[Poll] Bed mounted on springs ( prusa-style ) ?

OK, now I have a super stiff frame, a flat tooling plate and everything is levelled to the max. ( mean error 0.03 and deviation -0.02 according RRF mesh bed leveling )
But now I miss the soft and forgiving bed mount I had on my Prusa i3.
The nozzle ran into every little blob, caused by the damn Bowden tube retraction. ( 2.5mm retraction @ 80mm/s ) and skipped steps.
On my Prusa it would just scratch a bit, and the flexible "frog" and springs would prevent the worst.

So the question is, should I replace the nylon posts that connect the tooling plate with the bed frame with springs? ( feels like a sacrileg )
How have you done it?

Edited 1 time(s). Last edit at 04/26/2017 02:28AM by o_lampe.

It sounds like over extrusion or maybe the retraction settings need tweaking, or both. I would have thought that you'd need more retraction for a Bowden tube extruder- 2.5mm is close to a direct drive retraction number. I thought Bowden retraction numbers were usually in the 5-7 mm range. Also, 80 mm/sec retraction seems awfully fast- the motor may be skipping and not providing the retraction you've set. In my direct extruders I typically set retraction to 1 or 1.5 mm at 30 mm/sec (acceleration is 2000 mm/sec/sec IRIC) and never see such problems.

Edited 1 time(s). Last edit at 04/26/2017 07:30AM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I agree, the Bowden tube would have to be short for 2.5mm to be sufficient. Small blobs at the start of travel moves are usually caused by insufficient retraction. I reckon on needing a retraction distance of just under 1% of the Bowden tube length plus 1 to 2mm.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Bed mounted on soft springs can be a good thing.
In the case of the MB Rep2, it had a bad habit of curling when bridging, around edges, or off the build plate.
The springs deflected under these small collisions, preventing the build from being dislodged (most of the time).

I have a bed mounted on thick silicone hose used in place of springs, its much more solid, allows a little manual adjustment by compressing the tubing. Doesn't really prevent damage, but my z motor runs the minimum current required and skips if there's a head crash.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Quote
the_digital_dentist
It sounds like over extrusion or maybe the retraction settings need tweaking, or both. I would have thought that you'd need more retraction for a Bowden tube extruder- 2.5mm is close to a direct drive retraction number. I thought Bowden retraction numbers were usually in the 5-7 mm range. Also, 80 mm/sec retraction seems awfully fast- the motor may be skipping and not providing the retraction you've set. In my direct extruders I typically set retraction to 1 or 1.5 mm at 30 mm/sec (acceleration is 2000 mm/sec/sec IRIC) and never see such problems.

Why do you think 80mm/s is to fast for retraction? There is almost no mass to move or to accelerate.
I've played around with retraction setting and extrusion ratio ( 5mm retraction@100mm/s and 90% extrusion ).
It helped a lot, but it seems my part cooling could use an upgrade too.

Also I noticed that blobs occur, when the gap between tracks is to short to use retraction. I might have to use faster travel-setting too...

There is low mass but it is stuck in the hot-end. Try pulling the filament out of the hot-end some time. It isn't a zero-effort thing, especially if you have a long Bowden tube adding friction. That's what you're trying to get the motor to do.

If 80 mm works, use it. I merely suggested that you check it to see if it's actually working as intended. If the drive gear diameter is 10mm, you're asking it to spin at 2.5 revs/sec. It just seems a little fast when it's under load. It's easy enough to test. Mark the filament at the entrance to the hot-end (on a piece of filament that's been in the hot-end and extruded), heat up the hot end and retract the filament at 80mm/sec and measure the distance your mark has moved back from the hot-end. Then try the same test at higher and lower speeds. If that's not easily manageable, just change the value and run a few prints and see if there's any change or improvement.

Are you using z lift on retraction? Pressure advance? Wiping? Coasting?

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I thought, I've sorted it out.
On my Prusa I disabled z-hop while retraction, but on a CoreXY it needs some air between nozzle and part.

I started another overnight print and it was almost successful.
This time the blue tape let me down and got loose on the bed
The part is warped sightly, so I have to look for a different bed surface ( and a new spool of filament )

PEI FTW!

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Sounds like you've got it sorted - but FYI the bed on my CoreXY is mounted on springs so that it's easier to level. I use a Duet v0.6 board and use the 3 levelling screws so that the feedback from the bed mapping routine is as good as can be achieved, and the software has to do the minimum amount of correction during a print.

Quote
the_digital_dentist
PEI FTW!

Will start to look into the options. I'm sure, all answers are there regarding surface materials.
So far I know of PEI, BuildTak and "Dauerdruckplatte ( FR4? )".
Anything else to look for? I'm mostly printing PLA, ABS and PETG

I decided to try something new and ordered a piece of LokBuild (R).

I'll be interested to hear your experiences with LokBuild. I have been using PrintBite and find it really good, with one minor criticism: you have to wait until it cools down before removing the print. As my heated bed takes a while to heat it, it means the time between prints is longer. As I understand it, LokBuild's adhesion does not depend on temperature.

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See my blog at [moosteria.blogspot.com].