Best posts made by nophead

I have added the Model to NopSCADlib if anybody needs an OpenSCAD model.

@deckingman said in Continuous vertical lines on shell:

coupled with the lower torque available for partial full steps (due to micro-stepping) might mean that the motor will have a tendency to jump to the nearest full step. i.e. small (say single digit) micro steps might not necessary translate into any physical movement of the motor.

This is a common fallacy / misconception that is all over the web. The torque available when microstepping is the same as full steps because the vector sum of the two coil currents is always the same. I.e. the peak current when only one coil is on is sqrt(2) times the current when both coils are on. So at any stop position the holding torque is the same. It isn't less at intermediate microstep positions.

It is true that the torque is always proportional to displacement from the rest position, so if you only move a very small step the torque applied is very low and may not overcome stiction. However that is only relevant at the start. If the the load does not move the displacement quickly increases and so does torque until it does move.

Once moving at constant speed the rotor lags the rest position by an amount that generates enough torque to overcome the dynamic friction. If that lag exceeds two full steps the motors stalls because the torque is sinusoidal so reaches a maximum. During acceleration it lags more and during deceleration it leads.

I use single outlines and make all my holes polyholes, see http://hydraraptor.blogspot.com/2011/02/polyholes.html. Then they always come out the exact size I want.

Yes but you also need to limit the number of sides to about twice the hole diameter in mm.

When the nozzle turns a corner the filament likes to take a shortcut and cut the corner, making it rounded. When you have a less corners they are further from the desired circle, so when they get rounded they are still outside it. I found empirically that when the number of sides is twice the diameter the rounded corners just about lie on the circle, so you get the roundest hole that is still the right size.

Since I design exclusively on OpenSCAD it is not problem for me to make all holes with poly_cylinders instead of cylinders. My STL files then print correctly with any slicer and toolchain.

When printing other peoples designs, my old machines that run from my own host and firmware have the ability to detect circles in the g-code and convert them. That enabled me to print thousands of Mendel parts without having to ream all the holes.

@asdasd1234 Do you have control over the number of line segments in the STL file? I have noticed with Cura it will generate ridiculously short segments if the model has them. As I model in OpenSCAD I can simply set $fs to half my extrusion width and then I don't get any segments shorter than 0.25mm. There really isn't any point in printing shorter segments. Skeinforge combines segments that are too small, not sure about other slicers.

@dc42 said in Laser filament monitor:

We might be willing to supply one of our prototypes to a user who meets the following conditions, to try to speed up finishing it:

I think I meet those requirements and would like to test one of these.

What is the timescale for production Duet 3's? I am designing a machine that has some CAN peripherals but I won't finish it anytime soon.

I like the idea of a small firmware that just does the realtime stuff and the rest on an SBC in Python. That is how my early machines work, including HydraRaptor and the very first Mendel90.

It is actually behaving like one of the sockets is shorted. The motor plugged into that one would not spin but the other would.

@thugmek The simplest solution is print ABS brackets. I run my motors so they have a 20C rise but they are in a 45C chamber, so they get to 65C. ABS is fine with that.

@dc42 The motion planning does not need to be realtime, only the actually stepping of the motors. As long as the data is produced fast enough to keep a buffer full it works. I sent trapezoids to my real time code encoded as a list of step durations during the ramps, the constant speed step duration and the total number of steps. My reatime code just did the Bresenham loop. Never had to change in more than 10 years and only needs a tiny 16 bit micro.

@phaedrux Actually they do stay in sync better in parallel in some situations, although I run mine in series.

I found in series if you stall one the other still spins. In parallel stalling one tends to stall the other. Something to do with the coupling because if you turn one it will act as a generator and turn the other. So I also think when it powers up they will both snap the same way.

The issue is if you power up on a phase that is exactly two whole steps away from where the motors stopped. In that case they could snap in different directions in series but more likely the same way in parallel. As long as your home position is not such a phase you should be OK assuming you only power off when homed.

I put pointers on my Z-axis lead screws that I can rotate to point the same way when homed and see of they get out of step.

As well as the spring effect of filament and motor there is also backlash if using gearing or a Bowden tube that has to be slightly bigger diameter than the filament. @dc42 does the pressure advance separate these two effects and compensate for them independently? I.e. to get over backlash you would want a very fast movement and then a slower accelerating speed once the filament is engaged.

The graph looks like heater lost its connection and regained it rather than a sensor fault.

If its a moving head machine how are you getting wires to the head? Moving wiring tends to break unless you take precautions to ensure a minimum bend radius compatible with the wire.

This is why I use flat ribbon cables on my 3D printers with lots of wires in parallel to handle the current. The bend radius you need for thicker wires is surprisingly large.

3D printers tend to make a very large number of moves compared to other CNC machines. I have thick cables in cable chains on my router but, being mainly 2D, it simply doesn't have the mileage my 3D printers get.

@jay_s_uk Thanks.