Drilled hollow bolts and axles

Hobot

Hobot

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Actually Phil Irving [designer of the Vincent] says in his book "Restoring and Tuning Classic Motor Cycles" that drilling the central 1/3 of the bolt actually INCREASES the strength: "Far from weakening the bolts, this treatment actually makes them less prone to fatigue-failure, and if carried out consistently throughout the whole machine, a perceptible mass of excess metal will be disposed of."

However, Irving didn't recommend drilling the whole bolt, but from the head down to the beginning of the threads. Also, the area you drilled is now naked steel, exposed to the elements, so some kind of protective paint is in order.

Mike Taglieri
Brit Iron list
 
Norton did this on their race bikes, if you look at photos of the regular production Manx Norton a lot of the chassis bolts are drilled out and the heads of the bolts have a concave depression on them. I think Irving goes over it again in Tuning for Speed. Something fun to do, but most of use could just lose ten pounds and gain more than many hours of effort and many dollars would do for the bolts on any performance motorcycle.
 
bwolfie said:
Basically the tube has about 10% less strength but much less weight. So you loose a little strength but gain lightness.
Click to expand...

If you study closely the links you supply, depending on what size the centre of the bolt is drilled out to, its actually STRONGER in many cases.
Within limits, of course...

Thinwall frame tubing also shows similar properties.
Within limits, of course...
 
On sort of similar note drilling a tube for less mass is better to drill all in a row not cross wise alternate drilling for best strength per mass removed. A listee tested this by crushing some tubes and makes sense when thought though. It might be more accurate to say proper drilled bolt is tougher rather than stronger. its a very expensive way to loose so little mass so main reason is more endurance. Peel's axles weight 1/3 less now though prone to bug nests.
 
Are they drilled all the way through or only up to the threads?
 
hobot said:
It might be more accurate to say proper drilled bolt is tougher rather than stronger. .
Click to expand...

Define tougher and stronger in this context ?
If we are going to misquote physics, and redefine terms to suit ourselves, we may as well all go home ?

Take a look at the latest front axles in the current (and not so current) crop of superbikes and performance bikes.
Big hollow tubes. Way way way stronger than little solid rods of old.
Keeps the front fork lowers solidly locked together, not like the bendy little solid axles of old...
 
Onder said:
Are they drilled all the way through or only up to the threads?
Click to expand...

Depends on the application.
A lot of modern stuff is drilled all the way through.
Doing it to older iron, it is not recommended to drill past the beginning of the threads.

As mentioned elsewhere, then needs to be painted, or otherwise prevent corrosion occurring.
Tough (& expensive) way to lose a little weight, as mentioned !
And if done roughly inside, with any sharp edges or lumps or bumps or notches, may seriously weaken things.

I had an older Norton mainshaft, with a very rough clutch action.
A little investigation revealed the mainshaft had been drilled from either end - and the drillings did not meet very well,
must have been half a drill width out, at least. Gave the clutch pushrod a very rough time moving smoothly through.
Should have been in the rejects pile... ?
 
Rohan said:
bwolfie said:
Basically the tube has about 10% less strength but much less weight. So you loose a little strength but gain lightness.
Click to expand...

If you study closely the links you supply, depending on what size the centre of the bolt is drilled out to, its actually STRONGER in many cases.
Within limits, of course...
Click to expand...

Words to live by.

There are instances where the common practice of dishing the head removes unnecessary material weight.

Drilling out the center of a bolt will weaken it. Plain and simple. Drilling out the center will increase the strength to mass ratio to a point as long as you are removing mass at a greater rate than the reduction of strength.

It is a matter of efficiency of material mass; the most strength for the least mass.
 
If you do the math, shown in that link, not so.

Almost the first exercise in Engineering 101 is to calculate how much STRONGER is a rod that has had a hole drilled through it.
Solid rods are not as strong as if they have a hole through them. Within limits.
This is the basis why TUBULAR frames are not made solid.

There is, of course, a balance between how big the hole is, and how strong things are.

Not nearly as obvious or intuitive as it seems.
Do the math...
 
P.S. The hole in the middle acts as a stress relief release surface. (= stronger).
And the total surface area is related, indirectly, to how strong the whole structure is.
So you have surface area increase and wall thickness (thin-ness) decrease acting against each other, in an integral function.
Not a simple relationship....

Wrist pins (gudgeon pins) are a perfect example, you never see them solid.
In direct shear, strength is everything there...
 
After all the calculus you refer to from the article you reference:

"This means a hollow cylinder is stronger than a rod of equal mass and the same material."

That is ............ "equal mass".

Yes there is the matter of stress redistribution and stress riser but this has more to do with durability, not ultimate strength. A perfect example of this is the wrist pin you cite where they design it for lightness, bearing load (diameter yields lower bearing load stress) and durability.
 
Furthermore, when looking at moments, this is a matter of bending. We are talking about bolts which should, by design, only be in shear and tension/compression.

This is freshman high school math so do the math ................................force/area.

Class dismissed.
 
Dances with Shrapnel said:
This is freshman high school math so do the math ..
Click to expand...

Why then are axles and gudgeon pins large hollow tubes, not thin solid rods ??

Anyone who can do this math in freshman high scool class is in the genius category..
Especially if they can get it right !!

Get those freshmen then to do the math on these 2 tubes. Same quantity of metal per unit length.
Drilled hollow bolts and axles
 
The stock M10/1.25 caliper bolts are drilled on the TL1000.

Anyone else make their own titanium fasteners ?

Drilled hollow bolts and axles
 
Time Warp said:
Anyone else make their own titanium fasteners ?
Click to expand...

On a Norton ? Overkill.....

I find sifting all that beach sand hard work, and the smelting is not so easy either.

Tell us more though.
 
Rohan said:
Dances with Shrapnel said:
This is freshman high school math so do the math ..
Click to expand...

Rohan said:
Why then are axles and gudgeon pins large hollow tubes, not thin solid rods ??
Click to expand...
Click to expand...


It's pretty much spelled out in one or both of the reference articles; when mass and bending stiffness/strength/durability are in play, this is a way to have your cake and eat it; tubes, not solid bars - plain and simple.

Rohan said:
Anyone who can do this math in freshman high scool class is in the genius category..
Especially if they can get it right !!

Get those freshmen then to do the math on these 2 tubes. Same quantity of metal per unit length.
Click to expand...

Drilled hollow bolts and axles


I am with you 100% on this :lol:

But, in all seriousness, the simple math I refer to pertains to the subject of a bolt, drilled or undrilled. A bolt should be used for tension or shear and that's it. Bending is not part of the analysis so analysis or discussion of Moments of Inertia, second, third etc. as in the referenced articles ..... pertains to analysis of bending stress/strain and components in acceleration.

The simple math I referred to is force divided by cross sectional area which yields stress, whether it is in simple shear or simple tension (as applied to a bolt).

An axle is not a bolt application but a round beam in a bending moment; this is where moments of inertia apply. A hollow axle is a tube beam in a bending moment; this is also where moments of inertia apply, this is where improved strength per unit weight can be achieved. An axle is a completely different application than bolt.

I have instances of drilled transmission through bolts on a few of the race bikes. This is an instance of a bolt having more capacity than actually needed. By drilling it through the tensile load capacity is reduced, the shear capacity is reduced and the strain per unit tension load is increased but it is plenty adequate. This means it was significantly more than adequate for it's intended use as stock.

In the instance of a solid axle, the center core of a solid axle contributes little to nothing to the bending stiffness, this is why some portion of the center can get bored out without much loss in axle stiffness.
 
Rohan,

Leave it to hobot to quote someone who is quoting someone. The text below only mentions bolts and is probably an incomplete quote and possibly out of context. This thread is titled "Drilled hollow bolts and axles". I now understand why you were harping on the moments analysis as I now presume you were referring to axles and tubes whereas I was reading and referring to drilling bolts. Confusion abounds! :lol:

hobot said:
Actually Phil Irving [designer of the Vincent] says in his book "Restoring and Tuning Classic Motor Cycles" that drilling the central 1/3 of the bolt actually INCREASES the strength: "Far from weakening the bolts, this treatment actually makes them less prone to fatigue-failure, and if carried out consistently throughout the whole machine, a perceptible mass of excess metal will be disposed of."

However, Irving didn't recommend drilling the whole bolt, but from the head down to the beginning of the threads. Also, the area you drilled is now naked steel, exposed to the elements, so some kind of protective paint is in order.

Mike Taglieri
Brit Iron list
Click to expand...
 
Hommer Simpson creators know strength refers to resistance to deformation, and also to a large elastic range. In the Elastic region of the stress-strain relationship, the relationship is described by a linear function, such that σ = E ϵ, where σ is the stress, E is the Elastic modulus, and ϵ is the strain.

At a point called the yield point, the relationship between stress and strain depart from linear, and the material yields meaning that permanent or inelastic and plastic deformation occur.

Toughness is the resistance to failure or crack propagation. It is somewhat related to strength. Very strong materials will have low toughness, i.e. low tolerance for flaws or defects, i.e. incipient cracks.

Toughness relates to the amount of energy absorbed in order to propagate a crack. Materials with high toughness require greater energy (by virtue of force or stress) to maintain crack propagation. Toughness is described in terms of a stress intensity factor (K) or J-integral, or the strain energy release rate of nonlinear elastic materials, (J) = J-integral.
 
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