Vortex, I don't calculate on a single batch of 50. Things likely improve a bit with multiple lots. If I lose 3 top bars in every 50, I reckon that is poor, but that will only mean recycling a couple frames from the used heap (where the side bars are bad at the bottom).
Polyanwood, were half the price of what? If they were half price of Th*rne seconds that was good!
kermit, yours seem about right 2% unserviceable, 1 frame in 50. Not bad at all.
chickendave, You may have been lucky and they were 'all-good' but I would strongly suspect they were not first quality. 'Knot free' is not the only criterion considered for reducing the part to 'second quality'.
Here are a few I notice with National frames from 'you know who':
side bars - wrong width, knotty, cross grained, poor surface finish, top slot not central, sprung, curved, bent, bottom slots not accurate, broken pieces at bottom, splits, groove not central.
Top bars - width, knotty, cross grained, bad staining, cracks, sap voids, shoulders not machined centrally, wedge weak, wedge not sawn adequately, poor surface finish.
Bottom bars - cross grained, too thin, bent, bowed, stained.
There may be a few more possible defects, but those should give you something to check out if they are not knotty!
m100, I remember those! def 'not fit for purpose'!!
MM, A417 Got to get the map book out now! Sounds Banbury-ish? (and then further) without looking.
Regards all, RAB