In part 1 I explained the plan for my exhaust
system, made a wall opening for the pipes and made and mounted a cover for the opening. Before I can lay the tubes under the ceiling,
I need some blastgates. Blastgates are needed to lock the different
exits of the extraction system to concentrate the suction caused by the air flow on one
exit. Such a Blastgate consists of 3 parts, an upper
plate, a lower plate and a slider in between. The two plates each have circular cut-outs
into which the tubes engage. The slider in between also gets a round cutout,
and of course an impermeable part to be able to shut off. To be on the safe side, I measure the outer
diameter of the tubes once again and then adjust my circle cutter. Then I mount a stop to the drilling machine
and adjust it to the appropriate distance to the circle cutter, about 26 mm. The circle cutter cuts the 110 mm diameter
of the pipes.
Left and right of it I leave 26 mm space,
so the total diameter is 162 mm. Because the individual parts are cut out of
a plate, I first cut a strip from the plate, which has the width of the individual parts,
so 162 mm. Then I just slice this strip into pieces,
and get all pieces with the same width guaranteed, and have less work at the same time. So I set the rip fence of the table saw to
162 mm and cut a few strips. The cutting to length is done with the mitre
saw. The circle cutter needs a small sacrificial
board under the workpiece so that its cutting blades do not get into the aluminium table
of the drilling machine.
And as I had to find out, the drill is literally
pulling itself into the workpiece. Which means you have to clamp it properly. I
want to apologize for the noise my neighbour made with his saw. For my request not to be so loud when I am
in my workshop he unfortunately had no understanding. The upper and lower parts of the blastgate
are already finished with that, but the slider is still missing. It can be a bit thinner, because no tube will
be attached to it later. All parts are then sanded smooth so that they
can slide past each other easily. I made a mistake with the sliding parts, and
put the circle too close to the edge, flush with the case. A small overhang is needed, where a stopper
can be glued on, and where you can grab the slider to open it. Therefore I cut the parts again, this time
with a little space.
From the same material I cut a few thin strips,
which I glue onto the plates. The slider must be between the strips so that
the distance is exactly right. But there is the danger to glue it down. I tried different variations to avoid this. On the one hand by precise and careful gluing,
so that no glue gets into the inside. On the other hand by masking the slider. Both variants worked equally fine. But it was a little too tight for the sliders. I thought if I cut the sides out of the same
plate as the sliders, there should be just enough space to fit them.
But the tolerances are too small to get them
in between. That means, I have to plane and sand the sliders
flat again. The engineer speaks here of a clearance fit. In the next step I cut the sides again to
create a smooth outer edge over the 3 layers. It wasn't about making the blastgates smaller,
so I try to remove as little material as possible. And then I can glue the stoppers onto the
sliders. They later give me a defined stop that assures
me that the opening is exactly right. I want to fix the tubes to the ceiling later. On the wooden beams this is no problem, but
a large part will run along under this double-T steel beam. I can't and don't want to just screw it into,
so I build some holders around it to guide the pipe safely. They should consist of a small multiplex board,
with a hole large enough for the tube to pass through.
The lower part should be removable to be able
to insert the tubes and held by screws. The upper part should wrap around the steel
beam with angles and hold on to it without being screwed down to the beam. So the holders only hang under the beam. I still have some 30 mm plywood leftovers,
which are perfectly suitable for this. The only problem was that 30 mm are too thick
to be penetrated by the circle cutter in one pass. So you have to cut up to half of it, then
turn the piece around and finish the hole from the other side. The central drill of the circular cutter is
therefore also long enough so that from the other side you have at least a guide hole
to which you can orientate yourself. And in order to fight the dust already now,
without an extraction system, I have fixed my vacuum cleaner next to the drilling machine
in order to collect a part of the sawdust directly. The holders were unnecessarily long on one
side, so I shortened them again here. Then I predrilled the holes for the screws,
without them the multiplex would split up and it will be easier to find the right position
later.
Of course the holes are countersunk, and because
the screws are longer than my drill bit, I used them to create a small passage before
I divide the holders in the middle of the hole. Then I screwed them together again so that
nothing gets lost. These small angles are now to be attached
to the holders. Therefore I clamp the holders directly together
with the angles on the steel beam and screw them together. Due to the clamping, the angles press tight
against the steel beam and the holder sits backlash-free, without wobbling under the
carrier. In the meantime, the blastgates have dried
as well. I scrape off any excess glue. Now I can start with attaching the tubes.
Where the tubes run along a wooden beam I
fix them with some plumber tape. There is a special lubricant to make it easier
to put the tubes together. But it is still not easy. I would rather say without it it is practically
impossible, and with bloody annoying and exhausting. You have to hit exactly the right angle, then
they suddenly slip together. But finding this right angle is a real test
of patience. You should try to avoid 90° angles with the
tubes and replace them with the largest possible arc, or at least two 45° angles. Either serves to slow down the airflow as
little as possible, and a tight 90° curve does slow down the airflow quite a bit. The pipe under the steel beam I attached here
a bit too fast, because I could not insert the angle pieces this way. By the way, I also installed it the wrong
way round, but I only noticed that when I was almost finished.
I should have noticed it at the branch at
least, because it points in the wrong direction. So I had to do everything twice… An old lamp was getting in the way, but because
it was out of order for years I removed it completely. When I was finished with it, I noticed that
the branch is flipped around. Sometimes it helps to clear your head for
a moment and to deal with something else, because you don't see the obvious things when
you are stuck too deep into something. A rubber mallet is by the way not helpful
at all to connect the pipes. Contrary to my original plan, I decided to
add a branch over the floor extraction to make it easier to collect the dust from my
belt sander. Because the pipes are a bit under tension
here, I reinforced the connection with installation adhesive. I hope that the tubes will give way over time
and take on their enforced shape. Now all the blastgates and tubes are in place.
The next part will be about the on/off-switch,
the last meters behind the blastgates and the floor extraction..