# Blast Gate control problem



## RobHannon (Dec 12, 2016)

So I had what I thought was a good idea that has proven not to work well at all. Maybe some of the collective creativity here can help me save this. I made some 6" blast gates that open and close on a pivot based off this design:

https://www.shigshop.com/blast-gate-plans.html

Above the pivot point I have a piece of steel barstock that extends and has a hole and grub screw tapped into it. This bar works as a lever to open and close the gate. The grub screw clamps down on a piece of wire that rides inside a semi flexible steel tube. A push/pull control like you would use for a manual choke on an older vehicle.

If I loosen the 2 halves of the blast gate to the point that it is barely together, this setup works about half of the time. I am not convince it would ever work with the added pressure of the DC running. Part of my problem is I need to reduce the friction opening and closing the gate, but I am not sure that will be enough. I could also move the connection point of the cable further up the steel bar to get more mechanical advantage, but that will require more travel on the cable than I think I can get with the parts I have.

Any other brilliant ideas? I need to be able to operate this gate from a distance as it will not be easily accessible once my outfeed table is back in place. I would like to avoid the expense of the off the shelf automated blast gates as one of them costs almost as much as my DC and I will need at least 2.

Anyone else tried something like this?


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## smitdog (Aug 20, 2012)

How about using UHMW plastic for the gate? May reduce enough friction to make it work?


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## Mike_D_S (May 3, 2012)

Rob,

I'd recommend a tip from when I used to fly large scale remote control. I used to use plastic pushrods like these

Or the wire ones like this

For smaller planes, you could use the push rod or the wire to both push and pull the control surface. For larger planes, the rods work fine in tension, but when pushing they buckle or flex.

The solution is to use two of the wire or plastic pushrods connected to the drive arm in a pull/pull setup. So when the actuator is moving one of the cable is always pulling in tension.

So I'd run a second cable to the other side so that when you pull or push your actuator the main force is always coming from a cable in tension. You can run a lot thinner wire since you don't need it to be able to push. You could sleeve it in 1/4" poly tubing to guide it around corners.

Mike


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## Loren (May 30, 2008)

I made some similar overhead ones using 
1/2" prefinished ply with 1/4" markerboard 
in between. I waxed the markerboard and
it works smoothly.


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## builtinbkyn (Oct 29, 2015)

Why not use some sheet metal for the gate? Use some UHMW tape around the inside of the frame to provide a slick surface. Link


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## Sparks500 (Jun 30, 2017)

I made the simple slide type blast gates and just used ¼" ply or hardboard for the slider.
Looks to me like it's too much mass to move around.


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## RobHannon (Dec 12, 2016)

Mike, I have been toying with the idea of having 2 cables in a push pull config like you are describing and moving to a control that works on rotation much like a motorcycle throttle control. I would need to move to a flexible stranded cable rather than a ridgid solid wire for that though.

My construction is all 1/2 MDF that is waxed. The surfaces are very smooth and slick, but there is a good bit of mass I need to overcome.

I may try a housing used for bicycle shifters rather than the coiled housing I am using now. It is not as strong, but supposed to be less friction. First thing is I need to get back in the shop and see if there is any way to improve the pivot point. I drilled it with minimal play and perhaps that was a mistake.


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## Holbs (Nov 4, 2012)

I made overhead blast gates using the pivot design. No issues opening and closing by hand. Actually, they slide rather smoothly. I could not read the small fonts about the build, but is there a 0.010" gap between front/back pieces and the V sliding piece? I used blue painters tape on both sides of my pivot piece to give me a little gap.


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## RobHannon (Dec 12, 2016)

I couldn't read the details that well either. M design is not an exact copy but painters tape is the same route I went. I had to triple the tape to get the cable to partially work. More of a gap than I would like. for the overhead gates. operating by hand will be fine but I have 2 gates that will be between an outfeed/assembly table and my table saw. In retrospect, I am not sure the pivot design was the best option for these.


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## pintodeluxe (Sep 12, 2010)

I don't know about shop made versions, but automatic blast gates are sure nice. Grngate and iVac both make them. Two or three gates makes a big difference.


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