The Sandblasting / Air Eraser / Etching thread

[u18b]

The purpose of this thread to is pool information in the way that makes The Railwire the great place it is.

Every couple of months, there’s a question related to sandblasting.  A specific question is asked (as it was a couple of weeks ago) and specifically answered.



I did a search of Railwire and there only appeared to be snippets.  There are some good suggestions here and there, but a person would have to do a lot of searching and reading across many threads in order to find useful information.

So I’d like to suggest that we share information here in one communal thread so that information will be comprehensive and more easily found when searching in the future.  I picked a title which would have a high likelihood of getting good search results for people.

Different people have different equipment, set-ups and practices, so there’s no one right answer.   Let’s just share what works for you- and what didn’t.  For example, I have a fair amount of experience (positive and negative) with etching brass with baking soda and aluminum oxide, but I have zero experience with more gentler substances like beads and ground walnut shells.

So I look forward to getting better because of this thread.

Oh!  And may I humbly suggest that you post your photos to your Railwire Gallery.  That way, the photo is much more likely to be preserved 5 and 10 years from now when someone in the future is looking at this useful thread.

[u18b]

So forgive me for being pedantic, but let’s start with some kind of definitions.

Sandblasting and air erasing appear to be generally synonymous (though they may not be).

In general, compressed air is used to hurl a fine medium at a modeling subject for mostly a few purposes…
--to remove paint
--to etch a material and make it rough.
--we could probably add that this can be used to clean corrosion and oxidation as well.  For example, working with Milwaukee Road EP-2  lead weights that are now 20-30 years old, it is amazing how oxidized they are.  So now, I’m sandblasting the weights to clean them, and then painting them to seal them and prevent further corrosion.
--I also sandblast the shiny wheels of my brass EP-2 so I can then chemically blacken them.   Trying to blacken them without etching does not work as well.
(are there other reasons?)

Removing paint is a bit self-evident.

But etching is designed to make a modeling subject rough so that it will allow paint to adhere better.

BEFORE


AFTER

The modeling subject can be metal or plastic.  For example, I sandblast brass models before painting.  However, when I need to paint plastic handrails, I usually sandblast the plastic handrails first so the paint will stick better since the rails will flex and the paint is more likely to chip off without sandblasting.  The same is true for brass or guitar string handrails- sandblasting causes paint to stick better.

[u18b]

Now right up front- so that a newcomer will read this sooner rather than later, let’s post about danger.

Sandblasting is a health risk and may lead to serious disease and damage other things (like your car paint) since it gets EVERYWHERE.

I’ll be up front and admit that I have been very careless, foolish, and ignorant in the past.  IN spite of a warning label.


I have sandblasted outside, with only an optivisor and no mask.
When finished, I was covered in silica dust- and there’s no telling how much I breathed in.   I have only recently come to see how bad and dangerous this was.

The potential lung disease is called Silicosis.  For some of you this will be old information… but for me it was new.

Here is some important reading for you.  Because of this information, I’m being more wise, and will be building a sandblasting booth (and I’ll be posting about that here too).

https://www.webmd.com/lung/what-is-silicosis
https://en.wikipedia.org/wiki/Silicosis
https://www.cdc.gov/features/preventing-silicosis/index.html

So be wise and careful.

[u18b]

There are several devices that can do sandblasting.

I’ve used two:  Paasche Air Eraser and the cheap imitation by Harbor Freight.  Though designed similarly, the parts are not interchangeable.

Yesterday, I bought a new air eraser from Harbor Freight.

So here are my three.

Top center- Paasche (pretty worn out)
Right- worn out Harbor Freight
Left- new Harbor freight



The reason I decided on the purchase was.... when I disassembled both my Harbor Freight and my Paasche tools for cleaning (the first one they ever had- I think I waited too long.... they were in bad shape).....

I was astounded at the way the blast hole was terribly worn.
In this shot, the tip on the left is brand new/mint.    Look how worn the one on the right has become.



The tip on the Paasche is described as carbide.  Not sure about Harbor Freight.

The Paasche costs in the range of 50-65 bucks at this writing.
The Harbor Freight runs about 29.

However, the HF tool is a use and throw away- since you cannot buy replacement parts (so far as I know).

The Paasche is more expensive, but you can buy replacement parts.



In a bit, I’ll post a disassembly of my HF tool.

[u18b]

Compressed air enters by a hose at the bottom.


It then moves forward and comes out very tiny holes at the bottom of the cup where the medium is housed.




The cup can be unscrewed (notice the black rubber o-ring for a good seal).  Now you can see how air coming from the bottom of the cup fluffs up the medium and pushes it through the larger tube downward. 


The front nozzle can be removed.  Harbor Fr takes a 5/16".


Nozzle is removed along with O-ring.


The cap to the cup has a needle sort of pin with a spring.  You fill up the cup with medium, screw on the cap.... and then your flow is controled by both air pressure and the screw in the cap.

So loosen the screw.  Put the cap on.  Screw the screw down.
Then back off the screw to open the flow until it is just right.

[u18b]

The air control unit is located on the bottom of the air eraser.  The hose hooks up to it.
You can remove it with a 7/16" wrench (Harbor Fr, Paasche is smaller).



The whole thing comes out as a unit.  (a caution is coming)
Used on left, new on right.  Notice the brass pin on the top.   When you press down on the button up top, it moves that pin down and allows air to move. 

Also note the O-ring.



CAUTION:  The Harbor Freight tool has a little screen which will fall out and become an offering to the carpet gods if you are not ready (ask me how I know).  Looks like it's made of tiny BBs.  I can't say in the Paasche has one- if it does, I lost that one too!    )
So work over a table and look for it when you remove the air control assembly.


The little screen goes in a nook in the front side of the opening.



When you remove what I'm calling the air control assembly, you can see a rubber disc in there.  Here is a mint condition one. 


And here is what it looks like after a lot of use.  The screw that holds the button up top presses the rubber down which then depresses the pin on the air control assembly.  But eventually, the rubber wears out and the screw now presses directly on the air control assembly pin.


You can remove the rubber disc now carefully.
Notice it is domed.  The dome goes up toward the button on top of the tool.



You can now remove the screw that holds the button.


You can now clean the air eraser tool.  I had never cleaned mine before, and a lot of grit had worked its way backwards into this air control area.
This made the button stiffer and stiffer and contributed to excess wear.

[u18b]

Now, the air control unit can be disassembled as well.  It has a plunger, a spring O-ring and retaining screw.
But I did not feel a need to disassemble this unit.

Periodically cleaning the new air eraser I just bought and getting excess grit out of the area should be sufficient to keep this unit working better.

[central.vermont]

Ron, thank you for doing this as this is something I am planning on investing in in the very near future.
This is very timely for me!!!

Now you need to do an article on your Nitrogen set up for painting!! 

Jon

[u18b]

Ron, thank you for doing this as this is something I am planning on investing in in the very near future.
This is very timely for me!!!

Now you need to do an article on your Nitrogen set up for painting!! 

Jon

Thanks.  I'll post that tomorrow after daylight photos.

[u18b]

Here is a terrible parts breakdown put out by Paasche.  Very low rez.



I found another one online, but the numbers did not correspond as above.  So I edited the photo to make it match... but... I'm uncertain about a couple of the parts in the valve/ air control area.  So use this with caution.  I included the Paasche original so you can compare.



And then I took a screenshot from a website that sells parts.  Never used them so no recommendation there.  But their parts are well described and match the Paasche numbers- so it was helpful. 

in this image, I combined the screenshot with the edited drawing above.  Once again, I could not match the edited drawing with every last part- so use as best you can.    This is all designed to get you started when looking for information.



And once again.... the Harbor Freight version does not have replacement parts (that I've ever found- they don't even list any in the manual).

[u18b]

Given what I know now, when the new Harbor freight air eraser I just bought wears out in a couple of years, I may buy a new Paasche simply to be able to buy replacement parts. 

[Chris333]

What type of media are you using?

[u18b]

What type of media are you using?

I tried the baking soda route and simply could not get good results.

I switched to aluminum oxide 220 grit and never looked back.

My local Harbor Freight used to stock it in the containers on the right side of this photo.


But they stopped. 
I went through a good bit of the white bottles, but when I could no longer buy it locally, i bit the bullet and just bought bulk- which was actually another good decision.

About 7 or 8 years ago, I bought a 25 lb box from a company in North Carolina.  I think I bought it off ebay.
It's the big box on the left of that photo above.

It's just a heavy clear bag full of white aluminum oxide.


Now, I use what I need from the smaller bottles I held on to, and simply refill them from the bulk box.
And as you can see, I'm getting a bit low.


Maybe by Christmas or some time next year I'll need to buy more.

Here is a search on ebay.  Several results.  The search words that work are:  aluminum oxide 220 blast

If you don't have the word "blast" in there, you'll get a million hits for sandpaper.

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2334524.m570.l1313&_nkw=aluminum+oxide+220+blast&_sacat=0&LH_TitleDesc=0&_sop=10&_osacat=0&_odkw=aluminum+oxide+220

[Mark5]

Now right up front- so that a newcomer will read this sooner rather than later, let’s post about danger.

Sandblasting is a health risk and may lead to serious disease and damage other things (like your car paint) since it gets EVERYWHERE.

I’ll be up front and admit that I have been very careless, foolish, and ignorant in the past.  IN spite of a warning label.


I have sandblasted outside, with only an optivisor and no mask.
When finished, I was covered in silica dust- and there’s no telling how much I breathed in.   I have only recently come to see how bad and dangerous this was.

Thanks Ron, important info to know when considering this process!

Mark

[Chris333]

I need to order some 220. I ran out and bought the next size up at HF and warped some brass.