Pietenpol-List: blast it
Posted: Tue Feb 04, 2003 12:28 am
Original Posted By: "Christian Bobka"
Pete,Here it is. An attachment will come as well. I have pictures here at hometo personally deliver on tuesday evening.ChrisBLAST IT! Part VIIIby Chris BobkaThis series was discontinued after the seventh installment when son numbertwo began to walk! That also coincided with David Kujawa leaving thechapter newsletter editorship and taking over editorship of Sport Aerobaticsmagazine and moving away to Arizona with his lovely wife, Diane. Instead oflooking forward to dropping off articles at David and Diane's and sharing afew beers, I was frought with fear at having to bring articles to ugly Peteand Bob. I hope you can find me some forgiveness for leaving you allhanging. So sorry. Much prodding on the part of Pete, Greg, Frankh, andothers from the Pietenpol chat group has gotten me back to finishing off theseries with this final installment.We left off with the gauntlets ready for installation to the front of thebox. I have included Figures 11 and 12 which show a cutting diagram for thegauntlet and what the finished gauntlet should look like. As shown inFigure 12, cut some darts into the big end of the gauntlet to help it layflat as shown in Figure 13. Put some caulk around the left opening in thebox and, using a heavy duty stapler, shoot some 1/4" staples into the boxaround the circumference of the glove to hold it in place. Don't do whatNorm did so make sure you use the left handed gauntlet in the left hole ofthe box and make sure you orient the thumb so that it is at about the 12o'clock position. If you put the wrong gauntlet on that hole, you will haveto stand on the cieling in order to sandblast. Like Norm. Put more of thecaulk on top of the gauntlet and then take one of the rings from Figure 3and and use enough 1-1/4" drywall screws to hold the gauntlet in place. Youcan clean up any of the squeezed out caulk at this time. Install the otherglove. Thumbs up!Next we need to install the door. You cut out the door opening in Figure 4and at that time, I instructed you to save the cut out piece. Go get it.Have an assistant hold the cut out piece in the door opening. Take two olddoor hinges from the junk box and mark off the screw positions on the doorand on the frame to the rear of the door. Ensure that the hinge pins liedirectly over the cut line and the hinge lines are in line with each other.Now take the door piece and lay it onto another piece of plywood that isbigger than it. Mark off the same general shape but about 1-1/2 inches allthe way around it EXCEPT for the rear edge. This mark off should be evenwith the rear edge of the door so the door can swing open.What we are making here is a piece of plywood that will overlap the doorjamb so as to contain the direct blast of the sand. With your radial saw,cut out the new piece. As the hinges on the door must lay in the same planeas the box, it will be necessary to make cutouts to allow this new piece toclear the door. Cut these out with a sabre saw. The top and side views ofFigure 14 clearly show this. You may design a better way and I know thatthere are better ways but this is the way I did it. Go for it! Make thelatch as shown in Figure 14 from some scrap plywood. Attach the door andlatch to the box. If you want, you can get some felt weatherstripping about1/8" thick and 1/2-3/4" wide and put it around the door jamb as indicated tohelp contain some of the sand. An 1/8" looks thick but it will compressright down.Well that is it. The box is done. Now we have to come up with the gun.You want a good one. The reason is that the gun uses air that passesthrough a venturi in the gun to create suction which pulls the sand up fromthe hopper, through the feed tube, and through the venturi itself,accelerating the sand along the way. At the venturi, the sand makes a sharpturn before it exits the nozzle. My dad, the physicist, says that forcetimes mass equals impact. We want impact as that is what does thesandblasting. Mass is related to the the size and density of the particle.Force is the effectiveness of the gun at accelerating the particle. Everyparticle of sand that comes out of the gun also is trying to wear down theventuri of the gun. A cheap ceramic nozzle coupled with a soft steelventuri will not last long as the sand will abrade it right down and theventuri will no longer be properly shaped to create a quality vacuum (if avacuum sucks, is it good or bad?). Lots of air will come out of the nozzlebut no abrasive. Then you will blame me that the sandblaster does not work.We need space age materials. We need titanium. We need carbide.So I will tell you what gun to get. It is shown in Figure 15. It isavailable at Grainger, among other places, and can be found on the internetas of February 2003 at:http://www.grainger.com/Grainger/catalo ... ge=1427You want model 3JT01 for the 12 CFM model. It lists for a wopping 77dollars but buddy Jim Markle at jim_markle(at)mindspring.com has agreed topurchase these guns from Grainger at his substantial discount and have themdrop shipped to interested buyers. The best thing is that parts areavailable too as listed on the same web page. The gun does not have atrigger. You do not want a gun with a trigger. A gun with a trigger takesup too much room and your finger gets tired holding the trigger. Instead ofa trigger, I merely connect and disconnect a Milton coupling right at theaft end of the gun. You could get fancy and use a foot pedal air switch oryou could put a valve at the point where the air line goes into the box.Use what you think you would like.Once you have your gun, attach it to the end of the pickup tube inside thebox with an appropriate length of 5/8" ID cheap clear vinyl tubing from thebig rack of tubing at Home Depot that I told you to get earlier. Use somehose clamps to hold the hose on at both ends. Drill the smallest size holeyou can get away with to let the air line into the box. It should belocated near where the pickup tube is located so that both hoses can floparound more or less together.You need a vacuum cleaner of the big shop vac variety. This is a necessityas you are creating a mammoth sandstorm inside the box. Without a shop vac,it will be so cloudy inside the box after a minute that you won't be able tosee your hand in front of your face. You are pumping air into the box at 100PSI and at 11-15 Cubic Feet per Minute. All the air has to go somewhere. Ifthere is no shop vac then this air will blow out through every seam and putdust all over the garage and make a big mess. It will also go into yourlungs and you will contract silicosis and die a horrible slow death. The keyis to create a negative pressure inside the box so that the dust is trappedby the filter of the shop vac. Better yet, use an extra long vacuum hoseand put the shop vac outside as even the filter on the shop vac won't trapall the fines.Their are endless varieties of abrasives to use. I use number five whitesilica sand. You can remember number five as that is how many fingers youshould have on one of your hands. It is the same stuff that you see in sandfilled ashtrays next to the door to elevators in office buildings. Manysandblasting supply outfits are reluctant to sell you sand for sandblastingbeacuse they are afraid you will not be using proper breathing protectionand they will be sued by your hiers after you die of silicosis. If you tellthem it is for ashtrays, then they will chum right up and gladly sell it toyou. It will come in 50 or 100 lb sacks. 100 lbs should do for starters.Dick Navratril, a Pietenpol builder here in the Twin Cities area(horzpool(at)goldengate.net), says you could also try a larger swimming pooldealer to get sand. In his swimming pool supply shop, he carries red flintgranite sand sized at .45-.55 mm. It is rather aggressive but doesn't dustnearly as much as white silica sands. Some may try to use glass beads orwalnut shells. It all depends upon the finish you wish, the aggressivenessof the cleaning, and the price you are willing to pay.You may consider building more than one sandblasting box. Each can have adifferent abrasive. It is difficult to change abrasives from big to littlefor the following reason: you will probably never get all the big stuffout. What will happen is that you will make a change from big particles tolittle particles. You will think you have it licked and you will beblasting away looking at the fine, uniform finish on your blasted piece.Just as the ten millionth particle comes out of the nozzle, a stray bigparticle will come out, and whamo! there appears what will looks like a hugecrater in your work as that single particle hits. It may not bother you andit may not matter based on the part you are blasting but sometime it maymatter. Again, the choice is yours. Once my new hangar is done, it willsport a couple of blasting boxes each with a different abrasive.Additonal abrasives management discussion is outside the scope of thisarticle. I am sure that industrious users of their new blast cabinet willseek out information on http://www.google.com for more information.A few tips on use are in order. All the debris you blast off of the piecesyou are sandblasting will fall down into the sand. Eventually, they willmigrate to the bottom of the hopper as it becomes their "turn" to be suckedinto the pickup tube. Large pieces of debris will clog the venturi of thegun. The short term fix is to hold your free hand over the discharge nozzleof the gun, forcing the compressed air down the hose abrasive supply hoseand the pickup tube and blowing all the junk out. This will work for awhile but sooner or later you will have to empty the abrasive out the bottomof the hopper and sift it. I use a big sifter from the cookingware aisle ofthe supermarket that looks like a bowl made out of screening. This is thelong term fix.Use a pair of pliers kept in the box to hold small parts so you are notalways blasting away at the fingertips of your gloves as you hold parts.The box makes for really good storage of parts that must be kept rust free.The large quantity of sand acts as a dessicant to keep the air in the boxdry.You can also experiment with different air pressures. 50-60 PSI works goodfor most work. It is hard for many air compressors to keep this up at 12CFM so from time to time you need to give the air compressor a chance tocatch up. Also, most air compressors have a duty cycle which means that itis expected that a certain percentage of the time, the air compressor shouldbe off and resting. It cools when it rests. You may consider asupplemental fan blowing on your air compressor to keep it cool.Do not take stuff out of the blaster unless you have gloves on. The prossay to use surgical gloves. Oils and acids from your skin will cause thepart to rust, even under paint.As stressed in the beginning of this series of articles, moisture is thebane of all sandblasters. you must have adequate moisture control in yoursystem. The ideal air supply system uses many feet of metal, not plastic orrubber, air line between the compressor and the sandblaster. The metalabsorbs the heat from the compressed air. As the compressed air cools, thewater in it will condense out and deposit, in the form of water droplets,onto the inside surface of the cool pipe. As the air passes through thepipe it will roll these droplets along until they hit a moisture trap thatwill inertially snag them and keep them from traveling further. It isimportant to note that moisture traps trap water droplets, not water vapor.Putting a mositure trap at the compressor outlet will not do much good sincethe air will carry mostly vapor here as the air is so hot. The best "final"moisture trap I know of is the 1/2" coalescing air filter as illustrated inFigure 16 and sold by Tip Sandblasting at 1-800-321-9260. It uses a roll oftoilet paper inside the unit to absorb all remaining mositure after the airhas traveled through the standard inertial moisture traps of your system.The price is up there on this unit bust the performance is spectacular.Finally, as you sandblast and between sips of Guiness, USE PROTECTIVEBREATHING EQUIPMENT APPROPRIATE FOR SANDBLASTING. If it is good for wearingwhile doing drywall work, it should be good for sandblasting but read thelabels on the devices you might want to use! Also, use hearing protectionif you have the shop vac next to you. Ideally you can use a Walkman and itslittle earplug type earpieces under your hearing protectors so you canlisten to the Grateful Dead as you blast away.Good luck with your new unit and try to imagine how life was before you hadit!________________________________________________________________________________
Pete,Here it is. An attachment will come as well. I have pictures here at hometo personally deliver on tuesday evening.ChrisBLAST IT! Part VIIIby Chris BobkaThis series was discontinued after the seventh installment when son numbertwo began to walk! That also coincided with David Kujawa leaving thechapter newsletter editorship and taking over editorship of Sport Aerobaticsmagazine and moving away to Arizona with his lovely wife, Diane. Instead oflooking forward to dropping off articles at David and Diane's and sharing afew beers, I was frought with fear at having to bring articles to ugly Peteand Bob. I hope you can find me some forgiveness for leaving you allhanging. So sorry. Much prodding on the part of Pete, Greg, Frankh, andothers from the Pietenpol chat group has gotten me back to finishing off theseries with this final installment.We left off with the gauntlets ready for installation to the front of thebox. I have included Figures 11 and 12 which show a cutting diagram for thegauntlet and what the finished gauntlet should look like. As shown inFigure 12, cut some darts into the big end of the gauntlet to help it layflat as shown in Figure 13. Put some caulk around the left opening in thebox and, using a heavy duty stapler, shoot some 1/4" staples into the boxaround the circumference of the glove to hold it in place. Don't do whatNorm did so make sure you use the left handed gauntlet in the left hole ofthe box and make sure you orient the thumb so that it is at about the 12o'clock position. If you put the wrong gauntlet on that hole, you will haveto stand on the cieling in order to sandblast. Like Norm. Put more of thecaulk on top of the gauntlet and then take one of the rings from Figure 3and and use enough 1-1/4" drywall screws to hold the gauntlet in place. Youcan clean up any of the squeezed out caulk at this time. Install the otherglove. Thumbs up!Next we need to install the door. You cut out the door opening in Figure 4and at that time, I instructed you to save the cut out piece. Go get it.Have an assistant hold the cut out piece in the door opening. Take two olddoor hinges from the junk box and mark off the screw positions on the doorand on the frame to the rear of the door. Ensure that the hinge pins liedirectly over the cut line and the hinge lines are in line with each other.Now take the door piece and lay it onto another piece of plywood that isbigger than it. Mark off the same general shape but about 1-1/2 inches allthe way around it EXCEPT for the rear edge. This mark off should be evenwith the rear edge of the door so the door can swing open.What we are making here is a piece of plywood that will overlap the doorjamb so as to contain the direct blast of the sand. With your radial saw,cut out the new piece. As the hinges on the door must lay in the same planeas the box, it will be necessary to make cutouts to allow this new piece toclear the door. Cut these out with a sabre saw. The top and side views ofFigure 14 clearly show this. You may design a better way and I know thatthere are better ways but this is the way I did it. Go for it! Make thelatch as shown in Figure 14 from some scrap plywood. Attach the door andlatch to the box. If you want, you can get some felt weatherstripping about1/8" thick and 1/2-3/4" wide and put it around the door jamb as indicated tohelp contain some of the sand. An 1/8" looks thick but it will compressright down.Well that is it. The box is done. Now we have to come up with the gun.You want a good one. The reason is that the gun uses air that passesthrough a venturi in the gun to create suction which pulls the sand up fromthe hopper, through the feed tube, and through the venturi itself,accelerating the sand along the way. At the venturi, the sand makes a sharpturn before it exits the nozzle. My dad, the physicist, says that forcetimes mass equals impact. We want impact as that is what does thesandblasting. Mass is related to the the size and density of the particle.Force is the effectiveness of the gun at accelerating the particle. Everyparticle of sand that comes out of the gun also is trying to wear down theventuri of the gun. A cheap ceramic nozzle coupled with a soft steelventuri will not last long as the sand will abrade it right down and theventuri will no longer be properly shaped to create a quality vacuum (if avacuum sucks, is it good or bad?). Lots of air will come out of the nozzlebut no abrasive. Then you will blame me that the sandblaster does not work.We need space age materials. We need titanium. We need carbide.So I will tell you what gun to get. It is shown in Figure 15. It isavailable at Grainger, among other places, and can be found on the internetas of February 2003 at:http://www.grainger.com/Grainger/catalo ... ge=1427You want model 3JT01 for the 12 CFM model. It lists for a wopping 77dollars but buddy Jim Markle at jim_markle(at)mindspring.com has agreed topurchase these guns from Grainger at his substantial discount and have themdrop shipped to interested buyers. The best thing is that parts areavailable too as listed on the same web page. The gun does not have atrigger. You do not want a gun with a trigger. A gun with a trigger takesup too much room and your finger gets tired holding the trigger. Instead ofa trigger, I merely connect and disconnect a Milton coupling right at theaft end of the gun. You could get fancy and use a foot pedal air switch oryou could put a valve at the point where the air line goes into the box.Use what you think you would like.Once you have your gun, attach it to the end of the pickup tube inside thebox with an appropriate length of 5/8" ID cheap clear vinyl tubing from thebig rack of tubing at Home Depot that I told you to get earlier. Use somehose clamps to hold the hose on at both ends. Drill the smallest size holeyou can get away with to let the air line into the box. It should belocated near where the pickup tube is located so that both hoses can floparound more or less together.You need a vacuum cleaner of the big shop vac variety. This is a necessityas you are creating a mammoth sandstorm inside the box. Without a shop vac,it will be so cloudy inside the box after a minute that you won't be able tosee your hand in front of your face. You are pumping air into the box at 100PSI and at 11-15 Cubic Feet per Minute. All the air has to go somewhere. Ifthere is no shop vac then this air will blow out through every seam and putdust all over the garage and make a big mess. It will also go into yourlungs and you will contract silicosis and die a horrible slow death. The keyis to create a negative pressure inside the box so that the dust is trappedby the filter of the shop vac. Better yet, use an extra long vacuum hoseand put the shop vac outside as even the filter on the shop vac won't trapall the fines.Their are endless varieties of abrasives to use. I use number five whitesilica sand. You can remember number five as that is how many fingers youshould have on one of your hands. It is the same stuff that you see in sandfilled ashtrays next to the door to elevators in office buildings. Manysandblasting supply outfits are reluctant to sell you sand for sandblastingbeacuse they are afraid you will not be using proper breathing protectionand they will be sued by your hiers after you die of silicosis. If you tellthem it is for ashtrays, then they will chum right up and gladly sell it toyou. It will come in 50 or 100 lb sacks. 100 lbs should do for starters.Dick Navratril, a Pietenpol builder here in the Twin Cities area(horzpool(at)goldengate.net), says you could also try a larger swimming pooldealer to get sand. In his swimming pool supply shop, he carries red flintgranite sand sized at .45-.55 mm. It is rather aggressive but doesn't dustnearly as much as white silica sands. Some may try to use glass beads orwalnut shells. It all depends upon the finish you wish, the aggressivenessof the cleaning, and the price you are willing to pay.You may consider building more than one sandblasting box. Each can have adifferent abrasive. It is difficult to change abrasives from big to littlefor the following reason: you will probably never get all the big stuffout. What will happen is that you will make a change from big particles tolittle particles. You will think you have it licked and you will beblasting away looking at the fine, uniform finish on your blasted piece.Just as the ten millionth particle comes out of the nozzle, a stray bigparticle will come out, and whamo! there appears what will looks like a hugecrater in your work as that single particle hits. It may not bother you andit may not matter based on the part you are blasting but sometime it maymatter. Again, the choice is yours. Once my new hangar is done, it willsport a couple of blasting boxes each with a different abrasive.Additonal abrasives management discussion is outside the scope of thisarticle. I am sure that industrious users of their new blast cabinet willseek out information on http://www.google.com for more information.A few tips on use are in order. All the debris you blast off of the piecesyou are sandblasting will fall down into the sand. Eventually, they willmigrate to the bottom of the hopper as it becomes their "turn" to be suckedinto the pickup tube. Large pieces of debris will clog the venturi of thegun. The short term fix is to hold your free hand over the discharge nozzleof the gun, forcing the compressed air down the hose abrasive supply hoseand the pickup tube and blowing all the junk out. This will work for awhile but sooner or later you will have to empty the abrasive out the bottomof the hopper and sift it. I use a big sifter from the cookingware aisle ofthe supermarket that looks like a bowl made out of screening. This is thelong term fix.Use a pair of pliers kept in the box to hold small parts so you are notalways blasting away at the fingertips of your gloves as you hold parts.The box makes for really good storage of parts that must be kept rust free.The large quantity of sand acts as a dessicant to keep the air in the boxdry.You can also experiment with different air pressures. 50-60 PSI works goodfor most work. It is hard for many air compressors to keep this up at 12CFM so from time to time you need to give the air compressor a chance tocatch up. Also, most air compressors have a duty cycle which means that itis expected that a certain percentage of the time, the air compressor shouldbe off and resting. It cools when it rests. You may consider asupplemental fan blowing on your air compressor to keep it cool.Do not take stuff out of the blaster unless you have gloves on. The prossay to use surgical gloves. Oils and acids from your skin will cause thepart to rust, even under paint.As stressed in the beginning of this series of articles, moisture is thebane of all sandblasters. you must have adequate moisture control in yoursystem. The ideal air supply system uses many feet of metal, not plastic orrubber, air line between the compressor and the sandblaster. The metalabsorbs the heat from the compressed air. As the compressed air cools, thewater in it will condense out and deposit, in the form of water droplets,onto the inside surface of the cool pipe. As the air passes through thepipe it will roll these droplets along until they hit a moisture trap thatwill inertially snag them and keep them from traveling further. It isimportant to note that moisture traps trap water droplets, not water vapor.Putting a mositure trap at the compressor outlet will not do much good sincethe air will carry mostly vapor here as the air is so hot. The best "final"moisture trap I know of is the 1/2" coalescing air filter as illustrated inFigure 16 and sold by Tip Sandblasting at 1-800-321-9260. It uses a roll oftoilet paper inside the unit to absorb all remaining mositure after the airhas traveled through the standard inertial moisture traps of your system.The price is up there on this unit bust the performance is spectacular.Finally, as you sandblast and between sips of Guiness, USE PROTECTIVEBREATHING EQUIPMENT APPROPRIATE FOR SANDBLASTING. If it is good for wearingwhile doing drywall work, it should be good for sandblasting but read thelabels on the devices you might want to use! Also, use hearing protectionif you have the shop vac next to you. Ideally you can use a Walkman and itslittle earplug type earpieces under your hearing protectors so you canlisten to the Grateful Dead as you blast away.Good luck with your new unit and try to imagine how life was before you hadit!________________________________________________________________________________