Best Practice for dimensioning a Sheet metal Bracket :
Best Practice for dimensioning a Sheet metal Bracket :
(OP)
Which is the best practice while giving dimensions for a sheet metal bracket.
1. Taking the fixing holes as a reference dimension and dimensioning the other features based on this fixing hole?
2. Taking some other flat surfaces as base reference and dimensioning all other features including the fixing holes based on those flat surfaces?
1. Taking the fixing holes as a reference dimension and dimensioning the other features based on this fixing hole?
2. Taking some other flat surfaces as base reference and dimensioning all other features including the fixing holes based on those flat surfaces?





RE: Best Practice for dimensioning a Sheet metal Bracket :
RE: Best Practice for dimensioning a Sheet metal Bracket :
Both your schemes are valid. My primary concern would be the functionality of your part.
Sheet metal presents a special problem. Bend edges can be located to ±0.15", or ±0.4mm. If you need more accuracy than this, you cannot locate from the bent edge. My understanding is that the flat layout is punched accurately. You have a couple of solutions...
Use a flat feature as your datum. This could be your mounting holes as you noted above, or it could be an un-bent edge. Your mount holes make a lot of sense to me. If you bend all the edges of your part to provide gussets, you don't really care where they are. You need accurate holes, and sloppy profile tolerances on your gussets.
If you are determined to use gussets as datums, you can apply a composite true position. Locate the holes to 0.8mm diameter WRT all your datums, and locate to 0.1mm WRT your primary datum. In this scenario, your gussets are not a good register surface at assembly.
You can make your holes grossly oversize. If your true position cannot be anything less than 0.8mm diameter, your holes must provide a minimum clearance of something more than 0.8mm. Maybe this is okay for you!
You can fabricate your small, accurate holes after bending. I would chat with my fabricator about this to make sure he does not just assume that I am an idiot.
The final solution is to machine the part.
--
JHG
RE: Best Practice for dimensioning a Sheet metal Bracket :
Tunalover
RE: Best Practice for dimensioning a Sheet metal Bracket :
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RE: Best Practice for dimensioning a Sheet metal Bracket :
RE: Best Practice for dimensioning a Sheet metal Bracket :
Datum A- Surface of initial mounting hole
Datum B- Mating surface around that hole
Datum C- Third item, usually second mounting hole (if there's one available!) or cut edge.
These are tube mounting brackets, usually welded on so I'll put an offset surface profile on the mating surface and a note giving a general surface profile elsewhere. Also a flatness on mounting surface.
But then it all depends on how it'll be fitted/gauged.