The Daily Beav/Owen Ping - Spray guns.

I've got my lovely new compressor sat in the garage now, & a Machine
Mart gift voucher to play with, so it's time to pick a spray gun. The
compressor's 2.5hp, 50 litre, 12.5 cfm. So....

Gravity or syphon? HVLP or 'normal'? What to avoid, what to look for
etc.

2.5hp looks like it may be too weedy for a gravity HVLP according to
the Machine Mart website - but the quoted figures may be as reliable as
bike manufacturers BHP claims so who knows[1].

[1] Hopefully you do.

--
Krusty
www.MuddyStuff.co.uk
Off-Road Classifieds

'02 MV Senna '03 Tiger 955i '96 Tiger '79 Fantic Hiro 250

 

Does it give you the pressure that the cfm was measured at?

Well, I've got a Sata Minijet 4 for bike related stuff and it was pointed
out to me that I'd need at least a 2hp compressor to drive that[1]. And
that gun is rated at something like 4-6cfm @ 2bar, IIRC.

[1] I actually need to sell a bike first so I can get the compressor in, but
that's a different problem.

 

The best is HVLP, but you may struggle with a 2.5 horse compressor, although
if you're sticking to small jobs, you should just about get away with one.
And it should be gravity. FAR less overspray with HVLP and as a result, less
wasted paint and a cleaner atmosphere.

It IS a bit weedy, but remember, the output is measured as "continuous"
because when a full hit paint job is being done, that's what the painter
will be doing. Painting continuously and he won't want a drop in pressure
part way through. Well not unless he wants an orange peel finish anyway.

For something like a bike fuel tank, a 50 litre reservoir on your 'pressor
won't empty to the point where it's gasping for air. It may be running in an
attempt to "keep up", but it won't run out of gasp. However, something more
you need to know before making your choice.

Air line bore. It NEEDS to be a big ****-off bore to make the best from an
HVLP gun and of course, the fittings to the gun/airline need to be HVLP
specific and Machine Mart don't fucking sell the bloody fittings!.

They sell the more usual PSP fitting, but the bore is slightly smaller and
although they're perfect for JGA guns like wot we used before HVLP (and like
wot I still use for jobs I do at home and you can't tell the difference from
the finish), they're restrictive to HVLP.

At work, the Boy Chic uses either Sata or Devilbiss HVLP gravity guns
running off a 100ish CFM compressor running between 150 and 125psi. It
rarely cranks up when he's painting, but it's huge.

At home, I use a 3hp 'pressor with a 50 litre res running at 125 to 100 psi
using either a Binks JGA siphon gun (Litre pot) or a "Clark special"
(Touch-up siphon fed 1/4 litre pot) and both will be working the compressor,
but not killing it and I've done some BIG paint jobs at home.

For a good finish, the more important thing to look at is the needle and air
cap size. Don't go bigger than 1.4mm for a blisteringly smart looking
finish. 1.6 AT MOST. Forget 1.8mm and 2.0mm is for spraying concrete I
think. The smaller the cap, the finer the spray, the better the finish, the
easier it is to get snotters

If you need anymore info.... well.


--
Beav

VN 750
Zed 1000
OMF# 19

 

That doesn't sound entirely negative then.

Ah, I didn't realise that.

It's mainly for doing the Corvette, but due to lack of space, I'll be
doing a panel at a time. So I guess the bonnet could be the troublesome
panel, seeing as it's so huge. However I'm not after show quality, just
'respectable', so if I have to do half at a time then so be it.

8mm good enough?

Oh great - that I didn't know.

I woke up this morning full of snot & with a few kilos of cut glass in
my throat, so I'm used to snotters.

Indeed. Thanks.

--
Krusty
www.MuddyStuff.co.uk
Off-Road Classifieds

'02 MV Senna '03 Tiger 955i '96 Tiger '79 Fantic Hiro 250

 

Who knows - that'd probably involve reading the instructions!

Not an HVLP then at a guess.


--
Krusty
www.MuddyStuff.co.uk
Off-Road Classifieds

'02 MV Senna '03 Tiger 955i '96 Tiger '79 Fantic Hiro 250

 

Any chance you could explain in a bit more detail? I got a compressor
and spray gun last year, mainly to help repainting all the house
radiators, but I don't even know what HVLP is, let alone how it would
make a difference.

Used it for three rads at the time, the first of which was fine, but
when spraying the others (a couple of weeks later) I was getting a lot
of splatter and couldn't work out why. I've got a fairly decent
compressor with a 100l tank and it happily keeps up to 8bars in use,
so I think it's more down to the gun than anything. Would the dilution
level of the paint also effect this? It's special radiator stuff that
says to dilute by 10%, but it's possible I made the second batch a bit
too thin.

<snip>

I really wish I could understand the rest of your post, but it appears
to be written in some arcane foreign language.

--
_______
..'_/_|_\_'. Ace (brucedotrogers a.t rochedotcom)
\`\ | /`/ GSX-R1000K3 (slightly broken, currently missing)
`\\ | //' BOTAFOT#3, SbS#2, UKRMMA#13, DFV#8, SKA#2, IBB#10
`\|/`
`

 

This bit I know. It's High Volume Low Pressure - meaning the paint's
fired out at a slower rate (but higer volume - duh), reducing
'bounce-back'. Therefore less paint ends up where it shouldn't.



--
Krusty
www.MuddyStuff.co.uk
Off-Road Classifieds

'02 MV Senna '03 Tiger 955i '96 Tiger '79 Fantic Hiro 250

 

I need more info please.
Would this type of item fit your criteria?
http://cgi.ebay.co.uk/NEW-44FT-44-F...7QQihZ011QQcategoryZ30906QQrdZ1QQcmdZViewItem
(shit that's long!)
What size bore? What size fittings?
This is for non-spray purposes, and I might need a long run
eventually to feed my workshop.

Advice please, or sources of info...

Thank you

 

But reading about the job you intend doing, I'd forego the HVLP and go with
a JGA. They're cheaper to buy and if you don't go at the job like a bull at
a gate, the finish will be just as good.

Air pressure and material viscosity are the two variable you don't want to
vary during a repaint, so going with a JGA gun will keep one of them under
control and a good eye will have the 2nd one sorted., so you're minimising
potential problems by going with a JGA if you're using a 2.5hp compressor.
(Check the CFM at spraying pressure too, and that should be around 100psi) A
gun that requires 6.5+CFM may only require that little at 50-60psi, but at
120psi it'll need a damned sight more airflow.

I know, we did a full on body resto of a '76 corvette some time ago. (I've
got the pics of the whole thing if you want to see 'em)

However I'm not after show quality, just

You'll **** up if you try to do half a panel. You need to keep a wet edge to
the paint and if you stop, the edge will dry. If your chosen colour is one
of the cunty one's (metallic silver being the cuntyist) you'll have a line
forever and nothing you do will get rid of it, except repainting it.

Just about, providing the compressor would keep up with an HVLP for the time
it'll take you to paint the aircraft carrier that is the bonnet of a 'vette.
Personally, I'd go with a JGA to reduce the chance of major **** ups.

Neither did I until I bought a couple of air tools recently and needed
fittngs. Tools were got from MM so I went back for the fittings. The tools
are still unused.

So you'll know just how easy they are to sand out without taking off paint
you don't want to

My plesh.


--
Beav

VN 750
Zed 1000
OMF# 19

 

For house radiators, it wouldn't. HVLP is High Volume Low Pressure so you
get a high volume of air for a given air pressure and this makes for a finer
atomising of the medium. Best suited to quite thin medium though, such as
car base coats, rather than chunky shit like Dulux. The "Low" in HVLP is a
little misleading though, because although the pressure IS lower, it's not
*that* much lower than normally used, but there *is* more airflow and that's
what counts. It's also what kills compresors.

Three possibilities. One is too little air. Two, your paint is too
thick/thin and the final one is (you guessed it) shit in the carbs, or in
this case, shit on the needle and cap. Modern guns don't tolerate shite.
They like to be uber clean and they like the paint at the proper viscosity
and the air at the correct pressure.

I've got a fairly decent

Absolutely.

It's special radiator stuff that

Or too thick. Too thin (or too much presssure/too close to the job) and you
invite runs, too thick and it goes on like treacle with nuts in it. Splatter
is usually a mancky gun though.

Arcane? I'm a norverner in I?


--
Beav

VN 750
Zed 1000
OMF# 19

 

Actually that should've been PCL (IIRC, we just call 'em airline
connectors), but whatever they're called, Machine Mart only sell those. Ask
for "Airline connectors" and they'll hand you any number of them.

Perfectly All HVLP friendly AND you get a few spare HVLP fittings too.
Obviously not from MM.

That's not nearly long enough. Believe me. When you've got it home, you'll
wish you'd bought two so you had twice the length.

The airline is 10mm bore and only the tail end of the fittings is different
to suit different bolre airlines. The business end of the connectors are all
the same size. A bit like a balaclava really. One size connects all.

See? I told you you'd want more length. Get two lines and join 'em.



--
Beav

VN 750
Zed 1000
OMF# 19

 

Well, the gun I can be sure of, and the pressure's no problem (my
compressor allows restricted pressure output if required) but how do I
tell if the paint's the right thickness?

I got quite a few runs, so I'm going with the too thin hypotheses. But
How should I check this?

It definitely wasn't manky - I'd made damn sure the needle and nozzle
were both spotless. But perhaps 'splatter' was the wrong word; it was
more that not enough paint was coming out, IYSWIM.

--
_______
..'_/_|_\_'. Ace (brucedotrogers a.t rochedotcom)
\`\ | /`/ GSX-R1000K3 (slightly broken, currently missing)
`\\ | //' BOTAFOT#3, SbS#2, UKRMMA#13, DFV#8, SKA#2, IBB#10
`\|/`
`

 

It should be slightly thicker than milk, but not as thick as the cream on
top. If the paint is thicker, it needs more pressure to suck it up the tube
and blow it out the front, but there's a point where the pressure needs to
be so high that the air bounces back off the job and that's not good. If the
pressure isn't enough to "work" the paint, then it'll go on like treacle, as
mentioned before.

Viscosity first, (see above) then the distance you hold the gun from the job
and the speed you move the gun across the job. And air pressure, never
forget air pressure.

Too thin = an invitation to the runs.
Too thin and too much pressure = a guarantee of the runs and also a room
full of paint mist.
Too thin and too close = a view of Niagra falls and a feeling of sickness.
Too thin, too close and too much pressure = wipe the runs off the carpet.
Too thin, too close AND too slow = the big time shits. And an invite to
start all over again.
Too thin, too close, too slow AND too much pressure = start again and buy a
new carpet, cos it's fucked

Possible air leak as that's generally the reason for the gun not sucking
properly and "spitting" is a symptom. It's tricky finding an air leak in a
gun though, so you just have to be methodical.

The only other thing it can be (given that it's not a mancky gun) is your
viscosity, so check that it's "just a bit thicker than milk". Easy done by
dipping your stirring stick in the paint, then watching the paint slide off.
It shouldn't take forever, but it shouldn't drop off the stick in a
milisecond either. Or you can get a series of viscosity "cups" where you
pour in a known amount of paint in and it takes a particular amount of time
to empty (or at least stop dripping). I have to say it's been a long time
since I used those things, but I imagine they're still available from a
decent paint supply shop/store/house/factor.



--
Beav

VN 750
Zed 1000
OMF# 19

 

Great stuff, thanks. I'll save this post for the next batch I do.

--
_______
..'_/_|_\_'. Ace (brucedotrogers a.t rochedotcom)
\`\ | /`/ GSX-R1000K3 (slightly broken, currently missing)
`\\ | //' BOTAFOT#3, SbS#2, UKRMMA#13, DFV#8, SKA#2, IBB#10
`\|/`
`

 

If you're doing a batch, I'll have two loaves and a couple of doughnuts.


--
Beav

VN 750
Zed 1000
OMF# 19

 

Ah yes, we can't have that...

Did I mention that you'd really want to look at the FAD numbers (Free
Air Delivery) as the normal cfm numbers are theoretical numbers derived
from the compressor's displacement and usually *hopelessly* optimistic?

 

Damn right - slippery slope that one. We'll be asking for directions
before you know it, & that way madness lies.

So my BHP analogy was spot on then? Good stuff.

--
Krusty
www.MuddyStuff.co.uk
Off-Road Classifieds

'02 MV Senna '03 Tiger 955i '96 Tiger '79 Fantic Hiro 250

 

Pretty much, yes. Harder to put a compressor on the dyno and measure
rwhp, mind.

 

As are the figures given of air requirements for HVLP guns. I see "6cfm" and
think "More like 16cfm", and I'm usually right.

I've yet to see one that's even close to the written spec.


--
Beav

VN 750
Zed 1000
OMF# 19

 

Heh. Any experience with Sata Minijets? Do I need three-phase in the
garage because there's no single-phase compressor powerful enough to
supply that gun for, say, painting a tank?