusions, which don’t have holes running through the 4 corners. I have some of these as well, but they are really really heavy, so decided not to use them. Trying to keep this “mobile” after all, and it’s already quite heavy with the current frame and a bit difficult to handle because of the dimensions.
As far as XY out-of-square (skew / parallelogram), I’m unable to flex it at all. We’re using large corner brackets (4 bolts each instead of 2) which seem to hold it into place very well.
> a bit difficult to handle because of the dimensions
How big is your frame - 3’x4’?
My first MPCNC has outside dimensions of roughly 2’x2’. I wanted it to be portable so I could through it in the back seat of my car. I’m using a 2’x2’ piece of 3/4" plywood as the base with 2’x4’s underneath the outside edges to try to prevent the plywood from bending/twisting.
The outer dimensions of the frame are 930x720mm, so that’s about 3’1" x 2’4".