Adam's Homemade Plenum chamber thread

adamnreeves · Post by **adamnreeves** » Fri Mar 23, 2007 4:43 pm

Spent a few hours on creating a pattern out of foam and filling with bodyfiller!

I have decided to ditch this approach. I want to ensure that I have the same height between the trumpets and the plenum roof and I think this is difficult with foam.

What I am going to do is create a series of structures out of plywood and then fit together to make an even plenum chamber. Then I will fibreglass over it and fill with bodyfiller.

kiwicar · Post by **kiwicar** » Fri Mar 23, 2007 5:01 pm

sounds like a good approach, are you going to make a female mould from this?
Mike

kiwicar · Post by **kiwicar** » Fri Mar 23, 2007 5:05 pm

I would think about plywood and plaster aswell, just plaster is alot easier to sand than body filler, then seal wirh emulsion paint and and once fine sanded use polyeurathane varnish and sand and pollish with florr wax.
Or whatever works for you
Mike

ian.stewart · Post by **ian.stewart** » Fri Mar 23, 2007 5:26 pm

For making my sump prototype i used stuff called FoamCard, my friend uses it for display work then bins it after the exibition, A lot of sign shops use it, possibly the same stuff they make soffets out of as well, superglues really nicely too, you can cut it with a stanly knife and sands really easily
http://www.v-8.org.uk/forum/viewtopic.php?t=811

Ian

adamnreeves · Post by **adamnreeves** » Fri Mar 23, 2007 5:33 pm

Yep I am making the pattern first which will be in the external dimensions, ie. mock up of the plenum chamber. From this I will make a female mould yes. However the bit I am not quite certain about is whether I will need to make a male mould for the internal dimensions. I say this because I do not want rough fibre glass on the inside as this would disrupt the air flow, I want the inside of the chamber to be as smooth as the outside.

kiwicar wrote:sounds like a good approach, are you going to make a female mould from this?
Mike

ian.stewart · Post by **ian.stewart** » Fri Mar 23, 2007 6:03 pm

I am using there people, very helpfull and not expensive,
http://www.google.co.uk/maps?hl=en&q=ch ... l&ct=title

unfortunatly I cant find an web site for them,

bit of a trek for you, either A41 and up thru ashridge forrest, or cut accross to the M1 and down to Dunstable
Ian

adamnreeves · Post by **adamnreeves** » Fri Mar 23, 2007 6:08 pm

Measured my trumphets and from the floor of the trumpet base the outer ones are 10mm high, the central ones are 25mm. The bore is 38mm, they are flared.

Apparently the gap between the plenum roof and the trumpets should be around 1.5 X bore. So I am going to round my bore upto 40mm because I am not too sure of the effect of the flare. So this means I need to aim for a gap of 60mm.

The plenum chamber mounts on the lip of the trumpet base which is 16mm higher than the floor, I am going to mount on top of a flange to provide more width for sealing to ensure air tight as possible. Estimate that this will be 1.5mm so this a total of 17.5mm needs to be taken into account when calculating the gap.

So to achieve 60mm gap for central trumpets I need to aim for 60mm + 25mm - 17.5mm = 67.5mm.

The outer trumpets would be 60mm + 10mm - 17.5mm = 52.5mm.

So the plenum chamber will be at it highest 67.5mm + laminate width and its lowest at each end will be 52.5mm + laminate width.

This is quite a bit shallower than the normal 90mm.

Does this sound reasonable?

Editted to say: Problem is , with a 71mm throttle at one end it will not fit. So I shall have to make the shallowest end no less than 75mm.

ian.stewart · Post by **ian.stewart** » Fri Mar 23, 2007 6:24 pm

+1.6% expansion at 650degs

Im not too worried by this in my calculations just add a wee bit more

adamnreeves · Post by **adamnreeves** » Fri Mar 23, 2007 6:28 pm

Hadn't considered that. I might go down this route if it is cheap enough
and I get bored of making it myself!!

ian.stewart wrote:I am using there people, very helpfull and not expensive,
http://www.google.co.uk/maps?hl=en&q=ch ... l&ct=title

unfortunatly I cant find an web site for them,

bit of a trek for you, either A41 and up thru ashridge forrest, or cut accross to the M1 and down to Dunstable
Ian

adamnreeves · Post by **adamnreeves** » Fri Mar 23, 2007 6:29 pm

What? wrong thread?

ian.stewart wrote:+1.6% expansion at 650degs Im not too worried by this in my calculations just add a wee bit more

ian.stewart · Post by **ian.stewart** » Fri Mar 23, 2007 6:43 pm

adamnreeves wrote:What? wrong thread?

ian.stewart wrote:+1.6% expansion at 650degs Im not too worried by this in my calculations just add a wee bit more

Not realy------------- you should add 1.6% to your dimensions so the casting will be spot on size when cooled.

adamnreeves · Post by **adamnreeves** » Fri Mar 23, 2007 7:05 pm

Oh right I shall bear that in mind if I go the casting route.

ian.stewart wrote:
adamnreeves wrote:What? wrong thread?

ian.stewart wrote:+1.6% expansion at 650degs Im not too worried by this in my calculations just add a wee bit more
Not realy------------- you should add 1.6% to your dimensions so the casting will be spot on size when cooled.

kiwicar · Post by **kiwicar** » Fri Mar 23, 2007 8:06 pm

if you get some very light woven cloth (less than 300gm/square meter, moddle aircraft wing surface cloth) for the last layer on the inside of the plenum as your last leyup layer it will be very smoote (at least as smoothe as a sand casting, easy to work as well.
Mike

ian.stewart · Post by **ian.stewart** » Fri Mar 23, 2007 8:28 pm

I have made air ducts in porous card before now, made up with masking tape then self adhesive plasterboard tape, then soaked in epoxy resin, only for the lack of smell, but Polyester would do as well, the bits I made were almost indestructable, I was everso impressed with myself.
This will probably male a prototype for what you want.

Post by **katanaman** » Fri Mar 23, 2007 9:52 pm

paint a topcoat (gelcoat with wax in it) on the inside. It is thick enough to make it smooth but thin enough to flow.
I wouldn't worry about it being a bit rough anyway as the air isn't flowing along the surface like say a pipe.

By the way has some posts been deleted edited out of here as the thread seems disjointed?