Why drilling holes in your frame is a bad idea.

Cavi Mike

Cavi Mike

New Member
2 years of vibration finally made my frame split and this wasn't even on a part of the frame that's under tension. Do you really want to find out what it's like to have your down-tube or chain-stay split because you weakened it with a hole?

Obviously I welded this back together before I took the pictures, I just noticed it as I was about to leave work tonight and didn't have a camera handy. I only welded the outside, you can still see the split on the inside in the second picture. I touched it up with a paint-marker also because I didn't want it to rust.

cruisercrack01.JPG


cruisercrack02.JPG
 
Because it weakens the frame? Yeah, ok, because it weakens the frame.

You do not want to drill holes in any part of a bike frame or component where stress is high, that's just asking for trouble in the form of stress fractures and such. Drill your sprockets and non-stress brackets but not your frame if you can help it.

dnut
 
i drilled the down tube,bolted the front mounting plate on and then welded it,it wouldnt hold the engine as well as i wanted it to.i will pull bike apart in winter and remove bolt and tune up the frame where i welded it.then repainting.

i wasnt too keen on drilling in the first place,seemed the only solution at the time.
 
I built several ul and experimental aircraft in the past with aluminum strucrures, and here is some stuff I had to learn about drilling and avoiding cracks on machines that had to stay togeter for me to stay alive!

I learned from studying, that one of the major causes of aluminum tubes cracking at the drilled holes is improper finishing of the hole, or holes drilled in high stress areas. The hole needs to be de-burred or chamfered slightly on both sides of each wall. Failure to do so leavs the sharp edges of the hole to easily start stress risers that make into cracks.

A hole drilled nearer the end of a tube doesn't affect strength much.
A hole drilled midway of a tube weakens it a lot more.
Joints can be sleeved inside or outside to strengthen the joint.

I would still drill only as a last resort, but with good tecnique and some structural knowledge or experience it could be safely done.
 
I am not big on drilling a frame at all and simply will not . Especially one of today's run of the mill generic department store type bikes with ultra thin ''too'' potentially of frail tubing. Good alloy steel tubing with a thick wall is the best. Like some old school bicycle's used to have. There is still the Worksman they are good steel from what I've heard..

I can see adding support and welding a mounting brace but there to me is only one way to do that. A compliant competent person who can weld such a brace. Not just slap it in there and blow holes through the bike tubing learning how to weld. lol.
 
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Here's a old pic from my collection. This crack wasn't from drilling the frame, but let's just say "don't jump your motorbike BMX style"! :-{

crackedframe.jpg
 
Here's another old pic I found of a drilled frame that cracked (& was rewelded).

There you have it... more proof not drill your frame!
I'll add that after it was welded, it's still working to this very day. :-{

a27e4080.jpg
 
really it seems to boil down to use common sence when you drill a frame , you can sleeve the hole or properly dress the area , but on some frames if you can bend the appropriate size washer to fit the tube an braze it in place before you drill arent you adding strength to the area by doing so? I see this in some automotive an motorcycle applications , esentially preventing the stress an redirecting it ?
 
thegnu said:
really it seems to boil down to use common sence when you drill a frame , you can sleeve the hole or properly dress the area , but on some frames if you can bend the appropriate size washer to fit the tube an braze it in place before you drill arent you adding strength to the area by doing so? I see this in some automotive an motorcycle applications , esentially preventing the stress an redirecting it ?
Click to expand...

Yes that's an excellent way to strenghten a hole. on steel.
Most of the stuff I mentioned in my post was for aluminum tubing with no welding.
 
wayne z said:
Yes that's an excellent way to strenghten a hole. on steel.
Most of the stuff I mentioned in my post was for aluminum tubing with no welding.
Click to expand...

thats just asking for trouble on aluminum , although there are a few adhesives we use in autobody that are designed to bond metals if you were to use a peice of aluminum sheet an as I mentioned with the washer bond the aluminum sheet to the tube with fusor metal bonder your esentially doing the same thing with out welding .
 
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