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Design and build a derrick crane

by Tolale
Tags: build, crane, derrick, design
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May4-10, 11:48 AM
P: 5
As an assignment for uni, we had to design and build a derrick crane.
After having designed it on catia, i've realised i havent made any tolerances for any of the holes.
All the holes are 8mm and 6mm diameter, but i dont know what tolerance limits I should put, as we built the crane without using any tolerances and everything was ok.
What tolerances should I put for each one of these holes?

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May4-10, 12:57 PM
P: 5
They are just clearance holes which do not have to withstand any forces, the only thing that goes through those holes are dowels.
May4-10, 02:25 PM
P: 2,047
If you have to put tolerances, then it depends on the machining tools available and how critical the dimension is and whether you need a symmetrical tolerance.

Put it this way: say your dowel was 5mm nominal. The dowel peices have a tolarance of .2mm and you knew you have to have a clearance between the peices. You knew you had .1mm tolerance on the drillbit. You knwo that you have to make the nominal hole at leat 5.3mm

As you are unlikely to know any of this information, you can't realistically put tolerances on to your drawings. Just say that all dimensions are nominal. Also you should always do 3D models at nominal dimension.

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