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drilled chainrings (calling on machinists)(22 posts)

drilled chainrings (calling on machinists)DougSloan
Jun 30, 2003 10:08 AM
If someone were to drill a chainring, more for looks than performance (an old bike), even with a drill press, how would you go about locating the holes precisely? Can anyone think up a jig for doing this, so that marking and measuring would not be needed? Thanks.

re: drilled chainrings (calling on machinists)boyd2
Jun 30, 2003 11:37 AM

It could be done fairly easily with an indexing chuck. This is standard equipment for most machine shops. It is a flat chuck like you would find on a metal lathe. THe chuck is fixed in a precision ground mount. The chuck has a handle and an angle indicator. You can rotate the chuck a precision amount each time you move it.

The problem is that you will have to find the exact center of the chain ring, and make a mounting fixture. This could be the most expensive part of the job. I would propose trying to mount the ring on a crank and mount the crank on an axle. You may be able to put the axle right in the chuck and then you will be fairly closely centered. The problem here is getting the axle mated firmly into the chuck so that nothing moves as you bear on it with the drill.

After centering in the chuck, all that you need to do is extablish the pattern of holes you want. It would be easyest to keep the holes on concentric circles. Drill a hole, rotate the chuck a fixed amount, drill again until you get all the way around. Reposition the chuck to a different radius and do it again.

One other option is a 4-axis (minimum) milling machine. I assume that you do not have access to one of these.

You could even do this job with a hand drill and an indexing chuck, if you build a good fixture.

One more idea, you could build a jig that indexes using the teeth of the chainring and incorporates a drill guide for a hand drill. This is a pretty good bet, but it may be hard to do. I will think about it though.
Everything is a factor of 5, don't you love it. N/Mcurlybike
Jun 30, 2003 11:59 AM
re: drilled chainrings (calling on machinists)boyd2
Jun 30, 2003 12:10 PM
I took some photos of my indexing chuck.

Pic 1
re: drilled chainrings (calling on machinists)boyd2
Jun 30, 2003 12:14 PM
I say again,


Notice the handle and scale at the bottom.
fancy stuffDougSloan
Jun 30, 2003 12:19 PM
I have a $100 drill press, and would hope to make it work with that. I imagine that chuck alone cost far more than that. Nice stuff.

re: drilled chainrings (calling on machinists)spincircles
Jun 30, 2003 12:09 PM
You could use a cartridge BB (minus the LH cup), a 4x4, and a Right side crankarm. Drill a hole in the 4x4 the same diameter (for a snug fit) as the BB casing, deep enough to accomodate the left spindle and a good inch or so of the casing. Pound the BB in with a rubber mallet until the left spindle hits the bottom of the hole (this will allow it to spin, but help hold it in place). Then mount the chainring on the Right side crankarm and mount that on the spindle of the BB. You should now have a block of wood with a spinning Right crankarm and chainring in it. In between the teeth of the chainring drill another hole (about 1-2" deep) for a dowl (make bit diameter a hair larger than the dowl diameter since you'll be removing it regularly). This will allow you to make regular spaced holes around the chainring by using it as a stop against which to place the chainring teeth as you work your way around the ring. You'll need to remove this dowl to advance the chainring for each new hole so make sure it's long enough that you can easily pull it out. hold the tooth against the stop, either by hand (watch your fingers) or some other more clever method you devise. Now you're ready to drill. Mount the block jig on the drill press and line it such that the first hole is exactly where you want with the chainring teeth pressed against the dowl, be sure to clamp it down good. Find a shim (scrap wood) to fit between the chainring and the 4x4 to support the chainring while the bit is pressing on it. Now you're ready to drill out your chainring. Email me if any of this is unclear. It's a reasonably good hack solution utilizing parts most of us bike junkies have laying around to make a reasonably accurate jig.
sounds doable; thanks (and a spin-off idea)DougSloan
Jun 30, 2003 12:18 PM
I like the dowel in the teeth idea. Indexing by the teeth solves several problems; I suppose anything that keeps the ring concentric works, too. I was thinking about a disc of metal the same diameter of the spider circle would work, and might be a little simpler. I might rig something up and post pix before drilling. Thanks, all.

Actually, now that I think about it, what if I took a piece of plywood larger than the chainring, and would place the ring flat on it; then drill holes for three dowels that would mate to three teeth in the ring; then, set the jig up in the drill press so that all I have to do is place the ring, drill, then rotate the ring one slot in each of the dowels/teeth? The dowels keep it concentric, right? (Am I missing something?)

Didn't think of that, quite a bit easier than my jig, nice callspincircles
Jun 30, 2003 12:52 PM
Your 3 dowel idea ought to work. Even 2 dowels will do the job as long as you press the ring snugly against them and 2 dowels may be easier, especially if the teeth are differentially worn, making the 3 dowel jig tight/loose as you rotate the ring.
good pointDougSloan
Jun 30, 2003 1:02 PM
I guess 2 dowels will precisely locate the ring. I guess the trick it to just get the jig located precisely for that first hole. Thanks.

Another thing -- what's the best way to camfer the holes -- just a larger drill bit?

sounds goodoff roadie
Jun 30, 2003 1:45 PM
I'd go for 3 dowels. You'd need a VERY snug fit with two to prevent the rign from moving in the plane of the ring in a direction bisecting the line between the dowels. 3 dowels would mean any such movement runs against a stop that much sooner. Plus 2 Dowels just wouldn't seem to work well for rings with odd numbers of teeth, which is most of them afaik...

For camfering, a larger bit will work, but you need some way to stop it at precisely the same dept every time, or the camfer diameters will vary. They can vary a LOT, because bit angles are so broad.
A metal loose sleeve over the bit that might make a suffciently reproducable depth guage. It would slide until you pressed the chuck all the way to the end of the tube. This actually seems like a good method because it indexes to the surface you are camfering, meaning slight warps in the workpiece won't result in different size camfers.

The other option might be just to use a hand held tool that looks like a fluted cone. They come in various degrees of pointiness. You put the tip in the hole, twist its handle, and voila, it cleans up the edge of the hole. Won't go to deep to fast because its a hand tool, so you can probably just eyeball it.
thanks -- and one more questionDougSloan
Jun 30, 2003 1:53 PM
Good ideas. Actually, my drill press has a depth stop, so that should do the trick, as long as the ring is secure.

I guess there is no harm in 3 dowels, so 3 it is. Can't hurt, so why not?

I post pix when I do this. May be a while until I get time, though.

Last quetion -- would you drill at the peak of the teeth or the troughs? I'm thinking at the peaks.

Thanks all.

Drill on-line with radius...MrDan
Jun 30, 2003 8:37 PM
Drill on-line of radius from center of ring centered through peak. Do not drill in the tooth. Drill well below that, in fact below the trough as far as possible/practical. If you are going for a classic look and not really looking to shave weight, then drill smaller... Don't forget to use paint to highlight any seatpost grooves that might be present as well as groves that might be on crank-arms... :-)
Good Luck, jig sounds good!
I think that you're making it too hard.Spoke Wrench
Jun 30, 2003 2:31 PM
Don't think about the chainring as a whole. It already has teeth accurately located around its circumference. If you locate the holes accurately as related to each tooth, the whole chainring will be uniform too.

You know that a chain has a 1/2" pitch, so if you take a piece of 3/4" plywood and accurately drive two finishing nails 1/2" apart, you're halfway there. Now clamp your "jig" onto the bed of your drill press so that the drill hits halfway between the two nails and a bit toward the center.

Push each chainring tooth between the nails and you should be able to drill holes that line up uniformly with each tooth. Sould work with any size chainring too.
I think that you're making it too hard.boyd2
Jul 1, 2003 3:45 AM
Take this idea one step further. Instead of finishing nails use a 6" piece of chain. Put the ring in the chain and perhaps trace around it to get the same location each time then clamp it down with a bar clamp.

I think that a really solid jig is key here. You do not want to mis-allign the holes or it will destroy the look you are going for. The eye is very keen on picking up on slight mis-allignments.
A few last thoughtsspincircles
Jul 1, 2003 6:31 AM
Odd or even tooth number doesn't matter, 2 dowels still works fine, the 3rd will give a little added security. For camfering the holes the larger bit works fine, especially if your press has stops. A countersinking bit allows you to do it all in one fell swoop (assuming you only want to camfer the outside of the ring, for aesthetics). I agree with drilling the peaks of the teeth, the peaks have the most material, but not too close (radially) to the tooth as you'll compromise its integrity. I'd also advise against using the nails and going with actual dowels. Small nails will have a tendency to bend altering alignment as you use the jig, and big, beefy nails will damage/warp the wood creating a slight rise around the nail and thus non-orthogonal point of entry for the bit as well as being prone to tilting as you use the jig b/c the wood is weakened.
maybe a bit to simpleoff roadie
Jul 1, 2003 12:55 PM
The idea with the nails is good, but maybe a bit simple. I still think you don;t want to be relying on clmaping force to keep the ring from shifting in its own plane.
But nails are certainly as good if not better than Doles. You could even drive the third (and maybe foruth / fith) nail of a "jig" into place while the ring is right in place on the jig, giving a very secure fit. I've actually created welding jigs this way, suprised I didn't think of it myself...
Actually, I made a hub drilling jig that way once.Spoke Wrench
Jul 1, 2003 2:37 PM
I had an Atom hub brake that had been drilled for monster size spokes. I made a jig out of plywood and a couple of nails and redrilled it for 14 gauge spokes. So far as I know, that wheel is still running around somewhere.
duct tape and baling wire solutionmaximum15
Jul 1, 2003 8:31 AM
If you are just trying to obtain a decorative pattern, try tying some string around the chainring. You can make loops of string between different teeth. Where two strings cross would be the centerline for your hole. Centerpunch those areas where you want holes, remove the string, and drill. The centerpunched spots will ensure you drill in the correct location. By tying the string between various teeth, you should be able to get some interesting geometric patterns.
here's an exampledesmo
Jul 1, 2003 2:05 PM
Here's a swiss cheese job on early NR stuff. Later on it was more common to mill off the inner rings like the SR. Anyway, make sure you buy some good quality fresh bits. A little bit of "wander" will quickly junk the whole piece (don't ask me how I know).
Jul 1, 2003 2:07 PM
That's a heck of a drillium job. Thanks. I may not get that fancy. -- Then again, if it's worth doing -- it's worth over doing. ;-)

Don't usa a regular drill bit, use this>Dave Waber
Jul 2, 2003 7:10 PM
I would highly recommend you start each hole with a combined drill and countersink like this They are much stiffer that a regular drill bit which will drift around on you as you drill even if you start the drill on a punch mark. They also make a beautiful countersink. Countersinking with a drill bit will look like crap.