[tanshi]

Let face it, lots of guys love lightening holes. we all see fabrication porn that has holes all over it and makes it look like art.

but how do you decide where, what spacing?, how many is too many. obviously if your removing more metal than your leaving its too much,

is alot of it an asthetic thing etc or do those nice looking pieces actually have some mathematical plan behind their placment that just happens to look awesome



seriously though, i have a rear truss that basically like this (with the other side obviously). where and how many holes?

[watermouse]

Run a few hole/non-hole scenarios through some Finite Element Analysis... random holes in things are a pretty complex engineering problem.

I think you will find that for the application in your photo you should chase maximum strength, so, no holes.
You might get a better strength to weight ratio by carefully choosing tube sections with cross-sectional areas suited to match the safety factored loads.

[watermouse]

Looking again at your photo you could probably get away with lightening holes in the webs out to the housing ends on the front and back side only. You would expect that this would mainly see compression of the top face, tension in the housing. The side faces are taking the shear forces between them.
In my experience with designing composite beams the shear elements can be substantially less strong (in terms of material properties) or downsized than the load bearing elements. (eg carbon fibre top and bottom caps in tension and compression and a fibreglass shear-web to make an immensley strong yet light composite I beam.)

The center hoop is going to see a fair bit of torsional load and perforated tube is not practical in high torsion scenarios. Round tube is much lighter for the same torsional strength than an equivalent mass square tube.

[fordem]

Also note that the lightening holes are often "dimpled", which compensates for the loss of strength.

[just_cruizin]

For the trusses Darren don't go the speed holes, more down side than up. The forces on these are complex therefore no one face is less involved than other, your truss is in a torsional stress situation.

[just_cruizin]

Better to just consider drainage and being able to flush it out

[alien]

Realistically, the amount of metal you'd take out with "speed holes" would be negligible as a % of the total unsprung weight. Sure, every but adds up, but if it's a question of strength why risk it?

[31zook]

Greg beat me too it haha.

No speed holes in small trusses.

[tanshi]

Cool no holes in the truss it is. I have dimple dies so might consider some in the outer bits with dimples maybe

[Gwagensteve]

Sounds like a plan. Personally, I don't think the strength loss would be all that great, but it's best not to take a risk on an upper link mount. Even mine is heavier than I would have liked because I know they deal with large loads.

[tanshi]

and the result

[JrZook]

How much weight did they remove?

[tanshi]

about 3/4 kilo
yeah not much. but all helps

[jdk81]

Looks pretty good

[just_cruizin]

Take out the corners near the centre as well so it will drain and be be flushed out

[pete_79]

Probably too late, but I would have gone for some symmetry in the center plate.

Maybe you could follow the center line of your 3 outer holes and only do 2 in the middle section, something like this;

[tanshi]

leaves the holes too close to the edges to dimple them.

good thought though