FREE plans for my home made design of blast gate are at the end of this page. This gate is similar to one Terry Hatfield made and posted on his site (thanks for the inspiration Terry) but I made a couple changes which speed construction and eliminate the chance of the slider not seating in the blind hole due to sawdust buildup.
Terry's plan calls for use of a "starter collar" or "flange" which I did not have luck in locating so I offer an alternative that should be readily available in the form of a 2-piece 8"-6" HVAC reducer. It seems that these "starter collars" are readily available in the USA but not in Canada so.
Starter flange update... Glenn Strome informed me that the proper name for the "starter flange" in the HVAC world is a "Dehumid Connector" and is used to connect a humidifier (or de-humidifier?) onto the 6" duct. Thanks Glenn.
I had made an earlier version using a couple pieces of scrap straight 6" pipe in place of the flanges but it not as slik as using the flanges (it is cheaper though as the pipe cost is under 3 bucks!). If you want to use 6" PVC you can modify the printed planby doing the following...
1) Route a hole to tightly match the OD of your PVC pipe ALMOST through the face of each frame plywood half (say within 1/8" of a through hole).
2) Next rough cut the hole in the ID of each frame half and then with the pipe inserted, use a flush trim bit to trim the ply even with the pipe ID.
I admit that this is NOT how I actually made the gate in the next 2 pics but it's how I would do it if I were using only 6" PVC again. I used 1/2" ply scraps on all my gates as I had some kicking around and had no 3/4". Using 3/4 allows you a little more room for comfort when installing the screws etc. and if using PVC pipe it allows the use of the routed "lip" as fashioned above where 1/2" did not.
Here's a pic of that first gate with the PVC pipe installed and some 6" durathane flex attached...
3) Next pull out the pipe, add some sealant and drill and countersunk about 4 small screws from inside the pipe into the plywood just to hold it from pulling out. After the sealant cures it is very solid even with 4 tiny screws. The drawback is that it is hard to get the screws flush with the thin walled PVC and they leave a bit of a protrusion but it's not a big deal. This is a handy and cheap way to build an in-line gate that mates perfectly with the PVC fittings.
This is the plastic pipe gate in service on my planer station...
As for the gates in my plans with the starter collars, they are easier to make and it's easier to slip flex hose onto etc. If you need to install one of these in a 6" PCV fitting you can by using a short piece of pipe slipped over the starter flange as shown in the pic below. You can see inside the white PVC pipe how snugly the metal flange fits. It required a bit of heat from the heat gun to get it on but it's a great fit! Looking closely you can just see the dimple at 1:00 where the sheet metal screw was ground off almost flush with the starter collar. There is another screw at 180° and some duct tape on the outside for good measure.
Note the hardboard slider inside has the smooth side facing the pic. Install the gate with the SMOOTH side to the blower as the rough side will not give you as good of a seal!
A pic of the gate open...
Note the dowel used as a reference against the frame for full open.
And closed...
And on this view note the finger hole lower edge at the frame is the reference for fully closed!
The slider is totally free to be pulled out if ever required.
That's it!
It takes little more than a few hours to build half a dozen and it can be done with scrap materials and a few $5 starter flanges.
Enjoy!
LINKS TO THE PLANS....
Here's a copy of the plan in .PDF (Adobe Acrobat 5.0 required)
If you have a CAD program that can import AutoCAD R14 DXF files look below....
Here's a importable .DXF (Drawing Exchange Format) - (Packaged in PkZIP.)