@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...

@deckingman said in What do you think about Dragon Hotend:

@theruttmeister As I'm being talked about, I thought it best to respond.

The main thing for me is solving the problem.

Best place to start.

And as a designer and I once started saying, if an engineer points out issues on your project... It's because he cares.

@CaLviNx said in What do you think about Dragon Hotend:

@deckingman

And as a designer and I once started saying, if an engineer points out issues on your project... It's because he cares.

I must remember this analogy, as when I point out the issues with a project at work I usually get called a "difficult cu*t"

I used to get that. Thankfully I'm now an overvalued 'expert' so they listen (and just think it instead).

The original version was actually 'if an engineer starts telling you what you did wrong...' The really good engineers will respond by explaining why they did it that way and why you are wrong about it. Which can start some great friendships!

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!

There's no reason to not use a commercial PCB. Especially if your intent is to make a tool, not a project.

The NEMA24's seem odd to me, but only because NEMA23 is a more standard size... you can get motors in '23 size with a identical performance as those '24s.
There's also no reason why you couldn't use something like the Duex and use 2 motors to drive the Y axis (although I'm skeptical they need such a massive motor for the Y) which would remove the need for external steppers.

You can setup both RRF and Marlin based machines with Octoprint, which has more functionality than DWC, but requires an extra SBC and that work (but can do things like stream a webcam out to the internet).

The main reason to use the Duet boards is that they are using much more modern stepper drivers (quiet printers are good, especially when they are huge). The A4988 is antique trash and people should stop using them.

The main reason to use the RRF is that its a more modern and capable firmware than Marlin, with much better capabilities. Its worth becoming familiar with it now, rather than later. It opens up things like a more modern CPU that can actually push high step rates...

The jump from Prusa/Marlin to RRF... minor. RRF is much more pleasant to configure, other than that, on a conventional Cartesian FDM machine? Its minor.

And while those silicone heaters driven with SSR's are the right way to go, make sure you include some kind of thermal fuse. SSR's can and will fail on, and silicone heaters will melt if they get hot enough. A 200C thermal fuse attached to the bed is not a bad idea (or do the simulation and make sure the bed can't get to a dangerous temp).

@whopping-pochard if you are looking for maximum thermal isolation, there are rigid nylon foams that are more than strong enough to be a layer between structural parts, similar to the way car engine mounts work.
You can find nylon foam on McMaster, it glues just fine with both acrylic type adhesives and epoxys. It will withstand temps to at least 150C. Plus its a lot cheaper than silicone foams or PTFE.
PTFE is a real pain to work with.

@barbarossa-cologne

An SSR is just a switch. The control side only needs to be 24V (actually anything from 3-48V is common, the SSR will be marked), the PSU is powering just the switching of the SSR, which uses a very small amount of power.
The whole point of using an SSR is that the other side of the switch can be for much higher voltages and can carry lots of current.

So your wall socket can supply up to 13A, your SSR can carry 25A and the bed only draws 11A. Everything is good.

The PSU is not powering the bed in any way at all. Its just controlling the switch.

I looked into linear steppers for 3D printing about 10 years ago.

I was quoted about $1000 per axis, with a 300mm stroke IIRC. That was at volume too.
Most of the companies making them are aiming for 1 micron repeatability, for machines were $1000 is a small cost.

I know of at least 1 person who was working on a low cost linear servo, but he was trying to raise money for it as part of a robotics startup.
You can build something very similar to those NPM linear servos for very little money, the electronics are not super complicated... the hardest part is the control.
With a bit of imagination, you could probably even build a linear stepper in the same style. Thrust output might not be great, but if you can make it a stepper at least control is simple.

@houpdelta

You are using the wrong g-code. M201 sets per-axis (X,Y etc). P (and T) is used with M204 to set acceleration when extruding or not.

So:

M201 X8000 Y8000
M204 P4000 T8000

Would limit acceleration while extruding to 4000mm/s/s. But allow travel moves to be at 8000mm/s/s
But:

M201 X4000 X4000
M204 P4000 T8000

Would mean that travel moves would still just be 4000mm/s/s.
Check your base M201 values and try again with M204

@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.

@theruttmeister
Answered my own question:

https://www.youtube.com/watch?v=FFCo5P0iQAI

I'd check your drive lever. Looks like a fundamentally flawed design. No wonder there are lots of upgrades on the market.
If they had just made that hole 4mm and used a shoulder bolt...
Guess that's how you get to a $300 printer.

@apex2011
Skimming through the thread.

Did you measure off 100mm of filament, mark it and then try extruding 100mm? If moving the spool about changed your prints, plus there was debris on the pinchwheel?
My first guess is the extruder drive is slipping. I have no idea how the compression force is adjusted on that extruder drive, but your fails look exactly like what you used to get on the old Makerbot Mk7 extruders. They used a delrin plunger that wore away, once that happens the filament just slips.
A good extruder drive should be able to drag a spool across the table, it needs to be able to exert a decent amount of force to extrude, even with a really good hotend.
I certainly wouldn't be expecting the board to be causing such a severe failure, not without a really obvious other symptom.

@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!

@Nxt-1
Perhaps a little bigger than I was imagining... but I don't see why they wouldn't work. Plus I bet they are cheap!

Location and number of the bolts might be a variable.
And the rubber would help reduce the risk of deforming the extrusions to match the no doubt not flat or true concrete.

@Nxt-1
I do not.
But imagine you made your printer (or CNC mill) from box section steel. You then stuff a rubber bag (like an inner tube) down the inside of the box section. Then you pump the rubber bag full of concrete, till the bag has stretched and the box section is now full of concrete wrapped in rubber. Then let it cure.
Presto, one very strong, very cheap, mostly concrete beam. Which they tell me is a very effective at vibration dampening.

@Nxt-1
I don't think it will add enough mass.

I think you need to bolt a big block of epoxy granite to each upright. You could try casting a simple block that you then literally bolt on. Or you could build a mold that lets you cast the epoxy directly onto the aluminum.

I had wondered what that base was made from. That's got to be helping a lot. But you still have 3 very long uprights and 2 big flat plates at the top, which will all resonate like mad.

Heck, it would be interesting to try some off-the-shelf concrete blocks, bolted on. That could probably be done for peanuts. The fancy CNC people tell me that rubber bags filled with concrete is actually the most effective damping option on a metal frame... so maybe concrete blocks with a thin sheet of rubber as a spacer?

I looked into linear steppers for 3D printing about 10 years ago.

I was quoted about $1000 per axis, with a 300mm stroke IIRC. That was at volume too.
Most of the companies making them are aiming for 1 micron repeatability, for machines were $1000 is a small cost.

I know of at least 1 person who was working on a low cost linear servo, but he was trying to raise money for it as part of a robotics startup.
You can build something very similar to those NPM linear servos for very little money, the electronics are not super complicated... the hardest part is the control.
With a bit of imagination, you could probably even build a linear stepper in the same style. Thrust output might not be great, but if you can make it a stepper at least control is simple.

Sand won't do much, its not going to be coupled to the aluminium.

Polymer concrete.

Or just mix the sand with some epoxy. People get all worked up about ratios, but basically, sand and epoxy.
Aluminum is really stiff and great at transmitting vibration... adding a bunch of mass (of a type that absorbs vibration, like epoxy filled with aggregate) is the best way.

I've been meaning to try adding a metal tube (bolted to the extrusion) filled with water (maybe with a gelling agent), but I've not got to a stage where I actually need it yet. You might want to think about that, as the voids in the extrusions are probably too small a volume.
You'll end up with a very heavy printer... but that's because the only solution to vibration is mass... well, unless you want to get all fancy with active damping, but who knows if that is even a thing in machine/frame design.

@bearer
Early gen3 electronics for reprap/makerbot seemed to have issues homing if they were in direct sunlight...

Who knows if that was real. Its not like they were reliable at the best of times!