inventabuild
Posts: 81
Joined: Sat Mar 19, 2016 12:29 pm

Coast Compensation

Sat Aug 31, 2019 2:11 am

1. In some situations Coast is the only way to mitigate stringing.
2. Please add back the quantity of filament that Coast subtracts to prevent gaps from eventually showing up due to the cumulative affect of a large amount of Coasts.
3. Add back the quantity of filament that Coast subtracts over the path length of the next extrusion instead of adding it back with Extra Restart Distance which can cause blobs at the beginning of layers.

S3D-Jake
Posts: 755
Joined: Wed Jun 20, 2018 12:45 pm

Re: Coast Compensation

Wed Sep 04, 2019 3:06 pm

Thanks for your suggestion. Can you please be more specific about what common scenario you're having where this is an issue? I'm happy to present the idea to our development team once I better understand what it is we'd be fixing through adding this feature.
"A bird does not sing because it has an answer. It sings because it has a song."

inventabuild
Posts: 81
Joined: Sat Mar 19, 2016 12:29 pm

Re: Coast Compensation

Sat Sep 07, 2019 5:33 pm

Hello S3D-Jake,

1. I'm using Coast to completely eliminate stringing when printing a lot of little letters which entails a lot of retracts occuring on the same layer.

2. My extruders are dialed in perfectly, so I am not using coast to compensate for poorly calibrated extruders.

3.1 Let's use round numbers to illustrate the issue:
3.1.1 If Coast is set to 1 mm then every time a line ends, the extruder stops extruding 1 mm before the line ends.
3.1.2 If I have 1 million lines to print on the same layer then the extruder stops printing 1,000,000 mm short for that layer. That is short 1,000,000 toolpath mm, not short 1,000,000 mm of filament; nevertheless the cumulative effect of printing short causes under extrusion to start occuring because eventually there is no filament in the heater block to melt.

3.1 Straight Extra Restart is not a panacea because it is can be difficult to dial in precisely to work with Coast and can cause blobs at the start of lines if overdone and still allow for under extrusion if not done enough. Besides Extra Restart is really meant to work in conjunction with the Retraction Distance (the Units of Measure are the same), not with Coast.

4.1 What I'm recommending is the option for a "Coast Compensation Extra Restart" distributed over the length of the next line (or some fixed distance) that prints after a Coast.
4.1.1 So for example if I'm printing line # 1 with Coast 1 mm, then I print line # 2 which is 10 mm long and this new proposed feature "Coast Compensation Extra Restart" has a value of 1 mm (to equal the Coast value), this "Coast Compensation Extra Restart" would occur over the full length of line # 2 (10 mm) and not just shoot out at the beginning of line # 2.
4.1.2 This will prevent blobs from occuring at the beginning of a line when trying to use an Extra Restart value to prevent under extrusion.
4.1.3 This will prevent under extrusion from occurring when using a perfectly calibrated extruder w/ Coast to prevent stringing.

Can you please implement this?

S3D-Jake
Posts: 755
Joined: Wed Jun 20, 2018 12:45 pm

Re: Coast Compensation

Thu Sep 12, 2019 11:46 am

Hello again. I believe I'm still not understanding. If the extruder is perfectly calibrated, what are we compensating for? Your retraction of 1mm in this scenario happens in place, then the line is finished. That same amount is then advanced at the beginning of the next line. If you're getting blobs on restart you should be looking to adjust your extra restart distance.

More on this here: https://www.simplify3d.com/support/prin ... -and-zits/
"A bird does not sing because it has an answer. It sings because it has a song."

inventabuild
Posts: 81
Joined: Sat Mar 19, 2016 12:29 pm

Re: Coast Compensation

Sat Oct 05, 2019 10:42 pm

It's not true that a perfectly calibrated extruder will not blob because the molten plastic starts dripping as soon as the hot end starts traveling in open spaces. I'm trying to eclipse this dripping w/ coast. I've noticed this especially when printing a large quantity of fine detail pieces separated by a few millimeters.

Frank Sonne
Posts: 14
Joined: Thu Sep 19, 2019 6:43 am

Re: Coast Compensation

Mon Oct 21, 2019 11:47 am

I think the root of the problem lies in the fact that the tool head get to where it needs to go, stops and then Retracts, the relatively long period the head is at a standstill, mother earth is messing things up, by having gravity pull filament from the nozzle. We need to remove the filament, so there is nothing left to pull out, when the head stops. The other main problem lies with the fact that filament is controlled by length, and not pressure/flow.

I am experiencing approximately the same issues with Coasting, The problem when coasting it that the constant identical pressure to the filament gives an even and predictable spread, but when you "release" the pressure by coasting, this lowers the pressure over the distance, and the flow during the coast gets unpredictable.

If you look at pressure for the beginning and end of a filament line, it should start moving slowly and accelerate as the pressure is getting to operating pressure, and the only way i can se for lowering the pressure sharply for endings, is by setting a "Pre-Retraction Distance" instead of Coast, so the flow is not only gradually and unpredictably lowered, but removed, while still applying the remaining distance through gravity, the amount of filament that can be laid down would limit the distance significantly, and will 0,1 mm be too much. That distance should be the same every time if the pressure is the same, when retracting. And that's when it gets hairy, if the previous line was short, did it get to full pressure or did it not, and then the under or over extrusion starts, due to unpredictable filament pressure.

If the temp of the filament is constant, and i assume it is, it should react the same way every time, so the pre-retraction distance should be the same, and you will never end up having spent filament while coasting, that the software has NO way of compensating for. With pre-retract, the result should be far more predictable. If retraction is setup for lifts, the lift should not occur at pre-retract, but at retract.

I guess a calibration tool would be helpful, as:
you would have to know exactly how much distance of filament you can put down after pre-retraction.
you would have to know how much distance is required to get to operating pressure. Though it should be the same as this will happen after pre-retraction, and distance of filament for pre-retract, tells you how much filament you lost and should compensate with by adding retract restart distance.

When i messed around with coasting, with some filaments (Wood specially), i needed a lot of coast, but that affected my infills, as they started out by being very under extruded, but if the layer was big enough, the pressure would be back up fine, but on small layers, the missing filament in the infill made the print weak, ALSO outlines suffers from coasting on small area layers.

The problem basically is, that there is no way of knowing how much filament is used during Coast, and how do you compensate for the unknown flow while coasting. If the filament to lay down is close to coasting distance will it ever add any filament, or will it take so long to add and remove pressure that it ends up adding way to much filament. Even moving while retracted, the pressure is changing down, so depending on the length of the move, the pressure is again unpredictable.

I believe that the whole issue is a question of timing of speed and pressure, but as pressure information is unavailable, we can only try to find the best solution. But gravity will ultimately be the biggest problem, it will pull filament out, no matter what we do.

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