Today I was working on the forge that I'm building. I thought I would share my poor man's indexing head with you all so you can see how I layout holes on the fly when I don't want to "get all technical". I've been feeling that my own need for perfection can sometime get in the way of making progress. I believe is was Salvador Dali that said "have no fear of perfection, you'll never reach it"; just something to think about when you're not getting work done due to the perfection issue...
The forge requires four evenly spaced holes around the circumference of the DOM tube to hold the burner. This creates a kind of "Christmas tree stand" that grips the burner securely. I needed to make many of these burner holders since I'm machining these inlet tubes for Chad and John as well as myself. I didn't want to spend time doing individual layout on each tube so here's the technique I use:
I use masking tape to create a flexible ruler.
I figure out my spacing on my holes based on the diameter of the DOM steel tube and then I create witness marks on the tape to represent that spacing. An extra mark is made to help line up the tape later (you'll see what I mean in a second).
My little 9" South Bend Model C has a smooth spindle adjustment nut on the back end of the spindle. I clean this nut off (as it usually has some oil on it from the rear bearing surfaces on the spindle) and then carefully wrap my flexible ruler around the smooth spindle nut. I make sure not to stretch the tape when I'm applying it. The final extra mark should line up with the first witness mark on the tape as you overlap it. If it doesn't then your spacing will be off. Make sure to get this right!
The old South Bend has this small gap between the bearing caps. This become my stationary witness mark that aligns with my flexible ruler when I rotate the spindle. In the past I have secured a sharpened paperclip to the lathe headstock if I need a thinner, more accurate "pointer".
I had already turned two grooves at the proper location that would allow me to align the marks along the length of the DOM tube. All I needed to due now is align my flexible ruler mark with the slit in the bearing cap and then I can use the lathe toolkit to scribe across the turned line to create a crosshair. I simply position the lathe bit and feed a little pressure into the workpiece using the crossfeed. Then (with the lathe off obviously) I just move the carriage of the lathe back and forth a bit to create the cross mark.
I lighten up on the crossfeed, move to the next groove, and make another mark. Just make sure your witness mark is still aligned before making this mark.
I rotate the spindle manually, align the next witness mark on my flexible tape ruler and repeat the process.
Now I remove the piece from the lathe; It now has four equally spaced witness marks that I can use to center punch the hole locations.
I used my digital calipers to make sure everything was equal before center punching the marks.
I used my automatic center punch to create a nice deep divot to guide the drill bit.
After all the marks are center punched, I'm ready to drill.
My friend Ian made this long section of wood v-block when we were in grad school. I just used the table saw to make this, but I use this ALL the time to hold round stock. It's not precious so I can drill into it and cut off sections for various jobs.
In my opinion ever serious maker should own a machine lathe. My students all know that I harp on this all the time. 3D printers get hyped, but the lathe is the original tool that we should all be singing the praises of (well besides maybe the hammer and the screw). Do yourself and find yourself a 9" South Bend. I guarantee you'll make more useful objects/tools than you can shake a stick at. You can use it to make more accessories and actually improve itself with (sound familiar 3D printer folks?; that's right the lathe was the FIRST tool to improve itself). You'll become more accurate, and you can use it like this, to speed up your productivity without getting too obsessed with accuracy. Go get a lathe!
I'll try to start posting details on the forges soon. We're all trying to get all of the various components made before we blog about them. We should be able to create a massive series of how to posts on the forge build in the near future.