Thread: Dust concentrations while drilling wood

A couple of years ago I did some quick and dirty dust testing of various wood working activities so that I could focus my investigations on the important stuff first.
One of the activities that surprised me at the low levels of dust generated was drilling, but I have not had the time to chase it up until now.

The method I used was as follows
1) locate dust monitor 150 mm from the bit, and 50 mm above surface of wood.
2) measure airborne dust background
3) drill 5 consecutive holes in wood
4) measure airborne dust levels in mg/m³
5) clear away all chips using a DC and running a 2300 CFM venting fan for 2 minutes
6) Remeasure background.

The variables I tested were:
- drill RPM (VSD came in really handy here)
- wood type (MDF and Jarrah)
- Drill bit type (6 and 10 mm Twist (T) and 25 mm Forstner (F) )

In the following graph the measured dust concentrations ( in mg/m³) are shown.
6mmTMDF stands for a 6 mm twist bit in MDF.

The OHS safety limit is 1 mg/m³ for hardwood and also MDF, although there is discussion on dropping the MDF level to 0.3 mg/m³



My interpretations are as follow
All results are below the recommended OHS levels. The high 500 rpm result for the 6 mm twist bit in MDF could just be due to me moving my hand on the drill press in a slightly different way that the others
No major difference in airborne dust levels generated by Jarrah or MDF or across the RPM range. Maybe the higher RPM maybe cuts through the wood faster and hence perhaps generates less dust?
Bigger drills tend to make more dust than smaller ones.
As far as Jarrah being drilled with a 6 mm bit is concerned, it appears that it would require drilling more than 50 holes to exceed the OHS limit.

Other observations.
I have the full particle size distribution but the results appear pretty complicated so I will have to look through these very carefully before posting
As I said above the results obtained were very sensitive to a number of factors. Although the drilling did not seem to make much dust, just moving my hand/arms carrying a piece of wood across in front of the sensor could upset the measurements and moving the wood with all the shavings on it generated about the same amount of dust or more as the drilling did ??? I suspect that if a pile of cumulative waste was flicked or swept off the DP table that would generate a big dust pulse into the air.

Initially I had located the dust monitor on the opposite side of the drill to where my VFD is located and could barely measure any dust levels above the background. Then it dawned on me that the VFD has a small fan in it and this was enough to pull the dust away from the drill bit keeping it away from the dust sensor. I could not turn off the VFD while drilling as this runs the drill so I had to move the dust sensor to be on the same side as the VFD. This will bias the results so the results shown are a maximum. Because the amounts of dust generated are small even without any venting the dust levels were able to dissipate into the main volume of the shed within minutes. Of course if drilling was undertaken for a long period without using a DC the dust levels in the shed would eventually saturate and less natural dissipation would be possible.

In terms of the dust levels involved, to put things in perspective, routing, ripping and thicknessing are in the 10 -100 mg/m3 range and sanding and turning can go even higher, so drilling appears to be a low level dust making activity. I guess it depends how much drilling you do but as far a fine dust levels are concerned I think you can safely put the DP on the end of the priority list for DE fitting.