My coreXY design is progressing to the build stage

I have started a blog posting details of the design and build here: [drmrehorst.blogspot.com]
The Z axis and bed designs are up and I'll be adding the frame and coreXY mechanism over the next few days.

The master CAD file has been posted to youmagine.com.

I'm finding my web site too tedious to maintain and too slow to update. The blog isn't quite ideal but makes it easier to post things in bite sized pieces. I may eventually migrate some of the stuff from the web site to the blog, but for now they'll both be there.

Edited 1 time(s). Last edit at 07/23/2017 07:44AM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

The CoreXY mechanism stuff is posted. [drmrehorst.blogspot.com]

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Hi Mark,

Very nice printer and blog. You have clearly put a great deal of thought and effort into it.

May I make two suggestions:

1. Consider bolting your printer to a wall. Your printer is very tall and the moving mass is at the top so no matter how stiff your printer frame is, it will sway during a print. That will definitely have a negative impact on tall skinny objects since the object will be swaying at a different frequency than the printer.

2. Mount a thermistor in the aluminium plate like sigxcpu did here Picture. The thermistor should be coated in thermal compound though. I am using the same 750W Keenovo heat mat you are using and found that it can take nearly 5 minutes longer for the aluminium plate (305X305X6.35mm on my machine) to reach the target temperature when using the thermistor that is mounted under the mat. So unless you have a pause in your startup gcode, you are probably printing the first layer at a lower temperature than intended.

Josef

Thanks for the feedback.

1) I run this printer at home and if I bolt it to a wall, it will end up at the makerspace like the last one because of the noise. The side bracing I added seems to have solved the slight wobble problem.

2) Mounting the thermistor on the bed plate is a safety issue. The heater will always run hotter than the plate and if the heater comes off the plate you have to rely on the firmware to protect it from damage. The massive bed plate will cool very slowly and by the time the firmware knows there's a problem, the heater will have already burned itself up.

The same argument applies to the TCO mounted on the plate. I'm relying on the adhesive that holds the heater to keep it in place which it may not, especially if it overheats due to a failed SSR. The next step will be to secure the heater to the plate mechanically, just in case. I think a wire mesh or a couple cross-bars anchored to the sides of the bed plate in a few spots will be sufficient.

As far as first layer temperature goes, it doesn't seem to be a problem. The gcode heats the bed up before it heats the hot end, and in the time it takes the hot-end to heat up, the bed surface reaches the actual first layer print temperature.

I've added sme stuff on extruders and hot-ends to the blog...

Edited 1 time(s). Last edit at 07/28/2017 12:23PM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Info on the frame is posted, as is some 3 pt leveling vs 4 point bed leveling, and some stuff about hot-ends and extruders. See blogspot link in my sig, below.

Next up: electronics, and setting up a printer's origin

Edited 1 time(s). Last edit at 07/30/2017 01:15AM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
xyze

... I am using the same 750W Keenovo heat mat you are using and found that it can take nearly 5 minutes longer for the aluminium plate (305X305X6.35mm on my machine) to reach the target temperature when using the thermistor that is mounted under the mat. So unless you have a pause in your startup gcode, you are probably printing the first layer at a lower temperature than intended.

Josef

Nearly 5 minutes longer? UMMD has a 300 x300 x 8mm bed plate and the 750W heater gets it up to 105C in 4.5 minutes. If it's taking more than 5 minutes to get your 1/4" plate up to temperature, I think there's something wrong.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Takes about 4.5 minutes to reach 110 degrees on mine, measured at the top of the aluminium plate (technically the BuildTak sheet on top of the plate). If I do not have the thermistor in the plate, it takes less time for the heat pad to reach 110 degrees, but another 4-5 minutes for the aluminium to reach 105 degrees, so my wording was bad. What I meant to say was that it took another 4-5 minutes for the aluminium plate to reach the target temp once the heat pad thermistor showed that it had reached the target temp, so it takes about 3 minutes longer in total for the plate to reach target temp when using the heat pad thermistor. My apologies for the confusion.

I'm using Marlin's "bang-bang" mode and not PWM to control the heat bed. The problem is that the heat pad is switched off when it reaches target temp and then it's only the latent heat in the heat pad that gets transferred to the plate and the plate in turns cools down the heat pad. Once the heat pad cools down enough, it gets switched back on and the cycle repeats till the aluminium plate reaches target temp.

If you are using PWM to control the heat bed, then it might speed things up a bit because PWM probably has a narrower margin for switching back on than "bang-bang" mode, but I'm still a little surprised that your aluminium plate reaches 105 in 4.5 minutes. May I ask how long it takes for the heat pad termistor to show 105 on your machine. If I recall correctly, it took about 3 minutes on mine.

I use PID control. Bang-bang can create print artifacts in printers that have warpy beds, but with 1/4" tooling plate that shouldn't be a problem. OTOH, PID is there and will keep the temperature regulated, so why not use it?

The 4.5 minutes in my printer is the reading from the thermistor. I'm sure there's some minor delay between that and the surface of the PEI, but it isn't enough to matter. Prints stick as fast as the printer will start up.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I will most likely switch to PID / PWM. Bang-bang seems to be holding actual bed temp within 3 degrees and it's a little easier on the SSR, but the SSR is not getting warm so it should be able to handle a PWM signal OK.

If you have an IR thermometer, you should measure the top of the bed while it's heating to see the difference between the bottom of the heat pad and the top of the heat bed. I usually do not sweat the small stuff, but the difference was more than what I was comfortable with. It should be worse on your machine than on mine because of the increased bed volume and mic-6 is less thermally conductive than 6061 (which is what I'm currently using).

I can understand your concern with fire, but the 3M adhesive is good stuff and Smoothieware has an "Out of range runaway detection" feature that should catch that situation. I'm more concerned with the SSR failing in the open position, which you have nicely taken care of with the thermal fuse. That's definitely something everybody using an SSR should be incorporating into their design. Now I have to go order one .

Josef

IR thermometers are crap. They only read correctly if the object they are pointing at matches the emissivity they were calibrated to (and cheap ones aren't calibrated at all). The emissivity of the top of the bed and the heater on the bottom are surely different and will read different temperatures even if the actual temperatures are the same.

The point of heating the bed is to get the prints to stick. If they stick, the numbers don't matter.

I'm running the SSR at the default PID frequency in smoothieware, 60 Hz, IRIC. It doesn't even get warm.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I was not suggesting that you measure the bottom of the heat pad with the IR thermometer (although I can see that it could be interpreted that way). I was suggesting that you compare the reading of the thermistor with that of the thermometer to see the temperature difference between heat bed and heater. Using some black electrical tape (a decent sized patch) on top of the PEI sheet should give a fairly accurate reading even with a cheap IR thermometer.

You are correct though, the purpose of heating the bed is to get the plastic to stick, so if it's sticking for you, why mess with it.

I have added some blog info on setting up a corexy mechanism and endstops in firmware here: [drmrehorst.blogspot.com]
Also some stuff on setting up the origin in slicing software so that the slicer knows the printable center of your print bed: [drmrehorst.blogspot.com]

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I've added a better print cooling fan- moves a lot more air and blows on all sides. It uses a small squirrel cage blower. The only problem with it is that it blocks the view of the extruder nozzle.



The blower hangs off the back of the printed part. The loop is an elipse centered on the heater block so it has good clearance everywhere and isn't liable to melt. The assembly is held onto the extruder carriage by two screws, so it's easily removed for printing ABS (no need to carry the extra weight, and removing it allows you to see the extruder nozzle). I printed it on UMMD with a 0.6 mm nozzle and 0.5 mm layers with ABS so it won't get soft at warm temperatures.

I want to be able to access the extruder carriage from the front and back, so I'm making a new top cover. It will have inserts that allow it to slide back and forth by about 50 mm. When I want to remove the rear upper cover to access the back of the extruder carriage, the top will slide forward enough to slide the rear upper cover out of the frame. Removing the front cover will work the same way- slide the top back and the front upper cover will slide up and out of the slots in the frame. I will drill the corners so I can put in 5/16-18 screws to hold the top in place, locking both the front and rear upper covers in place. That will keep people from putting their hands into the machine at demos, etc.

The lower front cover will attach to the frame in a similar manner. I'm going to drill the slots in the front vertical frame members with a 12-13 mm diameter bit, in 4 or 5 places on each of the two front vertical frame members. I'll print a "shelf" that snaps into the bottom horizontal frame member. The lower front cover will have "knobs" that fit into the 12-13 mm holes, positioned so that they will drop into the slots and hold the lower front cover in place. When printing PLA I'll remove the upper and lower front covers, and when printing ABS I'll put them both in place.

Edited 1 time(s). Last edit at 08/13/2017 08:21PM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Is there a possibilility of getting clear view or stl file of the cooler?

Here ya go. It's designed to fit UMMD's extruder carriage, so it probably won't do you much good. It uses a 40 mm blower like this.







stl file is here

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Thankyou.

The fan design is almost universal. I'd be interested to see a cross-section of the air channel. I guess, it's hard to print the top layers?

In other fan discussions people were afraid, such a design would create a dead centre.
Would it be better to arrange the air holes in a "campfire tornado" way?

Edited 1 time(s). Last edit at 08/15/2017 03:11AM by o_lampe.

I don't know about "universal". My printer allows for a lot of room at the back of the extruder carriage, about 15 mm or so on either side, and 10-15 mm off the front. I designed it to fit in the available space and it fits with no interference with the printer's frame, cables or anything else.

I printed it without support material and it worked fine on the first attempt, and everything fit as intended. I used 3 top and bottom layers. The top layers are printed as bridges.

These things don't necessarily do what we think they will- air is a compressible fluid. The holes are unlikely to blow air evenly, and if you factor in the random shape of the print that will cause turbulence, nope, no dead zones. Or many. Who knows? It doesn't pay to over-think things like this. The important thing is to get air moving from multiple directions, and it does that. The rest is up to the print and the air.

Here's the cross section:


from the top



from the bottom:



Is it optimized aerodynamically? Definitely not. The shell may be a little heavier than it needs to be, too, but I have bigger fish to fry. Moving on.

Edited 2 time(s). Last edit at 08/15/2017 07:37AM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

John Olson was at the makerspace meeting with his FLIR camera tonight and we were able to take a couple pictures of UMMD's bed heated up.

Here it is with the controller set to 70C:



The hot spot at the front edge of the bed is a reflection of the hot-end that was heated up when the image was made.

And here it is set to 105C:




Both images were made after the bed was sitting at the set temperature for a few minutes, so I have some slight offset between the bed surface temp and the controller temperature. The front side of the machine was open.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Getting ready for Milwaukee Maker Faire at the end of September. UMMD will be on display and printing. We get a lot of kid traffic, and if kids see a pulley spinning inside a motor mount, fingers are going to get pinched. I made a couple covers for the motor mounts today.





There are complementary pieces on the back sides of the mounts, and they are held together with two screws each. I initially considered making them just snap into the motor mounts, but I don't want to take a chance on someone getting hurt.

I'm really liking the aluminum tube motor mounts.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Saftey third!

I'm getting my milling machine honed in (got to install the dro) and once it is done back to the core xy. I like the covers, but you should have made them with t-glase

Yeah the Alu Tube mounts are cool, I'm thinking of some longer ones that have a tongue left over for attachment, by cutting 3 sides off at half the length. Do-able with little tools so something of good use to make easy. I'm also thinking of hand doing some 5mm plate stuff, sure it'll not be quick but I think many useful parts could be made.

The tube allows mounting holes to be drilled on the bottom or sides, and stays rigid because it is a tube. You can mount the motor inside the tube or on the outside, as I did. I think that if you cut three sides off at half length you will essentially be left with a thin piece of aluminum and it's going to flex. If you don't care about it flexing, you may as well just mount the motor on a thin plate or angle bracket or print a motor mount.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Ah yes i forgot walls where not thick enough, though could do a 45deg cut so it had some ribs, though all depends where its going.
So you got 50mm tube? or bigger 60?

One motor mount is made from 1.5" x 2" tube and the other is 2" x 2". inches.... suck....

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Have you considered the volcano hotend? It seems like a good hotend considering how big your machine is.

Yes, I have and will probably put one on there when I use large diameter nozzles.

I've been working on final-final preparations for demoing the printer at the Milwaukee Maker Faire in about 1 month. I've been getting the UV lighting sorted out and have the final design for the LED holders and the electronics ready to go- just have to install it, which should happen this weekend.

See: [drmrehorst.blogspot.com]

I still don't have the PC sheet for the lower front panel, but I have worked out how it will be mounted. I will probably order it later today

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

UV lighting is done. The switch that controls the LEDs has a center off position- if I leave the printer running all night in my garage I don't want the light to attract bugs, because then I'll get spiders and webs. Here's a short video of the lighting in use during a print with fluorescent yellow filament. The cell phone camera doesn't really render the colors accurately. The yellow plastic glows so brightly it's almost painful to look at.

https://vimeo.com/231215833

Here's how the UV LED light bars were assembled:



I got some 300 x 10mm aluminum PCBs for 6 LEDs connected in series, soldered down the 1W 400 nm LEDs, and clamped the PCBs to aluminum L stock using printed clips (green). The L acts as a heatsink and shield that prevents the UV LEDs from being viewed directly from the front of the printer.

Here's one of the long vertical light bars. It is screwed to a pair of printed ABS clips that hold it in the slot in the t-slot frame of the printer. The white LED bars are screwed to the clips, too.



The UV LEDs are powered by a current limited buck converter. I set the output voltage to 19.6 and the LEDs pull about 1A. I'm running them at a little less than rated power so they don't get too hot. I set the current limit on the converter to 1.3A so as the LEDs heat up and they try to pull more current, the buck converter will switch to constant current mode when the drain gets to 1.3A.

There are two 600 mm long, 12 LED bars placed on the two front vertical frame members mounted alongside the two white LED bars, and one 300 mm long, 6 LED UV light bar placed in the top of the printer between two 3W white LED light bars.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Is there a specific reason you used 4040 extrusions for your bed? I'm thinking smaller aluminium extrusions can be used to reduce weight.

No specific reason - I had some left-over pieces and didn't have any smaller stuff. Since there are no lateral forces on the bed smaller extrusion should work OK. I wasn't too worried about the weight- the Z axis drive I used can handle a LOT of weight.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]