Why can't you just cast in black ABS from the start?

Dan - Owner
http://www.Hi-TecDesigns.com

Ream before painting to a plus tolerance with paint allowance? How precise does it have to be?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

If you must paint, and you must paint before reaming, what about a hot reamer? Basically, melt the plastic rather than make chips that the paint peels with.

Dan - Owner
http://www.Hi-TecDesigns.com

They have to pretty precise. We use it for inserting goldman inserts. the inserts are also plastic and they are press fit. So it can't be too tight nor too loose. The paint finish has to be specific flat black matte due to some functional requirements. Black abs can't do that. I will sure try your suggestions. But I was thinking more like an appropriate paint or painting pre/post processes.

Thanks again.

Something just occurred to me. The plastic part is Soda/sand blasted before priming. Obviously they are cleaned before the primer is applied but could there be static stored? Could that be a reason why the paint doesn't stick properly. In all honesty the paint finish on the surface is all good before I use a reamer. But after I use a reamer it chips near the hole entrances. We are also going to perform scratch tests on the paint surface to see if it is just there or everywhere.

But just thought may be the ABS has static stored which no matter the surface prep attracts dust and this dust accumulation can lead to flaking and peeling during any post processes. I do understand that the next thing everyone may say is don't do post processes on painted plastic, trust me if I could do it any other way that does not involve 200 holes to be manually done each time I would do take it. Also the precision has to be spot on.

Hence trying to find what the problem in current process. Static? Anyone?

Is this for an LED integration sphere?

Dan - Owner
http://www.Hi-TecDesigns.com

Since money is spent pre-treating the ABS for painting and the painting is there any chance you can skip painting and instead sand blast or perhaps etch the ABS to reach your matte goal? I've seen some reaaaaally BLACK ABS.

I used to go thru conniptions getting Input Output Controllers (IOCs) 14x6x4" metal enclosures painted correctly and reliably in a reasonable amount of time. I finally hit upon just getting them electro-zinc galvanized. All the problems went away the customer was happy and it didn't even cost as much.

Keith Cress
kcress - http://www.flaminsystems.com

Can you not 1) blast, 2) ream, 3) mask reamed holes with silicone plugs or similar, 4) paint, 5) assemble?

Alternatively, what paint are you using? Simple acrylic paints rated for plastics (Krylon has one) ought to adhere pretty nicely.

Finally, if none of the above work for one reason or another, try sanding the painted edge of the hole with a tapered stone or similar prior to reaming. Like one of these

http://www.mcmaster.com/#4257a69/=13fr9ki

but mounted in a holder and turned by hand, or in a fairly low rpm motor tool.

Macgyver - Yes

itsmoked - yes those are the next options that are to happen if we can't fix the existing ones

btrueblood - they are vaccum formed abs with only post processing being holes. Yes its a simple acrylic flat black paint that never caused any problems before this! The edges cannot be chamfered and blasting is something I am very skeptical about at the moment due to the finish requirements. But if nothing works I shall consider it. But I will consider a different reamer to what we have now. Thanks for the tip.


The painting process did not have an issue till recently when we changed the supplier due to a fallout. And the new ones can't seem to get it right. Hence I thought it could be pre-processing set up issues or like I said before static or the cure temps are not properly followed.

"The painting process did not have an issue till recently when we changed the supplier due to a fallout. "

Ah. Painting processes are often a black art, you just opened a can of worms my friend. Check coating thickness, if possible, from old parts to the new ones. And yes, static may either help or hinder the painter in getting the coating to go down with a proper matte finish, which may explain different thicknesses in the coatings. Also, temperature differences may play a part in causing crazing (micro-cracking) of the paint. See if the paint booth is fairly well temperature controlled, and whether the parts are drying in similar temperatures, and for similar durations. What temperature are the parts at when you are doing the reaming operation (warmer should be better). Past that, the chemistry of the paint and thinner needs to be controlled to help a) provide good adhesion (usually more solvent is better here), but b) not cause crazing of the styrene content of the base polymer (too much thinner causes this). What thinner are they using, and what dilution ratio. Try switching to a "hotter" (higher vapor pressure) solvent if possible. You might look at the base polymer, and see what the styrene content is, and how well controlled it is; if possible to switch to lower styrene content, it could help.

Can you not ream, install the inserts, and then paint, again using a suitable masking plug if necessary, or paint with masking over the reamed holes, then install inserts (asked before and not answered).

And that's just from a few minutes of thinking about the problem, it might obviously be one of a myriad of other issues.

Thanks btrueblood - You know how hard it is to implement the changes, going through everyone above me. I had thought about reaming prior and masking but since they reckon its been working this way for years and now all of sudden when we changed the painter there are issues hence only the way it is painted is incorrect is what everyone seems to agree for now. (me too) So just thought I'll try the other things first.

I guess we will soon find out.