I posted something about this in another forum but since then I have expanded this and here are the results.
The experiment is to see what sorts of numbers and sizes of dust particles are made by using a thin (1 mm) kerf cut off wheel in an angel grinder and using the same wheel in a much lower revving setup (i.e. a table saw)
the test cuts were of the same piece of steel, cut was 114 mm long so basic geometry and density of steel says that at least 5.7g of steel needs to be removed to make these cuts.
On the angle grinder the amount of metal cut was 7.51 g with a net loss in the weight of the wheel of 1.4 g.
On the table saw the amount of metal lost was 6.55 g while the amount of wheel used up was 3.5 g so more than twice as much wheel is used up to make the same size cut (you guessed right Karl :2tsup:)
The thin wheel in the table saw removes 14% less metal in making the cut which is probably an indication of how unsteady it is to hold an angle grinder versus working the metal against a fixed wheel.
Now lets look at the numbers and distribution of particles.
Before I started I took some background readings (these are the readings at zero time) and then performed the cut and then took readings over the next 48 minutes to see how the dust levels changed with time
Remember, the small particles are invisible and are the ones that penetrate further into airways AND stay suspended for much longer that the heavier ones.
Here is the angle grinder results.The numbers of particles for a range of dust parcels sizes is shown.
The heaviest particles (>5 microns, probably metal) fall out of the air very quickly having 1/2 residence time (time taken to reach half of previous value) of about 1.5 minutes
The smallest particles (0.3 - 0.5 microns, probably mostly from the wheel) stay in the air much longer. 1/2 residence time of ~17 minutes.
Whether the # of particles represents a danger I still have to do the maths but this represent about twice the amount of dust generated by sanding wood on a lathe for 2 minutes. (Wood turning is one of the worst dust making activities for woodworkers)
Here is the same thing for the same wheel in a much lower revving situation of a table saw
1/2 Residence time in air for the finest dust is now 40 minutes (i.e. stays suspended in air much longer) while for the heaviest particles it's now around 10 minutes.
To assist you in comparing the first 2 graphs I show a 3rd one which plots the % difference between the two setups.
Values >0 represent more dust from the angle grinder and VV
The angle grinder clearly produces more fine dust than the table saw during the grinding but the dust from the table saw cutting setup hangs around much setuplonger.
The table saw produces more heavy dust that also hangs around longer.
The table saw produced a blue smoke during cutting which, because its visible, represents the 2-5 and >5 micron dust.
Because this takes so long to settle I suspect it's wheel material and not so much metal.
All in all it does not look good for either setup and because the 1/2 residence time is long for the finest particles (even for the angle grinder) it's no good enough to just wear a mask or respirator for the period of cutting - they will need to be worn for hours after the last cut. If you do this regularly you are much better off install dust extraction that removes this dust from the shed.
Like I said I now need to do some homework i.e. look up the composition of wheels, the OHS limits of their contents, and then calculate the milligrams/m3 of the dust in air and make some assumptions about the mix of metal V wheel in the dust.
FWIW I do all my cutting either under or adjacent to my fume hood. If I run the fume hood the dust levels drop to near background, in fact they never rise much above background - I just need to remind myself to turn it on!!!!
The experiment is to see what sorts of numbers and sizes of dust particles are made by using a thin (1 mm) kerf cut off wheel in an angel grinder and using the same wheel in a much lower revving setup (i.e. a table saw)
the test cuts were of the same piece of steel, cut was 114 mm long so basic geometry and density of steel says that at least 5.7g of steel needs to be removed to make these cuts.
On the angle grinder the amount of metal cut was 7.51 g with a net loss in the weight of the wheel of 1.4 g.
On the table saw the amount of metal lost was 6.55 g while the amount of wheel used up was 3.5 g so more than twice as much wheel is used up to make the same size cut (you guessed right Karl :2tsup:)
The thin wheel in the table saw removes 14% less metal in making the cut which is probably an indication of how unsteady it is to hold an angle grinder versus working the metal against a fixed wheel.
Now lets look at the numbers and distribution of particles.
Before I started I took some background readings (these are the readings at zero time) and then performed the cut and then took readings over the next 48 minutes to see how the dust levels changed with time
Remember, the small particles are invisible and are the ones that penetrate further into airways AND stay suspended for much longer that the heavier ones.
Here is the angle grinder results.The numbers of particles for a range of dust parcels sizes is shown.
The heaviest particles (>5 microns, probably metal) fall out of the air very quickly having 1/2 residence time (time taken to reach half of previous value) of about 1.5 minutes
The smallest particles (0.3 - 0.5 microns, probably mostly from the wheel) stay in the air much longer. 1/2 residence time of ~17 minutes.
Whether the # of particles represents a danger I still have to do the maths but this represent about twice the amount of dust generated by sanding wood on a lathe for 2 minutes. (Wood turning is one of the worst dust making activities for woodworkers)
Here is the same thing for the same wheel in a much lower revving situation of a table saw
1/2 Residence time in air for the finest dust is now 40 minutes (i.e. stays suspended in air much longer) while for the heaviest particles it's now around 10 minutes.
To assist you in comparing the first 2 graphs I show a 3rd one which plots the % difference between the two setups.
Values >0 represent more dust from the angle grinder and VV
The angle grinder clearly produces more fine dust than the table saw during the grinding but the dust from the table saw cutting setup hangs around much setuplonger.
The table saw produces more heavy dust that also hangs around longer.
The table saw produced a blue smoke during cutting which, because its visible, represents the 2-5 and >5 micron dust.
Because this takes so long to settle I suspect it's wheel material and not so much metal.
All in all it does not look good for either setup and because the 1/2 residence time is long for the finest particles (even for the angle grinder) it's no good enough to just wear a mask or respirator for the period of cutting - they will need to be worn for hours after the last cut. If you do this regularly you are much better off install dust extraction that removes this dust from the shed.
Like I said I now need to do some homework i.e. look up the composition of wheels, the OHS limits of their contents, and then calculate the milligrams/m3 of the dust in air and make some assumptions about the mix of metal V wheel in the dust.
FWIW I do all my cutting either under or adjacent to my fume hood. If I run the fume hood the dust levels drop to near background, in fact they never rise much above background - I just need to remind myself to turn it on!!!!
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