Just a quick entry to cover a point asked by Antonio about using templates.
I'll use an example of some leg components from a hexapod that I am working on currently. Here is how I made them to be accurate to each other, and also accurate to the design. I'll add pictures to this post when I get home.
The component is a joint between two servos, and is a complex shape - A circular section at the end of each joint with a curved centre brace between the two.
I will post a picture of it at some point, but it's essentially the middle leg joint of a bot like this:
http://www.hexapodrobot.com/images/MSR-H01/MSR-H01_Wake_Red_SRF_Look_ISO_s.JPG
Here is my method for making 6 of them exactly the same.
1) Draw out the shape on paper at full scale. It needs to link to two servo horns, so I kept two servo's with horns on my drawing desk to keep laying up against. Use a fine engineering pencil and keep rubbing out, changing lines etc.
Important bit. Also mark on 3 small drill holes somewhere where it doesn't matter. So for the legs, I put one mark near each end, and one right in the middle.
2) When it's right, go over the final outlines with a thicker black pen. Mark up any holes and draw a cross through the hole so you know where the exact centre is.
<<If your a CAD whizz, do the same in CAD - but I like drawing freehand more >>
Remember to add your three extra marks.
3) Use a photocopier to make multiple copies of the shape. So for the hexapod I made 8 copies ( so I had an extra one and a spare ). These are then cut out fairly roughly and glued to the wood ( In this case the hexapod is made out of plywood ). I use PVA glue so the paper can be wetted and removed later
4) I get the plywood - I am using 5 ply 4mm wood for this bot - and chuck it in the oven for 10 minutes at about 75 degrees. This drives out any water and gets the wood hot.
When I remove it, I cover both sides of the plywood with Celluose Dope - you can get it from any model shop. This will raise the grain of the plywood and feel really bad. After about 1/2 hour, use some fairly fine grade sandpaper to sand everything flat. You will find the plywood is now very smooth. Add a second layer of cellulose dope and sand again when dry.
What you will now find is that the wood is now very smooth, which makes it easier to mark up, and for a 2-3% increase in weight, the strength of the plywood has increased by at least 50%. It also bonds the wood grain much tighter, so you can now use epoxy glues if you need to. Lastly, you will find that the wood doesn't splinter or crack if you cut it with a scroll saw or a band saw.
So far you've spent a lot of time in preparation. Thats OK - it's not been hard work - you can do all of this in front of the TV. The pay off is that everything is now much easier.
5) With the paper templates glued on, now cut everything out roughly with your saw. Leave a 1-3mm aay from every line and curve - it doesn't need to be neat.
6) Now use a 2mm drill to drill out the three drill holes you identified earlier. Make sure your very precise with the positioning. Use a punch to make an indent in the hole first so the drill doesn't wander.
7) get some cocktail sticks and snip the ends off one side. Hammer these through each of the holes in turn. Go slowly and the cocktail sticks will fit themselves in very tightly You now have a stack of roughly cut legs exactly aligned. Now get one of your spare paper templates and prick holes in the three drill marks with a pin or a punch. Carefully fit this over the three cocotail sticks, and glue to the back.
What you have now is an set of legs with the templates exactly in line, and a template visible in either side which you can see.
8) Now you can set to with a file and get everything to shape. Put the deck of legs in your vice, and start work with a bastard file ( with large teeth ) initially. Don't get to the templates themselves with the rough file, just get pretty close.
When your nearly at the template, flip to the Number 1 file and get all the way to the template.
Keep flipping the deck of legs around in the vice and work from both sides and in all angles. That way, everything stays dead true and exact.
9) This all sounds hard work, and like a long time to do, but it's really not. If you've not had a lot of practise it might take you ten minutes. If you have had some practise, it'll take you five minutes. Just get into a rythem of filing and the wood will just evaporate. The cellupose dope makes the filing a lot easier as well.
10) If you have a good drill press, now is the time to drill holes through the entire deck if you need them for bolts etc. Otherwise, do it individually when you pull the deck apart.
11) When everything is done, pull the legs off the cocktail sticks. You'll now be left with legs with three holes. A quick smear of filler and a once over with the file will get them back to a mirror finish with only a few seconds actual work - and you can watch TV for the half hour while the filler drys.
Cutting the legs in this manner is more work - in terms of elapsed time - than trying to cut everything out exactly with a fret saw. However, in terms of time it's taken you actually touching tools and wood it's probabably about 20%-30% *faster*. It's also vastly more accurate. Every single one of your legs is *EXACTLY* the same as all of the others now and you can be confident that you haven't got any issues there when you build.
It also means you can be a bit more sociable when your using this method. While the wood is drying etc, you get to spend time with your wife - which earns you extra time in the future building robots. The downsie is, at least in my house, I end up having to watch TV shows I don't want to see.....
If you have a component that you need to make a lot of them,and you want to do it quickly or you can tolerate absolutely no inaccuracy, another route is to use a steel pattern.
If you wanted to make perhaps 50 of the hexapod legs, a much easier route is as follows:
1) Draw out the pattern on paper again, but this time transfer to a piece of sheet steel - lets say 3-5mm thick. Drill three small holes - say 1.5mm. You need to use a carbon steel - this will not work with mild steel.
2) cut out the pattern. This will take more time, but I promise you will get it back. Set to with the files and get the pattern absolutely perfect. Drill out the three holes.
3) Cover the steel with washing up liquid - liquid soap - and then use a blow torch to heat the part until it is dull orange - the colour of boiled carrots. Immediately dunk the pattern in cold water. This has hardened the steel and you will find that you can't really make a dent in it with a file.
4) Clean it up with hot water - the liquid soap has made this much easier.
5) Push three needles through the small holes, so there is perhaps 1mm sticking out of one side. Use solder to hold then im place. Break the long piece of needle off and file flat.
Right.... breath out. You've spent maybe 1 hour on this so far, but now you get to save LOADS of time and still be accurate.
6) Cut a load of pieces of material - wood, plastic etc into roughly the right shape. Rectangles will be good enough. Put the pattern over one of them and put them in the vice. The needles will push into the material.
7) Now you can just use your files are really quickly file all the way to the steel pattern. The steel is hardned so will stay intact, so you can work the file really hard. Keep flipping around the material - the three pins will keep locating in the same hole.
8) In this way, you will find that you can do something like the hexapod legs in under a minute once you get into the rythem of it.
This is far too much effort if your just makinbg one robot, but if you ever think you have a lot of components to make, you can trade a little bit of time up front for lots of savings over the next few years.