Only my 3rd frame… just a hobby. Just looking for advice on this filet thickness… top of the top tube / head tube. Is this sufficient or should I thicken it up? Small gravel frame, 60 kg rider
Thanks for any advice.
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It’s a good idea to thicken it up as well as the one under the ht/dt.
On the top of top tube / head tube I would aim at least for the same size that the fillet on the sides of the joint has.
The one below ht/dt I’d recommend to make the biggest because that’s the most stressed spot on a bike frame.
I think you should ride it hard and report back,
I’ve read that fillets on bike frames are larger than they need to be structurally and the mass of material is more for aesthetics.
But I don’t know if that’s true!
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I concur with the above statement, as long as you got good penetration in the joint these should be fine.
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I’m 125 kg, and some of my first frames had fillets that small or smaller. I have never had a fillet fail because I always made sure to do 2 passes to insure an internal fillet before I had the skill to do it in one pass. As long as you managed to flow an internal fillet, you will be totally fine.
Check out some or Arregui Velázquez’ work/ testing/ research (find him on IG).
He’s built frames with pretty small fillets which passed testing.
My own experience tells me your fillets will be fine. And if you look at the tensile strength of your filler alloy, you might be surprised.
Theres a lot we don’t know from a couple of pics but yeah looks fine to me. I aim for a slightly bigger fillet but I’m making mountain bikes.
Tidy work 
Edit: if the frame isn’t for you and you’re in any doubt just go back in and add some more filler. It is only a short section after all and you can’t put a price on peace of mind.
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A rule of thumb is make sure the leg lengths are at least 4 times the thickness of the thinnest member of the joint. You should also have brass inside the tube.
So, if the thinner top-tube is .035" then you would want to see a fillet at least .140"
Your fillet looks like it should be OK to me!
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Thanks everyone. Looks like I’m good to go. The penetration will be good as I always flow each small section in the joint before I build it up.
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As others have said, you’re fine. The fillet should be (iirc) 3x wall thickness which isn’t very big. If you search the internet or this forum probably, you’ll find a diagram that shows this. Actually a bigger fillet causes more damage to the tube than a smaller fillet because of the time it takes to cool so, you’re fine (assuming good penetration; as others have said).
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