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Prusa 3D Printer Heated Bed Sheet Mileage Replacement

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For those who use 3D printers and maybe wondering what to expect as far as life expectancy of heated bed sheets on a Prusa machine might be. I just had to replace my bed on the Prusa Bear upgraded i3 MK3 3D printer as the bottom layer was slowly degrading with some lifting and voids occurring, not pretty. The bed on this machine had to be replaced after 200 miles of filament. I figure not bad, but the older Prusa i3 with the same bed has over twice the filament mileage, hum. The bed was replaced with a new Satin Powder sheet bed and the results are really nice a few test pieces as compared to the original heatbed steel sheet. Any one have similar /  better / different results??

kgg

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I upgraded the heatbed on mine a few months back as it was not magnetic, it was one that came with the printer and i got tired of changing the PEI sheet. It now has a new magnetic one with a metal poder coated PEI double sided and is going really good up until now. The only thing i miss is the smooth side instead of the rugged one it has now with the new plate. I was thinking of trying a mirror again as this gives a really nice finish if you can get the part to stick! I used a piece of old glass and a small piece of old mirror to test a while back and it worked pretty good but the longer parts would warp and some of the smaller ones would unstick. It could have been the wrong type of glass or mirror?? not sure, i might give it a try again one day again but at the moment the longer/wider parts with a little brim has worked ok.

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30 minutes ago, jimi said:

but the longer parts would warp and some of the smaller ones would unstick

Try a thin coating of ordinary glue stick on your bed to help with the filament bonding to the surface of the glass.

kgg

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21 hours ago, kgg said:

Try a thin coating of ordinary glue stick on your bed to help with the filament bonding to the surface of the glass.

kgg

Yeah i did that Kgg and it did work sometimes but then you loose the mirror finish also on the first layers. This was the point i was trying to use the glass for, to get a good finish on one side.

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4 hours ago, jimi said:

This was the point i was trying to use the glass for, to get a good finish on one side.

What I am seeing in the photo's that could be contributing to your print problems:

1. Not enough extrusion on first layer. We typically run at 105 percent for the first layer to get more squish but not so much to cause elephant footing.

2. Improper "Z" height. I would open your 3d cad software and make and make 2"(50 mm) x2"(50mm) squares. Then make columns and rows on the bed in your slicer and slice them. As each square is printed.... lower "Z" height until the TOP of the square starts to ripple from pressure. Step back to the previous square. Z height well now be as close as it can be before causing ripples.

3. Nozzle Temperature to low. With unheated beds... nozzle temps should be higher.  We don't use std PLA anymore. We use 3D850 and 3D870, which is kinda sorta like PLA but not. With our mosquito head we run the temperature at 240 and on the e3d v6 at 250 (e3d v6).  If you are using std PLA run it at just a touch before it starts to burn. Probably 230. It will flow faster and easier allowing for you to push up your speed (our first layer is laid down at 50 w/ rest at 100  w/ accerleration at 850) and stick better to a cold plate.

With all this said you will NEVER get a perfectly smooth surface like it was vacuum molded. There will almost always be a line (even with 10 percent overlap) from where border and infill patterns meet. To REDUCE it, go with lines not the celtic knot pattern you are using now. It will be less work and faster to print.

What machine are you using and nozzle temperature. The quality of filament (China vs North American or European made) will also affect the print quality of your items. I relate filament to sewing thread where cheap quality equals poorer product and added frustration.

Hope this helps.

kgg

 

 

 

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For what is worth.... I have never had to use tape or glue or any other medium to get a good adhesion on a print. I have always used either glass or mirror and the only problem I have had at times is getting the print to come off without taking a chip of glass with it. This is rare thankfully. I always give my bed a spray with isopropyl alcohol and wipe it in. What I use when I wipe it in does have an effect on the adhesion. Some toilet paper must have more of a starch or something in it and if I use it, it stick like s..t to a blanket and may make it very difficult to get the print off. If I use a chuck cloth instead then the adhesion is way less. @jimi I would try playing with my z height on the first layer until you can get a better connection between your lines. If it looks thin and a bit transparent you are way too close and stand the risk of blocking the nozzle, if it looks like it is full and high then you are asking for adhesion problems for sure along with a rough finish at the end.

A little while back in the paint section at our local hardware store I found this very thin and cheap springy scraper tool . I sharpened the front edge and rounded off one corner and I have found it to be the best by far for prying in under a print job to get it off without any damage.

Edited by RockyAussie

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Thanks for the advise Guys, i am going to try the mirror at one point again when i do more remote plugs as i prefer the mirror finish to the rugged, the rugged seems to hide more my first layer cock ups! :thumbsup: 

On 8/6/2021 at 1:37 AM, RockyAussie said:

A little while back in the paint section at our local hardware store I found this very thin and cheap springy scraper tool . I sharpened the front edge and rounded off one corner and I have found it to be the best by far for prying in under a print job to get it off without any damage.

Kgg, I am using Sakata PETG at around 230-235º and there is a basic/cheaper PETG which i have tried and works just as well, the only difference i can see is the shine (and price). So it is obviously the donkey pushing the buttons that needs to get things together :lol:

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5 hours ago, jimi said:

I am using Sakata PETG at around 230-235º

The filament you are using has a good reputation for a quality product. We have on occasion used PETG but use a lot of PLA+ and really I cant give specifics other then we hate the damn stuff. PLA is stronger but less flexible then PETG (snaps versus bending). It either won't want to stick (when too cool) or stick like S to a blanket when to hot and needs hairspray as a release agent.

This is how we dialed in our printers which may or may not help you with your setup.
1) Design a 2" (50mm) x2" (50mm) by one line height cad object. Then slice it do the bed so there are squares with about 1 inch gaps between them.
2) Dial in Z at temp we run (for example we run 240 to 250c for 3d850 and 250 to 260 for 3d870 w/ bed at 70c. To put this in perspective 3d850 typically is run at 230 and 60. Hotter is better, right up until it burns the plastic. The trick is to stay on the lower this side of burning. The hotter it is the better, as it will want to run together and make for stronger bonds between the layers/lines. w/ zero fan for first 5 layers (further allowing the lines to blend together).
2a) Lower head until you start to see ripples in the top of a square (this means too much pressure and its flow is UPWARD). Then back off by 50 microns for next square. Repeat until it is what you like.
3) Then we re-slice with 105 initial line width and first layer extrusion at 110. We then increase first layer extrusion until it starts to ripple. IF bottom is nearly perfectly smooth we back of z height until it is no longer smooth... and then play with extrusion multiplier vs z height. This will vary greatly from bed to bed and machine to machine. One of ours runs at -1.505 w/ 110% the other is -.985 w/ 130 percent. Or did until those plates wore out and we are now back to square one and have to start again.
4) We then dial in elephant foot compensation - typically "-.4" range so that walls are straight.

Over the next 50 or so prints we then dial it in until its perfect.
Your Celtic knot bottom layers looks good but you will never get perfect bottoms. Jerk and acceleration gets reset when it has to turn or start a line. This faster/slower/faster pattern builds up pressure in the nozzle which causes random bursts of plastic. You want it to start a line and end it slightly inside a wall so that any extra bursts of goop just makes the wall stronger. We run at 850/850 for jerk and acceleration. We run walls and infill (at 98 to 99 percent to allow any small ripples to fill up the micro gaps at the same speed - 100. So that pressure is constant. We run first layer at 50. constant speed means constant pressure which gives you a better chance of dialing in the 'perfect' first layer and every other layer.

Hope the info makes sense,

kgg

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Thanks for the Info Kgg, I will give this a go when i get the plugs up and running again so i might pick your brain further in the future :thumbsup:

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Anytime.

kgg

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