I guess it is time to start posting my progress on my MPCNC build. I decided that I am going to build it such that it has a 2’x3’ cutting area (X & Y lengths of 35"x47" with Z length the same as in the recommended set up).
First, I built a worktable to use for the MPCNC out of 2x4’s, particleboard and a workbench kit.
All of my plastic parts are assembled, I just need to cut the EMT to size and then proceed with the assembly.
The question I am struggling with is this…How long should I cut the legs if I am planning on using a second piece of plywood on top of the table as my scrap board? Should I leave the legs the suggested 4" in the recommended set up?
I know this doesn’t help too much but at that size I imagine you are planning on cutting a lot of thin sheets? I would cut the legs as short as possible, probably shorter than recommended. I’m not sure if you are too far into the table build but I made the bottom feet so the legs can pass through if you can drill some holes where the corners will mount. That way you can leave a little extra and move it up if you need too.
That’s how I do It. I stack material to get it as close to the gantry as possible. It is better for the legs to be shorter but I prefer the versatility of a taller machine and accept a little slower cuts.
My 2 cents about your leg heights. You say you are cutting sheets of styrene, mainly.
I know it has been stated to keep the Z height to a minimum, but the load against the
tooling for styrene would be very little, so you should be able to get away very comfortably
with 4" of leg height.
The fact that you will be reducing the height with the 1/2" waste board, only helps you.
So I would say that a 4" height would be more then fine!
I use a 4" (100mm) leg height and cut pine wood with a 6mm single bladed bit, at 4000rpm, 15mm/sec with no problem at 2.0mm depth passes.
Well, I got more work done on assembling my MPCNC as well as my first big screw up.
First, my son and I got the majority of the pipe cut for the frame. He was so excited to see what it looked like that I put the frame together for him. Had some issues getting some of the pipe to fit into the corner blocks as they were quite the tight fit. However, managed to “coerce” them into place.
And now the screw up. In tightening the lower corner blocks up this evening, I managed to split the screw hole on one and possibly a second. I was being quite careful in tightening the screws, I would turn one a couple times and then the other in order to get a more even compression of the pipe.
Not really sure what I can do at this point. Will cyanoacrylate work to secure the parts? My 3D printer isn’t able to print at the moment so making a couple new ones are not an option. Will the break have any adverse affect on the performance of the MPCNC? the pipe is already rather tight fitting so I do not think it will come loose.
I cracked one of those same holes too. So far, no problems.
Since I didn’t read anything about actually screwing the corner blocks into the top part for the legs…I just CA glued them on since I’m using a laser with absolutely zero horizontal stress. So far so good on that too.
Hit a few snags last night as I proceeded to attempt to drill the holes in the pipe for the Z axis. First, I couldn’t find a pencil long enough to mark the pipe in the right spots. Then I couldn’t get the pipe to stay put (even w/ clamps) on the drill press so the bit traveled some. I need to go back and re-think my strategy.
Also, a question if someone can clear something up for me. On the Z-axis, how should I position the holes for the tool mount? Should the bottom most one be as close to the bottom of the pipe as possible?
Once I got a new set of drill bits this part has been very easy for me. I drill a small hole, then go back and then drill the over sized hole. I actually just put a foot on it and drill it on the floor. Nice bits are key.
The old way I did it was to use a dremel cutting disk and score an X where I want to drill the holes and do as above.
As for where to drill, use the nut trap part as your guide, short side down is best, backwards from how I originally designed it but slightly increases rigidity. Drill the holes over sized by a large margin so you can adjust the tool mounts a bit. You aren’t trying to screw into the metal just clamping to it. This is how I fix an odd tool angles when I switch tools.
I finally got the holes drilled in the z tower pipes and now I am pretty much all assembled. Of course, the “final assembly” did not happen without its issues. When I went to remove the middle assembly so I could attach the Z-axis, I noticed a crack in one of the parts.
Well, I decided to use some super glue reinforced by some Steel putty to hold its strength.
It isn’t pretty, but it’s functional. And to be honest, I don’t remember tightening those screws that much. I try to keep things snug and not “put the uglies on it” as my wife would say. Worst case is I print up some replacement parts as needed. I am planning on printing and adding a vacuum holder to the CNC anyways.
Okay, now onto the good stuff. I got the Z-Axis installed as well as the motors mounted and the belts installed. I used the belt clamps from GeoDave to secure the belts on so I can easily tension the belts as needed. I also left a good bit extra on the various belts for added sanity in the event further tensioning is needed.
I also managed to get the X & Y motors wired up and attempted to get them moving via the RAMPs . Well, that was a huge flop as my laptop would not fully install the drivers needed to talk to the RAMPs . However, I managed to figure out the issue this morning and I can connect to the RAMPs just fine now. I will reconnect the motors later tonight and give it a test run.
Interesting. I didn’t realize there was a choice of rigid or flexible. I have been using my flexible one for two months without issue. What kind of problems would you anticipate using the flexible one?
Well, i do not have any experience with cnc, I still building my own and first cnc. But i have build 3d printers and used both flexible and rigid couplers in the past.
The flexible coupler are great to use where the z axis have little weight and the threaded rod is upper and the motor in lower position (in an prusa printer for exemple). The flexible coupler will allow to have a more “fluid” movement and reduce the shock of abrupt movements.
In the case of the cnc you need to have very rigid axis and the use of the flexible coupler can give you the next problems:
allow an unwanted movement of several mm up and down. When you try to make an precise hole of 10mm for example, pretty sure the flexible Z will go up 1 or 2 mm when you will start to make the hole, was final result the hole will not have an precise 10mm deep.
if the z axis move a lot, this will up and down movements and create vibrations.
-imprecise deep cuts, sometime it will cut less deep, other it will compensate and cut more.
But you can correct some of this problems by simply have the 5mm motor shaft and 8mm rod all inside the flexible coupler and touching.
