Cylinders for 'The Priest'. Laser cut valve face (with ports cut), flame cut end-plates (25mm) and flame cut valve chest (50mm plate)

The technique (or facility) of profiling is one of the basic tools for me now (in this amatuer engineering life, and in my day-to-day work), and I've recently realised that I've not said very much in a coherent form about profiling, and how to get it done.

There are two fundamental advantages with having parts profiled. First, it saves on a massive amount of hard work in reducing a slab of plate or bar down to whatever complex shape is required, and secondly, it means you don't have to have all these materials in stock - or go to the trouble of procuring them!

As a generalisation, it is much cheaper to get componants laser or flame cut than one might expect. The connecting rods for 'The Priest' are about three foot long with bosses at both ends, 25mm thick, and cost £15 plus VAT each. Her coupling rods were about £10 plus vat each.........(all flame cut)

It is possible to get most sheet materials CNC profiled if necessary. Plastics, woods, alloys, stainless and carbon steel can all be cut either from a faxed fully dimensioned drawing (which an operator will then draw or programme in), or ideally from a dxf format drawing. Some companies will make a small charge for transcribing information from a fax or posted sketch into a usable format, whilst others will take the extra expense on the chin. Either way, It's not a big deal, and not having the facility or skill to draw on AutoCad or similar should be no bar to getting the job done.

Send or Fax dimensioned sketch / drawing, or e-mail dxf file, or dimensioned pdf

In this engineering context, most of our requirements are going to be in mild steel - hence ending up quite cheap.
Different componants (and the requirements thereof) are going to require different techniques to achieve them - and as a very basic guide, these are the parameters in order of price:

Flame Cutting
The cheapest (pro rata) technique, commonly available up to six inch plate to +or- 1.5mm, but coarse in comparason to laser cutting. I only use it when I really need to go over 20mm thick, and when I will be able to clean it up with an angle grinder.
Draw-backs. This process tends not to cut at exactly 90 degrees, and the angle of cut or draught (or is it draft?) can cause problems if you have not negotiated with the provider first. Flame cutting puts a lot of heat into the job, and therefore the hardening of the edge is more pronounced, as is the coarseness of the cut. there is usually a small burr, but I find this perfectly acceptable for things like coupling rods, which I then clean up with an angle grinder fitted with a flexible pad. (a coupling rod takes me about ten minutes to clean up).
The plate used in flame cutting is often still covered with mill scale, which also needs cleaning off (not as nice as laser.....)

Laser cutting
Good for accurate work from thin sheet up to 20mm plate. I would expect an accuracy of plus or minus 0.4mm in reality. The profile is a burr-free cut from a clean sheet of plate that may have been shot blasted - certainly the finish is usually very good, requires little cleaning up, and this service is fairly widely available.
Draw-backs of laser cutting are that it hardens the slightly corragated edge (as it is a heat process) meaning that it will blunt your file or milling cutter. Also, if you are cutting holes or slots in thick plate, the lands or remaining material should be at least as wide as the thickness of the material itself, otherwise distortion may occur, and the company in question may decline to do it (at the very least they will make a disclaimer warning about be possibility of distortion).

Water-jet Cutting
This is something of the Rolls-Royce process, and available for thin stuff right up to plate 6" thick. It is more expensive than the other techniques, but has some real advantages. First, it is very accurate, second, the edge finish is very good, and third, being a cold process, it doesn't harden the work, so you can machine it or file it with impunity. All these qualities lend themselves to precision elements like expansion links for example.
(I recently ordered from Sciss a set of frames, cab sheets, buffer beams, coupling rods and motion brackets cut this way for an 1/8 scale model of "The Priest' to run on 32mm track. These were cut from a combination of 2mm, 3mm and 4mm steel, and cost delivered £56, and I was delighted.)
Like the other processes, the draught angle can be a problem, but Joe Nemeth tells me that you can specially request a zero angle (which involves running the machine slower, I gather) for an extra 15% or so on the price. An extremely useful thing to know!
Draw-backs a little more pricy than the other techniques, but I don't know of any other problems!

There are other processes such as wire-erosion, but I personally have had no experience with them. I would be interested to hear if anyone has used them, and if they add significantly to our portfolio of techniques.