Variable coasting

[WTLgrinda]

Hi.

I've moved to S3D a couple of weeks ago. I'm amazed at how simple it is to get good prints.

I'm an ABS guy. I'm mostly printing for prototyping parts using a 0.6 nozzle and sometimes a 0.8 on a bowden setup and a volcano hotend. One thing i realized is that controlling oozing and zits is a lot harder. Retraction won't help because the plastic in the nozzle doesn't get sucked in (and there is more because of the volcano). I've took a lot of time tuning the extra restart/wipe/coasting settings but one thing i realized is that coasting is the most important parameter when you use a bigger nozzle.

So yeah, here's the request and the theory behind it. In a bowden setup the hotend tends to accumulate more "pressure" compared to a direct extruder setup. The duration/length of the extrusion will change the coasting required. If i'm doing a 20mm diameter circle, it will tend to "overcoast" and i'll get holes in my surface. If i'm doing a 80mm diameter circle i'll get it just right and get a smooth seam with no zits.

One way to implement the feature would be to put a "Maximum coasting extrusion length". Then just do a linear scale down of the coasting distance if the extrusion length is under the specified parameter. That way long extrusions would get full coasting (and pressure reaches a "cap" in the hot-end at some point) and shorter ones (where pressure doesn't build as much) wouldn't suffer from the full coasting setting.

Am i making sense here or missing something?

[upsm]

There is an experimental algo in marlin that calculates built in pressure in the nozzle and reduces the extrusion till the end to relieve that pressure .. sort of like varable coasting directly in firmware. Can't remember the name of the feature off the top of my head but try joining merlin irc channel and discuss with ppl there you should get quite a lot of info about it... should help you fix your problem (especially if you are using marlin )

[WTLgrinda]

I know the feature, it's called LIN_ADVANCE, i've read a lot about it. The problem is that it doesn't work so good with bowden setups.
If all else fails I plan to try it, so far i don't need a "perfect" finish for the parts i'm making. I can't switch to a direct extruder because of the design of my printer (i'm working on something experimental here) and i will most likely move away from Marlin in the future.

You can read about it here : http://marlinfw.org/docs/features/lin_advance.html

I think it would be easy for the slicer to handle those calculations because that's basically what the firmware does with LIN_ADVANCE. Or perhaps the people at S3D will tell us that tuning the linear advance will yield better results... But i don't think they would do that since they sell us a software to get great prints

[upsm]

I know the feature, it's called LIN_ADVANCE, i've read a lot about it.

That's the one! As I said, read about it somewhere sometimes, haven't used it, but shows potential.

The problem is that it doesn't work so good with bowden setups.

As a total "anti-bowden" person I don't find that to be a problem but I understand how it can be a bummer for you.

If all else fails I plan to try it

It's open source so you can easily try and make it work better for you if you have ideas how to make it better. Waaaaaaaaaaay more room to test stuff then with a closed source slicer . Even better, if you make it work good, your contribution will benefit much bigger audience then just Simplify3D users

I can't switch to a direct extruder because of the design of my printer (i'm working on something experimental here) and i will most likely move away from Marlin in the future.

I, mostly, moved away from marlin myself, but if you make that thing work with marlin that can be ported to most other firmwares, once the code is shown to work and give good results. Being able to change it yourself makes all the differences, at least for me.

As for the direct extruder, I had a serious issue with heavy extruders and wanted something better but also had serious issues with bowden that was just too far of the goals I had so I was trying out some "remote torque" solutions but I never made anything I was actually satisfied with. Then Jason made the flex3drive and solved all my problems , now I have his dual extruder (with 2xhexagon) and few of his single extruders and I'm a happy puppy... there are also those guy's from Cyprus that tried to copy his design but made it unprintable on FDM so they have to print it on SLA using shapeways or similar services... all in all there is a solution to have direct drive that's small and light. Good to have different options; dunno what you are designing but more options always helps especially as you can integrate number of extruders directly into carriage, you do need 2 ptfe tubes for each extruder apart from only one for the bowden but I doubt that's a serious problem

[WTLgrinda]

Hey,

The reason i'm sticking to bowden is because I need to produce a medium quantity of the same printed parts.

My plan is to install 4 hot-ends on my printer, use a bigger extruder motor with a longer drive gear so that it's actually pushing 4 strings of filament into 4 different PTFE tubes. Since the XYZ movement are the same for all parts and my 4 hot-ends will be 200mm apart, i'm printing 4 parts at the same time instead of one. Basically i'm just fooling the printer by splitting the bed into 4 smaller sections. In theory it works, it might need a bit of tweaking but this is why i plan to stay away from direct extruding for this printer.