Sanding Residue - get thee gone!

#1

Hi all, I hope this doesn’t seem like too trivial a question. As I suspect many others do, I use wet & dry sandpaper to remove support nubs on my prints. The removal works well but I often find it difficult to get rid of the pale residue left by the sanding process (presumably fine particles of the paper and/or the resin). Even after brushing under water, usually more than once, when the print dries 9 times out of 10 I’ve missed a bit, and another bit and another and a big bit there and so on. It’s a pain because as soon as the print gets wet, you can’t see the residue, and on large/complex parts it’s impossible to remember where all the problem areas were and there’s no way of telling if all the residue is cleared until the print dries again.

I appreciate the answer is probably just a good soft brush and lots of water, but being metered for water usage I’d rather find a better (and more automated) solution. Has anyone tried a jewellery cleaner or other such “agitative” device? Any other tips?

#2

I think the white residue you are seeing is more accurately the microscratches in the part from the sanding process. Therefore I don’t believe it can be washed away and you are more likely buffing out the fine scratches. Similar to this guide from FL on making gin-clear parts.

The easiest process I can imagine to eliminate the marks is to spray your sanded prints with acyrlic clearcoat from a rattlecan to give it that always wetted look. Biggest downside would be a possibility of losing fine details. (Or if you wanted a matte finish.)

I believe I’ve heard of this being done before so hopefully someone with more than speculation can chime in on the suggestion.

#3

Check your local camera store for antistatic lens brushes. Works great.

#4

The white residue is a combination of both the removed material and the low “specularity” of the abraded surface. You can clean the print with soap and water to get rid of residual powder material, but the surface will still have a reduced albedo. If you intend to paint the model, it doesn’t matter, priming will fill the scratches and the surface quality ought to be invisible with a final coat of paint. If you don’t want to paint the model, you can wipe the abraded surface with some uncured resin and hit it with UV light or sun if that’s all you’ve got, and the surface will “shine up” again almost like new…

#5

For a quick fix if you are using the matte surface resins, are not going to be priming/painting, and the project will not have a food-baring surface, you could try applying Armor All (the stuff you use on car surfaces to seal and protect) on a lint free cloth and lightly buffing it in. It’s low viscosity allows it to flow into the micro-abrasions helping to increasing the “specularity” without changing the surface detail/matte appearance, provides a bit of UV protection, and doesn’t introduce a tacky feel or sticky feel after drying.

  • Al
#6

Hi folks, thanks for the replies. While I’ve certainly seen the abraded (or smoothed!) surface issues, here I’m specifically talking about an actual residue - a fine whitish powder that tends to collect in corners and details where no actual sanding has taken place. I know it’s a physical residue because it does wash from the print with just water, leaving no marks, it’s just that it’s a pain to get it all clear and I was wondering if there was a quicker, more effective solution.

I’m familiar with the issues associated with the actual surface finish, that’s something else.

#7

You can also try canned air to spray out the hard to reach corners once the part dries. That with a small paintbrush is all you need for the dust.

You can rinse with IPA instead of water and it will dry a lot faster for final cleaning.

#8

As a few other users mentioned, this is due in large part to micro scratches and residual powder left on the surface of the part. There are a few ways you can go about correcting this.

The mechanical route is to use increasingly fine grit sandpaper as far as 1600 or 3200 grit. A cloth or cork and Novus polish helps for the final finish. This is the technique we used for the functional camera lenses.

The technique we use most often is mineral oil applied with a micro fiber cloth. The general idea is to apply the oil and then remove as much as you can. This will inhibit painting or other processing techniques afterwards and can wear off over time but it does produce a nice surface finish.

Spray coatings or other epoxies are more permanent solutions but can be a bit more challenging to work with as they will trap any dust left on the part and can be tricky to get an even coating with. We’re testing these now and you can expect a post in the near future but so far, most clear coats seem to work well and we’re seeing good results with the Rustoleum 2X Clear Coat.

#9

Just to throw in my $0.02 I hit the item with sandpapers in order, 200, 400, 800. Then at 1200 I put mineral oil on the item. I further sand with 1200 and 2000 grits. I then soak in IPA another 10 mins or so, dry, then 1200 and 2000 with mineral oil again. Maybe a bit overkill but it leaves me with unbelievably smooth surfaces with no residue and no abrasive marks. What it does to clear is amazing…not quite as comprehensive as the camera lens technique, but good enough for general purposes.

#10

OP seems to be describing something different from what we’re all talking about.

The only thing I can think of is that your IPA is “dirty” and what you’re seeing is particulate resin that’s in suspension in the IPA, that’s then left behind where surface tension allows the IPA to accumulate instead of running off the print.

Assuming that is your IPA has exposure to some UV so the resin that’s been washed off of your prints, that’s dissolved in the IPA, will be cured. Otherwise, it would still accumulate in the corners, but it wouldn’t easily wash off with water.

#11

Thanks kevinduhe, I’ll give the mineral oil treatment a go with the next print.

#12

@Randy_Cohen, the residue is definitely from the sanding process, not the IPA bath. When the models are first removed from the IPA and dried, there’s no residue, it only builds up as you sand with the wet & dry. It’s a common thing with wet & dry - it happens when you use it for sanding vehicle body repairs, etc. It gets all over your hands and the paper itself - I’m a little surprised more people haven’t seen it - I thought sanding with wet/dry was a common practice.

#13

I usually use 400 grit emery paper and wet sand the part. If I need it smoother then I use 4x steel wool and buff the part.
I have one trick where I take the steel wool pad and roll it up in a strip of copy paper nice and tight then use a piece of tape to keep it from unraveling. This makes a nice cleaning stick that is less messy.
If you have a piece of magnetic sheet it will work great as a work pad and collect any pieces of wool that shed. For the most part it will not make your part crystal clear but give you a nice satin finish.

#14

It is common. But the slurry you generate when wet sanding is a fundamental byproduct of the process. I for one thought you were talking about something else. I didn’t understand what you were talking about. Now I do.

No, there’s no way to prevent the slurry. It’s the material you’re removing with the sandpaper, after all. If you’re wet sanding anyway, sand under running water or dunk the part in a bucket of water every once in awhile to clean it off. If you’re dry sanding, then wash the part off when you’re done. I suppose you could blow it off with compressed air, but I’m not sure you want to be breathing a lot of resin dust.

#15

This residue you are seeing is from the IPA bath. You can remedy this by refreshing your IPA more often ; or by rinsing in clean IPA before drying.

#16

Hi @Telemetry3D, as discussed elsewhere in the thread, it’s not a residue from the IPA - the parts are completely clean after the initial IPA wash - it’s a by-product of wet sanding, small particles of the resin itself, as described by Randy_Cohen.

#17

Maybe try cleaning with a water pik or some other higher pressure water jet?

#18

An ultrasonic bath will clear this residue, especially if a detergent is used as this will keep the swarf in suspension in the bath. Ideally the ultrasonic should be used before each time a finer abrasive is used as this will ensure that any detached particles of the coarser grits are removed and not rubbed into the surface.

#19

The sanding dust sticks to the model because of a static charge. Go to the camera store (if there are any left) and get an anti-static brush.

#20

I use mystic sprayer water gun to blast off models
http://www.american-niagara.com/Mystic-01A-Spray-Gun-110volt_p_1486.html