Hurricane Mark

Proper air pressure for glass etching using a sandblaster

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I am new to glass etching and I am using a sand blaster. The $180 harbor freight blaster with the modifications you can see on youtube. I lso have a Dust Deputy and a 5 gallon shop vac. I have a 26 gallon craftsman air compressor. I am using 80 grit aluminum oxide blast media.

I am blasting onto glass mugs and using 651 vinyl for my designs.

I have yet to find a proper answer for this after searching the internet so I joined this site to specifically ask this question: What air pressure should I be at with my air compressor to do this glass etching?

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Shoot I only blast with like 35lb pressure on glass. The 80 grit may take a bit more to lift and float but I doubt it. (I use 100 grit crushed porcelain that is now broken down to probably 120ish after many items) 

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I'm usually around 50psi. It really depends on air flow and how well the siphon pickup is working. Different setups will need different setting. The lower the setting you can get away with and still get a good etch the better so it won't rip through the vinyl.

One thing that took me awhile to discover, and made a big difference, on the siphon pickup, the top of it needs to be above the media. If the entire tube is under media you'll get a surge of media, then just air, then another surge.

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And always check pressure before you start.

130psi is not a good starting point.

I used the compressor for something else and forgot to turn it back down.

1: masking is useless.

2: etch is way to deep.

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It can take some playing around with pressure settings to get a good consistent flow of media from a siphon gun like the one in your cabinet sometimes.  Pressure settings can also vary based on blasting media type.  Siphon guns use a Venturi nozzle to lift media up the feed hose until it can be accelerated by the high pressure air stream in the gun.  As a consequence, air pressure inside the gun needs to increase in order to lift larger, heavier, media types.

Given the same media type, a higher pressure setting will also cut deeper and faster than a lower pressure setting.  A faster cutting action means you will have less dwell time available before your media obliterates your masking.  Less dwell time means less detail can be achieved.  As @darcshadow said, the lower the pressure you can use the better.

80 grit will certainly etch glass, but as others have noted, it will give a very rough finish.  I use 120 AO and have been able to achieve an evenly frosted appearance, with good depth of cut, even in relatively small areas of my designs (using 651 for masking).  I'd be curious to see how 220 grit would turn out, and have considered possibly going that route in the future.  70-80 grit blasting media has the advantage of being inexpensive and readily available, but going with a finer grit is definitely the way to go in my experiece.

Don't know if you have done so already, but consider putting a water separator on your setup.  Compressed air can't hold the same amount of water vapor as air at atmospheric pressure can.  The resulting condensate inside your compressor will work it's way through your air hose and into whatever tool you may be using.  When it comes to media blasting, nothing is more frustrating than clumping of media, and clogging of nozzles cause by moisture.  Separators are cheap insurance against that, and are usually installed close to the point of use.  In this case, somewhere inline near your blasting gun, but still outside of the cabinet.

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1 hour ago, Tenfour86 said:

It can take some playing around with pressure settings to get a good consistent flow of media from a siphon gun like the one in your cabinet sometimes.  Pressure settings can also vary based on blasting media type.  Siphon guns use a Venturi nozzle to lift media up the feed hose until it can be accelerated by the high pressure air stream in the gun.  As a consequence, air pressure inside the gun needs to increase in order to lift larger, heavier, media types.

Given the same media type, a higher pressure setting will also cut deeper and faster than a lower pressure setting.  A faster cutting action means you will have less dwell time available before your media obliterates your masking.  Less dwell time means less detail can be achieved.  As @darcshadow said, the lower the pressure you can use the better.

80 grit will certainly etch glass, but as others have noted, it will give a very rough finish.  I use 120 AO and have been able to achieve an evenly frosted appearance, with good depth of cut, even in relatively small areas of my designs (using 651 for masking).  I'd be curious to see how 220 grit would turn out, and have considered possibly going that route in the future.  70-80 grit blasting media has the advantage of being inexpensive and readily available, but going with a finer grit is definitely the way to go in my experiece.

Don't know if you have done so already, but consider putting a water separator on your setup.  Compressed air can't hold the same amount of water vapor as air at atmospheric pressure can.  The resulting condensate inside your compressor will work it's way through your air hose and into whatever tool you may be using.  When it comes to media blasting, nothing is more frustrating than clumping of media, and clogging of nozzles cause by moisture.  Separators are cheap insurance against that, and are usually installed close to the point of use.  In this case, somewhere inline near your blasting gun, but still outside of the cabinet.

I have a $15 husky brand air filter/water separator on it.

Another issue is constant flow of media...i get a few seconds of media then nothing but air...then media...then air..its frustrating. The cab comes with 3 different size nozzle openings...ive used the middle sized one and larger one thus far...they both work about the same with the lack of stead stream of constant media.

 

And suggestions to help remedy that also?

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3 hours ago, darcshadow said:

I'm usually around 50psi. It really depends on air flow and how well the siphon pickup is working. Different setups will need different setting. The lower the setting you can get away with and still get a good etch the better so it won't rip through the vinyl.

One thing that took me awhile to discover, and made a big difference, on the siphon pickup, the top of it needs to be above the media. If the entire tube is under media you'll get a surge of media, then just air, then another surge.

I haven't looked at the siphon placement..i just know I have the bottom of it at the bottom of my pile of media in the cab.

You are saying set the siphon exactly on top of the media?..not an inch or two in it?

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This setup will get you a constant flow of media:

http://www.tptools.com/USA-Cabinet-Gun-and-Pickup-Tube-Upgrade-Kit,2320.html?b=d*8026

 

I have two cabinets, one is the Harbor Freight table top model.  I converted both of them with this TP Tools upgrade and it makes a big difference.

I also blast glass and mirrors at 50-60 psi.  I boost it up to around 80 to do Yeti style mugs.

As for media coarseness, play around a bit to see what you like.  Personally I favor a coarser and deeper etch on glass rather than a smoother frosted look.

To each their own.  Play around and see what you like best.

Cal

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If the media is dry and the gun is surging like you describe, clogging is probably not the issue.

This could be an air to media ratio issue on the siphon intake.  I've found that some siphon setups are more sensitive to this type of problem than others.

I'm completely unfamiliar with the Harbor Freight setups, but here is an attempt to explain what you might be seeing.

Because siphon guns need to lift the media up to the gun, they use air as a carrier; sucking both media and air into the intake tube.  Most siphon gun setups will have a metal pipe attached to the end of the flexible intake tube.  The design of the metal pipe can vary, but most I have seen look like they are double walled, having a smaller pipe secured inside of a slightly larger pipe.  Media is sucked up the bottom, while air enters the top of this assembly (see diagram below).  If the flexible tube is pushed down onto this assembly too far, it will cover the gap needed for air to enter the top of the larger pipe, which can cause surging.  This is also the reason why @darcshadow was saying the top needs to be above the media.

This type of assembly isn't very adjustable, other than moving the flexible tube up or down on the metal pipe to change the air intake gap slightly.  In other designs, the flexible tube can be moved up or down to cover or reveal air vent holes.  

siphon.jpg.045de175a2354c465726a87f3ed9dad3.jpg

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This was done at 40 to 50 PSI using what looks like 80 grit. Some kind of titanium mix from the Canadian TSC. I actually wanted the deep etch on this one.

651 held up no problem on the small letters.

20171123_121642.jpg

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