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This article was first published in 2006.
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If you want to impact someone with technical
language, say: “Yeah, I jigged up for that.” Either the person won’t have a clue
what you’re talking about or, on the other hand, they might be quite impressed.
Jigs are used whever objects are being made repetitiously, so that the results
are as similar to one another as possible. Guides? Well, they’re just a bit
simpler than a jig. And a template? It’s kind of a combination of a jig and a
guide!
Guides
Let’s take an example. You want to drill a line of
holes just inside one edge of a flat plate (or square tube or...). The holes all
have to be the same distance in from the edge and spaced evenly along the plate.
You could mark out and centre-punch each hole, or you could bolt a guide to the
drill-press table and push the work up against the guide. The guide could be as
simple as a piece of straight timber.
With the use of the guide you immediately know
that all the holes will be the same distance in from the edge – then it just
becomes a case of getting their spacing in the other direction correct. It’s
even possible to mechanise this aspect if you make a guide and a pin, with the
pin slotting into the hole just drilled and so creating the spacing to the next
hole. Even a simple guide like this will provide much greater consistent
accuracy than is possible by marking-out alone.
Another example of where guides can be used are
when cutting material. An electric jigsaw is often used when cutting plastic,
composite timber sheet and metals. When cutting straight lines, clamping a guide
to the material being cut and then holding the jigsaw hard up against it will
result in a far straighter cut than will be achieved free-hand. If cutting a
circle, a guide that bolts to the jigsaw base (often there are slots provided
for this) and then pivots from the centre of the circle will again give a much
better result than doing it by hand alone.
Jigs
Jigs are more complex guides, sometimes even in
three dimensions. Jigs also vary from guides in that usually a prototype of the
item is made first, then the jig is matched to the prototype.
A good example of the use of a jig is in the
construction of exhaust extractors (headers). Making a prototype set of
extractors is a time consuming, laborious job where the snake-like bunch of
pipes is made from short lengths of bends welded together. The way they connect
to the head, the way they miss engine brackets and the sump and the bodywork –
all requires lots of trial and error, cutting and welding. The time taken to
build that first set of extractors might easily be three or four days – and if
subsequent iterations took this long, each set would cost thousands of dollars.
But instead the prototype is used to make a jig.
Normally the jig consists of angle-steel uprights
welded to a rigid steel base. Each pipe of the extractors is supported by
U-shaped bits of steel of the jig, so that when the pipes are the right shapes
and head in the correct directions, they nestle into the jig. Some jigs have
removable sections that bolt or clamp back into place, while others are quite
simple. When the pipes have been assembled in the jig, they’re ready for
welding.
Which brings us to the next point regarding jigs.
Jigs are very often used when things need to be held in the right positions for
welding. Especially if the person building the object is not the one who will be
doing the welding, a jig ensures accuracy and location. If the jig is strong
enough, it can also prevent distortion that almost inevitably occurs during
welding. But that requires a very rigid jig – most jigs are for positional
location rather than to prevent distortion.
Jigs are used when hand fabricating suspension
components – for example, even if only two wishbones are being made, it is
usually worth jigging-up for it so that dimensional accuracy can be maintained.
Note that a two dimensional jig can be as simple as some nails banged into a
thick piece of particle board – especially if it is to be used only once or
twice, there’s no need to spend a week making it.
Templates
Templates differ from jigs and guides in that
they’re usually used when a shape needs to be replicated. For example, if two
brackets of a complex shape need to be cut from thick plate, a template can be
made from thin material and then traced onto the thick material. The benefit is
that the thinner material is easier to ‘work’ into the correct shape and that as
the thinner material usually costs less, any mistakes made in the development of
the template can be more cheaply remedied.
In some cases more than one template might be
made. In this example, where a supercharger bracket was being developed, two
templates were used. The first (1) was made from thin plastic sheet able to be
cut with scissors. It underwent numerous changes and extensions, being stuck
together with adhesive tape. Note also that the middle hole has been elongated
to fit the engine block pick-up points. The second template (2) was made from
thin aluminium sheet. It is one piece (no sticky tape here!) and the hole
locations are now correct. The shape of the aluminium template was then traced
onto 10mm thick steel plate to make the final part of the bracket (3).
Here’s another example, this time the front
suspension upright of a human-powered vehicle. In addition to supporting the
stub axle, the upright had to locate and support the hydraulic brake caliper.
This required absolute accuracy in the hole locations – a template (1) was a
necessity. It was used to form the right-hand upright (2) and then by a mirror
image reversal, the left-hand upright (3).
Another approach where two identical objects are
being made is to produce the first and then use it as a template for the second.
A template is often used where holes need to be
drilled. For example, in both cases shown here, the hole locations were
specified by laying the template over the work and then drilling through the
template’s hole with the drill press. Care needs to be taken during this process
that the template does not get distorted – you don’t want the drill-bit rattling
around in the template’s holes.
Conclusion
They can be as simple or as complex as the
situation requires, but jigs, guides and templates all make work more accurate
and easier to accomplish.
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