Drilled hole and structural integrity

[creighton]

Just wondering....

I am looking at the TT/ HT juction and using a healthy brass fillet for the joint. Drilling a small hole in the HT for drainage aint no big deal.. however I ask what would be the largest diameter hole safely drilled here using a fillet joint? Twist/failure in the HT because of a larger hole?

I plan on using something like .028" wall strait gauge 1.125" dia. 4130 TT mated to a heavy wall 1.25" HT. Sorry about the english dimentions.

Thank you for your time,

CW

[Eric Estlund]

I wouldn't go bigger then the outer diameter of the intersecting tubes....

Are you looking to poke big holes, or is this mostly an academic question? Not busting chops, just wondering about motivation. I usually stick to 1/4" because its plenty big for cleaning/ drying and easy to drill. Having done the pre/ post scale game with uber vents I can say that any weight savings isn't worth it for my bikes, though I still change hole size for some applications.

[Zimmermanbicycle]

I'm with mr Estlund on this one,I usually do a 1/4" hole but it would of course be possible to go much larger.
Why are you asking?
-Eric

[creighton]

Internal TT routing of dyno wire for a tail light. Which also means a 'modified' steerer. I have checked and double checked with those that have a head for this stuff. and they say its good. The steerer itself will be heavy walled as well. ALSO an external steering stop brazed onto the HT so the wire will not shear or bust the head light off.

I know that this is not a conventional approach but I feel it will work...

All in the name of clean routing vanity.

Again just asking and thinking.... nothing is made yet.

[Archibald]

Really depends on the intersecting tube, but don't go any larger than about 1/8" smaller on the radius than the ID of the intersecting tube. There is some evidence that too large a hole in the HT can lead to head tube cracking that originates from the hole and propagates through the weld to the intersecting tube or down the head tube itself. I'm not sure I understand what set of conditions causes this to happen, but I've talked to enough builder's who've seen it that I believe it.

[WadePatton]

I wouldn't go bigger then the outer diameter of the intersecting tubes....

dewd, i spilled beer on that one! thanks.

now slips quietly back into the shadows...

[Dave Kirk]

Really depends on the intersecting tube, but don't go any larger than about 1/8" smaller on the radius than the ID of the intersecting tube. There is some evidence that too large a hole in the HT can lead to head tube cracking that originates from the hole and propagates through the weld to the intersecting tube or down the head tube itself. I'm not sure I understand what set of conditions causes this to happen, but I've talked to enough builder's who've seen it that I believe it.

That happened to me a good 18 years ago with a fillet MTB. I made the hole in the head tube pretty large and the down tube pushed right through the headtube. The joint never failed but the headtube just flattened.

Not good.

dave

[creighton]

this is not a MTB... Rather an ice/ dark Knight ( ergo dyno power) runner here in flat Chicago. Heh... Two movie references in one sentence

Funny you say that Archibald.. the 7/8" bore through the HT leaves 1/8" radius distance to the I.D. of the TT. This is the one joint I overbuilt. The 4130 heavy wall tube is stout. The new HT mill/facer kit I picked up from Andy will be put to work to prep. I did however size the HT to fall middle entry ramp of the reamer tool.

Dave.. With a proper cope and careful brazing I dont think/hope that the HT will compress.. yeah...

Like I said, I am not hopping off of big rocks and the HT is beefy indeed. but still need a sanity check.

this is a weird sorta build and cutting a hole in the steerer tween the cups???

[marten]

I've learned my lessons with big holes too.
Assume you are bending the tube. If you cut a large hole in the tube, you've got to patch it with something to restore stiffness. Now you are patching it with a thin tube which will easily ovalise so it is much more flexible than the piece you drilled out, which will cause large forces on the edge of the hole and could start a crack.

I would never drill a hole in a steerer, but if you have to play stupid drill it half way up in the side.

I can't understand the obsession with hidden wiring. If you need a degree in origami and engineering to wire a bike (or regrease the headset) , it will end up with flex taped to the outside of the tube before long. KISS rules.

[creighton]

Thank you fellas..

Not going to drill any holes. I appreciate your time to offer your thoughts.

CW

[steve garro]

i have run 3/8" on light person's bikes but you must smooth out the holes or it will grow cracks like Dave said. usually i just drill 1/4" vents and call it all good.

[zank]

I guess I better stop using the 7/8" hole saw for my breathers.

Hey, KIDDING!!

[cement shoes]

after i set up the tubes in the fixture, I mark the tube intersections top and bottom with a sharpie, then draw a dot between the marks. I also mark the h20 boss locations. then over to the drill press and .25" holes all around. done.

[Dave Porter]

I have cut holes as big as 3'' (boom tubes) or nearly the full diameter of a main tube. Of course I then insert another tube perpendicular to the hole and all the way thru, then silver fill the joint.
This is an old trick I learned from Pino Morroni. It's very strong and also helps the tube resist twisting under torque loading.
Dave
Pino did this on his TI frames. I do it on track and tandem frames.
see
porterbikes.com/
PS small holes just let water and dirt in...

[N@Weller]

I have cut holes as big as 3'' (boom tubes) or nearly the full diameter of a main tube. Of course I then insert another tube perpendicular to the hole and all the way thru, then silver fill the joint.
This is an old trick I learned from Pino Morroni. It's very strong and also helps the tube resist twisting under torque loading.
Dave
Pino did this on his TI frames. I do it on track and tandem frames.
see
porterbikes.com/
PS small holes just let water and dirt in...

Dave was the stand-over (ie. not filed flush with the main tube) on those tubes significant , or did they just sound nice rolling around the track?

cheers, N@

[Dave Porter]

Nat,

Quiet as a mouse... Unfortunately the frame has been put up for sale (see classified herein). A bunch of factors conspired to kill the attempt..
So, I'm looking to recoup some money so I can do another one that is road worthy and not limited to the track only..
dp