Thread: Festool Kapex SCMS dust hood.

I have heard differing stories on this saw, some say the DE on it is fantastic and others complain about it. Have you run this yet cutting timber?

Even if you use 50 mm hose, the problem is the ID of the saw's dust port is much smaller, so no conventional DC will be able to pull much air through such a small port.
The narrowish gap between the cowling and the blade also restricts air flow.

Only something like a vacuum cleaner, which operate at 2 to 3 times higher pressures, will be able to get anything through that dust port.

Short of boring out the port there's no other choice but using a vac and living with the vagaries of a Vac in the shed.
Of course you an put the vac outside and run an independent system of ducting.
A second best option is to use a vac such as a wet and dry vac with a hose type outlet and feed the outlet into the DC ducting

I don't recommend connecting any power tool to a DC unless that power tool has a built in dust extraction fan, Then the flow limit is not the size of the orifice but the flow rate of fan which a DC can easily keep up with.

Yes, have been cutting pine and MDF and throwing loose workshop materials at it, such as small balls of masking tape, floor sweepings etc.
just to see what the dust hood is capable of sucking up.
My main concern is to get more suction to the Kapex dust port, and the way that I've configured it with the 50mm feed is not sufficient.
I don't have any flow rate monitors, but it is very week compared to having the shop vac connected to that port, when you can feel the suction it is creating.
At the moment i have the 50mm line connected to the 150mm line with a normal wye configuration.
I was wondering if i extended the 50mm to penetrate into the main line if it would achieve more suction, albeit at the expense of decreasing the main line area and suction.
Will have to suck it and see (ha ha) .
There must be some perfect amount of draw between the main hood line and the Kapex port.
What that is, and how you do it .... well, will keep experimenting.

Originally Posted by Sea

At the moment i have the 50mm line connected to the 150mm line with a normal wye configuration.
I was wondering if i extended the 50mm to penetrate into the main line if it would achieve more suction, albeit at the expense of decreasing the main line area and suction. .

It won't make any difference - see my post above.

Originally Posted by BobL

It won't make any difference - see my post above.

Bob is correct, in my case it did make make a big difference on my TS when I took the 50mm hose away, installed a 100mm hose to the port with a simple adaptor and I did not need any instrument to tell me that the flow had gone up hugely as I could hear and feel the difference and see the lack of dust and debris on my TS top. On my Glide saw I initially used a hose from the port to the plenum in my original (now demolished) saw hood and it simply did nothing. Bob may not know that the DE port on the Kapex is set up entirely different to every other saw as it draws directly from the blade guard high up whereas most other SCMS rely on the blade ejecting the debris into a port that is not attached to the actual saw blade guard.

Hi, thanks Bob, just saw your replies.
Well, yes i think i will have to reconfigure the setup and maybe include the use of a another vac, or
what if i have no connection to the drop saws port and just let it vent into the hood and rely on its dust extraction capabilities.
If you consider the theory of collecting at the source such as a table saw, with a hood over the blade, the drop saw seems a bit more difficult although its another spinning blade with dust flying off it.
It would be near impossible to connect a close to source, 100mm (at least) port to a SCMS which would allow full range of movement.
I think this problem would extend to all varieties of SCMS, not just Festool.

Thanks Chris, from what I've read from other sources, the Kapex is supposed to collect 90% of dust through its port.
So it would be great, if thats true and i can utilise that.
I have a somewhat reserved believability about manufacturers dust extraction claims from recent experiences.

The Kapex has some very vocal critics for a lot of reasons but it is always down to the user and how he finds it in my view. I would be tempted to wrap your hood tighter and make removeable or hinged panels for the bits that very occasionally get in the way which is what I will do when I get back to it. On mine there is no need to use front panels as the dust simply gets pulled into the hood because of the air speed and volume in a smaller space. I think I use compound cutting maybe once a year but of course if you do it all the time it is a major consideration.

What is the ID of the dust port?

ID of dust port is 36mm.

Originally Posted by Sea

At the moment i have the 50mm line connected to the 150mm line with a normal wye configuration.
I was wondering if i extended the 50mm to penetrate into the main line if it would achieve more suction,.

When you have a duct setup with two branches, the static pressure drop through both branches following the junction will be the same. The static pressure drop through each junction, as a function of airflow volume, is dependent on the length, cross-sectional area, perimiter and roughness of each junction, as well as any additional bends or kinks in each. In your case, you have a 150mm duct with 10 times the cross sectional area of the 50mm duct (as well as some additional restriction due to the 36mm port), not to mention smooth bore vs flexible ducting. Thus the 50mm branch will create far more static-pressure drop than the 150mm for a given volume of airflow. The split in airflow between the two will therefore be very unbalanced (would have to look up some tables / coefficients to work it out) to provide a state of equilibrium. If you have a powerful 3-5HP system then you may have a total of around 1000CFM, but your 50mm duct would only be getting a very small percentage of that. Maybe 50 CFM at a guess? A shop vac would do much better in this case.

Festool DE relies on high velocity flow as I understand it. The splice into the relatively low velocity high volume 150mm ducting, would benefit from a venturi arrangement most probably, ( think Weber carbs), if one knew enough maths and flow dynamics, and had enough time and creativity...

Use 2 systems. I have tried my Kapex with 50mm Festool hose and Clearview Mini CV6, connected to a CT26 and noticeable drop off in collection compared to 36mm for same length. 36mm hose seems to work best. I have played around with manometer and an airflow meter (poc lasted 2 tests) but not got anywhere with actual numbers. From what I have read, keep the connection as short as possible, and flow as fast as possible.

Also planning a shroud, hooked to a separate collector.

Well i think using a seperate vac for the Kapex port might be the go then.
Seems a bit crazy to have to run 2 systems for one tool but if thats whats required, then so be it.
I can use my big shop vac ( which i plan to set up with a mini cyclone) and which has a Hepa filter,
although this will have to be removable from the saw so i can use it around the shop.
Or i have an old Festo vac ( i think thats what they were called before becoming Festool )
I can plug the Kapex power cord directly into it and it will be triggered by the saw,
it could be left under the bench as a permanent fixture.

I agree its unfortunate that you should have to add a vac for that machine.
If you do that I would move the vac outside because most Vacs make more fine dust than they pick up.
Even vacs with Hepa filters have problems, unless their motor cooling loop are HEPA filtered then their motor cooling loops eventually become fine dust generators.

The 50 mm hose diameter is nearly irrelevant because the flow is dominated by the 36 mm ID orifice of the saw cowling.

Under regular DC pressures this orifice will typically transfer about 30 CFM while that of a shop vac will be around double that, so say 60 CFM.
Now on top of that has to be added the fact that the blade cowling is quite restrictive so the flow will drop - say 50 CFM for the vac and 25 CFM for the DC.

That saw blade moves at around 100 mph and will this generate moving air speeds and chips at around the same speed.
OTOH, 50 CFM through 36mm equals about 50 mph and 25 CFM will be only 25 mph so no wonder the DC has trouble with the dust collection. Remember those speeds are inside the duct and speed drops dramatical outside the duct.

In practice chip speeds drop rapidly, and the air speed drops even more rapidly, with distance (even with mm) from the source which is one good reason to set the dust collection back even a little distance from the blade as by then chips will have slowed down and there is a chance for a high volume low speed system to catch the dust. But if low flow systems like a vac are used they won't have the flow to grab the fine dust.

I have measured the air speed about 50 mm away from a 12" blade and its typically 23 mph, chip speed will be somewhere between air speed and blade speed.
A 4" duct connected to a DC will pull a max of ~425CFM.
Inside the duct the air speed is nominally 55 MPH but drops rapidly with distance from the port hence the significance of a bell mouth hooded port.
As well as increasing the overall air flow through the port, BMH ports generate higher air speeds further outside the duct opening which has a greater chance of grabbing more chips and more fine dust.

So if you want to collect chips and fine dust direct from the cowling with a DC you will need to redesign the saw cowling to allow for at least 4" ducting to be connected.