Cheers guys, I will do some tit investigation when next in the shed
I suspect they are solid. I have been using a foot pedal & I have down slope adjustment so I'll try tailing off the power more slowly.
I really should be practising the basics more on nice easy flat stuff before attempting all the changing join angles & section thicknesses on these fiddly lil bits of tube & bush, but the racks needed doing & are now ready for the weekends ride
My next major bike project with the TIG will be a 3mm alu bash plate which will have lots of nice straight downhand runs for me to get dialled in on.