[OP]
Member
What grit aluminum oxide to use for marble/granite for sandblasting letters ?Originally Posted by Gary Hair
This machine will work https://www.bormanntools.com/portfolio-items/bwr5065/ ?
What nozzle must use ? 3mm ceramic is ok ? what modifications needs the previous machine ?
Contributor
I used 80 grit for deep engraving and 120 or 180 for surface etching. That sandblaster looks a lot like the Harbor Freight one that I used so it should be fine. A ceramic nozzle will wear very quickly and you will be changing them very often, a boron carbide nozzle will last a long time. They are not cheap but they will save you money in the long run. The modifications are too detailed to list here, most of there were learned from a sandblasting forum that is no longer in existence. It would be best to start with a good nozzle and then as you work with it make any changes necessary to improve media flow, reduce clogs, etc. Get lots of practice pieces of granite, marble, stone, etc., and take your time to learn how to get the results you desire. There may be some videos on youtube that may help but I haven't looked for any in years.
[OP]
Member
I got a machine like this 44liters capacity
https://www.directmarket.gr/ebossima...DF18888947.jpg
A standard chinese cheap sandblaster with ceramic nozzles..
What diameter boron carbide nozzles you suggest for granite sandblasting?
What sand/grit is better for granite? aluminum oxides or silicon carbide ?
How many liters/power air compressor this sandblaster needs ?
Can you suggest me some modification that improve the operation ?
Contributor
The nozzle size will be determined by a few factors - grit size, detail of the engraving, and most importantly, the cfm your compress puts out - continuous free cfm, not "rated" cfm. The 5hp, 10cfm, 60 gal, compressors at places like Home Depot are really not adequate for anything besides very light etching of glass and small text and detail work on soft stone. For granite and most harder stone I used a 3/32 nozzle for small text and detail work and either a 5/32 or 3/16 for large work. I had a 40hp diesel powered rotary screw compressor that put out 125 cfm at 100 psi so I could very easily run the 3/16 with no loss in pressure. A rotary screw compressor typically puts out so much air that they don't have a holding tank. The minimum compressor to run even the 3/32 nozzle would be something that puts out 25 cfm and has a 90 gallon tank, but even that will run quite a bit to keep up. Quite often I used green diamond for granite, it isn't as hard as either AO or SC but it's cheap - $15 for a 90lb bag. If I was onsite blasting and couldn't contain the media for reuse then I would always use green diamond, that or the customer would have to pay for the media as an extra charge. AO works well but creates a lot of static electricity so either you ground yourself or it will shock you often! SC is better because as it breaks down it retains the sharp edges that do the cutting where the edges on AO round off as it breaks down - SC is more expensive initially but you can reuse it more because of this. Whatever you do, do NOT use silica sand, playground sand, it releases silica dust and you risk the very real possibility of silicosis - google that for more info.
As for upgrades - the hose and nozzle that come with them are junk and 99% unusable. The only time I used the deadman nozzles was on a couple of very large jobs where I needed 1/4" nozzles and didn't want to rebuild the one I normally used to take the larger nozzle. I have attached a picture of a nozzle similar to what I used. You'll have to go to a hydraulic supply shop and have them help you put together the various fittings, make sure you get a good quality hose, they will wear so keep an eye on it for soft spots indicating a wear point.
The other upgrade was fitting a piece of copper tubing in the media outlet of the pressure pot to make the media flow better. I attached a rough drawing so hopefully this will make sense. I cut a piece of 1/2" copper pipe to about 6" long and drilled a lot of 1/8" holes in it. I fit this into the top of the mixer that screws into the bottom of the pressure pot. This made it so that instead of the single hole in the mixer for media to flow from the pot, you now have dozens of holes - this reduces the potential to clog when media doesn't flow perfectly for some reason.
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