I had some issues from the very beginning with the z motor mount. The first time i put my machine together i cracked the part where the bolts tighten up. I replaced it shortly after, but was very careful not to over tighten. Recently it actually came off of the tubes and my spindle free falled into the material. Not good…So i found an existing stronger motor mount on thingiverse and modified it. I extended the round portion down to just above the bearing plate below. Because this has a lot more bearing surface it also keeps the part more square when tightening down. Around the bolts this part is much beefier as well, and i could crank it down without cracking. This part also has the provisions to actually drill a through hole in your tubing and pass a long 6-32 bolt through all of it. There is a recessed portion for the head of the bolt and a flat for the nut on the opposing side. It turned out really great, hope someone else can use it. Thingiverse is going through maintenance right now, ill add the .stl and link it as soon as it comes back up.
Nice, I never ran into that one. The one I modified was just a slightly thicker version of the original. I still can’t get Thingiverse to come up on the computer, just mobile…when it does I’ll link to the original I modified and add this one.
Will totally give this one a try. I primarily build my MPCNC for milling aluminium, and for now the weakest part of it is the gantry/Z-axis with its backslash.
Is there any particular reason you printed it (instead of milling)? Actually I plan to rework the corner blocks in alu (or steel) right now, maybe more parts. Sure your new Z-motor-mount is a bit stiffer then the original, but printed in plastics will still give some clearance.
Is this clearance intended? Any reason to NOT build this plate out of alu? (either 7075 for alu for max. stiffness, or a softer alu with lead)
edit: instead of milling alu, could also work with POM (Polyoxymethylen). When I built my machine, even with sufficient infill (I though I went with 50%, so slightly less then Ryan suggests), all parts still feel… weak.
I’m no engineer but I design stuff for custom cars on a daily basis…the strength of one part is only as effective as the next weekest link. Overkill is not a good thing past a certain point. Adding a lot more mass at the very top of the z axis will actually make the machine cut worse. If you ever experience chatter with the mpcnc you can see the whole z axis go into a vibration. This would only be amplified by more mass at the top. The mpcnc wasn’t design for aluminum although with spot on CAM settings it appears to do a pretty good job. Building the easier flat parts out of aluminum wouldn’t gain you much in my opinion. You would have to start from the middle assembly out and build everything from aluminum. It’s all about harmony between strength, mass, and feed power. I mill aluminum a lot with a big manual mill. With the side of a good bit you can take a lot of material at a time. When you start plunging and using both the end and side of the mill as you would normally with the mpcnc, you have to take a lot less. Im pretty impressed it can cut aluminum as well as it does…also, I really like 70% infill, seems to be just right.
I understand the want to make parts bigger, but I just don;t understand it for the most part. I will make some different design choices on the next revision, mainly longer screws. The corner blocks do very little actual work and I do believe I will be making them smaller as they just hold the belt tension with short legs they really don’t need much. All my tubes can be rotated by hand. I’m actually looking at my corners now and most of the screws don’t have nuts on them.
As for the z parts it is the same thing, all they do is hold the weight of the “spindle”. All the major forces on this thing are in pretty much every direction except the Z the router will cut with it’s own weight. Hence the giant center gantry.
I have no issues with bigger parts, but as Andy points out larger moving mass means slower accelerations.
My tip to anyone with issues is a drop of super glue. on plastic and metal it acts as locktight and comes off of both surfaces. Get your parts snugged up and add a drop at the interface of the rail and the clamp if you have issues.
With every revision I learn something. I will start on some new parts coming up pretty soon and longer screws will solve most peoples cracking issues, with the trade off of …added cost.
Ryan i gotta give you credit for such a great machine, you have designed it very well.
I think there’s a few reasons people look to make “bigger” parts and improvements…first of all if the end user has the machine built and has used it for a while they are not thinking so much about cost after that initial investment. A little filament, some hardware from the store, a add on here and there, no big deal.
As it was in my case, an incident or experience that people have, create the desire to optimize a particular part…another reason is simply for the enjoyment and challenge of making a viable improvement to an existing design (it’s just human nature). Lastly, people just don’t have there CAM settings even close to right. When things aren’t going well they blame the machine. Suddenly it needs all of these improvements (Again, human nature). I have done quite a lot of cutting in the short period of time I have had mine and I am just now nailing the CAM settings. Everything becomes a variable. The type of bit, the material of the bit, the size of bit, the type of wood, the type of spindle, the spindle speed, etc etc…I know you know all of this I’m just reiterating.
I was a bit discouraged at first, but now that I have the kinks worked out and the CAM settings nailed, it cuts without any extra stress on anything. I’m loving it, just did this map in mdf as a test for a nice sign…let me tell you, it’s a pain to manually select every state twice. I had to pocket them with a finishing allowance and then “finish pass” them with a 1/16 bit and a slightly smaller finishing allowance to give me the state lines effect. I couldn’t do it any more efficiently with Inkscape and offsets, so I just did it with allowances in estlcam. Turned out good though.
I ran into the same problem and ended up strengthening a few parts, primarily the Z-axis mounts to keep the gantry from slipping. https://www.thingiverse.com/thing:2531659
In my case it was a fix for some already broken mounts from the first person who attempted to assemble the system.
I consider this a tweak on an excellent design and we’ll be assembling 2-3 more MPCNCs in the near future.
Thanks, and very glad it helped. I noticed in the picture that you had not used the screw holes to secure the bracket to the tubing. That is what I primarily designed the unit for to avoid the bracket slipping.
I like your end caps and will have to do the same!
I use the screws all the time. I just removed the top section this week so that I could install the new spider coupling that arrived from the slow boats of China.
