On a fillet brazed frame, would larger fillets strengthen joints in the same way that gussets like these would? I imagine it’s not a true replacement but in my head I feel like it would work in the same way, distributing stress further down the tube.
And another unrelated question:
Are there practical reasons for using straight gauge tube? The price difference is minimal it seems. The only reason I’ve heard is that it’s ideal for bending. Or maybe if you’re making a bike with abnormal tube lengths.
Yeah nah. Larger fillets in brazing are awesome. Spread the stress over a bigger area and a better transition of shape. Much less heat in fillet brazing than there is in welding. All the gussets do is transfer the stress and drop it off at the end as was initally developed in bike design to deal with production TIG welding. Using the approriate wall thickness and and good welding or brazing shape and technique you shouldn’t need to use gussets. In my opinion.
It’s a subtle, and probably irrelevant distinction, but my understanding is that this specific sort of gusset, partially welded caps, distribute stress from the highest stressed centreline to the unstressed neutral axis, thereby somewhat evening out stresses across the structure.
With enlarged fillets, fully brazed, or welded all round gussets, they reinforce the highest stressed part against that stress, and thus reduce strain, but do not re-distribute stress. So the neutral axis remains unstressed, and so under utilised.