Conical (tapered) tubing?

[thomas.hood]

Hi,

I'm trying to get hold of some tubing which tapers. The smaller aperture must be >=150mm and the larger end >=270mm over ~1m. Other than the minimum sizes specified the dimensions aren't critical.

Alternatively, if there's a way I could taper a ~300mm plastic water pipe in this manner I'd be interested to hear. I could imagine doing this by cutting a triangular piece from the tube and then using a series of router-cut (with a suitable bevel) plywood discs. The 'waste' cut-outs could then be slid (inverted) over the tube to assist forming and gluing the discs to the inside of the cone. This sounds a PITA though and I'd rather buy something.

Thanks,

Tom

[Brett]

If it's not structural, ie doesn't need to support weight or load like the rear tube on a Nautilus mid for example, then a couple of layers of construction cardboard cut and glued at the edge and coated with resin would be workable. That or sonotube cut and glued the same way.

Not sure you're going to find like that pre-made, but you never know.

[The Space Egg Corp]

Originally Posted by thomas.hood

Hi,

I'm trying to get hold of some tubing which tapers. The smaller aperture must be >=150mm and the larger end >=270mm over ~1m. Other than the minimum sizes specified the dimensions aren't critical.

Alternatively, if there's a way I could taper a ~300mm plastic water pipe in this manner I'd be interested to hear. I could imagine doing this by cutting a triangular piece from the tube and then using a series of router-cut (with a suitable bevel) plywood discs. The 'waste' cut-outs could then be slid (inverted) over the tube to assist forming and gluing the discs to the inside of the cone. This sounds a PITA though and I'd rather buy something.

Thanks,

Tom

Hi Tom

I made a similar conical horn type shape some time ago for an acoustics prototype.

I can totaly recomend Styrene sheet, which comes in black, white and grey mostly.

It's available from people such as Plastruct, who supply countless plastic shapes, tubes, squares etc. to industrial model makers.

It's available in thicknesses from a few thou, up to 1mm or so.
And usualy in big sheets.

I rolled a few turns of thin sheet to get a nice even shape of the right dimension.

Then all you do is run the very liquid solvent 'glue' along the exposed lap joints and at the ends whilst it's held to the right shape.

The solvent gets sucked under the plastic lap in just the right amount.
And very quickly evaporates and drys, leaving you a perfectly finished plastic shape.

The plastic takes acrylic spray paint well if you don't like black, white or grey.

Or if you want the plastic origanal colour, if you've used a few turns of the thinner plastic, say 10 thou", then you can sand down the seam and you don't even see the join.

No messy glue, quick, cheap, any shape you want !!!

Cheers

Simon

[The Space Egg Corp]

Hi Tom

I forgot to add.

When you start to roll the horn/tube etc.

Use some tabs or strips of the clear, super thin double sided tape to hold the inside seam in place.

As you roll it more tabs can be added as needed (they just stay where they are and become an integral part of the shape, but the solvent 'sets' it permanent).

Once the solvent has melted the plastic enough to bond (weld) the shape the adhesive tape bond is unimportant.

On a long shape like yours, hold it up and launch some solvent down the inside seem carefully with an eye dropper, it will run into all the right places.

I used regular sponge foam to support the inside of the shape where needed.
I cut or squeezed the foam to shape.
And then if you put it inside a clean thin food bag the solvent doesn't melt it, as it won't affect polythene !
Comes out easy, not welded to the inside of the tube !

Simon

[The Space Egg Corp]

Hi Tom

As well as Plastruct the industrial modelmakers supplies.

Another good source you might find local, are people doing vacuum formed shapes.
Then often use styrene.

Also sign printers and silkscreen printers supplies.

Simon

[picowallspeaker]

Wow ! You're so much experienced , Space Egg BTW which is the Corporation ? The stars ?
But you forgot to mention heat ...also vinyl ,home made and baked .
To me it sounds best , when mentioning tapered AND conical ,that a single sheet can be curved ,modeled and folded for your purposes ,and such combination exists : it 's oven + plastic + iron hands

[The Space Egg Corp]

Originally Posted by picowallspeaker

Wow ! You're so much experienced , Space Egg BTW which is the Corporation ? The stars ?
But you forgot to mention heat ...also vinyl ,home made and baked .
To me it sounds best , when mentioning tapered AND conical ,that a single sheet can be curved ,modeled and folded for your purposes ,and such combination exists : it 's oven + plastic + iron hands

Hi picowallspeaker

I'm not sure if heat comes in to it ?

Styrene can be easily shaped without heat (unlike acrylic).

And welded without heat using solvent.

The shape wanted sounds like a cone, dia one end, dia other end & length.

Should be easy to use a single rolled sheet.

If not any shapes or sizes can easily be layed together.

The only limit is the imagination. Into the stars & further...

No heat needed.

No complex equipment needed.

Easy to do at home, and not expensive.

Little bit of care, professional result, job done, next question.

Cheers

Simon

[thomas.hood]

Originally Posted by The Space Egg Corp

Hi picowallspeaker

I'm not sure if heat comes in to it ?

Styrene can be easily shaped without heat (unlike acrylic).

And welded without heat using solvent.

The shape wanted sounds like a cone, dia one end, dia other end & length.

Should be easy to use a single rolled sheet.

If not any shapes or sizes can easily be layed together.

The only limit is the imagination. Into the stars & further...

No heat needed.

No complex equipment needed.

Easy to do at home, and not expensive.

Little bit of care, professional result, job done, next question.

Cheers

Simon

Plastic sheet sounds good however, if I understand you the solvent/ glue would just be wicked down the overlapping seam of, say, 50mm. If I built up the thickness by using multiple layers I fear they might buzz or at the least have little rigidity. I intend to use this as combined base and mid driver enclosure (for a Linkwitz Pluto), with a 100mm tube running down the center. I.e. the midrange will face upwards from the small end of the truncated cone and use the 100mm tube as it's enclosure. The base driver will utilise the remaining volume and fire downwards.

Now that I've thought a little I like the suggestion of making the cone from thin sheet seems best though.

As an alternative to the plastic sheeting, I may try thick, liner-wallpaper and making a laminate with wallpaper paste. I'll add a layer-a-day until I've got a decent thickness and stiffness. My chief concern is making it uniformly round(-ish) so I intend to see what I can get by way of flower pots, or buckets to use as a form. If I cut the bottom out of these then one placed at either end and possibly mid-way should do the trick. This will require vessels that have the same taper and one which is sufficiently shallow - so may be a non-starter if I can't find anything to suit.

Thanks for your responses,

Tom

[The Space Egg Corp]

Originally Posted by thomas.hood

Plastic sheet sounds good however, if I understand you the solvent/ glue would just be wicked down the overlapping seam of, say, 50mm. If I built up the thickness by using multiple layers I fear they might buzz or at the least have little rigidity. I intend to use this as combined base and mid driver enclosure (for a Linkwitz Pluto), with a 100mm tube running down the center. I.e. the midrange will face upwards from the small end of the truncated cone and use the 100mm tube as it's enclosure. The base driver will utilise the remaining volume and fire downwards.

Now that I've thought a little I like the suggestion of making the cone from thin sheet seems best though.

As an alternative to the plastic sheeting, I may try thick, liner-wallpaper and making a laminate with wallpaper paste. I'll add a layer-a-day until I've got a decent thickness and stiffness. My chief concern is making it uniformly round(-ish) so I intend to see what I can get by way of flower pots, or buckets to use as a form. If I cut the bottom out of these then one placed at either end and possibly mid-way should do the trick. This will require vessels that have the same taper and one which is sufficiently shallow - so may be a non-starter if I can't find anything to suit.

Thanks for your responses,

Tom

Hi Tom

Just read the application above you wish to use the tapered tube for, which wasn't originaly posted.

Personaly I can't see you having much luck with paper & wallpaper paste.

As for formers the styrene plastic is quite rigid once rolled, and unlike an amourphous mass of wet paper, would not need a continuous former along it's length.
Perhaps several formers would help as previously mentioned, they could be foam or card circles inside polythene bags as mentioned to prevent them getting stuck.

It seems to me that styrene is essentialy a pretty non resonant or buzzy material.
If you were worried however some solvent could be applied as the tube was rolled.
The instant dry solvent, unlike wallpaper paste, would allow the tube to be rolled progressivly.
I would have way more than a 50mm overlap if I were making this shape.
I would think about 3 - 4 whole turns of maybe 30-40 thou styrene to form the shape.
Any shape like this whether paper or plastic will need internal ribbing of some kind or another.
I would think styrene circles & ribs could be solvent glued quickly and easily for this purpose.

Of course mould making is the other option, but knowing the huge amount of time and materials involved, for a 'one off' this seems inapropriate.
Home matting and resin is very smelly, messy and costly & would be unlikey to produce any more of a rigid structure than rolled styrene.

My experiences also suggest that matted resin structures can be potentialy quite resonant especialy in a shape like this.

Cheers

Simon

[Brett]

Originally Posted by thomas.hood

I intend to use this as combined base and mid driver enclosure (for a Linkwitz Pluto), with a 100mm tube running down the center. I.e. the midrange will face upwards from the small end of the truncated cone and use the 100mm tube as it's enclosure. The base driver will utilise the remaining volume and fire downwards.

Why bother? With it sealed and filled with any of the stuffing types you'll get 100% absorption anyway.
http://www.bobgolds.com/AbsorptionCoefficients.htm