@zapta Thermocouples are accurate to +/- 3C (at room temp). That accuracy will degrade over time because the construction inherintly suffers from galvanic corrosion.

RTD's, like a PT100 or PT1000, at the lowest class, are accurate to +/-0.5C at around 250C.

Which is a long way to say: RTD's are significantly more accurate than thermocouples.
Although both are much more accurate than thermistors (which I have seen be +/-20C at 250C).

RTD's have a longer service life, use normal wiring and are less prone to electrical noise than thermocouples. Basically you use thermocouples when you need to measure very high temps or a very wide range. Otherwise RTD's are the better choice. Thermistors are for low temps and really low costs.

*is printing a multi part file...

One of the parts as apparently on a blob of oil or some nonsense, is going to fail and probably ruin the whole print.

Pause print. Sigh.

Remember that the g-code viewer has a cancel part function.

upload version 3.2 of DWC.
enable Gcode Viewer plugin.
cancel the failing part.

RESUME PRINT!

ALL. OF. THE. WINNING.

Like seriously, epic epic feature to have.

@whopping-pochard

What you have designed, because its floating on 3 points (which is elegant), runs the risk of not running true to ANY of the linear constraints... you could end up with a bed that translates and rotates relative to all three axies as it moves in Z.
To prevent that, you would need to precisely align 3 rails on three separate planes, which themselves need to be precisely aligned to be at least parallel.
Possible, but a lot of work.
You also now have the issue of CPE in the screws compounding (only an issue if you buy cheap leadscrews though).

The advantage of reducing the number of rails, is that you greatly reduce the challenge of aligning those rails relative to each other.
Lots of commercial printers use just 2 linear constraints and a single screw because of the need for a simple (hence cheap) assembly process. They then rely on the bed/frame stiffness to compensate for the cantilever.
The big advantage of rails on extrusions is that they can handle very high side-loads which means you can have just 2 rails and a large cantilever. Do that right and you only have to align 2 rails on the same piece of extrusion.
And given that good quality rails are expensive... fewer is generally better.

All of which is probably academic, in an FDM printer, especially a home built one.

And for custom leadscrews. Misumi. Not cheap, but very high quality.

The number 1 issue I normally see is beds that are not tightly enough constrained in the x/y plane, so things move about and cause vertical ripples.

Identical g-code run on machines with significantly different accleration settings can have quite dramatic differences in print time, for the reasons already described. There are lots of machines out there that claim huge print speeds but can't actually deliver. And even if your printer really can hit 600mm/s within its own travel, printing huge thick layers at low feed rates will always be faster than thin layers at high speeds.

The deep details of print speeds and slicer settings are not widely understood, that often even includes the people writing the software.

I'm fairly certain that both Cura and S3D still don't actually calculate extrusion volumes correctly...

@ziggymanpopo said in Max wattage for extuder heater:

So here is my concern
At 12v and @ a 60w. Heater that converts to 5amps.
Since 5amps is max or 100% for the heater output, It makes me wonder if a ssr is needed considering continuous load.. by elecrical standards we can only load up to 80% of full load current if used for more than two hours.
In my book this would be considered a continuous load. Do i need to take precautions to protect the board by using a ssr. Second what can i do to prevent the possable runaway scenario if the ssr. Were to short closed i plan on using a thermaly controlled over temp sensor in line for the bed heat but this is upractical for the hotend i believe the firmware protects against a runnaway extruder heater.. but will that still work when a ssr. Shorts closed .. with out some sort of secondary input the duet would be able to fault.. but not stop the runnaway heater. any input and ideas would be appreciated...

A 60W heater, on most normal printheads, if run at 100% duty cycle for 2 hours, hopefully will have triggered an over-temp shutting off the board, and if you are not using a well designed all metal hotend... might well have melted something important.

An extruder heater is not a 100% duty cycle, continuous load. It is PWM controlled and will run well below 100% duty cycle for the majority of the time.

There are ways to design fail-safe setups that would cut off the power to the board in the event of the type of failure you describe...
That said, based on my experience the way to deal with this is to size your heater correctly and have an extruder that will not melt.
A failure of the board is rare enough that its not worth the trouble to build in a fail-safe if you have an extruder that can withstand the temps of a thermal runaway.
PTFE has no place in a hotend

It can also be motor resonance. Stepper motors will move more smoothly at certain speeds. You can try just changing the speed to see if that helps.

Printing a tower that changes speed by ~5mm/s every 5mm is a nice way to see if that is what is causing the artifact.

What @thwe said.
Aligning two rails on the same plane (assuming you align the frame well), is much much easier.
Oddly one of the very interesting bits of design feedback I've heard, is put the rails under the extrusions, not on top. That way they don't collect dust.
Seems silly, but its actually really nice.

Not using coreXY would be more rigid. Don't get me wrong, H-bot (or a weird monstrosity I designed) would be less stiff.
Basically, with the type of bearings, mounts (I'm assuming metal) and frame you've selected, all of your lack of rigidity will be from belt stretch. Two ways to minimize that stretch are to reduce the length of belt and increase its width. CoreXY uses a longer belt than you would have on a conventional cartesian/flying X motor. The flying X motor adds more weight and wiring complexity, so it might outweigh any advantage...
TLDR:
Wider belts is the easiest way to get more stiffness.
Its also really important to design in a way to adjust the belt tension!

2
I wouldn't.
Having the bed be structural and heated is a big challenge. If you are going to heat that bed (which will take lots of power, look at an SSR) then you want to both mechanically and thermally isolate it from a separate frame that is the actual Z stage. I've had great results just using nylon foam as a structural spacer. It can be glued, is a great insulator and rigid enough to work well mechanically. Its still a foam though and will happily absorb any expansion of the bed.
Screws and rails in-axis, its theoretically better, I think your bigger issue is that you seem to be relying on the motors own bearings to carry all the vertical load. They are not designed to do that, you should think about including a thrust washer.

3
How much does that gantry weigh? I'm guessing 450g for the extrusion. Plus the weight of the rail, rotational mass of the motors etc, if you are worried about the weight of the pulleys, don't be. If you mean the extruder? Its more significant, but the difference is going to be small compared to the mass of everything else, at least for acceleration not involving X.
If you really want to get higher speeds use bigger motors. NEMA23's are not much more expensive and produce vastly more torque. I don't know why everyone is so fixated on NEMA17's...

4
How fast do you need to go? 24V, 32 tooth GT2 pulleys and NEMA23's get me up over 500mm/s... Which given the huge mass of my extruder, is quite scary.
More voltage is better for speed... And you can always just use the Duet3's heated bed circuit to drive your extruder and only supply 24V to it.
You shouldn't need to actively cool the steppers if they are big enough. People tend to have to when they undersize the motors, overdrive them to get enough torque, then discover they get crazy hot (although good steppers will run hot enough to burn you without being damaged themselves).
You could also get an external relay or SSR to drive an extruder heater, although I'd try and avoid that myself. There is also the Toolboard 1LC if you can get one.
I'd suggest trying 24V at first.

5
How are you actually connecting your uprights to the crossbars? I don't see anything for that. But there are lots of easy ways to do that. If you haven't already go look through Misumi's website and see the millions of options. Including getting them to machine stuff into the ends of the extrusions.
The rest seems fine, although I wouldn't use u-channel for the gantry. If you change it the way @thwe suggests you can use flat brackets, which is way easier.

And to echo what @whopping-pochard said, if you move (in fact you can probably just remove completely) the 'front' crossmember, you get a much better view of the printhead/nozzle.
Similar theme, with the extruder mounted on top of the gantry, you have very little space around it for things like fans for cooling prints. Or fans to cool the extruder itself.

Don't forget to plan for filament mounting, and electronics!

@Nxt-1 said in To rigidify or not to rigidify? - vibration issues:

@H2B
I wonder how applicable that technique is to the size of machine I have.

@mrehorstdmd said in To rigidify or not to rigidify? - vibration issues:

How about a couple strap clamps?

I tried with the only strap clamp I could find and did not really notice a significant difference sadly, worth the try though.

I suspect that right now, adding more rigidity is not going to do anything. In fact its probably just going to add things that can resonate.

@theruttmeister
I got myself four bag of ready to concrete mix and will play with it, hopefully in the coming days. Most likely I will go with the M5 bolt+t-slot nut approach as drilling holes trough the extrusions is just asking for troubles with all the interrupted cuts, at least with the tool I have at my disposal. I'll report my findings once I have something to report.

That seems the most sensible path. You can use the same 3D printed mold technique you used for the base, and mold the through holes for bolts right into the concrete. Don't forget a draft angle!

Other people have covered it but...

220VAC is not the issue, all of Europe uses that voltage without everyone suddenly bursting into flames
But I'm guessing that your heater is not just a couple of hundred watts.

The rule of thumb is, either design your heated bed to be able to withstand the max temp it will reach if just set to 100% for an indefinite period of time.
Or add a fail-safe device like a thermal fuse.
And make sure the fuse is either inside the heater (if you can get it made that way) or mounted somewhere that its going to be the first thing that overheats.

Grounding the bed is excessive, a silicone heater should be double insulated, if its shorted to the bed its because you have drilled through the bed, or some other nonsense.

@dgrat said in To rigidify or not to rigidify? - vibration issues:

Have you enabled interpolation on your machine? I have the feel, that dampening 800 Hz vibrations is also not that easy. There are too many Alu parts which can resonate, even if you add endless weight.

Its not about adding endless weight. Its about adding the right kind of weight.
Metals like aluminum are essentially great big crystals, that propagate vibration really well.

CNC machines traditionally use cast iron, not steel, because its actually much more of a granular structure. Because the vibrations are having to cross lots of boundaries between the grains, the materials soak up a lot of the energy. Epoxy granite is used a lot because it has this property, its a mix of aggregate, with epoxy as a binder. Its almost all boundaries between rocks and epoxy, so its really good at absorbing vibration (plus you don't have to wait weeks for it to fully harden like cast iron, and you don't need a foundry).
Regular concrete isn't quite as good as cast iron or epoxy granite, but its still much better than aluminum, and its so cheap and easy compared to those others...
There are lots of people out there building cnc machines using steel or aluminum bonded into concrete or epoxy granite, its a very effective.
Will there still be bits that vibrate or resonate? Probably, but this is a test that will cost tens of dollars and is fun. And based on what the machining world has been doing for over a century, its probably going to work.

@Dizzwold

Remember that magnetic force decreases with the (IIRC) square of the distance, so the blind holes are cool, but decrease the force a little.
The beds I built I just used through holes and superglue, 305x305mm and 25 magnets of similar size to the ones you are thinking of using (the ones by the edge are set back ~12mm). The critical thing for any glue is getting the surfaces really clean.

The only issues were if the glue failed, but those ( a couple IIRC pulled out) I just scraped out the old glue and re-glued.

The beds are now several years old and still work just fine.

@hbm-3d change between relative/absolute values for E. See if that does anything. You'll need to change in both RRF and slicer.

@hbm-3d given that it seems to be an error based on layer number, my guess would be some sort of compounding error in either firmware or maybe mismatched slicer settings.
Steps/mm on Z or E causing some sort of trailing offset.

I'd start by trying to confirm that the machine really is doing what is commanded in Z and E.

It's that or you have really really bad CPE on the ballscrews.

@semi55 yes.
Gearing it down with a belt reduction will sacrifice top speed, but might be preferable. From the picture it looks like you have a huge pulley, or is that just for testing?

And there are RRF/duet closed loop driver boards, but I have zero experience with them.

There are also multiple options for servo's that can be driven with the step/dir output from the Duet.

@semi55 stepper motors might have a lot less slip than a generic electric motor, but they still have some.
It sounds like you are seeing that slip. As the field rotates relative to the rotor, the difference between the two (slip) is what generates the torque. If you are close to the limits of the motor and moving slowly... You can see that slip. Maximum torque it generated at the half step, so basically you are seeing the microsteps being lost in that slip, with the motor catching up as it gets to the half step (or maybe the full step).
The big CNC boys have always said that open-loop steppers are only accurate to the half step for this very reason.
And 2Nm of force needed is quite a lot!

@deckingman having shipped thousands of "reasonably accurate, good quality' thermistors... I wouldn't do that again.
It's hard enough to just get the same damn thermistors over several years. A PT100 is an actual standard, a 100k thermistor is whatever the manufacturer felt like making that day.

@deckingman

When you are shipping thousands of machines, the support burden of in-accurate sensors is non-trivial. Plus finding a good thermistor for temps above 250C is still a challenge.

But for the solo hobbyist, no it's not critical.

@zapta PT100's are more readily available, although the sensors for FDM are already a custom part so that's kinda academic.

@zapta Thermocouples are accurate to +/- 3C (at room temp). That accuracy will degrade over time because the construction inherintly suffers from galvanic corrosion.

RTD's, like a PT100 or PT1000, at the lowest class, are accurate to +/-0.5C at around 250C.

Which is a long way to say: RTD's are significantly more accurate than thermocouples.
Although both are much more accurate than thermistors (which I have seen be +/-20C at 250C).

RTD's have a longer service life, use normal wiring and are less prone to electrical noise than thermocouples. Basically you use thermocouples when you need to measure very high temps or a very wide range. Otherwise RTD's are the better choice. Thermistors are for low temps and really low costs.

@kuon ballscrews are a lot more expensive than belts, and unless you have really long axis' you are not going to see the benefits (they are mostly good for really high loads, far greater than an FDM printer). So long as you increase the belt width, they work well to quite long runs. Screw-drive works well if you really need that extra stiffness.
The crossed gantry doesn't scale well (it's not a commonly used design). H-bot and the MarkForged style gantry give you better weight savings. CoreXY will save a little more weight and space at the expense of a very complex belt system.

For a 600x3 machine I'd do either H-bot or MarkForged gantry. Maybe servo's, but going to big NEMA-23's with big pulleys will get you plenty of speed without a noticable drop in resolution.

@c310 there's a blender plugin that visualizes gcode into a solid model. Or you could try to write some code to convert the gcode back into an STL, but that's a bit complicated. Needing to correctly offset things would be a challenge.

Or print the parts and get some calipers.