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Lightening Holes
JB - 30/9/04 at 05:09 PM

I have seen many instances of holes being drilled in items such as pedals, chassis members etc.

Do you realise that putting a hole in a part does indeed reduce its weight but also reduces its strength to a very large degree?

Drilling holes in a brake pedal is very dangerous (not the foot pad but the actual upright part).

Drilling holes shows lack of understanding.

A better way of making a part lighter is to reduce the material from where it is not required. This generally means having more material around areas of high stress. So where it joins something else it will be thicker. Around a fixing hole it will be thicker etc.

Its all about reducing stress raisers and having smooth transitions between different sizes.

I hope this helps,

John.

stephen_gusterson - 30/9/04 at 05:37 PM

where?

ive never seen that on this forum?

atb

steve

stressy - 30/9/04 at 05:56 PM

John,

I haev seen examples of drilling standard part elsewhere resulting in failure, this is a BAD idea.

However, if your talking about making new parts i think youll find it all comes down to tools and money!!!

Cheers

Chris

Jon Ison - 30/9/04 at 06:23 PM

no comment, now where did i put me drill.

Hellfire - 30/9/04 at 08:22 PM

JB - total b0llox... you can't lighten a hole - they don't weigh anything

On the hole I agree with you though...

However, it depends on where, how big the hole is but more importantly whether it has been designed this way. i.e. the material thickness in relation to the stresses apllied.

I bet Cymtrix and others, could come up with a design to prove the fact.

Hugh Paterson - 30/9/04 at 10:50 PM

Feck now he tells us, wheres the bits I drilled oot the Brake pedal, help ma boab, wonder if thats why the brakes are spongy
Shug.

Hugh Jarce - 1/10/04 at 02:58 AM

quote:
Originally posted by JB
Do you realise that putting a hole in a part does indeed reduce its weight but also reduces its strength to a very large degree?

How can you make such a broad sweeping statement as that? Putting holes in items doesn't necessarily reduce the strength and the degree (if any) of weakness would not necessarilly be "large".


quote:
Originally posted by JB
Drilling holes in a brake pedal is very dangerous (not the foot pad but the actual upright part).

No it's not! Drilling holes in your head could be. There's nothing wrong with lightening parts as long as it's informed and done sensibly.


quote:
Originally posted by JB
Drilling holes shows lack of understanding.

Bollox! (unless speaking from experience)That statement itself displays ignorance.


quote:
Originally posted by JB
A better way of making a part lighter is to reduce the material from where it is not required. This generally means having more material around areas of high stress. So where it joins something else it will be thicker. Around a fixing hole it will be thicker etc.

Its all about reducing stress raisers and having smooth transitions between different sizes.


I thought lightening was all about lightening.

If you're going to start threads like this, please show an example or some form of supporting evidence and don't just waffle on in general terms. It doesn't help others at all.
If you have any practical, helpful information specific to lightening holes, why not type up a short "how to" and post that.

JB - 1/10/04 at 07:11 AM

OK, I will work on a brief article with examples, good methods, bad methods, references and further reading on the general subject of stress raisers and design.

Hugh, you are correct when you say "There's nothing wrong with lightening parts as long as it's informed and done sensibly. " but drilling holes is not the sensible option.

Check an F1 or WRC and see how many structural parts have lightening holes in them. This should tell you something.

John

David Jenkins - 1/10/04 at 07:50 AM

What brought this on anyway?!

I don't recall seeing any life-threatening pictures of lightening holes recently.

The only lightening holes that I do remember were on the back of Terrapin's.. er... Terrapin, and that was a really neat job in a bit of barely-critical chassis. He even expained how he did them!

Perhaps the most telling thing is the "building" information in JB's profile (i.e. theory, rather than practice).

cheers to the builders,

David

[Edited on 1/10/04 by David Jenkins]

Hugh Jarce - 1/10/04 at 07:53 AM

quote:
Originally posted by JB
Check an F1 or WRC and see how many structural parts have lightening holes in them. This should tell you something.


OK, while not F1 or WRC (and neither are Locosts by the way ), here's a selection of lightening holes in race cars including one lightened brake pedal. Rescued attachment dimpled_holes01.jpg
Rescued attachment dimpled_holes01.jpg

David Jenkins - 1/10/04 at 07:58 AM

I can't/won't comment on the structural integrity of those bits of metal - but that welding is magnificent!


David

leto - 1/10/04 at 08:35 AM

Very roughly: To gain the equivalent of 1 hp you have to drill out about 5kg.

Cheers!

James - 1/10/04 at 08:37 AM

JB,

I've drilled out the centres of all my suspension bolts to save weight- is this ok?

Cheers,
James

Hugh Jarce - 1/10/04 at 08:46 AM

quote:
Originally posted by leto
Very roughly: To gain the equivalent of 1 hp you have to drill out about 5kg.

Cheers!

It's not all about horse power. Lightening suspension components can lessen unsprung weight. Handling, responsiveness and nimbleness would be my priorities for lightening parts.

timf - 1/10/04 at 09:07 AM

quote:
Originally posted by James
JB,

I've drilled out the centres of all my suspension bolts to save weight- is this ok?

Cheers,
James

coping the bike racers then james

JB - 1/10/04 at 09:22 AM

You will notice that the holes in most of the pictures are not actually drilled they are punched then swaged. The swaging is very important.

Drilling the centre of bolts is OK as the centre is actually a nuetral axis. However it is a lot of work for a small saving but every little counts.

I know my profile is a bit vague but I prefer to remain a little anonymous. I have read and understood all of Carroll Smiths books, I have studied many of Vizards books, I have Millikens / Millikens book (I admit I do not understand it all).

I have been building vehicles for 20 years and I am sure much of my work is known to a lot of you.

JB.

Matthew_1 - 1/10/04 at 10:45 AM

I tend to agree with Hugh on this. The main problem is the wildly sweeping statements people are making.

E.g. "to gain 1hp you have to loose 5kg", what in 500kg car or a 2000kg car ?

Or, "drilling the centre of bolts is ok" - take a 10mm bolt, and drill out a 9mm hole, is it still ok to hold your wishbones on ?

Drilling holes is just one of a number of methods to make a part lighter, to sweepingly say its a daft idea IS daft. Its just part of the design and engineering process. If the part has been designed to have sufficient strength to have holes punched in it, then punch holes in it.

I agree mindless hole-drilling is a bad idea, but I don't think anyone here is advocating that ?

MikeR - 1/10/04 at 11:32 AM

So whats the difference between drilling a hole and punching and swaging a hole (and why can't you drill and swage a hole)?

This isn't intended to be inflametory, i'm just curious as to what swaging does.

David Jenkins - 1/10/04 at 11:53 AM

John,

Apologies for calling you a 'theorist, not a builder' - but your opening statements seemed to talk down to everyone, with a lecturing/'I know best' tone. Perhaps a "Do people think that drilling holes is risky..." approach wouldn't have got peoples' backs up so quickly. The fact that no-one had been discussing or advocating lightening holes lately didn't help either!

As for anonymity - being provocative and anonymous makes people think that you are a troublemaker trolling for an argument! Now, I don't think that you are... are you?

Perhaps we can all start again from the beginning...

rgds,

David

Bob C - 1/10/04 at 12:18 PM

E.g. "to gain 1hp you have to loose 5kg", what in 500kg car or a 2000kg car ?

actually it's only dependent on what speed you're doing.....

Bob C
PS and I'm probably wrong.......

JB - 1/10/04 at 12:19 PM

Sorry I did not mean to offend anyone or spoiling for an argument. I am just trying to pass on my car building experience.

Hopefully I will get an article together tonight which will better explain what I mean.

A drilled and swaged hole will be as good. The tools I have seen punch and swage the hole in one go.

JB

Matthew_1 - 1/10/04 at 12:45 PM

Having read the thread it does seem more like it should have been started "listen folks, don't just start drilling holes in things to lighten them", rather than "drilling holes to lighten is bad".

Terrapin_racing - 1/10/04 at 12:58 PM

Regardless of the "politics" this is a very interesting topic. Liked James's bolts - did you know that Allan Staniforth's colleague Richard Blackmore drilled the centre out of every single bolt on his Terrapin racecar (early 1970's) in order to save a few lbs ?
Years late the car was only identified by this fact. No know failures - just to re-assure you.

I'd be interested if anyone knows of a source of reasonable cost swaging tools?
I have always ended up making them because the ones I have seen (aircraft tool supplies) cost a fortune.

Cheers
Rob Rescued attachment Terrapinchassisbare.jpg
Rescued attachment Terrapinchassisbare.jpg

Hugh Jarce - 1/10/04 at 01:27 PM

quote:
Originally posted by JB
You will notice that the holes in most of the pictures are not actually drilled they are punched then swaged. The swaging is very important.

Drilling the centre of bolts is OK as the centre is actually a nuetral axis. However it is a lot of work for a small saving but every little counts.

I know my profile is a bit vague but I prefer to remain a little anonymous. I have read and understood all of Carroll Smiths books, I have studied many of Vizards books, I have Millikens / Millikens book (I admit I do not understand it all).

I have been building vehicles for 20 years and I am sure much of my work is known to a lot of you.

JB.

Granted, the majority of the holes in those photos are swaged, which goes to support my submission that all holes are not bad. Swaging a hole often leaves a part stronger than if it had not been holed.
The brake pedal, interestingly enough, is laser cut and folded - with out swaging or any loss in strength.

JB, you are perfectly entitled to remain anonymous, but if you do, don't expect to be taken seriously without substantiating your every comment. I repeat: it does you no good to blurt out like that, but more importantly, it is detrimental to this knowledge base.
If you have indeed got 20 years experience in car building, then you could be a great asset to this forum.
Either put up or shut up.

Bolts are dificult to drill concentrically (at least, anything over 25mm long), and if high tensile, and in a highly stressed location, they should really be internally honed to reduce the possibility of stress risers.
I have used both hollow bar and thick walled chrome moly tube for making various fasteners from. I thread both ends: the "head" has only enough threads to fully engage a nut which is then rose-welded from the top.
I always replace the long engine mounting bolts with these when mounting a motorbike engine. They are also perfect for any double shear suspension pivot bolts. Rescued attachment hollow_bolt.jpg
Rescued attachment hollow_bolt.jpg

derf - 1/10/04 at 02:24 PM

Personally I believe that things should be overbuilt. In the case of drilling a hole, it should be swaggered, not just cut out. I have seen many people drill out bolts, and for my personal feelings I would never drill one out. I have seen too many bols sheer, and it scares me that there is a hole in one. I have no scientific data to back up my "cautiousness", but the little bit you save in weight from drilling out a bolt is almost negligable, and even if you drill 100 bolts and save 10 pounds I dont believe it is worth it.

leto - 1/10/04 at 08:32 PM

This the first time I read anything on this forum that actually scared me.

"Drilling the centre of bolts is OK as the centre is actually a nuetral axis."

This statement is not wrong, it is true IF the bots are bended or twisted. If a bolt is in tension or in shear, and most are, there is on “neutarl axis”, the whole cross section of the bolt supports the load and drilling out the center will make it weaker.

I love speed :-P - 1/10/04 at 08:41 PM

just 2 add something which i will probly regret, wasnt the whole point of holes, used in aeroplanes, 2 a make them lighter, but also, 2 move the stress points or something?

Cita - 1/10/04 at 09:14 PM

The pr guys widely misuse the quality of aircraft material to compare their own products.
What those smart guys dont tell you is that for example a helicopter,even the most advanced military one,would fall apart after a few thousand miles on the road if it would be used like you drive your daily car,if you understand what i mean.

All i'm saying is that it is damn difficult to compare things so drilling holes to enlighten a part is not per definition a bad idea,or for that matter a good one.

David Jenkins - 1/10/04 at 09:35 PM

True - most aircraft have maintenance schedules that car drivers would never want to achieve!

David

Hugh Paterson - 2/10/04 at 12:22 AM

Thats it had enough all this article has done is pee me off because that weldings the mutts nutts (not a pun), i thought i had it cracked until I saw that O well back to horseshoes
Shug.

silex - 2/10/04 at 04:38 AM

OK, the engineers out there can argue about holes an swaging and how bad they can be, but you also know that this depends on the direction of force and how much material it removed and that a well place hole can in fact add stress relief.

Perhaps a simple guide for the non engineers out there should be to ask yourself the following question

If what I drill breaks, could I die or cause serious injury because of it ?

If you think there is a possibility that the answer it yes...........don't drill the hole.

Cita - 2/10/04 at 05:45 AM

Drilling out parts by amateurs (me and 99% of us homebuiders)would be done for the looks.Most of us,and certainly me, dont have the knowledge to make a dependable analysis and according to this design the ultimate part which incorporates sometimes enlightening by drilling.
Other things can be done to improve the looks and most of the time this will add weigth instead of remove weigth but what are we talking about in terms of actual weigth?A few kilograms at the most!Transform this to percentage and you will see that it's neglectable.
Furthermore most of the drilling is done on parts which are hidden so ...

Perhaps it's time that a more knowledgable builder than myself will come up with some sort of list which deals with all these myths like drilling brake discs-putting extra wide tyres on etc....
I dont think that any of you guys go's to the toilet every time you take your seven out for a drive like Schummi does before every race to win a few thousends of a second,or dou you...?

JB - 2/10/04 at 06:08 PM

I put Ti bolts on my mountain bike and a mate joked why dont I just shave my eye brows and hair and cut my nails to save a bit more!

Jb

David Jenkins - 2/10/04 at 06:24 PM

To be honest, I could reduce the all-up weight of my car by 50-60lb without lightening holes anywhere - I could go on a diet!

The heaviest thing on my car is the nut holding the wheel...



David

cymtriks - 2/10/04 at 08:46 PM

Holes can be OK if properly thought through.

Take a look at an Elise pedal, it has a network of triangular holes through its width making the lever arm into a little spaceframe. That's fine if you have Lotus Engineering to tell you that it's strong enough. There must be a few crashed Elises around by now. Maybe these pedals are waiting in a breakers somewhere to be fitted to locosts.

I have been looking at some shafts for jet engines lately at work. At various places along their length they have holes to allow air and oil to circulate to appropriate places. Every time there is a hole the shaft has it's wall thickness roughly doubled around the hole. This is not an accident. We spent weeks thinking about those holes.

I can't think of any part on a locost that I'd put a lightening hole. I don't think it's worth it in most cases. You will have to drill a lot of holes to make any real difference and either spent a lot of time crunching the stress sums or taken a big risk in the process. Personally I'd spend the time and effort elsewhere and not take the risk.

The best parts to save weight from are probably the wheels and tyres followed by the hubs and uprights. This helps three times over. It saves unsprung weight thus improving handling and ride. It saves dead weight thus improving cornering, braking and acceleration. It saves rotating mass thus improving braking and acceleration.