low acceleration / no jerkyness helps with bed adhesion
 
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Pepe le Vamp
(@pepe-le-vamp)
Trusted Member
low acceleration / no jerkyness helps with bed adhesion

Hi all.

As a student of terrible bed adhesion I noticed the kinds of movements that cause the filament to lift up. I found the big problem is when the printer is traveling along then stops & reverses direction suddenly. Or any kind of almost-360 degree turn.

I turned my acceleration down to ~45 on the first layer and it has been a catch-all improvement for my prints. When the printer needs to do some tiny details it will slow down in advance all by itself. When it can do a big long straight line or a big arc, it will gradually speed up.

My speed is now at 60mm/sec for first layers when it does eventually get up to speed, which is often due to me printing a lot of square things.

I couldn't find the best place to put this information but I wanted to get it out there. Cheers all.

 

Posted : 10/12/2019 1:25 pm
bobstro
(@bobstro)
Illustrious Member
RE: low acceleration / no jerkyness helps with bed adhesion

You can try to dodge the bullet, but your underlying issue is still adhesion.

This is a common problem that can be caused or aggravated by two factors that need to work together well for successful prints. Here's mama's tried and true copypasta recipe to get you going...
You are having bed adhesion issues. Filament should lay down cleanly on the PEI print surface and hold throughout the print. There are 2 main causes of bed adhesion issues. Even if you're dubious that these are the cause of your problems, they're 2 fundamental troubleshooting steps that you need to complete to rule out the basics:
 
  • A dirty PEI print surface. Even if you don't think this is the cause, it's always a good idea to make sure your PEI surface is clean before trying any other fixes. If it's a smooth PEI sheet, take it to the kitchen sink and give it a good dunk with Dawn (original formula, no vinegar or hand softener variants) dishwashing soap or your local equivalent (e.g. Fairy in UK). Use a clean paper towel to clean it off, and another to dry it. Avoid using any sponge or cloth that has been in contact with grease. Above all else, avoid touching the PEI print surface. Once it's good and clean, you should be able to use 91%+ isopropyl alcohol between prints, 100% acetone when that fails , and another dunk when acetone fails. Worst-case, use a 3M 7445 ScotchBrite pad or equivalent on smooth PEI to give it a very light buff, but only infrequently. If you've got a textured powder-coated PEI print surface, the official instructions are to use 91%+ isopropyl alcohol on it only. Rumors persist that some tribes deep in the jungle have had good luck getting started with these sheets by giving them a wipe with 100% acetone and a dunk with Dawn. Either way, there's no real warranty on these sheets. YMMV.
  • If you have not already done so, try using Jeff Jordan's "Life Adjust" procedure for calibrating your Live-Z setting. It is much easier to use and understand than the on-board routine. It's much easier to make mid-print adjustments accurately with. In general, start high (less negative) and work lower (more negative) in large increments (e.g. 0.1mm) until the filament starts to stick on its own. When you've got your Live-Z setting adjusted properly, you should be able to gently rub the extruded lines on the PEI surface without dislodging them.  Then start lowering (more negative) the level until there are no gaps between layers. 
 
Remember that the effectiveness of a solvent such as isopropyl alcohol is going to depend on concentration and volume relative to the amount of grease you're trying to remove. 71% pads work... on very tiny amounts of grease. A squirt of 91% works better, but if there's a lot of grease, you need a lot more alcohol. This is why the wash under the sink with Dawn is so effective: There's a much larger volume of Dawn-and-water rinsisng stuff away instead of just moving the broken-down grease molecules around.
  
And above all else, avoid touching the PEI print surface.
 
Glue stick is NOT necessary for PLA on the PEI print surface. You paid the big bucks for a Prusa with a removable spring still sheet with PEI, so clean it up and take advantage of it. Save the glue stick for printing sticky stuff like PETG that might adhere too well. Even then, I only find I need glue stick when printing high-temp PETG at 260C+ temps.
 
Try those 2 steps. If you're uncertain of the Live-Z results, post pics here of the 75x75 print bottom and you'll get quick help. If you want more detail, I've consolidated my notes on Prusa PEI adhesion, bed cleaning, and Live-Z calibration
 
A bit of trivia - The reason higher concentrations of alcohol seem to be harder to find is that isopropyl alcohol is most effective against bacteria at roughly a 71% concentration. A  bit of distilled water helps break down the bacterial cell walls. If you're looking in pharmacies, that's why 91% and higher seem to be hard to find.
My notes and disclaimers on 3D printing

and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan

Posted : 10/12/2019 3:52 pm
Pepe le Vamp
(@pepe-le-vamp)
Trusted Member
Topic starter answered:
RE: low acceleration / no jerkyness helps with bed adhesion

i don't quite understand why you're copy-pasting a diary about bed adhesion. i already know to have a clean print bed and do. and i already know how to adjust z-level.

the point of my post was to consider acceleration because the jerky movement is more significant for adhesion than moving in a straight line. you are coming across as patronizing.

Posted : 11/12/2019 6:21 pm
bobstro
(@bobstro)
Illustrious Member
RE: low acceleration / no jerkyness helps with bed adhesion

Reading your first paragraph, you seem to be saying that adhesion is only a question of reducing acceleration. The "student" reads as if bad adhesion is your thing and that this approach is some magical work-around. Nowhere in your original post do you mention the need for proper cleaning and Live-Z calibration. If you meant something else, that was not clear. Apologies.

Reducing acceleration may help to a point, but bed cleanliness and a properly calibrated Live-Z setting are the basis of good adhesion. I think you are trying to say that reducing acceleration will let you print your first layer at higher speeds, which is true ... provided you've met the other conditions. Of course, reducing acceleration slows down portions of each extrusion, so the net gain may be minimal. Actual testing results might be interesting.

The post is indeed cut & paste. The response is intended for anybody interpreting your post the way I did. The approach described is correct and hand crafting a personal response would only increase the odds of leaving something out.

Sorry you've decided to be offended, but that's your choice. I am more concerned about creating confusion and dissemination of bad info. It's not all for you. 

My notes and disclaimers on 3D printing

and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan

Posted : 11/12/2019 10:42 pm
ZombiPach liked
Pepe le Vamp
(@pepe-le-vamp)
Trusted Member
Topic starter answered:
RE: low acceleration / no jerkyness helps with bed adhesion

Ah right. Well you misinterpreted.

"Reducing acceleration may help to a point, but ....."

"I think you are trying to say that..... "

You're still being patronizing. I'm not trying to say that. I said reducing acceleration is an improvement and lets you print at higher speeds. The end. Anything else inhibiting the ability to print at high speeds is a factor and an issue in itself.

Take it as 'hey, reducing acceleration on the first layer is a significant improvement and can mitigate a lot of other factors'. I don't need to mention everything else on earth in addition to what I'm drawing attention to. Take the tip & run.

Posted : 14/12/2019 6:06 am
Jonathan liked
bobstro
(@bobstro)
Illustrious Member
RE: low acceleration / no jerkyness helps with bed adhesion

I can't tell in advance what you're going to find informative or not. Sure, if you have good adhesion to start with, you can get away with higher speeds with lower acceleration and jerk settings. You seemed happy enough to get the information about Cura's variable layer heights. This is a  support forum, so yeah, we tend to explain things.

My notes and disclaimers on 3D printing

and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan

Posted : 14/12/2019 6:12 am
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