Drilled the two brake discs (rotors) today:
Here's what I needed to do it:
1. Roll of wall lining paper (£2.99) for drawing templates on (one tempate need for left hand disc and one for the right hand side one)
2. Prototractor (99p) , compass (99p), 12 inch rule & pencil for drawing out the templates
3. bit of parcel tape to stick the templates on the reverse side of the discs.
4. Centre punch to mark the discs for drilling before removing the temapltes
5. On single 8mm 5% cobalt drill for all 144 holes. (£4.85). One 12.4mm countersink bit (£9.99)
6. Bottle of cutting fluid (£8.99)
7. 2nd hand pillar drill picked up for £30 at a car boot sale
What I did:
1. put the lining paper over the disc and used a pencil to mark the circumference
2. found the centre of the circle on the paper using the compass.
3. marked out 24 sudivisions of the circle
4. Used the compass to scribe arcs and circles on the template to get the hole positions
5. Stuck the template on the reverse side of the disc using parcel tape
6. Used a centre punch to mark the positions of the holes through the paper onto the disc
7. Took the templates off the discs
7. Used a single 8mm 5% cobalt drill to drill all 144 holes in both discs. Pillar drill set at lowest speed (540rpm) and used plenty cutting fluid, making a single pass for each hole using even and constant pressure (ie no reversing back out part way through)... if its going right you get lovely spirals of swarf coming of, as in pic below
8. Gave each hole a light countersink on each side.
9. Job done.
(later on ...see my seperate thread at http://forums.sohc4.net/index.php?topic=125869.0 for the agonies I'm going through with setting up my Dual Discs)