Thursday, 4 July 2013

Frame and Steering Progress

This was always going to be a slow build, but I'm in no hurry.

So, having realised that genuine fibreglass core materials were going to be on the expensive side, I bought four sheets of 1200x450x50mm cavity wall insulation for £20 all in.  Having extended the frame templates by 15cm to give me a bit of leg room, this meant the templates overhang the end of the foam sheets.  no problem, as there's plenty of scrap foam so I stuck some of the scrap on at the front with the glue gun.  This turned out to be a small error, as hot melt glue doesn't sand very well, so I've got a bit of a lump in the frame.  This is being rectified with a sharp blade, and by the time it's covered in epoxy, you'll not notice it's there.
Template on top of insulation board.
After a lot of cutting I was left with a bin bag full of random offcuts, which I'm not wanting to throw out yet. I also had something resembling a Groundhugger frame, at least in profile.
Frame blank, awaiting sanding.
The core of the frame needs to be 68mm wide at the rear, tapering off to the front.  the black lines are a guide for me to start sculpting this down.  Using a hacksaw blade, a surform file and a length of M8 threaded rod for fine detail sanding, I turned this block of foam into three carrier bags full of fine white dust and the foam core for the frame.
With apologies for the bleached out picture - the phone camera is OK.  Just OK. There's a couple of bits still look a wee bit rough, but I'll be dealing with them before the fibreglass goes on.  One thing I have already done is to mix a small bit of resin, just to make sure the foam won't melt.  It's OK. 

The disadvantage of using insulating foam instead of other core materials, at least as far as I can see is the occasional void in the foam.  They aren't too large, but I would imagine f you were doing anything more detailed, they may present a problem.

Now the steering.

The original Groundhugger design calls for a universal joint at the head of the steering tube.  I just don't have the facilities to engineer something like that, and I'm concerned that this could lead to play in the steering that I'm unable to correct for.  Instead I'm going to use a linkage from the top of the headset up to a set of handlebars in the "cockpit" and use traditional push-pull bars.

I have a threadless headset stem that allowed me to clamp in two 28mm diameter bearings.  These will take an 8mm bolt attached to a pair of metal brackets which are in turn attached to the frame. 

Rough design with completed brackets.
Brackets with bearings. Bolts need shortened and the nuts will be Nyloc. There's a washer missing as well.

Completed bracket and steering stem.

Both brackets are the same length.  Perspective is making them look different.

That's all for the moment.  Next step is to wrap the frame in a single layer of glassfibre before starting to add carbon.

No comments: