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Slots & Tabs

Slots & Tabs

(OP)
Is anyone (successfully) using slots & tabs to locate parts in a welded assembly?  We are in the agricultural equipment industry, so we use a lot of hot rolled steel.  The thickness tolerance of the material has a direct effect on the thickness of the tab, which affects the locating ability.  However, we also have more generous location tolerance than many of you work with.

I am trying to write a design standard for slot and tabs and am not even convinced it will work on a large scale.

RE: Slots & Tabs

I used slots and tabs extensively at one job. It reduced tooling considerably as far as required welding jigs.  I was easily able to maintain tolerances of +/-.040" for weldments that were 30"x50", and +/-.025" for weldments half that size.

"Art without engineering is dreaming; Engineering without art is calculating."


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RE: Slots & Tabs

Tried it with mixed results.  YMMV.

Had the blanks laser cut; they were beautiful.
The assembly resembled a bicycle wheel, split in two parts for radial assembly on a gas turbine unit.  The flanges had arcuate slots, ~.008" wider than the material thickness.  The center had mating tabs projecting, and was narrow enough to be bent to the 'wheel' radius by hand.

The tabs extended into the flanges only by half the material thickness.  My intent was that the remainder of the slots would be filled with a puddle weld, using our standard TIG process, left underflush and not ground, as I depicted with some proper symbols.

However, most of the welders in that shop couldn't actually read a weld symbol.  We hardly ever used them; the default was 'weld the s!!t out of it'.  They also were more likely to reach for a snag grinder than a phone when something wasn't quite right.

Well, nothing was wrong with the parts; I had test-fitted them myself, but the welder decided to fill the slot, _and_ 'butter it up', which required that he then had to use the snag grinder to bring the axial face of the assembly down to sort of flush.  ... instead of the nice flat unground surface I had asked for.

I guess it was my fault.  I had walked the parts and the print out in the shop, pointed out the symbols, explained what I wanted, explained it again, drew a sketch on the print, explained it again, and walked away.  I should have welded one myself as an example.


 

Mike Halloran
Pembroke Pines, FL, USA

RE: Slots & Tabs

Yes, and no.  Properly implemented, they can save time and money on jigs and weld setups.  Used them for a motor frame assembly, and it was effective enough to hold alignment across the welding procedure, and allowed us to use prepunched holes for alignment of motor and driven equipment.  We then used them on an aluminum alloy vacuum tank, and found that the puddle welds to close the slots had an unacceptable leak occurence.

RE: Slots & Tabs

When designing for slots and tabs, never design for the tabs to be centered in the slot in regards to the material thickness.  You always want tabs to be clamped against the inside of a slot to act as a stop.  My experiences were normally 18-10ga sheet aluminum and SST, and 1/4"-1/2" plate steel.

"Art without engineering is dreaming; Engineering without art is calculating."


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