Minimum Thickness of Aluminum

Here is a picture, may help.

How much of a load must the clamp hold?

I will be applying 25 ft-lbs torque to the two screws. The maximum weight on the bracket will be 100 lbs but it will be subjected to bouncing.

Thanks,

Just to be clear:

That is 100 lbs static weight that will be subjected to impact? How much of an impact/bounce - try to quantify:

very high cycle fatigue

low cycle high impact (for example - one cycle per hour and maybe 500 lbs force ....)

The bracket will be used on an off-road vehicle to hold jacks, fire extinguishers, etc. It should be low cycle but the impact could be all over the place.

Thanks,

good thought.

You should be safe with 1/8" thick under the socket head.

(if you were thinking thinner, that may be possible as well - I could be a little more accurate in my calcs - but if 1/8" does it for you, so be it )

Thanks,

I was thinking 0.218" but was afraid I needed more.

Nope - you would definitely be alright with around 0.218" (I would go as thick as possible - then you can rest assured when you beat the h@$l out of your 4X that they woun't break)

"I will be applying 25 ft-lbs torque"

IMHO, this is too much torque.

recommended torque for a 5 / 16 ~ 18 coarse thread bolt is 80 ` 90 INCH lbs...for standards ms 20365 and an 310;315's...

torque for shear bolt : 48 ` 55 INCH lbs

should you decide on fine threads ...5/16 ~ 24..100 ` 140 INCH lbs

fine threaded shear bolts ..60 ~ 85 INCH lbs

imho: id go to 7/ 16 ~ 20 's..tap the inside cap... spot face the front cap.. a nut driver in the pouch and away we go ..7/16 ~ 20 standard bolt torque 450 ` 500 INCH LBS

Thanks, I mistakenly wrote ft-bls instead of inch-lbs.

Thanks,

hi there,..

well interesting idea you have..the rack is inside? or exterior..? if inside maybe the 5/16's is ok.. but.. with the creek then the bank...i'd want the optimum hardware mount possible...don't know about how many times on the trek we'd need to get this stuff out...the difference is . less than 8 Cents a bolt..setup

i believe : the advantage of tapping the rear cap..vs nuts washers ...1. i could use my other hand to help align the " cage"..vs .. fumble with the thru holes to get the bolt to clear.. then reach around with my finger tips to start the nut..2. no nut to lose..

in any case good luck..

Forgive my ignorance, but is this a top view, or a side view?

And will multiple clamps be used to secure these items?

Have fun!

This is the top view, material is 3/4" X 3" X 3" to start.

Multiple clamps will be used with heavy items like jacks, etc.

might a diagram for a " spot face " be applicable here ? to spot face the cap might that not facilitate the hardware seating ?..kinda like the cap on the rod end of your piston..?

dgibson,

I thought this was an offroad endeavour ( I am an old dirt track racer ); I think you have a poor design; I would extend the mount on each side, for two reasons. One is to allow the fire extinguisher or whatever is secured to fit closer to the frame rail or interior metal and two, with a "leg" on each side of the mount, you can coutersink for a good quality socket head capscrew with a locking nut on the back side, thus having a much stronger mount with more "clamping" force spread over the entire face of the mount. Fire extinguishers are not heavy units, especially those we use in race cars, but the forces that we subject them to is sometimes incredible. I know that you are trying to save weight and also have a good installation, but trust me, go on the side of integrity for the mounts and make up the weight somewhere else.

Look at some of the mounting methods for "accessories and the like" in heavy equipment design (Caterpillar, etc); they are not subject to the same harmonics, but do have very similar demand characteristics.

Remember, wheels down (even while you are in the air), and you can't place if you don't finish...

old golfer

just had another thought...

oh boy..lol...

this " cage"..if your puttin the emergancy , 1st aid kit , firebottle space blanket..h20 etc..in side..

i've got one hand behind with the wrench one the nut...one hand out front turning the bolt..what hand am i usuing to support the cage from opening up on me when i remove the bolts?

yeap .. tapping the end cap..don't want that firebottle landing on my ankle..