Re: Question about Orange Peel

MR185 - 60-70 deg F
MR186 - 70-80 deg F
MR187 - 80-90 deg F
MR188 - 90+ deg F
MH167 - 60-75 deg F
MH168 - 70-85 deg F
MH169 - 80-95 deg F

If it seems to be in the higher end of a range at the time of painting, I may choose to use the next hotter product. However, I wouldn't go hotter than MR186 at 70 deg. Since I do everything outside and am extremely dependent on the weather, I keep MR186, 187 and MH 168 on hand as the most likely to use. I don't like painting at all below 70 or above 85.

The gun I've been using for all the work on my AC-B so far has been my spot gun. That's an HVLP model so I doubt it's an issue of HVLP vs. non-HVLP. For a spot gun it has a good sized pattern at 4-5" but it's still less than the typical pattern for a full sized gun. I don't think it's an issue of pattern size either. Perhaps I am confused with your use of the term "overspray". To me, that suggests a dry, rough spray rather than orange peel. If your problem is a little orange peel in your "overspray" areas, then you are probably correct although I have not noticed that as a problem as far as any overspray is concerned. I think my own problem with orange peel in the clear resulted from holding the gun too far away and having too fast a travel speed - on a consistent basis. Not getting enough material down quick enough and wet enough to permit the best flowout on the first coat. I noticed it and tried to correct by compensating on the second coat but failed in the effort. I suppose if you are at a poor spray angle, that the overspray that you mention can result in the same effect as being too far from the surface. I have just never noticed it. I would expect the overlap on the next pass, which should be within seconds, to melt it in well - that is unless the next pass is also to far away for some reason. I have not had an orange peel problem with the MTK or even with the MC on any of my AC-B sheetmetal to date, including the gas tank - except that once with the MC on the fender. Anyway, I don't have an answer to your problem.

It would seem to me that no matter how you approach it, transitioning from a vertical surface to an attached horizontal surface (or vice-versa) will result in half the pattern falling on a just painted surface at an angle that is not perfectly perpendicular and therefore a little farther away than "normal".

Another thing I read about not long ago was the recommendation to use a greater than normal overlap for HVLP, in addition to a closer gun-to-surface distance and a slower travel speed. More like 70% (?) than the standard 50% overlap. I have 50% engrained in my thinking and simply continue it with my spot HVLP with no noticeable problem although I do try to get a little closer and travel slower than I am otherwise used to.

My guess is when you go down from a 1.5 tip to a 1.3 tip you will decrease the paint flow rate, assuming the same paint viscosity. I don't think the pattern size will change automatically unless you choke down on the fan control knob. To keep the same application rate with the smaller tip and w/o changing the fan control, you might try slowing down your travel speed a little to see if that helps. You could also try cutting back a bit on the air pressure at the gun (say 5psi), especially with the smaller tip, since less paint per minute means less required air per minute to atomize. If you haven't already done so, you might want to check your atomization and pattern shape by rapidly triggering the gun on and off for just a fraction of a second on a piece of cardboard just to verify a smooth, uniform pattern that does not take on an hourglass shape. I can't think of anything else to suggest.

I can't remember where I read the 70% and I am not even sure it was 70%. But it was greater than 50%. Here's what Dr. Gun at Sharp says:

"Here's a recap when spraying with HVLP

Depending on the brand of spray gun, you will see a wide range of inlet pressures to equal 10 PSI @ cap. Having enough CFM is critical. Spray at a closer distance. Use a faster stroke. Use a higher percentage of pattern overlap. On larger re-spray areas, never use faster than the medium temperature solvents; especially with high solids clears. Low noise doesn't mean slow gun speed. High solids, low VOC does not constitute high viscosity. Spray a balanced gun, i.e.: air to material ratio. The use of HVLP is just what the Doctor ordered. Don't buy it unless you can try it."

The recommendation to not use a fast reducer, apparently even if the temperature calls for it, is a new one for me. I haven't made any changes in reducer selection whether I use my HVLP spot or my non-HVLP full size. The MC161 HS clear that I use doesn't call for any reducer generally but does permit up to 10% retarder (again, if needed). I hadn't had a problem prior to the fender but I'll have to keep that tidbit in mind for a possible try the next time.

There shouldn't be a problem with matching up to and melting in with a pass that was done previously as long as the time is not too long. Think of doing a '60s full size Pontiac car hood in place - w/o touching the fenders with your midsection. You can't get all of it from one side. You have to do it halves from each side - unless you have those six foot long arms :o). That four foot long hood should not be a problem either. Plus it's probably narrow enough such that you can do the entire top and one side from one side if you choose. I just don't think it's the procedural things that are causing your problem - but I also don't know what might be.