Half Cage

So, today was fitting the half cage, harness eyelets and gas cap etc. I haven't been looking forward to all this cutting, but with careful measurements it really wasn't that bad. I did use measurements for the holes for the rear stays provided by one of my fellow builders, which helped a lot. As the rear stays enter the body at an angle, you need to figure out an ellipse, but in practice an elongated circle works best. I also took a few other measurements, made a template in cardboard to check, and then transferred the measurements to the bodywork, after applying plenty of making tape.

Key measurements were:

• Hole for rear stay: 47mm x 66 mm rounded to 47 mm diamater, which is the diameter of the spice jars in the kitchen, so I pinched a jar of curry for the job (see below) 
• Spacing for rear stays (inside to inside): 860 mm. The rear stays are parallel on the half cage, so none of the tapering issues other builders have referred to with the FIA roll bars. 
• Spacing for centers of innermost mounting holes on front mount: 885 mm. This means that inside of rear stay is offset 12.5mm from the centerline of the mounting hole. 
• Centreline of mounting holes on front plate to inside of rear stay: 160 mm 

These measurements give enough information to be able to get an approximate location for the rear hole. The diameter of the rear hole (47mm) just happened to be the same as one of the spice jars in the kitchen, so I used that to mark out the circumference (and used the jar later with some sandpaper around it to smooth out the hole). The following picture shows the measurements - a little messy, but hopefully it will help any body else tackling this:

I did think about using this as a template to trace the holes, but it was too difficult to line it up properly, just using the two bolt holes for reference. Transferring the measurements was straightforward.

The side impact bars come with spacers to level out the cage in case you only fit the impact bar on one side. They were perfect to outline the hole for the front mount, after drilling up the holes from below. The spacer was not a perfect match for the mount, but it was close enough. Strangely enough, the third bolt hole wasn't drilled in the spacers, but the cone drill made easy work of that (I put the spacers in so that the height of the front mount was at the level it will be when the side impact bars are modified and mounted):

No putting it off any longer. Time to get cutting

I then cut the hole undersize with a Dremel and then used a sanding drum on the Dremel to finish it off. Lots of blue/white dust everywhere! I took the masking tape off once I was close to the line to get nice straight edges (well, mostly straight).

Not too bad actually. Just need to go carefully with the Dremel as it has a mind of its own sometimes

I used the masking tape template I had made earlier to locate the eyelet mounting holes - it worked perfectly - no measuring needed! You can actually locate the two end holes by eye, as they are right next to the hole cut out to mount the half cage. I drilled though the marked holes and checked via the boot opening that the drill was going inside the eyelet mounts. I then enlarged the holes with the Dremel:

The moment of truth for the masking tape template experiment

The hole for the gas cap was located from the centerline of the two inner eyelets, using measurements I had taken prior to fitting the body. I used I a rattle can cap over the gas tank to stop any debris going in (and to mark the centre) and drilled a pilot hole to ensure I was centered. I then used a 2 1/8" hole saw, which was undersized and expanded the hole with a Dremel until the gas cap fitted. I then used the cap as a template to locate the mounting holes:

Gas cap hole drilled and ready to mount

All in all it turned out quite well. I don't have the spacers for the eyelets yet, so they will have to come out, and the cage will have to come off to remove the outermost two!

The finished item

Hole around rear stay is a little oversized,
but that is perfectly acceptable in my book

The holes around the rear stays are a little larger than needed, but that is fine. I may get some rubber edging to finish them off. By the way, if you are careful, it is possible to do alone - you just have to attach the bottom stays to the chassis at the right angle first, so that the stays on the cage can just slide over them (do that before you fit the body). The lower bolt won't fit because the light housing is in the way - I am waiting for the right sized bolts so I can't do it up at the moment anyway. I imagine one bolt each side should be sufficient, given there is a single mounting bolt at the bottom (although it is a little thicker). I will have a think about this and possibly drill another hole so two bolts can be fitted - it will distribute the load in the event of inverted driving.

Tomorrow I will screw in the dashboard and fit the aeroscreen - I intend to use the same method as for the harness bolts, making a template out of masking tape. If I have time, I will do the orange cycle wings also, which will info some fiberglass work.

I feel a trip to the DMV coming on this week, but first I will need to hook up the speedo sensor and check the oil pressure.

Half cage fitted

The half cage does sit high, but that is good. When you are upside down at the track, a bit of clearance is a good idea.