Building a Blast Gate

[Alan in Little Washington]

My editor asked for tip or short article on how to build a blast gate. Though this is not a tip nor a "short" article, I decided to send it anyway, and let them decide what to do with it.

Make Your Own Blast Gates

Are you building or expanding a dust collection system? Make your own inexpensive, self-cleaning, and easy- sliding blast gates quickly and easily with shop scraps and a few pieces of PVC pipe. The secret to their smooth operation is a slide made from two back-to-back layers of high pressure laminate and a laminate-lined gate body. I designed this gate with a male and a female side so it can connect to PVC Sewer and Drain (S&D ASTM 2729) duct work and most quick disconnect fittings. Change the inlet and outlet and it can be used with any duct work. If you need a number of gates, it is easy to build them mass production style.






To build a 4" blast gate (It is easy to scale up to a 6" gate):

• Cut two 6" x 6" squares of 1/2" (or 3/4" MDF), one for each half of the gate body. You can also use flat, smooth plywood. It may be difficult to attach the sides to Melamine coated particle board.
  

• Cut a 4-1/2"* hole for the inlet in the center of one square and a 4-3/16"* hole for the outlet in the center of the other.

* Sizes are for a 4" PVC S&D connector fitting (inlet) and pipe (outlet). Use a spindle sander or file to achieve a good fit.

Parts:

• Using adhesive, apply 6-1/4" x 6-1/4" pieces of laminate to one side of each gate half. (See sources for laminate below). Trim with a router and flush trim bit.

• Use a table saw to cut a 4" PVC connector in half. Set the blade 1/4" above the table and adjust the fence. Advance the connector until the blade just cuts through the bottom, then rotate the connector towards you until the cut is finished. Roughen the outside of the last 1/2" of the cut end and glue it into the inlet hole with epoxy or urethane glue. Glue a 3" length of PVC pipe into the outlet hole. Make sure they bottom out against the laminate.

• When the epoxy/glue has hardened, drill a clearance hole and use a flush trim bit to open up the holes in each piece.
  

• Use adhesive to join two 7" X 14" pieces of laminate, back to back, to make the gate slide. Trim it to 5-15/16" x l3".

• Double stick tape the slide to the laminated face of the inlet gate body so it extends 1"past one end to allow room for a handle. Drill an access hole in the laminate and use a flush trim bit open up the hole in the slide.

• Make gate sides from two 1-1/2" x 6-1/2" pieces of laminate. Apply a 1/8" wide strip of tape in the middle of the back of each piece to keep adhesive from the area where the slide contacts the side.

• Sand the sharp edges of all pieces of laminate.

• Carefully apply laminate adhesive to the backs of the two sides and two edges of each gate body piece. Remove the strips of tape before the adhesive sets up.

• To ensure clearance for the slide, put 2 to 3 layers of painter's tape near the edges of one face of the slide. Wax the laminate faces of the gate halves. Position the slide between the gate halves, lightly clamp them together, and apply the side strips. Tap the strips with a mallet to ensure a good bond; trim them flush with a router.

• Pull the slide from the gate and remove the tape. Clean and wax the slide. If you add handles make sure one is removable.

Sources of inexpensive laminate: Home centers often sell damaged sheets of laminate at a big discount. I get FREE laminate scraps from a counter fabricator's trash - the backs are often coated with adhesive, but acetone takes it off very quickly and easily.

[JimmyC]

Once again nice job Alan, on both the building process and the tutorial. I hope they figure a way to publish the whole thing.

[jhreed]

Electrical engineer, hvac engineer, journalist. How much talent can God grant one individual. I always look for your posts. know that they will be factual, understandable, and pleasantly readable.
I did not know that you were a journalist. Where would I find your work?
James

[Alan in Little Washington]

Originally Posted by jhreed

Electrical engineer, hvac engineer, journalist. How much talent can God grant one individual. I always look for your posts. know that they will be factual, understandable, and pleasantly readable.
I did not know that you were a journalist. Where would I find your work?
James

Thanks! But you know what they say- Jack of all trades, master of none. And I noticed you politely left out videographer and actor!

I'm no Hemingway, but I have been doing a little article and tip writing. I'm still not too good at it; thank heaven for editors. One of my tips was just published in the Oct issue of Wood Magazine. I have a full-blown, two-part article (torsion boxes and my assembly table with adjustable height legs) coming out in the upcoming issue of American Woodworker Magazine. It should be on the news stands in week or two. (I finally got a check for them last week! Yahooo!! )

I have a couple of other shop tips that so far have made it past initial screening and are being considered by various magazines. I am also currently in negotiations with one mag for another full DIY article. (Anybody need a customized tool cubby like the one in my shop? I might be selling a new one in a few months for the cost of materials )




The biggest news (hopefully) is that I licensed one of my designs (invention?) this year. I am traveling to Dallas, next week to visit the manufacturer/licensee. If things go as planned it should hit the market sometime this winter. I'll try to get one of first run models to donate to North Carolina Woodworker for a raffle. This "thing" won't make me rich by the farthest stretch. No Shelix for the planer and LN's will probably still not be on my shopping list, either, but at least it should pay for restocking my sandpaper and more frequent blade sharpening.

Maybe it has taken this long for the mind-numbing Fed Gov't job to wear off?

[JimmyC]

Originally Posted by Alan in Little Washington

And I noticed you politely left out videographer and actor!.............

.....and senior swimming champion, sailboater and the one and only inventor of the storpedo !

[mlzettl]

Alan,

This is excellent in all respects. Thanks for sharing a fine example of penny tech.

Matt

[toolferone]

Alan, the pics and drawerings are great. I have a question about the attachment of the two sides. It appears that the 2 laminate sides are what is holding the 2 halves together. I am worried about the strength there. Some blastgates get a lot of twisting and tugging with a flex hose attached and the machine being rolled around. I know I don't have one in my hand to see for myself, just my .02 cents worth. How are you cutting the holes in the mdf? Keep up the good work.

[Alan in Little Washington]

Originally Posted by toolferone

Alan, the pics and drawerings are great. I have a question about the attachment of the two sides. It appears that the 2 laminate sides are what is holding the 2 halves together. I am worried about the strength there. Some blastgates get a lot of twisting and tugging with a flex hose attached and the machine being rolled around. I know I don't have one in my hand to see for myself, just my .02 cents worth. How are you cutting the holes in the mdf? Keep up the good work.

Tom, using laminate sides and adhesive is very strong, as strong as glue and solid wood sides would be. The stress on the adhesive and laminated is all in shear so they are not going to move. All my gates have been holding up fine, though they are now mounted behind the walls. If something were to give, it would be the MDF itself not the adhesive or the laminate. If you tried to pull them apart, the MDF would come apart. A glued-on side would be exactly the same. Though you could put screws into the sides, I don't recommend it. Unless you were careful and/or used long and thin screws. Screws have a tendency to split the MDF which (from experience) can cause the slide to bind. You would likely need to use thicker, 3/4", MDF.

The only way to make MDF gates tougher is how I made a few many years ago- make them 2" bigger in each direction, add narrow spacers between the halves that are slightly thicker than the slide, then through-bolt the halves together. I subsequently found that extra complexity and parts were just not needed.

As far as failure from wear and stress, I would hope before a gate fails, the hose fitting or quick disconnect would slip out. Really these gates are strong and durable. You can't pull the laminated sides off without damaging the MDF! Have you ever tried to remove laminate from MDF or particle board- it really doesn't want to come off!!!!

I drilled a starter hole then used a jigsaw to cut the big holes in the MDF. The shape and edges of the hole can be fairly ragged because when you attach the PVC inlets/outlets the polyurethane glue or epoxy fills any gaps, especially poly glue which expands. Making the big hole in the MDF first, applying a solid piece of laminate over it, and then installing the PVC inlet/outlet, gives you a nice surface for the bearing on the flush trim bit and yields a perfect gate hole, as visible in the pics (FYI, these pics were staged- though I could have used my Bosch Colt, I didn't have a flush trim bit with 1/4" shank so I actually did the flush trimming on my router table- if you look close, there is no bit in the router ).