Honeybadger
Plastic
- Joined
- Oct 12, 2016
Hi folks,
I'm an absolute metalworking newbie, so please forgive me if this question seems absurdly silly/simple.
The backstory of my conundrum- it's a bit of a ramble.
I am in the process of rebuilding a honda comstar wheel for a '75 CB400T. It's a split aluminum spoke wheel (two spokes on either side of each of the five points of contact with the rim) with an aluminum rim. One of the joining rivets was loose, and finding replacement wheels is a nightmare, and there is an unbelievably small amount of information out there. People have just been replacing these rims when this happens for decades, and the supply is now running low, and the costs going up, so I decided to look into rebuilding it. Everyone screamed "DON'T DO IT, the rims say 'DO NOT DISASSEMBLE!' The wheel will lose its true and never regain it!" but I figured that the wheel was junk anyways if I screwed it up. So I used my drill press (floor standing, heavy cast iron, chinese made 16 speed belt drive with 220-4000rpm range. It's not milling machine accurate, but it doesn't wobble and feels quite accurate when drilling wood) to drill out the rivets one spoke at a time, checking the wheel on a balancer. No change in the runout, the fitment of the spokes is definitely not under tension. I then proceeded to carefully bore out the rivet holes to an m8 size (less than 1mm of material taken out, it was too big for an m7) and again, everything fits up nice and true.
I was agonizing over the type of bolt to use. I hear all the old tales regarding a lower grade bolt for these applications because they'll "stretch" before failing, but I've also read all the rebuttals regarding the fact that by the time a lower grade bolt stretches to shear, you still won't even hit the shear point of the higher grade (10.9 vs 12.9) in this application. I called ARP and they told me that I was right in that, even for shear load, two bolts side by side, loaded in shear, on an unstressed member of a motorcycle wheel, the higher grade the better, so I went with m8x20 12.9's from a reputable local bolt/nut store. My only concern here is that the bolts are being loaded across the threaded portion, since there is no 20mm bolt with a shoulder at all, but again, the previous hardware was aluminum, the bike isn't heavy, the spokes aren't tension set, and this isn't some racing application, just an old japanese UJM. To prevent any bolts loosening, I plan on using loctite 648, and I'd like to add an extra layer of security (and teach myself a skill) by learning to corner drill nuts and safety wire them.
Now onto the problem -
So now that I have the hardware (m8x20, coarse threaded in grade 12.9) I have been absolutely unable to drill a single corner in any nuts. These small nuts are only accepting of a 1/16th bit. a 3/32nd drills the hole, but chews off the whole corner of the nut, negating any ability to thread safety wire. I have a nut drilling jig with guides for 1/16 and 3/32, my vise is clamped tight, everything looks square, no visible runout in the bit/chuck of my press, using loads of tap oil, I'm using cobalt jobbers (I'd prefer stubs but can't find them) and they're either work hardening so bad that they simply stop drilling and then snap less than 1/4 of the way through, or chip off the teeth of the bit immediately. I've tried speeds ranging from 220rpm to 3000, with no real change in performance, I take firm, small bites, taking care to pull it out completely to eject chips, but in the nut drilling jig, I think chip buildup is a problem. I've broken maybe a dozen bits without successfully drilling a single 1/16th hole.
So I pose this question, with a regular joe drill press, is this possible? for drilling 12.9 grade bolts, will I ever really be able to get this done? My bits are mostly all irwin. I feel like my main problem is that I'm work hardening the cutting surface. How can I prevent this better? I'm using a ton of tap oil and only taking 2-5 second bites of the material.
I'm an absolute metalworking newbie, so please forgive me if this question seems absurdly silly/simple.
The backstory of my conundrum- it's a bit of a ramble.
I am in the process of rebuilding a honda comstar wheel for a '75 CB400T. It's a split aluminum spoke wheel (two spokes on either side of each of the five points of contact with the rim) with an aluminum rim. One of the joining rivets was loose, and finding replacement wheels is a nightmare, and there is an unbelievably small amount of information out there. People have just been replacing these rims when this happens for decades, and the supply is now running low, and the costs going up, so I decided to look into rebuilding it. Everyone screamed "DON'T DO IT, the rims say 'DO NOT DISASSEMBLE!' The wheel will lose its true and never regain it!" but I figured that the wheel was junk anyways if I screwed it up. So I used my drill press (floor standing, heavy cast iron, chinese made 16 speed belt drive with 220-4000rpm range. It's not milling machine accurate, but it doesn't wobble and feels quite accurate when drilling wood) to drill out the rivets one spoke at a time, checking the wheel on a balancer. No change in the runout, the fitment of the spokes is definitely not under tension. I then proceeded to carefully bore out the rivet holes to an m8 size (less than 1mm of material taken out, it was too big for an m7) and again, everything fits up nice and true.
I was agonizing over the type of bolt to use. I hear all the old tales regarding a lower grade bolt for these applications because they'll "stretch" before failing, but I've also read all the rebuttals regarding the fact that by the time a lower grade bolt stretches to shear, you still won't even hit the shear point of the higher grade (10.9 vs 12.9) in this application. I called ARP and they told me that I was right in that, even for shear load, two bolts side by side, loaded in shear, on an unstressed member of a motorcycle wheel, the higher grade the better, so I went with m8x20 12.9's from a reputable local bolt/nut store. My only concern here is that the bolts are being loaded across the threaded portion, since there is no 20mm bolt with a shoulder at all, but again, the previous hardware was aluminum, the bike isn't heavy, the spokes aren't tension set, and this isn't some racing application, just an old japanese UJM. To prevent any bolts loosening, I plan on using loctite 648, and I'd like to add an extra layer of security (and teach myself a skill) by learning to corner drill nuts and safety wire them.
Now onto the problem -
So now that I have the hardware (m8x20, coarse threaded in grade 12.9) I have been absolutely unable to drill a single corner in any nuts. These small nuts are only accepting of a 1/16th bit. a 3/32nd drills the hole, but chews off the whole corner of the nut, negating any ability to thread safety wire. I have a nut drilling jig with guides for 1/16 and 3/32, my vise is clamped tight, everything looks square, no visible runout in the bit/chuck of my press, using loads of tap oil, I'm using cobalt jobbers (I'd prefer stubs but can't find them) and they're either work hardening so bad that they simply stop drilling and then snap less than 1/4 of the way through, or chip off the teeth of the bit immediately. I've tried speeds ranging from 220rpm to 3000, with no real change in performance, I take firm, small bites, taking care to pull it out completely to eject chips, but in the nut drilling jig, I think chip buildup is a problem. I've broken maybe a dozen bits without successfully drilling a single 1/16th hole.
So I pose this question, with a regular joe drill press, is this possible? for drilling 12.9 grade bolts, will I ever really be able to get this done? My bits are mostly all irwin. I feel like my main problem is that I'm work hardening the cutting surface. How can I prevent this better? I'm using a ton of tap oil and only taking 2-5 second bites of the material.
