Failing Mirror Suface after cleaning - WARNING

Ive logged a ticket on this with support: Few weeks ago I cleaned all the mirrors as advised by support with 99% IPA and PEC pads and the printer has ran fine through 2L of resin. On my last run, I started to get failed messy parts so inspected and (dust/oily) gave the main mirror another clean. I could see these little odd coloured spots so appear during cleaning and I attempted to remove them thinking that these were oil residue. After a few passes I look and see a big area of damage. Looks like the top surface of the mirror has just eroded completely on one of the spots. I have been very careful the whole time and followed the exact instructions provided and was very cautious of causing damage. I have some very expensive camera equipment so have a decent idea of what not to do. I ran a test print and the parts came out messy or broken. I’ll await response from support, but the mirror has definitely had it.

Keep an eye out for this spots, they look golden in colour.

1 Like

@LeeFields I had this before as well but not such a big spot. I guess formlabs calls it abletions. To that time when that happened formlabs advised to use kimwipes so I thought it had something to do with it. After the last repair on my printer I never touched the mirrors directly so I got no oil. Only a bit of dust that can’t be avoided. The worst thing I ever did was to use compressed air. This made me using 99,9% IPA to get rid of the oil. The mirror was as clean as ever before but then I noticed the abletions. The mirrors are extremly sensitive. Have you used some different cloth or cleaning spray or anything else? If its the alcohol we have a problem I think. What if the violett laser reacts with the alcohol or another cleaning solution and leaves burn marks ( abletions ).

BTW… I can see scratches on your mirror like you were wiping in circles with the pec pads. Did you blow the dust particles away from the mirror before you wiped on the surface around? Could it be you got the scratches from particles beeing in the pec pads? Maybe this made the surface brittle?

Ive only used PEC pads and 99% IPA alongside a manual optical blower and have been incredibly careful. The scratches were on there when I got the unit back after a + upgrade when the first unit died after 2 weeks of receiving. After I change out tanks, which has been a couple of times since the first big clean up a few weeks ago, I inspect the mirror before sliding the tray in and start a print. I always saw the odd bit of dust which I blew or gently removed with the corner of a dry PEC pad until totally clear. I had clear print after print doing it this way along with massaging the PMS and filtering my resin a couple of times during colour/resin changes. That damage came on incredibly fast. Quite literally there was no damage at all a few days ago on the last check and i noticed some residue build up that needed and IPA clean. Here is a print after the damage occurred. Lots of very thin outcrops of cured resin whereas there are no actual structure failures or bits that you would associate with dust refraction.

Ive just done a heap of research on first mirrors and I think we have a problem. Cleaning more than once in a year is a bad idea and using circular motion as a bid no. Also, 100% Acetone apparently is what should be used as it deals with oil quicker and less wiping (=less damage). This information and lots more that have me nervous was obtained from astronomy forums from guys who have very expensive mirror based kit. Basically, our machines need to be regularly cleaned but no matter what we use, we cause damage each time we clean. And, we do need to clean. I mentioned this before, but really our optics should have been designed inside a a sealed unit with an optical window. I don’t see how this machine can be sustainable for any real use…

At the moment my printer works but I am feared of the day it needs to be cleaned. My small mirror near the galvo mirrors got some oil and there is a very tiny spot on the printing area that fails to print. Until know I was able to position the models out of this area. I don’t know what happens if I print one big model that can’t be repositioned. If acetone deals better I would like a reply from formlabs to that! Against the official suggestions of cleaning the first surface mirrors by formlabs there is another statement: “As to the first contact polymer, yes you could use that. It does indeed
work very well. I’m not sure how much the polymer costs, but it may be a good investment to have on hand. It’s much easier using the polymer than the PEC pad method.” I asked the support out of the forums if “first contact polymer” can be used. ( ) If I read which problems you are going through although you did nothing wrong I guess it might be the only solution. I wouldnt be surpised if formlabs will be advertising this FCP with their branding on it some day :smiley:
What do your astronomy guys say about this polymer?

I suppose it all boils down to whether polymer or Acetone breaks down the Formlabs resin enough to actually clean. I have some acetone, ill run a small rest. Not on my mirrors obviously.

Yup, Acetone breaks down the resin just fine. I don’t have anything that would mimic a first mirror to try in on to see if it takes care of smearing. The guides do say you need 100% grade Acetone, i don’t know what level I have. One major thing though is that Acetone will eat through paint and metal coatings so you have to be very car full with it incase it touches something and drags it onto the surface


Support have got back to me very quickly and are sending me a new mirror to instal which gives me my old damaged one to run some tests. Turns out i have 99.5% acetone and as in IPA, its that last 10% thats the important part. I’ll try a few things out and post here.

cool mate! My mirror was replaced by formlabs but I would like to know how to replace it! Can you give me some hints how to replace it later or show me some pics?

@MarcusKnorr I pinged the people working on your ticket and we’ll get you the instructions right away!

Just to clear it up a bit, only PEC*PADs should be used on the Form 1 and 1+ mirrors. We’ve tested many brands and have determined that these don’t cause microscratches or other damage to the mirrors if used properly. We now have a support article up detailing the best way to clean the mirror here:

@LeeFields If you have any interesting findings please let us know! We always like hearing about this kind of thing. :smile:

1 Like

It seems that a lot of the mirror issues stem from the fact that the beam is extremely tight and stays thin to the target. On other lasers, where they are used for burning things, they are put through a collimator to get a wide parallel beam then focused back down to a point. In theory, that should mean that individual specs of dust shouldn’t cause a catastrophic failure like the thin beam method can. I guess the issue with that theory is that the beam would focus in more of a sphere from the galvos, so it would need a special theta lens or special mirrors to compensate for that. I wonder if another optical means of doing the same thing might be possible. The result would be that the laser could still function well even with a few specs on the mirrors.

Another train of thought is to allow the mirrors to easily be accessed for replacement or cleaning. CO2 lasers typically have easily interchanged lenses and mirrors.

I’ve had a lot of success cleaning my main mirror (never touched the galvo mirrors myself). I’ve gone from 100% success to 0% success back to 100% and up and down over and over again.

That being said, I feel like the main mirror should be a consumable and should be sold. I know one day, my luck cleaning the mirror will run out and I’m highly suspicious Formlabs is going to leave me out in the cold.

Replacing a mirror is simple - all you need is a suitably sized surface first mirror (eg 150mm square) and a 5.5mm socket wrench with a universal joint.

In the UK I found this mirror for £34 - which I bought and have tested several times while debugging my printer during the various issues it’s had, It works perfectly.

The Form1 mirror is glued into a bracket that’s bolted into the machine frame with a couple of machine screws, you undo two nuts with the socket wrench and the mirror and bracket lift out easy as you please (having first removed the the top half the form1 and the front panel by unscrewing a bunch of hex screws with 2.5mm hex key) .

The replacement mirror will then slot into the same position - although obviously without the bracket it won’t be locked in place, it just lays in position under it’s own weight - so you have to be careful moving the machine.

Here’s a pic of the type of wrench you need…


Very useful. Support has been great and I’ve received the mirror (within 4 working days), so once I’ve had the old one out I’ll keep you guys up to date. Im toying with the idea of designing and printing a frame on my Ultimaker to take a section of optical glass with a vue to protecting the mirrors from dust and crap getting in there.

I bought a second hand form1+ and the prints so far have not been very successful. Upon inspection I’ve noticed these marks, similar to the ones you have on the main mirror. I’ve tried using IPA 99.9% and the pec pads to try and clean the surface but no luck so far. So is this a mirror problem itself? not a stain/oil problem I gather from this post. Does this mean the only way forward is replacing the whole mirror? I have sent a support ticket to formlabs. They are only visible in some light.

Yes mate, that mirror looks ruined to me. It’s a first contact mirror so the slightest pressure can damage it which means you cannot vigorously rub at marks like that as you will scratch the mirror. You may want to contact the seller and ask for a slight refund to cover the replacement cost for a new mirror, or try your luck with a free replacement from formlabs.

I just gently wiped the dust off my large mirror with a pecpad using a slow down to up motion. Again very gentle pressure. Just did a print and it didn’t stick to the build platform but pancaked to the bottom of the tank. Can doing something to the mirror cause this? On inspection the mirror looks immaculate. Though the model I was printing was large and had thick walls.

Also not sure it its anything to do with the model as it would have at least printed the base?