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Old 28th January 2008, 04:23 PM   #1
samtny is offline samtny  United States
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Default Fix spray paint run on MDF box?

Hi all,

Still finishing up my very first project, the Zaph ZBM4's, which are coming along pretty nice. However;

I accidentally got too close with the Krylon enamel spray last night, now I have 2 *very* faint runs on the face of one of my baffles. Everything else looks perfect, but the runs are very distracting IMO.

Am I taking the correct approach by waiting 24hrs, and then sanding with 220 sandpaper, and then re-spraying with the enamel? Will this get the runs out, or am I making my problem worse?

This is a matte black enamel, btw.

Any advice much appreciated,

Sam T
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Old 28th January 2008, 06:16 PM   #2
Bobken is offline Bobken  United Kingdom
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Hi,

Yes, so long as you carefully sand out the slight ripple due to the 'run' and the substrate is quite flat again before any repainting, another coat of paint on this should obliterate the unwanted effect, especially with matt finishes. It is best to wrap the sandpaper around a flat (wooden?) block when sanding out runs, as you need to reduce the 'step' around the edge of the hardened run, and not remove paint from elsewhere. Check progress with a good straight-edge until there is no step.

If it helps to know, you are less likely to end up with runs like this is if the panel being painted is laying flat down on the bench. Runs are more prevalent when the panel is vertical as gravity encourages this problem which is due to an excess of wet paint in one area, of course.
You do need to be more careful that nothing (like drips or whatever) falls from the spray gun when panels are being painted horizontally, but you can add many times more paint in one pass without a run forming, as the excess paint tends to level itself out, rather than running anywhere.

What did you do about the tweeter step in the end?

Regards,
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Old 28th January 2008, 07:09 PM   #3
Thawach is offline Thawach  Thailand
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hi bob


I have a problem very much when i paint black piano color.

It's not smooth. do you have any pictures? it's easy to understand.

Thanks

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Old 28th January 2008, 07:20 PM   #4
peter_m is offline peter_m  Canada
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How do your ZBM4s sound? Have you crossed to a sub, if so a what freq?

Regards,
Peter
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Old 28th January 2008, 09:15 PM   #5
samtny is offline samtny  United States
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Quote:
Originally posted by peter_m
How do your ZBM4s sound? Have you crossed to a sub, if so a what freq?

Regards,
Peter
Will letcha know soon as I try them out! For various reasons I haven't tried the drivers inside the enclosures yet, only tested separately with my crossovers to be sure they worked. I will be crossing to a Dayton SUB-100 10" sub, nothing heavy-duty, but I understand the ZBM4's benefit from a little help on the low end.

Bobken; thanks for the great tips, I'll put them to use tonight! Oh, and regarding the tweeter step; I carefully sanded around the *backside* of the baffle to remove enough material to let the tweeter sit a little deeper. Then I chamfered the edge on the front of the baffle just a tiny, tiny bit with 220 grain sandpaper. The combination of the two makes a smooth transition between flange and baffle, though this is still not "flush."
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Old 28th January 2008, 09:47 PM   #6
Bobken is offline Bobken  United Kingdom
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Quote:
Originally posted by Thawach
hi bob


I have a problem very much when i paint black piano color.

It's not smooth. do you have any pictures? it's easy to understand.

Thanks

Hi,

Unfortunately I don't have any pictures which I can show, and I haven't done any spray painting for a couple of years. In my time I have sprayed cars, boats, speakers and all manner of things, and it is an excellent way of obtaining good results compared with using brushes etc.

Techniques for actual spraying haven't changed much in over 40 years though, except that nowadays low VOC is much preferred for environmental reasons, and sometimes (often) this relies on chemical action to set the paint, instead of air drying.

It is harder to get a really top quality finish with any gloss (shiny) finishes as any slight discrepancies show up as the natural light falls differently on the surface and reflects the marks. Black and other very dark colours are the worst to get a very good finish with, but it can be done with the right techniques. You will probably need to spray a heavy coat of paint in all, and then rub this down flat with fine rubbing paper (wet & dry) and then bring the polish up again by burnishing with rubbing compound and then fine abrasive polish. This will provide a very flat, smooth and shiny finish, and can look just like glass when done properly, but it does require quite a lot of work.

What is the problem with the results you have seen so far?
Is it what is known as "orange-peel" which as the term suggests is where the surface isn't smooth but has a lot of little bumps all over it?

If you can describe or show a pic of the results it would be easier to offer some worthwhile advice here.

Also, Shinobiwan (one of the Moderators) had some excellent pictures and descriptions of his results a couple of years ago in a very long thread on this Forum which described his techniques and type of paint he used, IIRC. I am sure that it would be of benefit for you to look up that thread as he was not a long-term spray painter when he started with this job, but he went through his techniques and how he learned about spraying, and he ended up with some excellent results on his speakers.

Regards,
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Old 28th January 2008, 10:24 PM   #7
Bobken is offline Bobken  United Kingdom
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Hi samtny,

I don't think that you will regret doing the mods for the tweeter, and at least it is 'fail-safe'. There is nothing more aggravating than needing to strip everything down again to correct something like this at a later time, if you do hear any problems.

At least you now know for sure that you have the done the best possible thing here, and I am sure from what you describe that you will not suffer from any diffraction effects.

Regards,
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