Core-XY based on Rat Rig V-Core and Duet 2 Ethernet

snoozer

The kit has arrived. No visual damage on the outside. This evening I will open the box and check the content. I have other obligations 1st so probably wont start the build until the weekend.

Have FuN!
Jan

snoozer

Hello,

today was the day I started the build. I was positively impressed with the precision of the extrusion cuts. I have no precise squares and I can measure the length only with a ruler but the extrusions of meant to be of same length really exact. The threats in the extrusions also worked flawless where straight. I had to remove some metal shavings but hey, that's OK. Here a pic of all that came in the box (except the tools etc on my workbench ofc).

And the extrusions:

I started at 10:00 with assembly and have the metal work done now 18:30. The instructions could have been better but its not a Prusa, I have seen to late that there has to be a washer between the bearing in the rollers. Had to remove them cause I had seen that to late. I am not yet 100% sure the cube frame is actually square yet. I will have to do some adjustment. I have used a ratchet strap to tie all together before tightening all bolts but the X gantry does not hit the ends equally, one side is approx 1mm off at the front and the other end 1mm at the back. Not shure what way would be a good procedure for that, suggestions are welcome.

Here the state I am at so far.

Now printing a tool mount in Colorfabc's Carbon Filled XT-CF20. I will continue the build tomorrow. Time for pints and friends now.

to be continued.....,,

mrehorstdmd

You can get things squared up by measuring diagonals across each parallelogram in the frame. If they are square the diagonals will be the same.

snoozer

@mrehorstdmd

I know how to measure it, just I have no clue yet how to adjust it. I was thinking of criss crossing the frame work with adjustable wires....... but that would only bend the extrusions, not fix the actual adjustments.

THX
Jan

mrehorstdmd

I'd square it up as I assemble it instead of trying to assemble it first then make it square.
Since the XY relationship is critical, I'd start at the top of the frame and get that part square before bolting the rest of the stuff to it. Match the bottom square to the top, then add the verticals. If the frame is also the Z axis, get those verticals square with the top first then add in the other two. Check squareness of everything with each frame member that you add.

Keep in mind that a 1mm error over a span of 500 mm is only a 0.11 degree error.

deckingman

@snoozer Your X gantry issue is most likely caused by unequal belt tension.

snoozer

@deckingman

This is the plain mechanic only sitting idle, no belts yet hooked up. The actual frame is the issue I think. Once I have finished printing parts for the V-Core on my Prusa I use the steel table that I have for the Prusa to check the V-Core frame is level and square. My "workbench" is a rather light Ikea desk, probably not really flat and level.

Jan

snoozer

@mrehorstdmd

The think is that I am not really clear how to "adjust" anything. The angles are set by the extrusions and the corner plates. The extrusions length is a perfect match, there is no visual difference. I will try if I can somehow make the double-t nut fix at different angles I suppose. Are those double-t nuts a good way to do it actually ? From feeling while assembly it felt much better to work with the drop in single t-nuts that came with the kit.

Jan

PS: I wonder, would it be better to leave 0.5 - 1mm room in the corners for the upright posts or is squeezing the horizontal extrusions agains the uprights (what I did) the way to go ? I am thinking leaving room could give maybe room for adjustments, on the other hand assuming the extrusions profile are the same fixed measurement all around squeezing it should result in a square.

mrehorstdmd

The angles should be set by the square cut ends of the t-slots and the plates should only reinforce the corners.

You can test the t-slot for square cuts by standing the t-slot pieces up on their ends on a table. Stand them next to each other. It will be obvious if they aren't square because the pieces won't stand parallel to each other.

If the ends are square, you can tap the center hole at each end of each piece, drill tool access holes, and bolt the t-slot directly together using button head cap screws whose heads fit in the t-slot. If any corner reinforcement is required, add plates later. If the cuts aren't square you might be able to shim the ends where they bolt together using strips of metal from a beer can.

alt text

If the plates have to be used to force square joints I'd probably use a rafter square to adjust for squareness of each joint as I proceed with the assembly.

alt text

I tried to include a couple images, but they don't seem to be working today.
Here are links:
https://cdn.instructables.com/FYM/776V/IA57RRJB/FYM776VIA57RRJB.LARGE.jpg
https://www.amazon.ca/Empire-Level-2990-Magnum-Rafter/dp/B0002YSAX8

snoozer

@mrehorstdmd

Thanks for explaining that so well. I did not stand them all up individual, but I have stood them on the cut all side by side and they looked straight. I put a metal ruler across to see if they are all same length and they where. If that's 100% true now IDK but nothing was obviously out of line. The V-Core does not really work the way you showed in the picture. Here how they intend it to go together:

Sure I could drill the parts and put them together as you suggested. I have had it on my steel table now and it stands straight, no wobble nothing. Another thing that came to mind is that I did not check the end mounts of the X axis if they are square to the actual X extrusion. Those are 3D printed, there is obviously a change they are a bit off.

Jan

Alexander Mundy

Maybe a little late, but to square the ends of extrusion I use a table style disc sander. A cheap one will work as long as you get the table and slide 90 degrees to the sanding disc which isn't tough with a spare piece of extrusion and turning it 90 degrees at a time and lightly touching it then observing the sanding marks and adjusting according. Once all extension ends are square I take a spare piece of long extrusion and put 2 set of t nut/ washer/round spacer/washer/bolt and space them apart so the shortest piece of extrusion in the same length group barely fits to make a jig. Then lightly sand the rest in the group to the same length checking often for go/no go in the jig. This will get you extremely close to the same length extrusions without a caliper long enough to accurately measure them.

mrehorstdmd

There's probably enough slop in the fit of the nut-strips in the t-slot to allow the joints to be assembled squarely. Pick up either a machinist's square or a rafter square and have another go at it. You can test the square for squareness by drawing a vertical line with it placed on a board, then flip the square over and check that the line you drew follows the edge of the square. Even cheap plastic rafter squares are usually square. Machinist's squares are "adjustable" and should be checked before first use.

What are those corners made of?

snoozer

@mrehorstdmd

The corner plates are made of aluminium.

http://www.ratrig.com/hardware2/openbuilds/plates/90-degree-joining-plate-black.html

I don't have a square of any kind here, I checked with the frame on a piece of cardboard and drew a line, turn it around and the line matched. Sure it may not be a 100% solution but I move forward from here now with the belt installation. I have a square next week and check again then.

PS: I do actually have the print bed which is square, yes I need to do a bit of adjusting. I better do that now before moving to the belts.....

snoozer

That was a lot easier than I thought, I have no experience with these extrusions, there is indeed enough play with those double t-nuts to square it up. Also the holes in those corner plates are bigger then the bolts, so there is some play there as well. It was only out by approx 0.5mm on a distance of about 320mm.

snoozer

Hello,

so the build is at a stage where I have wired up my Duet2 Ethernet to have the following connected:

Steppers
Endstops (NC)
Hotend Fan
Hotend
Extruder

And I am running into trouble already. When I try homing the X or Y axis it moves to the endstop, and then instead of backing off a little it keeps ramming into the switch. I am pretty confident I have the switches configured right.

; Endstops
M574 X1 Y1 Z1 S1

In the machine properties I can see the state of the endstops correct as hit when it should be. Running the homing of for example the X axis and pressing the switch manually I can observe how it tries to home fast 1st, and the speed reduces BUT it does not reverse direction. Here the homex.g content:

G91 ; relative positioning
G1 Z5 F6000 S2 ; lift Z relative to current position
G1 S1 X-305 F1800 ; move quickly to X axis endstop and stop there (first pass)
G1 X5 F600 ; go back a few mm
G1 S1 X-305 F360 ; move slowly to X axis endstop once more (second pass)
G1 Z-5 F6000 S2 ; lower Z again
G90 ; absolute positioning

Where it says go back a few mm it does actually not, it keeps moving to drive against the switch.

Physically left should be home and that's where the switch is. So G1X5 should move the head 5mm to the right but it does not. Have I maybe overlooked something elsewhere that would explain this ?

Thanks
Jan

snoozer

OK, IDK what went wrong but I have reconfigured it from scratch now with the RFF Config Tool and it now works.

Endstops in config.g
; Endstops
M574 X1 Y1 Z1 S1 ; Set active high endstops

Homing in homex.g
; homex.g
; called to home the X axis
;
; generated by RepRapFirmware Configuration Tool v2 on Mon May 06 2019 14:46:11 GMT+0100 (Irish Standard Time)
G91 ; relative positioning
G1 Z5 F6000 S2 ; lift Z relative to current position
G1 S1 X-305 F1800 ; move quickly to X axis endstop and stop there (first pass)
G1 X5 F6000 ; go back a few mm
G1 S1 X-305 F360 ; move slowly to X axis endstop once more (second pass)
G1 Z-5 F6000 S2 ; lower Z again
G90 ; absolute positioning

Jan

snoozer

I have been playing around with speeds, acceleration and currents. My concern was that I would not get the speed out of my 0.9 degree steppers. I was so wrong, the head if flying around REAL fast, way faster than ever needed for a print. Even the bad moves pretty quick. Light at home is pretty crap, did not bother taking a video yet.

The print bed is a bit of a worry however. I have 2 motors for the Z axis which are mechanically independent. When playing around with speeds etc I would ofc come to the point where the motors just stall. Unfortunately not both at exact the same time. While that is only a matter of adjustment I am concerned that if I have build up of material on the nozzle and the head does catch on a blob of plastic that my motors ger out of "sync" and the bed is no longer level. Also I dislike the idea of flexing couplers between lead screw and stepper shaft. They are provided with the kit and I have them put in for now. Is my concern about the two motors getting out of sync justified or am I just to worried ? Would you put a belt between the two ?

My bed is only temporary and I dislike a 4 point mount anyway. The kit did not come with any means of bed adjusting. I just got a few springs and printed brackets for them to rest in and push against the bed from below.

I am not 100% happy with that at all. The bolts are supposed to go into the small slot, they are M2 or something small. I will modify that to a 3-point mounting and countersink M5 bolts in the print bed. I wont bother with magnets on this. The final setup would be a 230V AC heated bed from E3D or a machined aluminium plate, not sure yet.

Jan

dc42

Motors will stall if you set the maximum speed (M203) and/or maximum acceleration (M201) too high. If you set the Z parameters in those commands to values that your printer can do reliably, then it's most unlikely that you will get one Z motor stalling and not the other.

So with the proper settings, you needn't worry about the Z motors getting out of sync during a print. OTOH they may get slightly out of sync when you power the printer off and on again. If your printer has a Z probe, you can resync them before printing as described at https://duet3d.dozuki.com/Wiki/Bed_levelling_using_multiple_independent_Z_motors,

snoozer

@dc42

Thanks for the reply. A Z probe is on my bucket list for this build. I have an inductive probe but I wont bother mounting it cause I want to be able to print on glass and prefer to give a piezo probe a shot. My speed tests have been VERY much on the edge, not at all settings for real printer set-up. I have reduced the speeds a good bit to have lower motor currents and reasonable practical speeds instead of show-room effect

Thanks
Jan

snoozer

One more thought about the bed and end stops. I have one end stop at the low logical end of the z axis for now which means homed the bed is lifted all the way up. That seems to be what I have seen on most or all printers in fact. its not really very practical from a operational perspective. To overcome this I can see two options.

A: Modify the homeall.g to have the bed drop all the way after homing to allow easy access and do the same after every print. Not clear yet how that would work when using a Z probe.

B: Having the end stop at the bottom (logical high end) and home the bed there. Again I have not yet looked into Z probing, no clue if this would be an option.

Which is the better approach, anyone has practical experience to share related to this ? It only really come into play where the bed moves for Z instead of the tool I guess.

Jan