PEI - How to fix scratches and divots

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mhackney
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PEI - How to fix scratches and divots

Postby mhackney » Fri Jul 15, 2016 6:28 pm

I originally posted this in the very long "PEI recap" thread but it is important enough that I'm pulling it out and making it sticky for others to find.

9/19/2016 IMPORTANT NOTE: I've discovered that this fix is not compatible with David Crocker's cool IR Probe. The CA patches have different IR characteristics. If you know exactly where your fixes are located you should be able to either rotate the bed or tweak the probe points in bed.g (in RepRapFirmware) to avoid them.

You've been using PEI for 100s of prints. You love it. Then you get the inevitable divot from removing a part in haste. Or you scratch the surface with a poorly set Z height. Never fear, a fix is here!

Let me preface this by saying I have probably spent more time trying to figure out how to repair PEI than almost anything else I've done on my printers! Why? Because the fly fishing reels that I print and sell require perfection. The surface finish from the print bed is the most highly visible part of these reels so it has to be perfect.

Image

I've experimented for more than a year. I tried dissolving PEI (I won't explain this as it uses very nasty chemicals), melting PEI, filling with HDPE and other plastics, filling with bondo and other polyesters, epoxy, epoxy with PEI dust and the list goes on and on. But, one technique not only works well and is quite easy, it lasts for a long time (I have repairs over 6 months old that are still holding up). How is this minor miracle accomplished you ask? With Bob Smith Industries Medium Gap Filling Cyanoacrylate! I tried many other varieties and viscosities of CA (aka super glue) but this one is sheer magic. It comes in a purple bottle so get the right stuff:

Image

Next, the process...

In order to get the best bond you need 2 elements: absolute cleanliness and a slightly rough surface. I start by sanding the area of the scratch or divot with 400 grit wet/dry sandpaper with water. This is important, don't sand dry or you will never get all of the dust out of the scratch. You can do this with the plate installed on your printer.

Once you've sanded, clean the area with isopropyl alcohol (IPA), the good stuff 100% not the 80% you get at the pharmacy (some pharmacies do carry 90-100% and that is fine). I use a squeeze bottle and flood the sanded area. Clean with a paper towel and repeat 3 times. Now, heat the bed to 50°C and allow it to soak at temperature for 15 minutes to make sure things are good and dry.

Next you apply the BSI medium CA. The idea is to fill the problem area a little proud. I use a straightened out paper clip as an applicator. Put a dab of CA on the tip of the wire and poke it into the scratch or divot. Filet the edges and let it overflow just a bit.

Now the tough part, wait! Seriously, you have to give this plenty of time to fully cure. A good solid 8 hours (overnight).

Once the CA is cured, fold a piece of 400 grit wet/dry sandpaper into thirds. This provides just the right amount of stiffness to sand the high spots without sanding a gouge. Use water and sand gently across the width of the scratch or narrow dimension of the divot. The goal is to knock down the high spot to make it level with the PEI surface. If you go too far or if you didn't put enough CA in the first time, repeat the above steps.

Once the CA is level, switch to 600 or 800 grit and sand GENTLY with water. Finally, clean off with IPA and print!

NOTE: this process is ideal for the matte PEI surface or for those of us who sand their PEI to make it matte. If you want gloss, then you really have to be careful when you sand. And sand from 400 to 1500 grit or so, then polish with a plastic polish and you should be able to restore the gloss.

Cheers,
Michael

Sublime Layers - my blog on Musings and Experiments in 3D Printing Technology and Art

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mhackney
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Re: PEI - How to fix scratches and divots

Postby mhackney » Fri Jul 15, 2016 6:48 pm

And I should add, I've been printing on PEI that has been repaired as described above for over a year and the repair is robust and works great.

Sublime Layers - my blog on Musings and Experiments in 3D Printing Technology and Art

Start Here:
A Strategy for Successful (and Great) Prints

Strategies for Resolving Print Artifacts

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Re: PEI - How to fix scratches and divots

Postby Qdeathstar » Fri Jul 15, 2016 7:33 pm

Placing my PEI order as we speak... nice tip

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Re: PEI - How to fix scratches and divots

Postby geneb » Sat Jul 16, 2016 10:11 am

That CA you got isn't made by BSI, that's just who sold it. :) You can get that stuff at any local hobby shop and it'll have the hobby shop's label on it. :)

You might want to try something called "kicker". It's a spray that causes the CA to cure INSTANTLY. I've used it for years when building R/C airplanes.

I'd also be curious to see how microballons wetted with thin CA would fill those divots... You'd fill the divot with the microballons and then put a single drop of thin CA on it, then kick it (or not).

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Re: PEI - How to fix scratches and divots

Postby mhackney » Sat Jul 16, 2016 4:50 pm

Yeah, I'm an RC helicopter and airplane guy too (in the past). I tried the kicker and as you know it causes the CA to turn white and it gets really hot when it cures quickly. It's best to let nature take its course and not use kicker. I have a LOT of glass micro spheres (hollow and don't ask why I have them!) that would be perfect to try, good idea. That would certainly reflect IR with the IR probe though.

Sublime Layers - my blog on Musings and Experiments in 3D Printing Technology and Art

Start Here:
A Strategy for Successful (and Great) Prints

Strategies for Resolving Print Artifacts

The Eclectic Angler


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