SV650 - Air Duct Design Part 1

The air ducts - something thats been put low down on our priority list but has always been there. The standard airbox has an inlet that sits just beneath the underside of the fuel tank. On the basis that an engines performance increases if it can breathe more efficiently, then this seems a rather daft place to draw air in. 

So we are designing a larger airbox (using the underside of the tank as the top of the airbox) with the air ducts either side of the headstock to help draw the air in from the high pressure point on the front of the bike.

Here's how we are doing it (this will be in several parts as a work in progress and may not be the best way to do it, but is the way we are doing it!) . . .

Above, we have modelled one air duct using MDF and styling clay (quick, easy and the way an Industrial Designer knows how to do it) which fits onto the bike (only one side as the other side will be a mirror image).

From the clay, we have scanned the part using a FARO Arm and processed it in CAD to give us a 3D representation of the air duct in Solidworks. If we were getting really technical at this stage, we could reverse engineer it into a manufacturable part and do all sorts of flow analysis to optimise the shape - but we didn't. 

This 3D model was then sliced in multiple 12mm parts (like a loaf of bread) to give us a number of profiles which could be cut out from MDF and laminated together to create a mold. In fact, there are four molds, one for the top and one for the bottom, then duplicates for a mirrored part to sit on the other side of the bike. (This stage could certainly be sped up by 3D printing or machining the parts from foam, but we always seem to take the hard, less expensive route).

Laminate MDF profiles then gave us these molds, which required a fair bit of sanding and filling, but these will only be used for the first prototype parts, so can still be a little rough. The important thing with these is that they are symmetrical to one another and that both the tops and bottoms fit together.

A close up of the contours. There are a lot of hard points for the air ducts to clear, such as frame tube, fork legs, fairings, light brackets and even stubborn wiring, so they have ended up with quite organic shapes. Once we get to a finish as seen above, we coat them in epoxy resin to give them a hard surface, then a quick sand down to smooth off any high points and its time to lay them up with some fibreglass.

We'll let them cure now, see what happens next in part 2 . . .

SV650 - The Molding Process - an insight.

Here is a bit of an insight of what goes into making the fiberglass mold from the plug for the fuel tank cover. I'll try to explain each stage and it may help show why this part of the build is taking so long to get through. 

Starting off, the tank cover is a fairly rough version of what I am trying to achieve. Originally taking off the mold from the clay model, it 's been hacked about a bit with bits added and filler built up, to fine tune it and to get the fit on the frame just right. This is the black part which has been in many of the photos of the bike to date.

This first fiberglass is then strengthened with wooden battens and screwed down onto a large board  to form a plug and to keep it stable whilst laying up. Any holes, such as where the fuel filler cap needs to access the fuel tank, are then filled, with an easily identifiable profile marked out in order to cut out on the final part.

Around the edges, flanges are created using sheet wax. This will allow the fiberglass mold to extend past the edge of the part by a few inches, making final layup easier.

As the tank cover is essentially a box, with an open bottom, the mold needed to be made as a split mold, in order for the final part to be released. This is done by creating a flange along the edge that is most suitable for the split. Thin aluminum sheet seems to be easiest as it doesn't require much release agent to remove from the resin and its easy to manipulate. This is glued in place using a hot glue gun with any gaps filled with clay. Tape creates fillets between each corner of aluminum; not very neat, but it doesn't need to be here.

Once the flanges are all in place, a few small locating bumps are made from clay and put on the flanges and the whole thing is then cleaned and prepared for molding. This involved two layers of a chemical release agent and a couple of layers of mold release wax (possibly not necessary, but I need to be sure this releases!). To get to this stage takes a good few days in preparing the plug and probably a further 4 or 5 hours to add the flanges, fillet the clay and add the release agents.

Next up, the thick gel coat can be applied to the first part of the mold. This is sticky, black and comes out really hard, but needs to be applied in two layers, with 4 hours in between, at a constant temperature. I tend to do this the day before I intend to layup the fiberglass mat, as it can be left for 24 hours no problem and its just easier this way to get it in around a full days work.

Following the gel coat and a day later, there is a layer of resin called the coupling coat which goes down with a couple layers of very thin fiberglass matting, aimed at getting into the very intricate areas. Fast forward another 3 or 4 hours, it will have gone tacky and the final resin with a thick matting can go down. This is around 4 or 5 layers thick, takes over an hour, ruins paint brushes, stinks and uses a lot of resin, though it does come out super strong. This then gets left a further 24 hours before anything can be done to it. There are no photos of this stage happening as it gets a bit messy!

 

With the fiberglass cured for 24 hours at a constant warm temperature, the edges can be trimmed (I use an old hacksaw blade) and the aluminum flanges removed. This takes a few hours to tidy up and remove any excess clay. Then its time to do the entire process again on the second part of the mold. Flanges don't need to be added, as it will use the existing flange of the part already layed up, but small aluminum pieces have been added to create a void, allowing a tool to be inserted when complet to split the mold. Time wise, 3 or 4 days can be easily added to do each part of the mold.

Now all three piece of the mold have been layed up, they can all be trimmed and drilled to allow it the bolt together when removed from the plug.

We are now at the point of being able to release it from the plug. There is no science behind this, its just a case of releasing the part that wants to come off first and being quite brutal with it. Fortunately most of the parts have come off without too much of a struggle so far.

Then we are left a pretty good representation of the final part on the inside of the mold. There were still a few imperfections which needed to be repaired, along with finishing all the surfaces to a 2500 grit finish (which again, takes longer then expected).

There is very little that can be modified or changed at this stage, so it has be right at the plug stage.

Following the 2500 grit treatment, the parts can all be polished. This stage is demoralising; you think you have the perfect finish, but the polish highlights the most minute ripple and faintest scratch. I may need to do a few sample pieces from here to see how good the finish needs to be for the final parts, as it may not be an issue for painted parts, but clearcoat carbon may be an issue, so some experimentation is needed.

This photo shows how the split in the mold works in order to make release possible.

I hope you have learned something and understand why its taking time to get through this stage.

There are something like 16 parts of molds to make, all taking this amount of time, but its just a case of keeping going and it the end product will be worth all the time and effort!

Clay Photo Session

Its the end of January and the SV concept has been wheeled out from the workshop for the first time. Its taken a little longer then planned to finish the clay and get it symmetrical but its now there and awaiting the first of the fibreglass molds to be taken.
 

There's a few more photos below of the clay model alongside the original SV.  Its certainly taken on a different appearance from standard.

SV650 - Dark, Cold Winter Days

 The heaters are back in action and the flask is full of hot coffee. Time to get the clay model finished.

Check back by the time the years out, I expect the clay will be completed by then.

SV650 - November's Progression

The clay is nearing completion in terms of design detail with surfaces beginning to be come finalised. Once this stage is achieved, the bike can be taken outside to finally assess the design from a distance.

SV650 - Hows it looking?

The design as it stands at the beginning of October.

SV650 - Progression in Clay

 

 

The SV project keeps progressing! Now its in clay, the design is being constantly refined to work with the SV package and achieve the original design goals.