July 4, 2019 at 6:50 pm #105212
I’ve finally finished printing the stock or slightly-modified parts, and partly assembled some of the parts. I’ve also gathered electronics and thick-wall tube (1″ O.D. and ~1/8″ wall) for the gantry rails and z-axis.
I am finalizing the design for the corners which allow the legs to pass through vertically.
I still have to buy the EMT conduit, and I also have a lot of wood to buy for the underlying table and for side panels to stiffen the box.
The outside dimensions are going to be 3′ by 4′, so about 2′ by 3′ of working area, and it will have about 300 mm of working Z travel, but the overall Z height will be much taller. The goal is to have tall Z working volume, while still having stiffness that is as good as a small machine.
Hopefully I can get all the woodworking done within the next week or so and get the thing moving and measure the stiffness. I also need to move some crap around in my garage to make room, but I’m hoping this doesn’t take too much time.
I just discovered that my printer is probably under-extruding. I measured the weight of the printed parts and they are quite a bit less than the values posted on the parts page https://www.v1engineering.com/blog/parts/ . I double checked that they had been printed at 55% infill. On the one hand this is troubling, because my parts might be low strength and low stiffness, but it also might explain why I had issues with the xyz part, when most people don’t have problems. I’m going to proceed with the parts I have, but I’ll probably be investigating the printer’s misbehavior and perhaps re-print the most critical parts.
Attachments:July 4, 2019 at 11:41 pm #105217
Could your filament just not be as dense? I think you need to put a density number into the slicer, but it will estimate the weight, which might give you a clue. Perimeters also are probably a big part of the weight.July 5, 2019 at 10:50 am #105260
In principle I think there could be a small difference in density but I am seeing huge differences of like 30% to 50%. Now that I’m looking, it appears I have a partial clog of the nozzle.
I am glad to have finally discovered this, but holy cow, how long has it been like this and how many parts do I need to scrap? How much plastic and time have I wasted? 🙁
Attachments:July 5, 2019 at 1:02 pm #105282
Ah the joys of printing 🙂 I finally replaced my whole hotend about 4 months back after dealing with an unrecoverable clog. It was an old ubis ceramic (printrbot metal plus) so the whole thing was due for an upgrade.
Did you get clicking in your extruder? That was my heads up. Prints weren’t as badly under extruded as your picture, but still not great.
GL on the fix!July 5, 2019 at 2:30 pm #105291
Oh bummerJuly 5, 2019 at 4:27 pm #105299
So I’ll proceed in parallel, completing the machine with these iffy parts, and printing replacements. I think this is a good time to switch colors, or else I’ll go crazy wondering which parts are the bad ones.
Here is a further partial assembly, and also showing the mix-and-match rails that allow 3/4″ EMT for side rails and vertical legs, while gantry (and Z) is all 1″ tube. It’s fairly easy to modify the parts since the mating surface and screws between Roller and Mount are essentially the same between C and J sizes, so I just had to bore out a 1″ cylinder on the C roller at the proper depth.
This also shows an attempt at the corners. Securing the ends of the belts will require some additional pieces, not yet designed, but probably resembling the after-market belt tensioners like this one: https://www.thingiverse.com/thing:1833934
Attachments:July 6, 2019 at 6:51 am #105327
Hi Jamie, how was the build? is you MPCNC working already?
I wonder if you have some inputs on how to setup the MKS GEN board in your machine, I have one like yours and have no idea where to begin.
Cheers,July 6, 2019 at 10:12 am #105354
I haven’t gotten it assembled yet or attempted to turn on the board, but I’m expecting the MKS Gen L to be equivalent to RAMPS as far as the firmware goes.August 13, 2019 at 8:55 pm #109574
In case there was ever any doubt, I am not a carpenter. It has taken me forever to get this table assembled, partly because it’s hot and unpleasant in the garage, and also because I am not a fan of real work! 🙂 Where is the robot that can assemble this table for me??
The table top is 48″ wide by 46″ deep (largest that will fit in my car),with 2×4’s around the perimeter, and two 2×6’s diagonally underneath to give it stiffness in torsion. I wanted high stiffness in torsion because the floor is not particularly flat and I don’t want the table top to be compliant and follow the non-flatness of the floor. The table top has several coats of polyurethane in case of accidents.
The machine itself will be 48″ wide by 36″ deep (external dimensions), so there will be a 10″ shelf in front for tools, maybe laptop, pen and paper, LCD, joystick…
In the picture are four X side rails (about 45″), four Y side rails (about 31″) and four corner posts at 5′, all of which are 3/4″ EMT. The two 1″ X gantry rails and two 1″ Y gantry rails are also shown. The 1″ rails for the Z axis are off camera.
Attachments:August 13, 2019 at 11:20 pm #109580August 14, 2019 at 5:26 am #109597
I’m sorry but I don’t understand what the second level is going to be used for and why it is so tall overall.August 14, 2019 at 8:48 am #109614
I’m sorry but I don’t understand what the second level is going to be used for and why it is so tall overall.
I think there’s going to be another spoil board in between, so he can have two jobs going at once.August 14, 2019 at 10:33 am #109621
This was described in a separate thread, and in isolation I can see the motivation is not apparent.
Short answer is to try for the impossible: simultaneously achieve high stiffness and a large Z working depth (right now it’s about 11″). The idea is to use a very long Z axis and support the far end (top) with another copy of the MPCNC mechanism to prevent it from twisting away from vertical. It will use the same controller, but each X and Y stepper driver will drive four motors in series instead of two.
Here is the original explanation with more details: https://www.v1engineering.com/forum/topic/quantified-stiffness/
Why do I want a large Z working depth? Partly for clearance for the tool changer system, and partly so I can experiment with a 4th (5th?) axis. And also to see if I can do it. The extra size in X and Y is room for the tool changer.August 14, 2019 at 10:36 am #109622
Oh, my mistake.August 14, 2019 at 6:39 pm #109675
I’m sure that gap between gantries only needs to be about 1/4 the max sickout right? Too much longer or shorter and you loose effectiveness right?August 14, 2019 at 8:32 pm #109689
I’m sure that gap between gantries only needs to be about 1/4 the max sickout right? Too much longer or shorter and you loose effectiveness right?
I was thinking the other way around actually, where the vertical space between gantries should be 2x to 4x the max stickout. Larger is okay but doesn’t improve anything.
If the two gantries are too close vertically then the Z axis acts as a lever where horizontal load at the tool will be multiplied into larger horizontal forces on the two gantries and reduce their ability to hold the Z axis vertical.
With a large vertical space, it still acts as a lever but the horizontal loads on the upper gantry are less than the forces at the tool, and the horizontal force on the lower gantry is not much higher than the force at the tool.
Thats the idea anyway. In my mind it should be as stiff as an MPCNC with an extremely short Z. I’ll be measuring the deflection vs force and we’ll see if there is something I’m missing.August 14, 2019 at 8:40 pm #109690
Boy, talk about making everything a bit harder to get square…. Quad endstops anyone? 😉August 14, 2019 at 8:47 pm #109693
Only nine motor drivers and eight endstops. Ryan can you whip up some firmware for me real quick? K thanks.
1 user thanked author for this post.August 15, 2019 at 6:36 am #109734
That has to be just a few copy pastes away from it working.August 16, 2019 at 7:51 am #109819
Gotcha, I guess I was thinking in terms of tube rigidity.
This is just me trying to work through this complicated problem in my head, no critiques or anything. Genuinely I have no idea, this is just really interesting to think about. I wish we could do an FEA on this….dam printed parts make that impossible.
Is this right? So think of it in terms of a standard build (2.5″Z) we assume the z tubes are good and deflections are coming from the gantry flexing and to some minor degree the XY rails, and lets use a generic load of [email protected]″. So if expanded from there to your larger stick out, the torque/force translated to the gantry is linear (T=F*L – double the distance double the force). We end up with ~5kg force at 10″….maybe
The sticky part is, now will the gantry nearest the force still be the pivot point or is it more of a distributed load between the two? Or the way I see this is going to be the top gantry will be more of the pivot point (less forces acting on it = more rigid) and the lower will still be doing more of the work. I think in either scenario what is actually happening is now the gantry twist is gone and what you are now fighting is the XY rails flexing. I see the lower XY rails being the new weak point and them flexing will be the limiting factor on Z rail stickout. Two Z rails (usually shorter) will always flex less than 1 X rail (usually very long).
No idea how to really test it but I am guessing you will be more limited by the lower XY rails flexing and most any dual gantry distance will stop lower gantry flex/twist. So maybe a purely X or Y move (single rail doing all the work) will flex more than say a diagonal (both rails splitting the load) when pushing your dual gantry with a long stickout where I don’t think that even comes into play on a short machine?
Can’t wait to see it in action….and no way, I really hope not to ever dive into marlin that deep again!August 16, 2019 at 11:20 am #109839
Yes that’s correct in what I am aiming for and what I think will happen. The tilt of the Z axis should be extremely low due to the second gantry but the horizontal deflection of the gantry rails will be essentially the same as a regular MPCNC and I’m hoping will be the new weak point.
Im thinking stickout should have minimal effect on stiffness but it does have some. At zero stickout it has effectively the same stiffness as the lower gantry. At say 1 foot stickout the leverage causes lateral forces at the tool to be multiplied into larger forces at the lower gantry, lets say 1.5 times to keep the numbers simple. With 1.5x the force, the lower gantry then deflects 1.5x the distance and again because of leverage this 1.5 at the lower gantry translates into 1.5*1.5=2.25 times the distance at the tool.
This leverage factor is influenced by the height of the second gantry and is the reason for making it very tall.August 16, 2019 at 7:05 pm #109865
So if the goal is a large z axis but still stiff wouldn’t a lowrider style rig be a better option? Or aluminum extrusions?August 16, 2019 at 8:08 pm #109872
As I understand it, Lowrider is not much better at remaining stiff over a large Z range, although they say it is stiffest at the bottom of its range, while MPCNC is stiffest at the top of its range. As for aluminum extrusions, according to my measurements the largest source of deflection comes from twist/tilt of the Z axis away from vertical. I am not seeing how aluminum extrusions would be used to improve this, but I am willing to entertain any suggestions.
I have not yet designed the mechanism to secure the belts in place. I guess that’s next, and wiring, and we’ll be ready to make a crown.
Attachments:August 16, 2019 at 8:48 pm #109879
So, will you wire the X motors on the bottom in series and the X motors on the top in parallel with each bottom motor? Or do the whole set of four in series? Or all four in parallel?August 16, 2019 at 9:58 pm #109891
All four in series is the plan. I got a 24V power supply and a board that supports it, so in theory each motor’s torque/speed should be just as good as running two steppers in series at 12V.August 17, 2019 at 11:32 pm #109989
Some of the people on this forum are actual psychos.
I love it!August 18, 2019 at 12:35 pm #110052August 21, 2019 at 12:42 am #110339
Okay, it’s moving and running gcode! Sorry for the crappy video (unedited).
Wires are still a mess obviously. That will need to get get cleaned up.
I had always planned diagonal braces or solid panels to keep the whole machine from racking. These are not in place yet and when jogging, the whole machine wobbles. Once the braces are installed, it should be much better.
I’ve got the electronics on a little board that is hinged underneath, so it folds up out of the way where metal chips can’t fall on it, but it also folds out for easy access. Right now it’s a MKS Gen L and 24V power supply and a Raspberry Pi with OctoPrint. To set up the servo for the tool changer I’ll add a buck converter, and then there’s the LCD and joystick which will have to hang off somewhere.
I’ve got two power strips, one is always on for the raspberry pi and maybe other things in the future, and the other power strip is connected to the E-stop button, so the 24V PSU that drives the steppers and any power tools will be hooked up there. This way I can cut power to the steppers and router without resetting the Raspberry Pi or the Arduino.August 21, 2019 at 5:16 am #110361
Very cool. The space under the xy pipes is clear, if you need to add anti racking pieces. Although a piece of ply on the whole side would do it.
I like your controller area. Easy maintenance and no frills, but also clean enough to keep sanity.
Just imagine. Now you can use really thick pieces of paper 🙂August 25, 2019 at 9:00 pm #110806
Getting really close now.
- The wooden cross braces on the upper part make a night-and-day difference in wobble, as you might expect.
- I’ve also got a tape measure and sleeve around the X axis wires.
- Also installed the joystick into the table.
- Also got a long cable for the Raspberry Pi camera so I can see the workspace with OctoPrint.
- Also got the blinky thing (MAX7219) installed, had to lengthen the wires for it to be visible when the board is stowed
I’m not sure what I’m going to do about the LCD. It works but the wires are too short for it to be convenient when the board is stowed. But on the other hand, with OctoPrint, I don’t really need LCD access. But I still might want to print from SD, so maybe I will mount it somewhere even if it’s not easily visible. Replacing the wires seems like a lot of trouble.
Next I think I will be trying to measure stiffness in the different modes of deflection!
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