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vertical lead in radius when plunging into a cut

I did put in a solid bar inside the tube to prevent the tube from collapsing - also at the far end of the bolt I put in a nylon lock nut along with threading the cross bar. How else do people connect tubes like this? Welding is an obvious choice but I'm never very good at welding these thin wall tubes together.

I've never seen those standoffs that's a good idea. I could maybe 3d print them...
 
I worked on a tube to tube right angle connection study. It uses the convex washer concept @PeterT suggested. Below I have a question. The horizontal tube insert is threaded AND I have put a nut on the end of the bolt. I was thinking this would be less likely to come loose but you have to have access to tighten the nut. Is this doubling up the threads a good idea? There are some complications - if you don't use full thread fasteners then the shank on the bolt is too big to go into the threaded part of the horizontal insert. Tricky drilling to make the insert work? I guess on bicycles nobody does this sort of thing - brazing or maybe welding is the answer.

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The braze-ons you often see on bikes or similar is usually to attach something light to the tube like water bottle, shifter assembly... where the tube itself handles the load.
Marrying tubes together structurally is a different thing. Usually a different external braze fitting that envelopes the tube ends more like a sleeve socket. Or welding/brazing the joint.
A knock-down / re-assembly like yours is a different animal again. Be aware that some of the general purpose tubes you might encounter may have some remnants of joint seam inside so fator that into your plugs and/or ID surface prepping

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PeterT said:
The braze-ons you often see on bikes or similar is usually to attach something light to the tube like water bottle, shifter assembly... where the tube itself handles the load.
Marrying tubes together structurally is a different thing. Usually a different external braze fitting that envelopes the tube ends more like a sleeve socket. Or welding/brazing the joint.
A knock-down / re-assembly like yours is a different animal again. Be aware that some of the general purpose tubes you might encounter may have some remnants of joint seam inside so fator that into your plugs and/or ID surface prepping

View attachment 36776View attachment 36775
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How are those braze on fittings made? stamping?
 
I think my bike terminology is bad. The corner fittings are called 'lugs'. I believe they are investment cast. The braze-ons might be made in same process or machined, not sure.
We have some forum frame builders, maybe they can elaborate.
My buddy built some race frames back in the day, but my recollection always began with 'this expensive box from Italy arrived...'

en.wikipedia.org

Lugged steel frame construction - Wikipedia

en.wikipedia.org en.wikipedia.org
 
John D suggested a bunch of ways to adjust the entry line, but me, I think I'd just adjust the part Zero over on the part so the end mill isn't diving direct in to the material.

Seems a wasteful layout, even when using 'free' material. Rotate the model around, about 45 degrees and lay it in so that the entry happens off the edge of the part, and you have a bigger 'free' block of stock left over to make something else with.
 
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