Our aim is to supply most of the parts you need to build a GNAT, excepting standard cycle components, and some things you can make or get for yourself easily, like nuts and bolts. This page tries to be a definitive list of the GNAT's parts. The 'official' names of parts below are written in *bold underline*.
I will try to be consistent in my use of these names in this site, although several parts have other names; for example, Mike Nelthorpe, who makes the mouldings, refers to the chassis as the monocoque.
You do not need everything here in order to build a GNAT. You might choose not to buy everything for a variety of reasons, e.g. because:
I have drawn some parts below as I do not have photos here - I am writing these notes from a Greek island where I am spending Jan-March 2006.
Some parts of the kit, such as the chassis, are pretty well essential. I try to indicate, either on this page or elsewhere in the site, how sensible it would be for kit-builders to make parts rather than buying from us.
If you want a GNAT of your own, the most important parts to buy are: the chassis and the front wishbones. The latter incorporate geometry which is tricky to get right. The same can be said to some extent of the (front wheel) axle carriers - now made in steel. You should really buy the other mouldings - the rear arm and the boom clamps - because although their dimensions are not critical, it would be hard to make good alternatives in other materials. The rear wishbones are less important in their dimensions than the front ones, so you could make these yourself if you really want to.
The GNAT has several parts made from carbon or glass composites. Currently these parts are made by HQ Fibre Products in Norfolk, England.
The *Chassis* is the most important part of the trike. If you want to build a GNAT, you definitely need a chassis. It is made from glass composite with a coloured finish.
The *Rear Arm*, which holds the rear wheel, is of carbon/epoxy construction.
The *Boom Clamps* are also made from carbon/epoxy. Two of these mouldings - both the same- are required
Several parts of the GNAT are made from tubular steel - mostly half-inch 531. You should be able to make out the following parts in the picture on the right:
We have had two goes at making the axle carriers in carbon-epoxy. Neither attempt was totally successful, and after wasting a lot of time and money I now make this part in steel again. The brake backplate (right) screws directly into the axle carrier, using a tubular bolt into which the quick-release axle fits. See this pic for the complete hub set (plus the old-style axle carrier).
The steering arrangement consists of around half a dozen metal bits and pieces.
The diagram on the left shows the setup inside the chassis - not easy to see in photos of the trike, although you can see the trackrod ends in this photo.
The *Steerer Axle* revolves in two bushes set into the front of the chassis. The top of the steerer axle has an 8mm-threaded 60° cone forming part of the universal joint. The *Steerer Crank* clamps to the steerer axle inside the chassis, supporting a 6mm threaded boss which moves the inner trackrod ends. If you make this part yourself, the critical dimension is the throw of the crank: 67mm.
The steering's *U/J Nylon Cylinder* (left; seen here begin machined, and at the top of this photo on the trike) has holes at 90° with conical bearing surfaces. Note that one cone is 60° (standard lathe-centre angle) while the other is 90° to fit a normal (8mm) countersunk-head screw. The GNAT's universal joint has a big advantage over certain others: it is adjustable, so you don't have to put up with backlash (free-play). Another point, which anyone designing their own trike should be aware of, is that this is not a constant-velocity joint: there are two ways you might mount it; one magnifies handlebar movement (in the straight-ahead position), the other reduces it. Not all trike makers seem to know this! On the GNAT, the cone on top of the steerer axle should be pointing backwards (as in the drawing above) when the steering is straight-ahead. Another point: because of the assymetry of the holes, the u/j cylinder is right-handed: there is a 90° clockwise twist between the two holes.
The *Steerer Length Adjuster* (right) carries the top cone of the steering joint, and clamps the bottom of the steering column. You get enough adjustment to ensure that the steerer nestles comfortably in your lap, after you have cut the handlebar column approximately to length.
There are two more tubular parts that make up the steerer set - both visible in the above picture if you look carefully. The *Handlebar Column* is simply a bent piece of half-inch tube, to which the *Free Handlebar* attaches. Alan has advised me that most people want to use indexed gearshifters, although my own preference is for old-fashioned ratchet levers (my favourite is the chunky 1970s Suntour). For this reason I intend, for the time being, to leave it to kit-builders to work out how to attach the brake and gear controls to the handlebars. I hope to offer something later. (Incidentally, I have improved the design of the steering column since making the trike in several pictures on this site, e.g. here).
Depending on how you do the handlebars, you may need some plastic balls. When I tried snooker balls they became smelly after a while in my sweaty hands, so I suggest you use proper ones sourced from an engineering supplier. For my trike I have fixed them with 8mm screws, but I the hadlebar ends I supply will not have a thread so I suggest you use the unthreaded knock-on type of plastic ball.
There are four pairs of aluminium brackets; one pair for each wheel, and one for the front boom. These will normally be supplied drilled and countersunk, but needing shaping. If anyone wants to drill their own, it will save me some fiddly drilling, but you need to be able to countersink holes up to about 16 mm outer diameter - to decent standard since the conical surfaces act as bearings; you will need a reasonably rigid drilling machine and a bit such as the one shown above left. The front and rear brackets are made in 25x50x6mm aluminium angle; the front-wheel brackets are 25x25x5mm. You need a bit more of the 25x50 section to make the seat-brace bracket, which also anchors the rear webbing (far right).
Three types of balljoints are used in the GNAT. Two are visible in the picture on the far left. The type with a hole through the ball, we refer to as a through balljoint. The other type in this picture, with a thread stud on the ball, is called a studded balljoint (these are my names for them; other suppliers may use different terms). The third type (right) is the inline balljoint, used at the lower ends of the rearmost wishbone.
Note the spring-wire safety clip in the picture (left), which prevents the type-2 balljoint from coming apart. You need to remove this clip when folding the trike, but it should be in place when riding the trike, for safety's sake. The picture shows the clip partially removed. The 6mm through balljoint used at the inner end of the trackrods is shown on the right
The size of these parts is specified by the thread diameter. (Types 2 and 3 have male and female threads of the similar size; the diameter of the hole of type 1 is the same as the nominal outside thread diameter.) The steering uses 6mm balljoints; the suspension uses 8mm, as follows:
With three of the 8mm balljoint sockets, I shorten the body (right) - to reduce the bending stress on the screw. I also thread the hole down with a bottoming tap. (You can still hold the body for tightening, as in this photo). If you have a lathe, you could do this yourself.
Other bits and pieces
The *Front Gearchanger Sleeve* machined from nylon or polypropylene, fits over the 5/8" stub on the boom tube, and enables you to mount a standard front gearchanger.
A *Pair of Rear Dropouts* (seen here mounted on a spindle). You need to get these from us, because the eye-holes need to correspond with the drillings on the rear arm (unless you get an undrilled rear arm and do the holes yourself; not recommended unless you are confident about being able to get things accurate).
The *Rear Pivot Bushes* are bonded into the rear swing arm. I make these out of stainless M12 bolts 30mm long - machining down the head, and tapping an 8mm hole through the middle. If you have an engineering lathe, you could do this yourself.