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Old 08-25-11, 09:45 PM   #1
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Sandblasting Question

I need to sandblast some frames, not many, and I won't be doing this often.

I'm currently trying to do a local barter for an air compressor (which will come in handy outside of the sandblasting). I've got some offers, but for some pretty low tier compressors. What is the bare minimum of a compressor I can get away with and still be able to use a hand sandblasting gun with its own reservoir? Will I be able to blast at all with, say, 4 CFM at 100psi? If not, what is the lowest I can go before I'm just giving the frames a sand massage.......

I don't mind if it takes awhile, and I realize a smaller compressor will cut in and out on me fairly often.....but anything is better then the tedium of stripping by hand

Thanks for the help!
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Old 08-25-11, 09:51 PM   #2
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The sandblasting gun will have specs listing the needed air volume/pressure capacity. You need a compressor with bigger capacity.

Without know what the gun needs, it's impossible to say how much air is enough.
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Old 08-25-11, 10:08 PM   #3
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Good point. I don't actually have a gun yet, and I was looking at some of the relatively cheap ones ($40 or less), but could certainly tailor the gun purchase to the abilities of my compressor. So, a better question might be, what's the lowest volume/pressure capacity that a sandblasting gun can use and still be effective?
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Old 08-25-11, 10:17 PM   #4
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Quote:
Originally Posted by Smithie View Post
Good point. I don't actually have a gun yet, and I was looking at some of the relatively cheap ones ($40 or less), but could certainly tailor the gun purchase to the abilities of my compressor. So, a better question might be, what's the lowest volume/pressure capacity that a sandblasting gun can use and still be effective?

You're still doing it backward. Don't buy a gun based on capacity, buy capacity to match a gun.

Since you don't yet have a compressor, shop the guns first. That'll give you a clear idea of how much compressor you'll need.

One thing I can tell you is that most small compressors, fall into either of two categories. Nail gun and similar low volume tools and spray painting, which usually need less than 4cfm at 90psi.

Larger power tools tend to need more volume, and I suspect anything bigger than a small hobbyist sandblaster will too.
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Old 08-25-11, 11:10 PM   #5
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Bottom line as FBinNY is trying to tell you is that if you do not provide a big enough compressor capacity and psi wise for the gun - you'll spend WAY more time waiting for the compressor getting recharged than getting more actual work done.

Even with a huge 40 gallon compressor powering the one I used two weeks ago - it came out to about 2 minutes recharge per 1 minute of work. It was a patience test already...took me fifteen minutes for the fork and an hour for the frame.

Imagine what it'd be like if your compressor was so small that its 2 minutes recharge and 15 seconds of work.

Research...research...match and then buy. Don't cut corners on gun vs. compressor cap.

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Old 08-25-11, 11:47 PM   #6
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Don't forget to check into the cost of the media you will be using, it can add up. I'm in about the same position and already have a decent compressor but I decided I'd just pay for the service on the few occasions I need it. I've heard that the siphon style guns are nearly worthless for anything but very small jobs so you'll probably want to get a pressurized tank type of blaster. You will also need some protective gear and a place to do the work.

I just had a frame stripped and powder coated. The total cost was about what just the blaster tank would cost. The outfit that did it has industrial equipment and buys their materials in bulk. They also do this everyday and do high quality work. As much as I'd like to do the stripping myself to save $30+ per frame on the re-finish, the numbers just don't add up. YMMV
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Old 08-26-11, 12:43 AM   #7
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Is stripping the paint w/chemicals an option for you? it might save all this confussion, and equipment purchases.
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Old 08-26-11, 08:45 AM   #8
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Also, be sure your electrical service is capable of handling the compressor you buy. Most compressors over 1.5 HP require a 220 V circuit.
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Old 08-26-11, 09:26 AM   #9
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So, I definitely agree that buying a nice, big compressor would make this a non-issue. But.....the only reason I even have the option of doing this is through trade (for an old welder I no longer need). I can scratch together enough for a gun, but buying a large compressor, even a well used one, is out of budget by quite a ways. So, if I need to do this shoestring, and knowing that I am in for some frustration for doing so, can I still put together a package that will work albeit slowly and annoyingly?

This is currently the compressor that someone is offering up: http://www.sears.com/craftsman-4-gal...p-00916638000P

It's 4 gallon, 1hp, and very, very small. It maxes out at 125psi, but the cfm are quite low at such a high pressure. But, he would include cash with the trade which gives me some extra play room for my gun, medium, and safety gear purchase.

I did some looking, and gun options at such a pitiful volume/pressure are either this: http://www.amazon.com/Gilmour-70HDG-.../dp/B0006U66CA

Or this: http://www.amazon.com/Paasche-AECR-R...4371565&sr=1-2

The Gilmour is a least a real gun....but even its low requirements of 4cfm at 70psi are barely in range of this compressor, so I imagine there will be long recharge periods. I am nowhere near versed enough to do the maths on exactly how long though.

The other option is that Paashe etching brush. I don't really know much about it except that this compressor would certainly be well within its volume/pressure needs, which means it might be slow going, but there would not be much waiting involved in the process.

So, outside of the fact that this is an extremely slap-dash set-up I'm trying to build......can I get it to work?
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Old 08-26-11, 10:14 AM   #10
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It would take a very long time to strip a frame using one horsepower; the spray pattern would be about the area of a dime. I would bet the finish could be sandpapered off faster. My mid-size blast cabinet used a compressor rated at 18 CFM @ 90 PSI and it ran continuously when I blasted. You might do better to farm out the blasting. I would suggest using glass bead blasting; it is far less erosive to the base metal than sand.
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Old 08-26-11, 10:47 AM   #11
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I used to restore old VW bugs and have done a lot of sandblasting of parts ect...

My advice. Calculate how many cubic feet per min. of air and at what pressure you will need for the gun you are using.....then set up for 5 times as much.
If you have not done any sand blasting before you will be surprised at how much air it takes, the time involved and how much work it is.
WEAR A RESPIRATOR!!!
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Old 08-26-11, 11:06 AM   #12
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First of forget the Paasche etcher. That size of "toy" is intended for jewelry or other very small jobs requireing intracate control. I'd go so far as to say that the area of coverage will be more about the size of a felt pen dab than a dime. It's intended for very small size and intracate jobs. Doing a bicycle is just not in the cards for such a unit. Neither is the normal sands or other media. In short that unit for a bicycle frame would be like trying to paint a battleship with a 1/2 inch artists brush.

The Gilmore gun at least looks more like what you need. But without knowing the actual consumption in volume at what PSI you're in the dark. In googling for "low volume media blasting" I turned up this interesting link;

http://www.harborfreight.com/gravity...gun-93221.html

Note the low volume of only 1.7 cfm. The compressor you listed shows a rating of 4 cfm so it should be able to keep up fairly well. This particular gun would appear to be fairly well suited to doing a small job such as a bicycle frame. And if you watch the video they do mention that this particular gun is only used with glass bead media. But from the looks of it doing a number on the painted metal it seems like about the right size and type of media.

You're going to need to learn a lot about media blasting. On any sort of good frame "sand" is the last thing you want to use. Most of the media grits which cut fast will also cut at the metal below the paint. The less abrasive media that will cut the paint away but leave the metal below intact are going to be a bit more specialized and likely not that cheap. Or if you insist on doing the job with the cheaper but more abrasive sand then you'll need to vary the operating pressure to set up a spray that minimizes any cutting of the metal. And when you do that it's not all that fast a job. Or as noted to use the glass bead media mentioned already.
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Old 08-26-11, 11:17 AM   #13
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The little bucket type gun you showed will work with that compressor.It will be a slow process but it will do the job and will make a HUGE mess.Some of the better ones,you will be able to change the tip size,depending on your compressor output.Even with a say 3/32 or 1/8 inch tip,real small in sandblasting terms,it will put out a pattern about the size of a pencil eraser or so.

The little etching gun is for delicate work,modeling,glass,it will only take real fine media.You won't live long enough to complete a frame and fork.It would be like painting a car with an airbrush.

One of the advantages of using a cabinet style,syphon or pressure,is that the media has many feet of hose in which to build up speed before impacting the part.Something you don't get with a gun style.So with low pressures,not much reserve air,and limited impact power,what does this all mean.

You should use maybe 30-40 lbs of air pressure,low by blasting standards,use an aggresive media(silica sand,coal slag or a man made media,say Starblast),and be prepared to use up some time.Go slow,the aggresive media with etch the crap out of the metal if your not careful,you'll have to sand it when your done.

Silica sand(sandbox sand) and coal slag(glass like remnants of coal production) is cheap,aggressive and DEADLY!!! If you use this,stand downwind,use a respirator not a mask and goggles.The fine dust,stuff you don't see,gets in your lungs and shreads them.If you inhale enough you will cough up blood.This is no joke,that's why there is a skull and crossbones on the bag!

For your purposes,sand or slag will work,an engineered media,while much less deadly,will cost too much to just blow around the yard.

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Old 08-26-11, 11:27 AM   #14
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Old 08-27-11, 11:31 AM   #15
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I did some DIY sandblasting about two years ago using this.
http://www.harborfreight.com/portabl...kit-37025.html

I was cleaning up some old wire wheels for a british sports car. I used play sand and laid out a large tarp in the back yard. You must use a respirator and other protection.
It's a big mess.

My advise is that you skip the sand blasting and use paint stripper instead.

It's not worth the investment and you are better off taking it to someone to sandblast it for you.

Sand blasting is best for smaller items that you can fit into a sandblasting cabinet.
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Old 08-27-11, 03:29 PM   #16
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I've done some old farm tractors with my Craftsman 4HP, 25 gal, rated at 7.0SCFM. Using a siphon hopper unit and sometimes had to wait for it to catch up or cool down as it isn't rated for 100% duty cycle.

I used black beauty media. Of course this wasn't thin wall bike frames
http://www.reade.com/eastern-region-(usa)/56

I made a booth out of some old plywood and tarps so I could reuse the media and not make a big mess out in my driveway. Fortunately we have a cabinet at work that fits a bike frame.
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Old 08-27-11, 08:53 PM   #17
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I've done a lot of sandblasting up to the size of truck boxes and frames and you will be very disappointed by the results of using a small "spot" blaster with an undersized compressor. I still have a spot blaster that I use with a 3/4 hp, 11 gal portable compressor and would never use it to strip an entire frame. It would be painfully slow and make more mess than it is worth. I use it mainly for giving aluminum parts a satin finish or removing rust. Unless you are going to do a lot of frames, you might be better off making a deal with a local shop that does sandblasting. My local guy said he'd do a frame and fork for $35. If you are going to have the frame professionally painted or powdercoated, many shops either have, or have contacts for sandblasting and will do it as a package deal for a decent price.
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Old 08-28-11, 04:29 PM   #18
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First, thanks for all the input. I really appreciate it. And yes, I know that if this was just one frame, out-sourcing would be far, far cheaper and easier than what I'm trying to do. But, I have at least three frames I want to strip right now, one just for painting, and two which need tube replacements. If I can get this sandblasting system to work, I figure I will be stripping at least one or two frames a year.

So, I got lucky, and somebody actually paid me cash for the welder I was trying to barter. That, and I noticed through BCRider's recommendation of the smaller gun at Harbor Freight that they were having a huge sale at the local store. All told, using the money from the welder sale and about 20 bucks out of pocket I was able to get an 2HP 8 gal compressor (4.5CFM @90PSI, 5.5CFM @40PSI), the 1.7 CFM spot blasting gun, hose, couplers, oil, all the safety equipment mother hen could desire, and a lvlp touch-up paint sprayer which this compressor can handle.

So now, my next question. I am planning on making a poor man's blast cabinet out of heavy cardboard. I bought 5lbs of 40-70 grit glass media, and I was considering lining the make-shift cabinet with a heavy duty plastic (at least 3mm) to make the media recovery easier. But, will this glass media just eat right through the plastic (the gun will be on 90psi shooting out the 40-70 grit glass)? Am I better off just trying to seal up the cardboard as well as possible and creating a small reservoir that way?

Thanks again for all the help!
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Old 08-28-11, 05:55 PM   #19
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Good choice, the glass beads, but they will eat through cardboard, or plastic, and then pieces of your cabinet will fall into the media and clog-up the gun when you recycle the beads. Consider building a wooden cabinet lined with sheet metal. A portion of your glass beads will turn to dust from impact so you'll probably need more than the 5 pounds. You'll need a window in your cabinet to see what you are doing and evening length rubber gloves to protect your hands and arms. Through your window, you won't see much, other than flying dust, unless you hook a small shop vacuum to the cabinet to pull out that dust. You'll also need a filtered inlet to allow air in for the vacuum.
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Old 08-28-11, 06:09 PM   #20
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I'm not sure the hp/cfm/psi you'll need but tank capacity is very important. I'm not sure if anything under 5hp is suitable.
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Old 08-28-11, 10:21 PM   #21
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Smithie,

It is much easier to use paint stripper to get the paint off of these frames.

Abrasives on power tools or naval jelly can be used to remove any rust.
You can even do electrolytic rust removal :
http://www.rowand.net/Shop/Tools/Electrolysis.htm

You will need at least 4hp compressor running on a 220V circuit to do sandblasting.
Even with this is it is still faster to use paint stripper.

For as often as you plan to do this I just don't think it's worth the trouble.
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