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Spraying questions
Author
Post
PJ

Total Topics: 12
Total Posts: 90
Hi guys - I want to try and improve my finishes. Presently I am spaying KTM 9 with a HVLP gun and a 1.4mm nozzle at 35psi. I've had good results, but this came with a lot of experimenting, and a waste of product. I have not yet succeeded in nailing down a procedure that works well consistently, and feel I can improve. My local store tells me I should increase nozzle size, and spray at lower pressures. I am also considering upgrading my entry level gun to perhaps an (entry level) DeVilbiss. Comment will be appreciated.

May 25, 10 | 11:39 pm
blues creek guitars Authorized Martin Repair Ctr

Total Topics: 52
Total Posts: 1011
It isn't the arrow , it is the indian. When spraying , learning the gun can be as much an art as building. You still have to do your wet sanding and final buff. Also what is your prep schedule ?
More problems start at the prep level than on the finish level

John Hall
Blues Creek Guitars Inc.
Authorized CF Martin Repair Center

May 26, 10 | 2:56 am
PJ

Total Topics: 12
Total Posts: 90
Hi John - here's the prep schedule: final sand down to 240; seal coat shellac; pore filling with epoxy or CA; level with 400 and ready for first coat of KTM9.

May 26, 10 | 4:07 am
Ken C

Total Topics: 30
Total Posts: 554
PJ, would be helpful if you elaborated on what about your process you don't like. You getting orange peel, inconsistent film thickness, runs? We can offer pointers but would be helpful to know specifically where you are struggling.

I don't spray KTM 9, but I spray Target's water-based lacquer with an HVLP Asturo Eco/S. I run a 1.3MM tip with about 20psi at the gun with the trigger pulled and shooting liquid. All guns atomize a bit differently. I would first dig out your manual and see what the manufacturer recommends for pressure. I have a regulator at the gun, but I set the primary pressure at the compressor and take readings at the gun.

Get a scrap board or piece of cardboard, adjust your air flow on your gun for the size of spray pattern you want, then adjust your fluid flow until you can lay down a nice wet spray from about 9" that looks wet but not so thick it runs if held vertical. You may have to tweak the air and fluid knobs a bit until you find the pattern and amount of liquid you are after. For backs and tops, I like a 4" to 6" fan. I make a pass using a nice smooth motion. If I am spraying the upper bout, I may start from the left and start the spray with the gun shooting lacquer into the air left of the guitar. I'll move the gun from left to right and won't lift the trigger until the gun is shooting into the air to the right of the upper bout. I then move back from right to left shooting into the air to the right of the guitar and passing the gun along the guitar overlapping what I previously sprayed by 30% to 50%. When I spray the neck, I'll drop my fluid flow and fan size.

If your spray looks dry, you don't have enough fluid. If it looks milky or sags, you have too much fluid. Note that when you spray the first coat, most of the liquid gets instantly sucked into the wood. This causes a couple of issues. Because your finish is waterbased, laying on a very heavy first coat will really raise the grain, so keep the first coat light. The 2nd issue is you really can't dial in your gun settings until that wood is sealed and you are spraying on a surface that is not absorbing your finish like a sponge.

With water-based lacquers, you really need to watch the quality of your air. Unless you have an oilless compressor, you may need more filtration. I was running just a single moisture trap about midway along my 50' line. This wasn't enough as I was getting small dimples in my finish. I added a small disposable filter at the gun, and the problem disappeared.

Ken

May 26, 10 | 7:32 pm
Adaboy

Total Topics: 64
Total Posts: 509
I have no spray experience so it's nice to read these type posts to learn more about spraying and finishing. Look forward to reading more.

May 26, 10 | 8:01 pm
PJ

Total Topics: 12
Total Posts: 90
Ken - thanks for the detailed reply. I do much the same re your comments adjusting the gun fluid flow etc and have sprayed countless pieces of scrap the get the right mix. My spraying techniques are similar to yours. I have shortened my hose to 5 meters to limit water retention and have a moisture trap at the gun. I rid the compressor of water once a day. The problem I have is that gun is not consistent, and, being entry level, that's where I suspect some of my problems may lie. The manufacturer (for what it is worth) is Fragram although I doubt the gun is available in your part of the world. I didn't get a manual with it. I don't have a regulator at the gun, and take my reading at the compressor. I think that with the short hose pressure falls little at the gun? I seal the whole guitar with shellac before I start with the KTM and normally spray the thinnest coat I can get away with without it looking dry. I filter the KTM pouring it into the cup and clean the gun after each coat with soapy water and denatured alcohol. I have tried thinning it (a spoon of denatured alcohol per cup) but it made no major difference, so for the last application I just used the stuff straight from the can. I have experimented with pressures from 20 - 45 psi and have now settled on 35. My problem is inconsistency. Sometimes the gun gun would spray too dry, and with a next application with the same settings, too wet. Sometimes, even in the middle of spraying a coat, the gun would start spraying to dry. I suspected clogging, but could find no trace of it. I spray in two consecutive days, 4-5 coats a day depending on thickness, one hour in-between.

May 27, 10 | 12:36 am
Ken Hundley

Total Topics: 40
Total Posts: 2169
If you are spraying at a consistent pressure and getting dry-outs, my suspicion is that you are clogging somewhere in the feed, not at the nozzle. Somethign is stopping the liquid from coming out, unless maybe you are using too much pressure.....my uneducated opinion anyway. I haven't developed a consistent method yet myself, but will post it when I get it right.

May 27, 10 | 10:09 am
Ken C

Total Topics: 30
Total Posts: 554
PJ, how are you cleaning your gun? I used to run water through the gun between coats then clean more thoroughly at the end of the day. But this wasn't enough to prevent clogging. Between coats, I'll rinse with water and run water through the gun until the spray runs clear. I then run denatured alcohol through, leaving some to sit in the gun until I spray the next coat an hour later. I'll then shoot out the remaining alcohol and run water through prior to adding my finish. This process will typically allow me to shoot three coats before disassembling and cleaning with denatured alcohol. Occasionally the third coat won't pattern as it should, and as I spray my final three coats, I'll usually clean the gun more thoroughly between each coat to make sure I don't bugger up my finish.

Ken

May 27, 10 | 1:03 pm
Freeman

Total Topics: 27
Total Posts: 668
PJ, my latest was KTM-9 over zpoxy (which is the combination I'll be using in the future)

http://www.kitguitarsforum.com/forum/threads.php?id=5573_0_9_0_C

I shoot with a small cheap detail gun, 1.5 mm tip at about 40 psi. I've got a small home compressor and other than the regulator, only have a simple water filter on the outlet.

The tricone got two pore fill applications with the epoxy scraped and sanded back almost to bare wood, then a total of 15 coats of KTM-9, shot three per day. Each day I leveled to 400 or 600, then shot the next three at one hour interval. One little trick is that I wash my gun with water between each coat, then put some denatured alcohol in it and shoot some into a paper towel, leaving some in the cup. When I'm ready for the next coat I shoot a wash of alcohol on the entire guitar - this will slightly "tack" the surface and the next coat goes on without witness lines (which I would sometimes get with SM water based).

I shoot a medium wet coat, not worring too much about orange peel or sags - if I happen to get one I'll sand it out the next day. After the final three coats I let it dry for two weeks, then leveled with each step from 800 to 2000, polished with medium and fine on a buffing wheel and a little bit of swirl remover.

One comment - LMI sells KTM-9 in 8 oz cans - that is not enough. Half way thru mine I ran out and had to rush order another can - the postage cost more than the finish. I was really worried about witness lines with the three day gap in the schedule but with the alcohol wash trick it bonded fine.

Most of that follows the article by Mike Doolin linked that LMI - Mike used to use KTM-9 and his finishes are spectacular (he now has someone do it in catalyzed poly)

May 27, 10 | 2:01 pm
Freeman

Total Topics: 27
Total Posts: 668
I'll add that while I don't thin the KTM, when I dump the alcohol out of the cup there is a tiny bit left and since it is a small cup the KTM is being thinned very slightly. My gun used to clog sometimes when I didn't do the alcohol trick between coats - it has never clogged since.

May 27, 10 | 2:05 pm
PJ

Total Topics: 12
Total Posts: 90
Guys thanks for that. Ken C - my cleaning process is again much the same as yours, but I take the gun apart and wash it thoroughly with warm(ish) water. What I don't do is then clean further with denatured alcohol immediately after. Just before I spray the next coat, I fill the cup about a quarter with DA and spray that out before I pour finish into the cup. The finish is strained through a filter each time.

Freeman, are you using a HVLP gun? I use a 1.4 mm tip and was thinking maybe that where the problem lies? Ken H - I've experimented with lower pressure, down to about 20psi but consistency still eludes me.

May 27, 10 | 11:48 pm
Freeman

Total Topics: 27
Total Posts: 668
No, I am using an inexpensive syphon type "detail" gun - what a paint shop sometimes calls a "jamb gun". I'm pretty sure it is a 1.5 mm tip. The nice thing about blowing the alcohol thru the gun immediately after you wash it with your soapy water is that water is soluble in alcohol and you will remove any bits of water that might cause rust in the nozzle.

I don't have my copy of Erlewine in front of me but as I recall he recommends 40-45 psi with a syphon gun for waterbased lacquers - I just set my regulator at 40 and never change it (less for the air brush, of course). I set the little bars on the nozzle vertically so the pattern is tall and narrow, and adjust the the neddle so it is maybe 6 inches tall and 3 wide. Set the trigger so you get a little pull to blow air thru the gun then smooth transition to full wet spray. btw - Erlewine does mention HVLP guns - you might want to see what he says about tips and pressure.

My "spray booth" is a cardboard box (an old guitar shipping box) - I've got a rod across the top to hang the git and neck. Before dumping the gun I shoot some of the alcohol against the cardboard to check the pattern, then mist the guitar. Dump the cup into a container (be sure to pull the trigger to drain any alcohol out of the pickup tube on a syphon gun), dump the lacquer in and shoot one more tiny pattern test on the box. Then spray away.

here is the Doolin article http://www.doolinguitars.com/waterborne/instructions.html


May 28, 10 | 6:59 am
Ken Cierp

Total Topics: 58
Total Posts: 2262
Are you using a Zahn cup?

http://en.wikipedia.org/wiki/Zahn_cup

This is a must for consistant results

Also was the gun designed for water borne liquids (all brass and stainless steel) if not it will corrode almost instantly.

The compressor tank should be large enough that it rarely starts during a spray session (a guitar has a tiny foot print).

A pressure regulator at the gun is a good cheap investment when looking for consistancy. $.02

Ken Cierp

Kenneth Michael Guitars est. 1978

May 28, 10 | 7:38 am
Ken Hundley

Total Topics: 40
Total Posts: 2169
You know, one thing I noticed with the cheaper guns was that you either have to make sure the vent hole (if there is one) in the top remains clear and doesn't skin over, or I have had to slightly loosen the cap on the cup once it is tight on the gun. What i noticed was happening was there was no air replacing the lost volume of finish coming out of the gun. Totally forgot about that. Basically end up sucking the finish backinto the cup instead of out the nozzle. Give that a try...worked wonders for me.

May 28, 10 | 11:11 am
PJ

Total Topics: 12
Total Posts: 90
Freeman - I'll have a look at the Doolin article, thank you. Ken C - no I am not using the Zahn, but reckon I ought too. Do you know what viscosity I will be looking for using KTM9? I use a 5hp compressor - it does come on at times, but seems to be able to maintain the pressure I am spraying at. The regulator at the gun is also on my list of must buys. Ken H - that's the one thing I didn't check out, you may have hit it on the head!

May 30, 10 | 11:35 pm



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