Center boring fasteners

Where can I find a formula to select an appropriate bit for a given fastener size?

 

find some older yamaha linkage bolts and measure. or just buy some Ti and be done

 

You mean drill size for tapping a threaded hole?

 

https://littlemachineshop.com/reference/tapdrill.php


metric
https://littlemachineshop.com/images/gallery/PDF/tapdrillsizes.pdf

 

I took it that the OP wanted to drill out the center of his bolts for weight savings.

 

no, a formula to figure out how much mass I can remove from the bolt

 

Shervin?

 

Start with removing any excess bolt length that sticks out beyond the "nut". The old navy requirement to have 2 threads showing is BS. The first locking thread carries 50% of the load. The 2nd and 3rd threads carry the rest. Everything else is gravy. (Note, this is for clean standard or coarse threads...NFT is a different story)

 

Of course!
But i still have many bolts that could stand boring. Like the 10mm going into the kick stand mount that holds an AL tab to a 6mm to hold the belly pan,

 

if it’s something like that that is holding only light weight static loads I would think you could look at some thread charts online and figure out what the minor diameter of the thread is and then subtract enough to leave a decent wall thickness. The main thing would be that the thinner the wall you leave, the more critical it becomes for your lightning hole to be concentric to the thread. If you’re just doing a rough drill job on a drill press, or even worse by hand, then I probably wouldn’t go much more than 1/4 the thread diameter. If you’re doing it on a lathe or a kneemill where you can better control concentricity than you can go bigger.

Legal disclaimer: under no circumstances should you do that to anything that is safety related. I don’t remember the exact formulas off the top of my head, but the sheer strength of the bolt is a function of the surface area of the cross section, and drilling it out exponentially reduces the sheer strength.

Drilling will also drastically reduce the fatigue life, so don’t do it to anything that will be loosened and torqued over and over again. I’ve twisted the heads off a couple large(ish) diameter bolts that had been drilled. It’s not hard to do.

 

Start at half the diameter, then report back oh and corresponding lap time improvement

 

Thats the formula I want

 

Hell man....i’m get double the hp’s I’m use to......

 

if there’s some stamping on the particular bolt you’re looking at you can probably google that or call the manufacturer and find out what grade the bolt is, which in turn should allow you to find out what the sheer strength is. I believe sheer strengths are typically spec’ed at ksi/in^2 for sae fasteners, but most likely you’ll be dealing with metric, as if it’s a jap bike the bolts will be to Japanese specs. From there you just have to calculate the cross section surface area of the standard bolt and subtract the surface area of the lightning hole. Easy peasy…. If you can chase down the bolt grade

 

So for example looking at this metric thread chart I get the nominal minor diameter of a 10mm x 1.5 pitch bolt at Ø8.141mm. Based on that, drilling a lightning hole of ØX would reduce the cross section surface area & corresponding sheer strength by Y%. No you just need to determine the sheer strength you're starting with.

ØX Y%

Ø2.5mm -9.43%
Ø3.5mm -18.48%
Ø5.00mm -37.72%

 

Certainly not worth the time, effort and risk. The amount of time and money spent on machining will be quite a bit, that’s assuming you are using a lathe. If I have to bore a bolt I’d make a simple holding fixture that’s threaded and a nut on the back side to keep the threads in tact and ensure it’s running true. That being said, even with as much stupid one off shit I build boring out a bolt for weight savings has never seemed like a good idea. Remember, it’s not just your life at risk

 

You do know this is done on production bikes, right?

 

Screw that plan. Go to the gym and eat right, and that's 15-20 lost and you'll never get close to that by drilling fasteners

 

My bike is 20+# over what I’m reading most SS bikes are. I have hours or boredom to spend

 

I think it was Kevin Cameron in his Sportbike Performance Handbook that said, "Building a superbike isn't about making a 100% improvement in one thing. It's about a 1% improvement in 100 things."

I think in that same book he wrote "If an engine builder is head and shoulders above the competition, it's because he's standing on a pile of broken parts."

I say if you have the time, tools and talent then go for it. That's a big part of the enjoyment anyway, at least for me. It's fun to do shit yourself and see if it gains you anything. I haven't been on a racetrack in 20 years, but the last time I was I was a young lad with no money, lots of time, the key to the machine shop I worked in and the owners permission to use chunks of scrap metal out of the yard to do my "government work" as it's called. I had a big rubber made tube full of a couple complete rearsets, foot pegs, handle bars and frame sliders all that I made myself. I had no fear of the lowside, I had so many spares it cost me know more than about 15 minutes to put it back together and get to tech. I even made my own slotted cam sprockets for my 97 ZX7R after my degree wheel told me the timing was off, so I could fix it. And of course if you're gonna dig that far into it, you might as well take the head off, deck a few thousandths off the bottom and flatten it up and do some deburr work in there. It was amazing to me how shitty the machine work is in those engines. I've never had the opportunity to speak to a professional engine builder and ask them, but after what I saw I'd guess a fair amount of the job is deburring and cleaning up shitty machine work.