Thread: Dust extraction strategies for underneath the table saw?

Originally Posted by BobL

It will probably be OK but how about front on photo of the grill. Also I'd need actual dimensions of the lengths and width of the gaps as seen directly from above (i.e. ignore the angles) in the post.

Photo attached.
photo copy 2.jpg

Bob, I've left it in its wrapper in case it needs to be returned. The grill is on the bench, and I've taken a photo from directly above it. As you may or may not be able to see, there is no "through" gaps, where you can look straight through the louvres.

The space between each fixed louvre is exactly 10mm, each space is 135mm long (or wide), and there are 6 gaps (7 louvres).

Thanks.

Another way to approach this but perhaps more bulky is to make a blast gate for the entry air so that the air speed can be regulated for best performance. It would be easy to build a wood frame with a sliding gate in it as big as you need. Once you have it set the excess blade sticking out could be cut off if need be and fix the blade remaining with a screw to prevent movement. Put a screen over the opening if you wished but I wouldn't bother as the entry could be used to see what is going on if required. If sited correctly it might be possible to see into the saw and watch what actually happens when something is cut, a camera could be used I suppose.

The Hammer slider I have now has the bottom half of the blade sitting in a narrow space a bit like a guard under the blade. This is hooked up to a 5" flexible line that goes straight to the extraction port. In effect it does not extract from the cabinet at all but from under the blade and is damned effective as hardly any dust goes into the cabinet. Like everything it has its drawbacks and if any larger offcuts finish up in there it can get blocked. Being a slider the top of the saw is effectively open at all times for air entry due to the construction of it.

Originally Posted by Chris Parks

Another way to approach this but perhaps more bulky is to make a blast gate for the entry air so that the air speed can be regulated for best performance. It would be easy to build a wood frame with a sliding gate in it as big as you need. Once you have it set the excess blade sticking out could be cut off if need be and fix the blade remaining with a screw to prevent movement. Put a screen over the opening if you wished but I wouldn't bother as the entry could be used to see what is going on if required. If sited correctly it might be possible to see into the saw and watch what actually happens when something is cut, a camera could be used I suppose.

The Hammer slider I have now has the bottom half of the blade sitting in a narrow space a bit like a guard under the blade. This is hooked up to a 5" flexible line that goes straight to the extraction port. In effect it does not extract from the cabinet at all but from under the blade and is damned effective as hardly any dust goes into the cabinet. Like everything it has its drawbacks and if any larger offcuts finish up in there it can get blocked. Being a slider the top of the saw is effectively open at all times for air entry due to the construction of it.

Hi Chris:

Thanks for your contribution. Your solution for making a home-made grate "sliding-gate" system sounds great. I've got some really pretty bits of New Guinea Rosewood which would do a lovely job! I've just posted about the best position of the grill -- I need all the help I can get!

As for your Hammer slider, all I can say is I'm jealous. My shop is not suited to a slider of any size, so I'm "stuck" with my Delta Unisaw for the time being. I've inspected the Hammers and Felders before and yes the dust shroud system really close to the blade is fantastic. The Unisaw was just not made for such a system -- not enough space inside the cabinet. Incidentally, I've just procured a used arm guard system (the really big one) from a Felder 700 series slider. Hoping to attach it to my Unisaw for above table extraction. But that's getting beyond the parameter of this thread!

Originally Posted by LuckyDuck

Photo attached.
Bob, I've left it in its wrapper in case it needs to be returned. The grill is on the bench, and I've taken a photo from directly above it. As you may or may not be able to see, there is no "through" gaps, where you can look straight through the louvres.

The space between each fixed louvre is exactly 10mm, each space is 135mm long (or wide), and there are 6 gaps (7 louvres).

Thanks.

Thanks for posting the picture. Now I understand what it looks like and that is important - I have these vents on the side of my sort-of-solar wood drying kiln

Long narrow angled gaps like that have a significant edge effects

I would treat the gaps as though they are only 7 mm wide. This dimension is just a ball park figure from experience.
This would then make it 6 x 7 x 135 = 5670 mm2 so you you would need 3 and abut of these to match a 160 mm duct - surprising isn't it - now this will still generate some restriction so you should use maybe five of these.

If you want to match a 100 mm duct you would just need two of them

Originally Posted by BobL

Thanks for posting the picture. Now I understand what it looks like and that is important - I have these vents on the side of my sort-of-solar wood drying kiln

Long narrow angled gaps like that have a significant edge effects

I would treat the gaps as though they are only 7 mm wide. This dimension is just a ball park figure from experience.
This would then make it 6 x 7 x 135 = 5670 mm2 so you you would need 3 and abut of these to match a 160 mm duct - surprising isn't it - now this will still generate some restriction so you should use maybe five of these.

If you want to match a 100 mm duct you would just need two of them

Thank you Bob for this. This sort of detail is really helpful -- and hopefully helpful for others planning to modify their TSs like me. After this post, it is clear that the grill is going straight back to Bunnings.

I think a much cheaper and more practical option will be for me to make a timber grill -- I will double check about the danger of fingers reaching inside, but I think there is plenty of space up high on the side of the cabinet.

I'm amazed at how much venting is required -- no wonder everyone's machines are choked with low flow!

First I tried to work out how many 30mm holes would be required in a timber plate. 32 holes would be required to approximate a 160mm port, so would be looking at around 60 holes to make sure that flow is not restricted? Ridiculous!

Then I thought about making long narrow slits into the side of the cabinet, say all across the top of the cabinet, just under the table. Say 500mm x 27mm (making an effective 500 x 25 cross section). I would need three of these to get to 37500mm2. That would reek havoc with the strength of my cabinet's sheet metal -- so I don't think that's a very good option.

Far out -- what do you recommend!

Was wondering when someone was going to raise the issue of weakening of the cabinet, which is required to support a few hundred kilo of cast iron table, arbor and gears, and motor!

Originally Posted by Dengue

Was wondering when someone was going to raise the issue of weakening of the cabinet, which is required to support a few hundred kilo of cast iron table, arbor and gears, and motor!

Well, I'm known to be a it slow at times!

Yep - taking the angle grinder to a machine to get it to breathe is not for the faint hearted.

Most of the weight is not really taken by the flat panels but by the corners of the cabinet.
Look at how flimsy the legs are on a contractor saw - they still have to carry a similar size motor motor and a cast iron top.
The means a 150 x 300 mm section of the panel could easily be removed without compromising the strength of the cabinet

If you are at all worried about strength you could weld up a 5mm x 25 mm angle steel frame say 300 x 300 mm in size and bolt it onto the inside of the cabinet, then get an angle grinder and using the angle iron as a straight edge cit out the panel inside the frame. Then it would be just as strong as having the panel.
Then i would use a 1mm x 20 or 25 mm square mesh to keep fingers out. SS would be nice. Such a fine mesh offers so little resistance you could probably make the opening 160 x 320 and it would still work.

You did say there was a lot of other gaps and slits in the cabinet?

If this was my saw I'd tackle it like thus... first install dust chute/piping mods as planned, then do a flow test, ideally with an appropriate test device but for a quick and simple test device a utube manometer, due to potential edge effects at the tube end that is inserted into the pipe in this instance we are only using it as a comparitor, what we are trying to see is a difference in water colum hieght in the utube, e.g. with the door open we might have 75mm, if we close door and we get an increase in WC say 100mm then we know there is a need to allow more air into cabinet via openings. If there is no difference then we know that sufficient air is flowing into cabinet via existing gaps.
Next is whether it is an advantage to block off existing gaps and reintroduce air via new openings that promote dust pickup.

Pete

Pete -- the point about the order in which to make the mods is a really good one -- first the port, then the vent/grill to reduce resistance.

Bob -- agreed with your observations about sheet metal cabinets -- I was probably reacting to the extent of cuts required with the solutions so far canvassed. Your suggestion of a square/rectangle with thin wire mesh (indeed ss would be nice!) is probably the best of all.

My cabinet has a couple of holes here and there (I don't know what they served originally) near the bottom which I will plug permanently. I have had a close look at the gaps between the cabinet and the top, and I must say they are not large, perhaps 5-7mm wide, all around the top, but only intermittently on account of cast-iron ribs. Probably not much influence?

Then there is a larger curving slit where one of the adjusting wheels protrudes -- it arcs to follow the travel of the arbor/saw unit when adjusting the machine for angled cuts. I would imagine it is fairly subjective to determine the influence this slit will have on reducing resistance as the arbor/saw unit is partially blocking the slit, and the axle/wheel also helps block it.

Anyway, the slit is 37mm wide, by 250mm long, and the axle/wheel sticks out of the slit and is approximately 50mm. So effectively we have a 37-200 slit.

One of your primary concerns, LD, was the amount of sawdust collecting in the corners, and not being sucked through. I have the same problem on my Carbatec THB-10 cabinet saw, so I just remove the throat plate and hit the cabinet with a blast of the compressed air hose at the end of the day, with the DC running.

More annoying is dust that gathers in the lower sloping part of the door. On opening the door it all falls on the floor. so I drilled a 10 mm hole in the side of the door and put the compressed air in there too.

I don't think there is too much wrong with the air flow on my setup, which is very similar to your Delta setup. I have a 25mm finger hole in the throat plate, and any loose sawdust I put near that gets sucked in pretty quickly, even with the motor running. The only dust control I have added is to add magnetic posters over the gap where the raise / lower wheel is to stop the sawdust coming out and spilling on to the floor.

Methinks you might be worrying a bit too much about it all, although anything you do to get better flow will be worthwhile.

Originally Posted by Dengue

One of your primary concerns, LD, was the amount of sawdust collecting in the corners, and not being sucked through. I have the same problem on my Carbatec THB-10 cabinet saw, so I just remove the throat plate and hit the cabinet with a blast of the compressed air hose at the end of the day, with the DC running.

More annoying is dust that gathers in the lower sloping part of the door. On opening the door it all falls on the floor. so I drilled a 10 mm hole in the side of the door and put the compressed air in there too.

I don't think there is too much wrong with the air flow on my setup, which is very similar to your Delta setup. I have a 25mm finger hole in the throat plate, and any loose sawdust I put near that gets sucked in pretty quickly, even with the motor running. The only dust control I have added is to add magnetic posters over the gap where the raise / lower wheel is to stop the sawdust coming out and spilling on to the floor.

Methinks you might be worrying a bit too much about it all, although anything you do to get better flow will be worthwhile.

These examples are understandable visual examples and apply to the visible dust, what LuckyDuck and others have realised is that these are symptomatic of poor all round (but especially very fine) dust collection while the saw is running.
If sawdust is coming out of gaps and spilling onto the floor that is a sure sign that the air flow through the cabinet is insufficient and means it will not be collecting sufficient air from the vicinity of the saw.
Don't forget that the throat plate and any holes thereon are blocked by the wood being cut will not be collecting dust while it is cutting.

Originally Posted by Dengue

Methinks you might be worrying a bit too much about it all, although anything you do to get better flow will be worthwhile.

No doubt! I'm a bit of a bulldog when I sink my teeth into a new idea, or become aware of a deficiency/problem!