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

Posted by o_lampe 
[Poll] Bed mounted on springs ( prusa-style ) ?
April 26, 2017 02:27AM
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.
Re: [Poll] Bed mounted on springs ( prusa-style ) ?
April 26, 2017 07:30AM
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.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: [Poll] Bed mounted on springs ( prusa-style ) ?
April 26, 2017 03:17PM
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.



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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: [Poll] Bed mounted on springs ( prusa-style ) ?
April 26, 2017 04:17PM
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).
Re: [Poll] Bed mounted on springs ( prusa-style ) ?
April 30, 2017 10:02AM
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.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: [Poll] Bed mounted on springs ( prusa-style ) ?
May 01, 2017 02:19AM
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 [email protected]/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...
Re: [Poll] Bed mounted on springs ( prusa-style ) ?
May 01, 2017 07:48AM
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?


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: [Poll] Bed mounted on springs ( prusa-style ) ?
May 07, 2017 03:16AM
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 sad smiley
The part is warped sightly, so I have to look for a different bed surface ( and a new spool of filament angry smiley )


Re: [Poll] Bed mounted on springs ( prusa-style ) ?
May 07, 2017 07:12AM
PEI FTW!


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: [Poll] Bed mounted on springs ( prusa-style ) ?
May 07, 2017 07:17AM
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.
Re: [Poll] Bed mounted on springs ( prusa-style ) ?
May 08, 2017 06:59AM
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
Re: [Poll] Bed mounted on springs ( prusa-style ) ?
May 11, 2017 03:04AM
I decided to try something new and ordered a piece of LokBuild (R).
Re: [Poll] Bed mounted on springs ( prusa-style ) ?
May 11, 2017 04:49PM
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.


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