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Blast Gates

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Blast Gates

Postby Wizard9999 » 24 Mar 2016, 20:07

I'm in the process of fitting ducting in my workshop to improve dust collection. For several reasons I decided to make my own blast gates:
1. it saved a chunk of change as the place where I got my ducting wanted about £20 each for 125mm blast gates
2. I could have bought cheaper ones from Axy but I am finding fitting one persons definition of 125mm duct to that of another supplier is an imperfect science so couldn't be sure they would fit
3. Neither of these gates were of the type available from Rockler in the US which self cleaned any dust that could collect in them
4. I thought it would be an interesting thing to do

Nothing rocket science here so I will keep blurb to a minimum.

First I started by creating the front and back plate of the gate by drawing a circle around the duct on a suitably sized blank and drilling / jigsawing it out
Image
Having got one to the point where I had a good fit for the pipe I then marked this as a master, subsequent blanks could then be cut out roughly and flush trimmed using the master blank as a template.

I then added spacers to create the slot the actual gate would run in and then did the only think I have not seen anyone else do on the countless YouTube videos on blast gates, I attached self adhesive felt to the inside of each of the front and back plates. The idea is that this will help keep the gates airtight, but it had an additional unintended benefit which I'll mention later.
Image

I created the gate using MDF and cutting a piece roughly twice the length of the blank and wide enough to fit between the spacers, I then attached a thin strip of MDF at each end to act as a stop and finally positioned a hole using one of the front plates to position it. The result was the following three component parts.
Image

One point to note is that the self adhesive felt (excellent value at 80p for an A4 sheet at Hobbycraft) means the spacers need to be thicker than the gate itself, something I had not taken account of initially. I have used 6mm MDF for the moving gate and found that a adding 3mm hardboard strip on top of the 6mm spacer I had already glued to one of the front plates gave just the right clearance. For the next one I will just try 9mm MDF for the spacers.

All the YouTube videos I have seen show the blast gates made with small sections of pipe. I understand this means the system can be re-configured more easily but I don't plan on changing any time soon and that approach means two additional joints per blast gate with the potential for more leaks of airflow. I therefore just fixed the pre-cut lengths of pipe for the relevant run into the blast gate. They were a tight push fit but I added a bit of sealant to the pipe before I pushed it in and then fully sealed the outside of the joints into the blast gate.
Image

I then had two halfs of a section of pipe with half a blast gate attached to each.
Image

I then screwed the two halfs together with the actual gate sandwiched in place.
Image

Now for the other benefit of the felt, it acts as a really good surface for the gate to slide between the two outer plates and means that it will slide even though it is a good tight fit and that it can slide but still stay in in place if it is held in a fully horizontal pipe run.

I didn't glue the gates together as I can be a bit heavy handed with the sticky stuff and was worried about squeeze out I could not then clean up blocking the gate up. As I had screwed I then used the ducting jointing tape as an extra barrier to any airflow wanting to escape the system.
Image

And here it is in place.
Image

Sadly I have not been able to test performance yet as the system is not fully installed, but I hope to make more progress of over Easter.

Terry.
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Re: Blast Gates

Postby tracerman » 25 Mar 2016, 01:12

Terry - very nice-looking job .
Did you get that metal trunking from Lindab at Chandlers Ford ?
Does that spiralling effect assist airflow ?

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Re: Blast Gates

Postby Andyp » 25 Mar 2016, 07:44

Good job Terry, nice when a plan comes together.
I do not think therefore I do not am.

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Re: Blast Gates

Postby Mike G » 25 Mar 2016, 07:55

Very nice, Terry. I like the felt idea, although I would worry that the edge of the moving hole in the blast gate would catch on the edge of the felt, turning it up and eventually tearing it. If you have to replace it in 10 years time, you'll be grateful you didn't glue the thing together.

Are you going to show us your extractor?
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Re: Blast Gates

Postby Wizard9999 » 25 Mar 2016, 08:02

No Steve, bought it from this place http://www.ductstore.co.uk/

They were very good,helpful when I asked a couple of questions even though I made it clear it was a hobby enquiry meaning it would be a small one-off order. Good communication around delivery. Finally, when I added up the price of everything it was basically the same price as 110mm sewer pipe - the lengths of sewer pipe are a fair bit cheaper, but the fittings such as bends are actually a lot more than proper ducting.

I would imagine the spiralling is probably a negative for airflow as it will creat turbulence, but it is much less pronounced on the outside than on the inside.

Terry.
Last edited by Wizard9999 on 25 Mar 2016, 08:20, edited 1 time in total.
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Re: Blast Gates

Postby Wizard9999 » 25 Mar 2016, 08:18

Thanks Mike. Yes the potential to catch the edge of the felt is a concern and maybe that is why I haven't seen anything similar done on YouTube :lol:. I'm hoping the fact it is such a nice snug fit will mean that even if it does catch the very edge it won't lift. But, as you say if it does prove to be a problem at least I can get ino the gathe to address it without completely destroying it.

I'm hoping to get the rest of the duct work up over the long weekend and then (after a quick tidy up) I take pictures of the whole thing and post.

Terry.
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Re: Blast Gates

Postby Rod » 25 Mar 2016, 08:30

Looking good - now you need some of Bob's motors?

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Re: Blast Gates

Postby Commander » 25 Mar 2016, 12:02

Nicely done Terry, I'm sure they will work a treat!
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Re: Blast Gates

Postby TrimTheKing » 26 Mar 2016, 12:48

Wizard9999 wrote:...but it is much less pronounced on the outside than on the inside.

Terry.


Do you mean it is MORE pronounced on the outside? I would have expected the inside to be smoother.

Cheers
Mark
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Re: Blast Gates

Postby Wizard9999 » 26 Mar 2016, 17:02

TrimTheKing wrote:
Wizard9999 wrote:...but it is much less pronounced on the outside than on the inside.

Terry.


Do you mean it is MORE pronounced on the outside? I would have expected the inside to be smoother.

Cheers
Mark


Yes Mark, absolutely correct, got my mores and lesses muddled!

Terry.
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