I dropped by the dealer today to pick up a 90 degree 4" ell for a temporary
dust collection setup. I've never purchased in PVC dust fittings before.
This was a Jet part number, but I think its the same universal
Taiwanese-made fitting that everyone sells (other brand Woodstock?). It
looked like reasonable quality, then I looked inside of it. Expecting a nice
smooth sweeping curve, I was shocked. The inside of the fitting appears to
be two pieces of PVC that have been cut on a miter and bent enough to come
together. The outside of the ell is simply a nice looking shell. Its not
smooth and it actually swages down to restrict the flow - not exactly what
you want for a nicely designed smooth flow network.
I'd take it back. If you read up a little, 90 deg bends are not really
optimal anyway, you may be better off just using tubing to make the largest
bend you can afford in your space (or hook a couple 45's together). Ideally,
the tubing would be straight for the highest possible flow rate - every bend
you add lessens your cfm.
I have read up and done extensive calculations. There is a balance between
ideal flow conditions and making things fit in the shop. A 90 degree ell
doesn't add that much drop. Its almost academic. What is really surprising
(but not if you think about it) is the drop associated with flexible dust
collection hose. A 2 foot length of flex hose has twice the drop of a single
90 degree ell. Most people use flex hose to turn corners. That's far worse
than using a well made 90 degree fitting.
If you're using regular DC fittings, they are already "high flow" design. If
you're using 4" PVC, (2) 45's work better, or find a local plumbing
supply(NOT a BORG) and get high flow 90's(wouldn't know this, but SIL is
commercial plumber, and our code calls for high flow 90's in sewer lines).
Those who know the least will always know it the loudest.
Use standard borg plastic pipe fittings. Its cheeper. Now the sizes
are a little off for the connectors but I watched a show on TV where a
guy did custom pipe work with a heat gun. Aparently with a little bit
of heat you can stretch, shrink, bend and shape PVC just about anyway
you want. He took a piece of 2 inch and warmed it up and made a 2 - 4
reducer by using a broom stick handle to slowly encrease the size of the
pipe till it fit in a 4 inch fitting.
If he can do this the slight 1/4 inch change needed to get standard 4
inch PVC to fit into duct collector ports should be a sinch.
Sometime I think it is a plot. Dust collector and shop vacumn fittings
are intentially made just a little bit different from standard PVC so
you cant use the cheep high volume stuff.
Now I caution you that I haven't tried this yet but I am going to.
After all a couple of dollars worth of PVC should provide you with
plenty of stuff to practice with. And if it doesn't work out then all
you wasted is a little time.
I couldn't stand it. I happened to have a heat gun that I've used for years
for heat shrink tubing (electronics wiring). I wondered if it would enough
output. I needed a 4" x 4" square nozzel that adapts to 4" S&S pipe. So I
took a 4"x4" fence post and put a 10 degree taper cut on four sides to make
a jig. Then I took a scrap of pipe and began heating it. I could tell when
it "went rubbery" and slipped it over the end of my wooden jig. Voila! I
had a perfect nozzle ready to hook up to my dust collection piping.
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