Thread: 2hp dust extractor mod - build

Originally Posted by fletty

Now, how could this POSSIBLY go wrong, you, Evan and a pot full of boiling oil............ ?

fletty

Fortunately it does not need to be boiling, 120 - 130º is all that is needed.

Boiling oil is the sort of thing that happens when quenching red hot tool steel pieces in mineral oil that is already around 130ºC.
The first thing that happens is that the oil erupts, foams and froths and catches fire - which is why keeping a lid handy to put the flames out with.
As the hot piece is jiggled about in the oil the boiling and colder oil mix and the frothing subsides and any fire on the surface of the oil puts itself out.
However if the container is not large enough the boiling foaming oil overflows the tank and the fire can spread to the floor.
Fortunately this drops the temperature of the oil so the vapour pressure drops and the fire goes out but it's still exciting to see it happening.

Tip; keep lid and burning oil rated fire extinguisher handy.

Originally Posted by fletty

Now, how could this POSSIBLY go wrong, you, Evan and a pot full of boiling oil............ ?

fletty

It should be fine. I was going to wear my safety thongs. 😝

I've got a few pieces of chicken and some chips to make the best use of the boiling oil!

Originally Posted by Trav

I've got a few pieces of chicken and some chips to make the best use of the boiling oil!

THen you will be needing the oil a bit hotter than the 130 degrees BobL specified for the PVC


Cheers

Doug

Originally Posted by Evanism

Mate! There are quite a few people who think I can be mighty handy with a couple of litres of oil!

Trav, Im more than happy to turn up a mould for you. I'll start making the stack tomorrow. It would be wise to know the ID of the 6" pipe (I can assume its 6" but every damn pipe I've ever seen is close-but-nowhere-exact)....

The mould will let you press out a heap of flanges, or flare the end of pipes.

Ev

I'm going to grab the pipe on the weekend. I've got the junctions but haven't been able to work out how to get 6m of pipe home on my roof racks. Will send the ID when I've got it. Maybe the cook up should be the following weekend.

Trav

I have doubts that hot oil and a mould is going to be able to stretch 6" Diameter PVC into a 9" bell mouth. That's equivalent to a 50% increase in length.

Hot oil can be used to soften and reform PVC to a different shape of the same cross sectional, and maybe even into a tapered opening that is a little wider , but we are talking about up to a 9" opening that is 90º to the pipe outer surfaces and all the surfaces kept wrinkle free.

Still I would really like to be proved wrong so lets see what happens.

And then when you have perfected the technique I can order some

Jane

Originally Posted by lovetoride

And then when you have perfected the technique I can order some

Jane

The chicken and chips OR the bell housing flanges?

fletty

PS, I'll be ordering both just to be on the safe side!

Originally Posted by BobL

I have doubts that hot oil and a mould is going to be able to stretch 6" Diameter PVC into a 9" bell mouth. That's equivalent to a 50% increase in length.

Hot oil can be used to soften and reform PVC to a different shape of the same cross sectional, and maybe even into a tapered opening that is a little wider , but we are talking about up to a 9" opening that is 90º to the pipe outer surfaces and all the surfaces kept wrinkle free.

Still I would really like to be proved wrong so lets see what happens.

Bob

Yes, I agree. This is a potential problem. Everything I've read is that it can stretch generally by 1/3 and with effort to 1/2. We will see how it goes and report back.

Trav

Originally Posted by Evanism

Trav, Im more than happy to turn up a mould for you. I'll start making the stack tomorrow. It would be wise to know the ID of the 6" pipe (I can assume its 6" but every damn pipe I've ever seen is close-but-nowhere-exact)....

The mould will let you press out a heap of flanges, or flare the end of pipes.

Ev, I've been thinking about this a bit more. The ID won't be particularly relevant as I'm trying to stretch it out anyway. As long as the mould tapers at the start to get into the pipe then the ID won't be particularly relevant.

Trav

Just a few thoughts on forming the pipe,
I have resized pvc pipe a few times, both expanded and shrunk it (I use the hot air gun just cos that is what I've got), one thing I have noticed is that the right temp needs to be reached before it becomes soft enough to take on a new shape but if I make it too hot it will be too floppy and will just wrinkle and distort, you are stretching so wrinkles won't be too much of an issue, also if you have too much length of pipe hot there isn't enough strength in the pipe to force the start of the pipe to change shape and you end up just forming folds, I try to make sure I have a temp gradient down the length of pipe with the hottest being the start of the pipe and at room temp just 4 inches away (if I am forming a new socket) for e.g.

My thinking is that you are going to have to keep applying heat to the start of the pipe to keep it soft enough for it to keep stretching.




Pete

So a repeated heat-pressing-reheat-forming process is needed. Makes sense.

Do you think and outer mould is needed that we can apply to the outside I needed? Sort of like two halves we can put over post-pressing to form the pipe against the body?

Originally Posted by Evanism

So a repeated heat-pressing-reheat-forming process is needed. Makes sense.

If you can arrange it, apply the pressure while it is being heated. It's not easy and quite dangerous doing this under hot oil.

Do you think and outer mould is needed that we can apply to the outside I needed? Sort of like two halves we can put over post-pressing to form the pipe against the body?

Both sides of the mould will have to be hot and kept hot during the pressing process.

If the mould is at room temp it will drawn heat from the PVC and solidify the outer 1/2mm or so.
This is a major contributor to folds and wrinkling.


Something else to think about
1) Figure A in the image below shows a theoretical bell mouth hood profile.

2) Unless the bell mouth is hanging out in the breeze, as used with a carby or naked port, the hood has to attach to something like a cabinet.
Theoretically that is represented by B where the brown line represents the cabinet.

3) However attachment requires the practical need for an overlap between the rim of the hood and the cabinet of some kind and although it looks possible to attach to the outer edge of rounded lip that is not as easy as it looks.
In practice attachment requires the outer rim of hood to be significantly larger than 1.5X so there is some overlap with the cabinet.
The alternatives are then attachment before or after the hood C or D.






This is why it is easier to turn the bell mouth out of something like an MDF sandwich and attach as shown below.
This also allows a recess to be turned into the sandwich that enables a smooth transition between the pipe and the bell mouth.
A bell mouth moulded out of PVC will also have this transition problem.
Even though it sounds ridiculous if you do this and have the space I would make the cabinet opening >2X


Unless space is an issue Even for a hood hanging out in the breeze there is some benefit in making the outer rim of the bell mouth >1.5X.
This does not mean making the curvature of the mouth greater than 1/4X, but extending flat edge of the rim out further.
This causes more air from in front of the mouth, and less from behind, to be drawn in.

It may not look like it but the outer rim of the mouth in the lathe hood shown in the picture below is ~10" - the outer edge of the bell mouth itself is only 9" (i.e. 1.5 x 6")
I would have made it even larger but it then takes up more space and also makes it less manoeuvrable.
This hood can be moved (left-right, up - down and rotated) on a rail and pivot point attached to the back to suit the shape and size of the work.
Having a much bigger hood would just get in the way.

Bob

Good points. I was thinking about how to mate the PVC to the impeller port cover. I was going to rout a rebate into the face of the inside of the port cover that was the same depth as the PVC. As long as the width of the rebate matches the lip of the PVC, it should be a smooth transition.

Something like this


But I'm beginning to think I should just great big round over bit.

Trav

Originally Posted by Trav

Bob

Good points. I was thinking about how to mate the PVC to the impeller port cover. I was going to rout a rebate into the face of the inside of the port cover that was the same depth as the PVC. As long as the width of the rebate matches the lip of the PVC, it should be a smooth transition.

Correct but it's not a simple right angle rebate although you could just filled the gap with a bit of sealant.

But I'm beginning to think I should just great big round over bit.

Yeah it would save a fair bit of time.