Sandblasting questions

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lmartine
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Sandblasting questions

Post by lmartine »

Hi,

I asked Santa to bring me a benchtop sandblasting cabinet this year ( :D ).

In reading about these cabinets, I found websites that mentioned that I also need a dust collector while others made no mention of that. Is it really necessary?

Furthermore, there is only one supplier of brown aluminum oxide in my neck of the wood, and he sells either 100 or 150 grit. Is 150 grit acceptable or I really need to purchase the 120 grit (a 250 km trip...) that is mentioned in most of the posts on this board? I only want to sandblast to get rid of stuck KW or fibers when that happens.

Cheers!

Lucie
charlie
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Re: Sandblasting questions

Post by charlie »

[quote="lmartine"]Hi,

I asked Santa to bring me a benchtop sandblasting cabinet this year ( :D ).

In reading about these cabinets, I found websites that mentioned that I also need a dust collector while others made no mention of that. Is it really necessary?

Furthermore, there is only one supplier of brown aluminum oxide in my neck of the wood, and he sells either 100 or 150 grit. Is 150 grit acceptable or I really need to purchase the 120 grit (a 250 km trip...) that is mentioned in most of the posts on this board? I only want to sandblast to get rid of stuck KW or fibers when that happens.

Cheers!

Lucie[/quote]

you'll find that it's much harder to work in a cabinet without a dust collector, but it can be done. a cheap shopvac with a hepa filter will do, but expect to replace it often as the dust will burn out the motor.

the 100 will quickly break down and become 150 after a few uses, and eventually break down and become 200, 300, and dust. the larger the grit, the more quickly you have to work and the larger the pitting is on the glass from the sand hitting it. that means you may have to go a bit hotter to get the glass to even out or become matte, whichever you're aiming for.
lmartine
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Re: Sandblasting questions

Post by lmartine »

Thanks Charlie!

Would this dust deputy (http://www.leevalley.com/en/wood/page.a ... 42401&ap=1) be a preferable to a HEPA filter? And I suppose that the shop vac has to be dedicated to the sand blast cabinet (that is, I can not 'confiscate' my spouse's for that purpose when I need it...).

Sorry for all the likely 'basic' questions. Really appreciate your two cents!

Lucie
charlie
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Re: Sandblasting questions

Post by charlie »

[quote="lmartine"]Thanks Charlie!

Would this dust deputy (http://www.leevalley.com/en/wood/page.a ... 42401&ap=1) be a preferable to a HEPA filter? And I suppose that the shop vac has to be dedicated to the sand blast cabinet (that is, I can not 'confiscate' my spouse's for that purpose when I need it...).

Sorry for all the likely 'basic' questions. Really appreciate your two cents!

Lucie[/quote]

this is not a dust collector. this is a cyclone separator, which takes a lot of the larger particles out of the airstream, and still requires you to have a shopvac. you would then need a hepa filter on the shopvac to remove all the ultrafine submicron particles, which are the real killers.

a woodworking dust collector doesn't, by default, have a fine enough filter on it for sandblasting work. you can use one, but you'll have to replace the dust bag with a finer filter.

here's a real one: http://www.mscdirect.com/product/09118878

if you're only using it a few minutes/week, i'd go with the shopvac/cyclone/hepa. if you're blasting hours or days/week, you need something more.
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Re: Sandblasting questions

Post by Brad Walker »

The dust deputy is not a HEPA filter, it's just a system for collecting large particles (usually sawdust) before they get to the vacuum.

Best to get a vacuum of some sort -- even just a regular shopvac -- and add a HEPA filter. As Charlie mentioned, the shopvac will eventually wear out because the motor is not as well shielded from abrasive dust as a good vacuum specifically made for sandblasting.

Tony Smith's website has some great basic information about sandblasting: http://blastedglass.com/sandblasting/in ... ginfo.html
DonMcClennen
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Re: Sandblasting questions

Post by DonMcClennen »

My suggestion is: go with the 100grit..... And try without dust collector/vaccum. I've been surface sandblasting (to prepare for satin finish refiring) for years with no dust control. It only takes a few minutes rest every 10 min or so to volume is clear enough for visability. Youv'e got nothing to lose by trying! Just let dust settle before opening up to remove glass.
Don
"The Glassman"
desjo
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Re: Sandblasting questions

Post by desjo »

If I may, let me ask a follow-up question to Lucie's. If looking to use a small cabinet for intermittent and light use as she mentions, what is the minimal size air compressor that would meet that basic need? Does it work well to use a smaller tip on the gun to help minimize air consumption?
Kopperwood
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Re: Sandblasting questions

Post by Kopperwood »

I use a cyclone in front of a small shop vac, it's been running for years that way. I think the cyclone does a good enough job of cleaning the air before it gets to the vac motor, to save its life. Also, the shop vac is actually outside, just knocked a hole in the wall to run the hose thru. If that is not an option, just attach a hose to the blower side of the vac (only works if it has a blower port) and blow it out a window. If you only have occasional use, should work well. With it vented outside, you don't need to be concerned with a HEPA filter, the dust that gets thru the filter goes outside and a regular filter is fine to protect the motor.

Perry
charlie
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Re: Sandblasting questions

Post by charlie »

[quote="desjo"]If I may, let me ask a follow-up question to Lucie's. If looking to use a small cabinet for intermittent and light use as she mentions, what is the minimal size air compressor that would meet that basic need? Does it work well to use a smaller tip on the gun to help minimize air consumption?[/quote]

did you read over tony's site? he makes recommendations as to minimum sizes.

http://blastedglass.com/sandblasting/pr ... cument.htm

a smaller orifice gives you more blasting time at lower pressure, but it takes longer and you can't do widespread areas as easily. also, as they wear, the orifice gets larger.
desjo
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Re: Sandblasting questions

Post by desjo »

charlie wrote:
desjo wrote:If I may, let me ask a follow-up question to Lucie's. If looking to use a small cabinet for intermittent and light use as she mentions, what is the minimal size air compressor that would meet that basic need? Does it work well to use a smaller tip on the gun to help minimize air consumption?
did you read over tony's site? he makes recommendations as to minimum sizes.

http://blastedglass.com/sandblasting/pr ... cument.htm

a smaller orifice gives you more blasting time at lower pressure, but it takes longer and you can't do widespread areas as easily. also, as they wear, the orifice gets larger.
Thanks, Charlie. I did read Tony's excellent overview. I should have been clearer, instead of minimum I was asking in regards to bare minimum. In my case I have a 15 gallon, 2 hp, 4.8 cfm compressor. As with Lucie, I'm looking at just occasional and not intense use. Has anyone found that a smaller compressor works sufficiently if you blast for a short minute or so and then let the compressor catch up, etc. I know small compressors are not meant for continuous duty but might handle my needs if only used on occasion. I wouldn't want it to only allow for very short blasts. Thanks!
Buttercup
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Re: Sandblasting questions

Post by Buttercup »

For the walk-in booth I have a 7.5 HP compressor. For dust collection in the booth I set up a temporary solution four years ago which I confess I'm still using. It may not work in all climates or situations. The 'temporary solution' is an ordinary pedestal fan available at Home Depot, no doubt, for about fifteen dollars. It points out a window which I open when blasting. It sucks air from the booth which blows the airborne dust out the window and disperses it across the acrerage. It is far enough from the end of the booth where the rack is and where the grit exits the gun for the good reuseable grit to fall to the floor of the booth for recovery. The dust which remains airborne gets drawn out the window. I wear an air-supplied hood. Visibility in the booth is excellent and the booth is dust free within a minute of finishing blasting.

When I lived in a colder climate the booth air was evacuated through a dust collection system powered by a furnace fan.

For the cabinet blast box I use a 2 HP compressor as I only use the cabinet for quick blasts so the compressor doesn't need to run for long. I can connect the 7.5 HP compressor to the cabinet if I ever need to as all the equipment has quick disconnects and the same size fillings.

The dust collector is a commercial quality dust collector on a mobile base. It connects to the vac. port on the cabinet and there is a sliding panel on the bottom which can be opened or closed to regulate the amount of suction in the cabinet or when disconnected from the cabinet it can be used to vacuum the shop floor. I bought it used on eBay for 112.00. Excellent deal.

KMS Tools has a good link to an article on choosing a compressor, as does Tony's site.
http://www.kmstools.com/blog/wp-content ... gGuide.pdf

The grit I use in both systems is 150 Alum. Oxide. As mentioned in the earlier post, it wears down to smaller particles. If you use a tiny nozzle you'll run the risk of digging trenches in you work if the pressure is too high. As you gain experience you'll avoid that problem.

Don't forget a water trap to remove moisture that collects in your airline as the air is compressed. Have a long enough airline to allow the moisture to form and run downhill to be collected before it reaches the gun or you'll have sputtering. Have fun..... Jen
misteroldhouse
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Re: Sandblasting questions

Post by misteroldhouse »

Hi All,

I too have a larger cabinet-style sandblaster, with factory-supplied dust collector, etc.

One, or even several, high-quality water traps are critical to removing all traces of moisture from the air-line. My current setup has two water traps in a row, situated about 2 feet apart and seem to effectively capture 99% of the humidity. I went through a couple of cheap iterations that definitely did not work before spending a bit more and getting a quality product.

Neither compressor size or horsepower are unequivocably relevant to whether a compressor is suitable for a particular function. Look at CFM or cubic feet per minute as the best indicator of air compressor suitability. Now, you will note that the higher CFM air compressors also tend to also have higher horsepower and be of larger size, but don't be confused. It seems that most sandblasting setups recommend 13+ CFM in order to achieve optimal results. Some larger industrial units require tens or hundreds of CFM, but those are used for industrial-level removal of rust, paint, etc and hardly suitable for glass.

I currently use a large upright Ingersoll Rand 240 Volt model that provides around 10 CFM and, 5 years ago, cost under $1K. Looking at these today, on the Northern Tool website, I can get a quite similar 10.5 CFM model for $730. For $900, I can purchase an 18 CFM model! Both look the same to the unitiated. The dual-stage and twin-screw style compressors provide considerable higher CFM that the single-stage conventional models like mine.

I currently use a Cyclone cabinet and an integrated Cyclone siphon-feed air compressor and use a lower-CFM nozzle designed for lower-CFM air supplies, as recommended by the manufacturer. The largest sandblasting piece I've done is 16" x 16". This setup is less suitable than I would like. When I replace the air compressor, I'll definitely get a larger CFM model. That will enable not only greater pressure and use of a standard nozzle, but will also allow me to use the pressure feed models which purportedly blast more aggressively than the siphon feed models such as mine.

Again, the setup that I have is certainly quite useable but not optimal. I use 100, 150 and, very occasionally, 220 grit aluminum oxide for either etching dichro/irid or for achieving a matte finish on my larger fused glass pieces.

Good luck! Happy Holidays.

Larry
Larry Pile
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Tony Smith
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Re: Sandblasting questions

Post by Tony Smith »

I realize this is a tome, but I'll try to cover the decisions that must be made by anyone considering setting up sandblasting in their studio.

By way of an example, I know a stained glass teacher who taught sandblasting for years with a Glastar cabinet, a Craftsman 20 gallon horizontal compressor, a Glastar pressure pot and a Sears shop vac. Not the best setup, but quite effective. In this case, the worst component was a Glass Passer cabinet that leaked terribly. For sure, the shop vac had to be replaced regularly as the abrasive wore through the filter and attacked the motor bearings. But this happens in commercial dust collectors as well. The point is that there are many opinions about what works and what doesn't. With the right combination of equipment, we may be able to get away with less than we are otherwise led to believe.

The problem of selecting equipment is complicated by some compressor manufacturers inflating their performance numbers and vendors of sandblasting equipment overestimating the amount of air required by their equipment or not publishing numbers at all. When sandblasting, it all comes down to air flow (CFM of lpm) and pressure (psi or kPa), so it's important to understand the variables that affect air consumption.

Every sandblasting cabinet comes with a siphon-type sandblasting gun. Some are better than others, and they come with different features, but the basic principle is the same; they use air flowing through the gun at high velocity to create a venturi effect or a vacuum, which sucks abrasive up a plastic tube, mixing with the air that's flowing through the nozzle. It's not a very efficient process and there are a number of components in the gun that wear out as the abrasive flows through them making the gun even less efficient if they aren't replaced periodically. With this type of gun, a smaller nozzle can help use less air, but there is a point of diminishing returns where the smaller nozzle restricts the airflow, which in-turn reduces the amount of vacuum created to draw abrasive up into the gun. There are also limitations to what you can do with a siphon blaster. General blasting and light etching are its strengths; sandcarving is not. That said, many people like the siphon blaster for its simplicity since the siphon blaster recycles abrasive and doesn't require the operator to drain abrasive from the cabinet periodically as with a pressure pot. For an average siphon blaster, I would estimate air consumption at around 8-10 CFM at a minimum pressure of 80-85 psi.

The pressure pot is usually separate from the cabinet and costs from $100 to $1000 depending on how comfortable you are using tools and adapting. For $100, you can get a Chinese import pressure pot that works okay... better after you make some modifications. For $1000, you can get a pressure pot that requires no modifications and is ready to plug and play. The pressure pot is a simple system: Abrasive is placed in the steel tank, which is then sealed and pressurized with air, which forces abrasive into a mixing valve at the bottom of the tank. The incoming air is split and a second line feeds into the mixing valve. Since the abrasive and the air are at the same pressure, mixing occurs very efficiently. A rubber hose attached to the mixing valve outlet carries the abrasive/air mixture to a ceramic or carbide nozzle in the sandblasting cabinet. A nozzle with a large diameter hole produces a spray pattern that covers a large area, but uses more air than a nozzle with a small hole and its smaller area of coverage.

Pressure is an important variable with the pressure pot as high pressure accelerates the abrasive to higher speeds creating a faster abrasive action. Faster abrasive action means removing more glass and allows glass to be carved deeply. A low pressure allows for minimal glass removal which is required for shading of etched designs. For comparson, normal etching takes place at 20 psi, shading at 5 psi and carving at 40 psi or more depending on the nozzle diameter. I estimate air flow for normal etching to be about 5 CFM at 20 psi. The ideal gas law says that volume and pressure are related, so assuming a constant temperature, 5 CFM at 20 psi is the same amount amount of air as 1.25 CFM at 80 psi. Compared to a siphon blaster, the pressure pot sips air and can be used with a much smaller compressor.

Look for cabinets and siphon guns from TPTools.com (they make cabinets for Glastar as well), glastar.com and northerntool.com. Pressure pots are harder to come by, but glastar.com and hisglassworks.com sell top quality units. Northerntool.com and harborfreight.com sell cheap imports.

With compressors, there are a few variables: one is the size of the compressor itself and how much air it can move without a storage tank; another is the size of the storage tank itself which acts as a buffer. Fully pressurized, a tank can put out a very high flow until the pressure drops below the regulated outlet pressure. The variable here is time - a small tank will only sustain a high flow for seconds whereas a large tank may be able to sustain the same flow for minutes. Pressure also plays into the equation since higher rated pressure means more air in the storage tank and longer time before the tank drops to the reglated outlet pressure. When the pressure drops below a factory setpoint, a pressure switch turns on the compressor motor which pumps air into the storage tank. The pressure switch turns off when the storage tank reaches its rated pressure. In typical use, a compressor will run until the tank is pressurized, then it will turn off for a period of time while air is used, then it turns on again and repressurizes. The ratio of on-time to on-time plus off time expressed as a percentage is called its duty-cycle. Industrial compressors are rated for 100% duty-cycle, which means that they can run constantly for an indefinite period without overheating or otherwise breaking down. Consumer compressors typically do not specify their rated duty-cycle and are expected to be less than 100% (and I would guess they are no more than 50% duty cycle). As an example, they should run no more than two minutes and be off for two minutes allowing the compressor and motor to cool.

Cost becomes the final variable. Anyone who does sandblasting will tell you to buy the largest compressor you can afford. Of course if you just dropped $1000 on a pressure pot, you may not be able to afford a large compressor... but then you may not need a large compressor. If all you can afford is the siphon blaster that came with your cabinet, you probably can't afford a large compressor either, so what do you do? One approach would be to buy the largest compressor you can afford and accept the inconvenience of having to wait for the compressor to repressurize every few minutes. This is fine for small jobs such as removing kilnwash and etching jewelry, bottles and small plates, but may be less tolerable when trying to etch large areas. In my opinion, any compressor with a storage tank smaller than 20 gallons will frustrate anyone trying to sandblast, but it can be done.

There are many manufacturers of compressors, some better than others. I would not hesitate to recommend Ingersol-Rand (available from Grainger and northerntool.com) for commercial compressors. They have a long history of making quality equipment. For consumer compressors, there are only a couple of manufacturers, deVilbiss and Campbell-Hausfeld, and major retailers buy from them and put their own name on them: Sears, Lowes, Home Depot, deWalt, Porter-Cable, etc... So choose the retailer who gives you the best service. For example, I know Home Depot will allow you to return a compressor if you find it's too small or too noisy for your application. If space is a concern, look for an upright available in 30 to 80 gallons. The 30 gallon units are available on wheels so they can be moved easily. Don't forget power since the larger compressors require 220 or 208 VAC. Homes typically do not have 3-phase, 208 VAC available, so make sure you know what you have for power before you buy.

With dust collectors, let's be clear; you cannot see inside a sandblasting cabinet without some form of air extraction. If you can't see, then you're blasting blind which will lead to poor quality blasting and frustration. Blasting outdoors in a cardboard box can be done, but abrasive gets everywhere, and I mean everywhere; you'll find it in your clothes, shoes, and folds of skin... and don't even try it without a full hood and dust mask. Also consider the damage residual abrasive can do to things like eyeglasses and watch crystals... ask me how I know.

So there are only a couple of options: shop-vac or dust collector. If you're good about emptying the shop-vac and cleaning/replacing the filter regularly, you can use a large shop-vac with a HEPA filter. The abrasive will eventually wear through the filter material whether it's a standard filter or a HEPA filter (smaller pores and larger surface area). Once the filter is perforated, damage occurs in two ways: first the abrasive gets into the motor bearings and does short work of making the shop-vac scream until you replace it; the second, and more dangerous effect is blowing abrasive and dust into your shop environment (see Greg Rawls posts).

The dust collector moves a lot of air and has a very large fabric bag or multiple fabric bags creating a very large surface area for dust to collect on. Many of the dust collectors have weights on them that shake dust off the bags and into the base when they are turned off. Some dust collectors have additional features such as a HEPA filter on the motor and a bag on the outlet as additional mitigations against dust getting into the shop space. Without regular maintenance, even the most expensive dust collector can fail in a way simlar to shop-vacs once abrasive wears through a bag.

Shop-vacs are available from Sears, Home Depot, Lowes, etc... I would buy a large unit with an add-on HEPA filter to ensure maximum airflow. You can find dust collectors from tptools.com.

I hope this helps answer some basic questions.

Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun
lmartine
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Re: Sandblasting questions

Post by lmartine »

Thank you all for your two cents! You guys rock! =D> Santa will have a blast shopping :)
Lucie
Kevin Midgley
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Re: Sandblasting questions

Post by Kevin Midgley »

Tony you forgot some crucial bits of information in your tome.
Oil-less compressors can have a run time of only 1000 hours.
Spend the money on an oil filled compressor, check the oil regularly and use the right oil.
They tend to be quieter too.
The tank will rust really fast with all that compressed oxygen inside so let the air out and drain the water from the tank daily
I ran for years etching plates with an oil filled Bostich 2 gallon air tank and pressure pot set at 10-15 psi.
I still like the lower pressures for more control and less blowing the resist off the glass with its resulting design destruction.
Tony Smith
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Re: Sandblasting questions

Post by Tony Smith »

Kevin,

I'm sure there are a lot of details that I neglected to include.

Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun
Tony Smith
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Re: Sandblasting questions

Post by Tony Smith »

okay, so a few more details...

I've been using the same single-stage, oil-free, sixty gallon, Craftsman compressor for about 15 years. After I figured out what I was doing, I realized that I should have bought a two-stage, oiled compressor and was waiting until this one died before upgrading... needless to say, it's still going strong. I do drain the water out of it any day that I use it, but have never drained the air... just differing opinions. It's also noisy, but it's in a separate room, so it's tolerable.

I've also used a 2 gallon pancake compressor with a pressure pot, but wasn't going to offer that as a viable solution for novices.

There are still many details including water traps, piping vs hose, types of nozzles, dealing with humid environments and many, many more. This is the stuff books are made for.

Tony
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun
Morganica
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Re: Sandblasting questions

Post by Morganica »

Tony, too bad we can't "like" these posts. Thanks.
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Tony Smith
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Re: Sandblasting questions

Post by Tony Smith »

:D :D :D
The tightrope between being strange and being creative is too narrow to walk without occasionally landing on both sides..." Scott Berkun
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