Compressor power needed to use Paasche Air Eraser?

[Maletrain]

OK, I bought a Paasche version of the Air Eraser.  I have no experience using these things, so I am working my way through it.  I intend to use it mainly with baking soda to gently remove lettering or paint from models and to roughen things like Delrin trucks to get paint to stick to them.

However, I have a small, nastier job to do first, which is to take the welding scale off inside corner welds in 1-1/2" angle iron, before priming and painting those structural parts.  I have the 240 grit to uses for that, but I don't think I have enough power in my 1/6 HP air compressor that goes with my paint airbrush.  When I hook the Air Eraser to my airbrush compressor, I can pump it up to 65 psi, but as soon as I press the trigger on the Air Eraser, the pressure quickly starts dropping.  Without grit in the cup, the pressure drops to about 22 psi before steadying out.  I don't know if putting the grit in the system would change that very much. But, I probably need to get to about 55-to-65 psi to properly remove the weld scale. 

The Paasche literature is very limited, but does say to use "at least" a 1/3 HP compressor.  But, it also says that Air Eraser uses 0.5 cfm and the compressor I tried says it puts out 0.9 cfm.  So,my problem is that the people writing the various specs seem to be talking "apples and oranges" with respect to cfm, apparently referring to different pressures for their cfm numbers.  I tried calling Paasche, and talked to two people, neither of whom could tell me what horsepower compressor I need to get 65 psi steady through their Air Eraser with 240 git in the bowl. They just seemed to want to sell me the biggest compressor on their product list (which is 3/4 HP).

So, I am turning to you guys for info based on real experience.  Help!

[thomasjmdavis]

CFM ratings vary with pressure.  For example, a 3/4 HP compressor I looked at is rated:
2.4 CFM @ 40 PSI
1.5 CFM @ 90 PSI

If your compressor is rated .9 CFM at 40 PSI or less (.9 seems like a lot for a 1/6 HP at any pressure- might be rated at 20 PSI or some such), then it will supply less CFM at 65 PSI.

Looking at a manual for a D500 https://www.paascheairbrush.com/wp-content/uploads/D500-Manual_English.pdf (closest I could find quickly to a "1/6 HP airbrush compressor") Paasche rates its "working pressure" at 0 to 40 PSI, "depending on the airbrush"- which is to say, the pressure the compressor can maintain with the particular tool attached and in use.  Apparently, for your air eraser, that is functionally 22 PSI. 

My advice would be to borrow a "pancake" or other small construction compressor with a pressure tank and regulator- more than enough air CFM and pressure, plus consistent pressure provided from the tank/regulator, not bouncing up and down as you release or press the trigger on the air eraser.

Additionally, read carefully the safety precautions and make sure you are wearing the appropriate gear- sandblasting at 65 PSI is hazardous duty.

[Lemosteam]

This small device is not really made for rust scale removal.  It simply does not have enough pressure or volume of air+abrasive to do what you want at least from what I see from my air eraser. the contact patch is tiny too.

You might fair better with a wire brush.

[C855B]

This small device is not really made for rust scale removal.  It simply does not have enough pressure or volume of air+abrasive to do what you want at least from what I see from my air eraser. the contact patch is tiny too.

You might fair better with a wire brush.

Quoted for emphasis. My experience with it is the same, not enough power and volume for 1:1-type jobs.

[Chris333]

Welding scale:
https://www.harborfreight.com/4-12-in-carbon-steel-knotted-wire-wheel-60488.html

Definitely wear safety glasses cause those wires do fly off. 

[Maletrain]

Regarding "not enough power for 1:1 jobs":  I have used a grinder with abrasive disk to clean nearly the entire surface, except that I can't get a grinding wheel into inside corners.  So, there I have done the best I can with sandpaper by hand.  What is left is small lines of scale right up against weld beads.  This Air Eraser tool should be able to handle that much area, going by what I am seeing people do with such tools on YouTube.  I want to get the scale lines off before painting, because my experience is that it will cause rusting and paint peeling later if I don't do the job properly, now.

What I need is enough compressor cfm to keep the tool at 55-to-65 psi at the tool's flow rate.  But, the tool's flow rate is not specified along with the pressure at which it is rated, and the flow rate is such that my airbrush compressor, which is rated at 1 cfm at open flow, can only maintain 22 psi at whatever flow goes through the Air Eraser at 22 psi. So, it is a guessing game how much flow I need at 65 psi to run this tool.  Surprisingly, two people at Paasche did not know the answer to that question.

So, I am hoping that somebody has done something like try to run a Harbor Freight Air Eraser with one of those 1/3 HP Harbor Freight pancake compressors and can tell me if that compressor is sufficient for this tool.

[peteski]

That thing is basically an airbrush spraying abrasive medium. I used mine (the Badger version) for roughening the slippery plastic handrails and walkways of older Kato locos, to improve paint adhesion.  As I read here, it can also be used to remove Tampo printed logos and lettering without removing the underlying paint on model shells, and other similar small jobs.

What you are planning to use it for is to me like using a toothbrush to fully scrub a bathtub.  But if you are up for it - have fun!   

[Point353]

What you are planning to use it for is to me like using a toothbrush to fully scrub a bathtub.

Sounds like the sort of punishment meted out in boot camp - except that you'd be relatively lucky if it was a bathtub.

[Maletrain]

I am beginning to think some posters here have a reading comprehension problem.  

My one nasty task for this tool (before I get to using it on N scale models) is to "erase" some thin lines of weld scale.  There are 10 such lines, each roughly 3" long, maybe 1/8" wide.  Somehow, that doesn't seem at all like trying to "scrub a bathtub with at toothbrush."  It is definitely on the same spacial scale as what I will be doing with the Air Eraser on N scale models.

The only issue is how to make the tool put out a stream of grit at about 65 psi.  If you look at YouTube, you can see people using this same tool at that pressure to etch glass and to roughen metal pieces for painting.  So, obviously, it is something other people choose this tool to do.

So, what I want to do is not outside the intended uses of this tool.  It is just that it is outside the design of my small airbrush compressor.  Hence, the simple question: what compressor do I need to get this tool up to 65 psi?  It seems that a lot of people are using very large compressors that the have for other reasons, not something they bought for this particular use.  So, that isn't an answer to my question. 

[Chris333]

I have an air eraser that i use just fine with a small 3gal compressor.

The thing only really works when it is full so you will be stopping to refill way before you run out of air. And the tip will keep clogging.

I have an automotive spot sand blaster that I use on my car, but that was with a huge 60 gal compressor. Also have a big sand blaster that holds about 100 pounds of grit, again big compressor.

Small compressor will be find for the eraser.

[u18b]

I use compressed Nitrogen- which by definition has no moisture.

A widow gave me an oxygen tank that (she had paid for).
I was able to trade it in at a welding company and have been using nitrogen ever since.

A great way to go if you can.

[Lemosteam]

So I use a 5 gallon compressor with a water trap outside that uses a 3/8 line into my basement and reduced to connect to a long airbrush hose leading to a pressure regulator/water trap and then into the eraser line that has an inline filter as well. I keep my outdoor compressor at 80 PSI into the pressure regulator where I can dial the pressure on the regulator down from there.  I have not tried it on rust, or metal yet, but I think that would work.

[Maletrain]

OK, I bought a 1/3 HP compressor with at 3 gallon tank at Harbor Freight, and that worked just fine for what I needed.

Thank you, Chris333, for posting the info that you were able to use that power compressor successfully with an air eraser.

The rest of this post is to pass along the info that I wish I had known from the start, so that others can benefit from what I learned in this endeavor.

While I was at Harbor Freight, I looked at their version of the air eraser, which is almost identical to the Paasche version I bought.  (But it supposedly has a 0.5 mm nozzle instead of the 0.6 mm nozzle of the Paasche.) The Harbor Freight air eraser the box says it has a 4 cfm flow rate at 65 psi.  A compressor that has a rating of 4 cfm at 65 psi is really large.  Getting to 4 cfm typically requires greater than 1 HP and is actually rated at 90 psi for the 4 cfm.  Not what I wanted to get into for one small job.

On the other hand, the "specs" for the Paasche version on Amazon say that it uses "20-75 psi at 0.5 cfm".  It also says "Requires a compressor 1/3 HP or larger that can deliver up to 70 PSI."  The (meager) instructions that came with the Paasche version say "Maximum air pressure 65 psi" in bold type.  A flyer that came with the air eraser says it is "fully adjustable", but it actually has no adjustment ability at all.  The only "adjustment" is how close you hold the nozzle to the surface you are erasing.  So the written material is not really useful.  Even the recommendation for "at least" 1/3 HP compressor is not that reassuring, given the suggested uses at pressures much lower than 65 psi.

The reality is that I was able to get good weld scale removal with #240 grit at about 52 psi indicated while actually using the eraser.  That is with the 1/3 HP compressor and 3 gallon tank pumped to a cutoff pressure of 100 psi and a restart pressure of 85 psi.  The compressor's regulator was set to 75 psi, and the downstream regulator on the moisture trap was set to 65 psi.  The surface scale came right off the weld when the nozzle tip was not even right down on the surface.  It typically took me about 1 cup of abrasive to clean both edges of a 3" long weld line.  I filled the cup about 3/4 full.  I did not experience a single clogging event.  I could clean about one weld without the tank pressure dropping from 100 psi to 85 psi and starting the pump.  When the pump did start while I was erasing, the pump was able to repressurize the tank, rather than allowing it to keep dropping as had happened with my 1/6 HP air brush compressor.  So pressure was not a problem with this rig.

A few exposed slag inclusions were a different story.  They were essentially deep pockets filled with slag/scale material, and it took a heck of a long time to get them mostly cleaned out.  Part of the problem is that the air eraser nozzle needs to be almost contacting those deposits to cut them, and that is difficult to get access to some places on inside corner welds with deep pockets. I had to use several cups of abrasive to get most of the stuff out of those pockets.  (These welds were not really even "sailboat quality", much less "nuclear quality", but they are OK for my purpose.)

So, now my nasty task is behind me, and this tool will be seeing only baking soda at substantially lower pressures to work on my N scale models.  When I get to doing that, I might see if my airbrush compressor can handle it, at its max sustainable pressure of 22 psi with this tool.  However the idea of having another compressor to use outside with baking soda, rather than taking my air brush compressor into that environment, seems like it might be a better idea.