|Forum topic by TheDane||posted 03-21-2010 06:39 PM||3233 views||0 times favorited||4 replies|
03-21-2010 06:39 PM
I bought a 16 piece Forstner Bit Set (Steelex # D3573) sometime ago, but had never used the bits in the set that are smaller than one inch. Projects I built using the larger bits did not require precise diameter holes, so I never checked them for accuracy.
Yesterday, I needed a 5/8” hole that would handle a 5/8” peg in a piece of furniture I am working on, so I chucked the Steelex 5/8” bit in my drill press for the first time. I clamped a test piece to the table and fence on my drill press and bored a test hole. Good thing I didn’t just start boring holes in my hardwood work-pieces.
To my surprise, the peg was loose in the hole … too loose for a decent fitting joint. I measured the peg (it is .6285) then measured the hole (it is .6325).
I removed the bit and popped the chuck off the spindle, cleaned the spindle and chuck thoroughly with steel wool, re-installed the chuck, re-installed the bit, and drilled another hole. Same result.
Out came the dial indicator. There is no discernable run-out on the spindle or chuck, but the Steelex 5/8” bit showed a little over 40-thousandths run-out. In other words … the shaft is crooked, which is why it produced an over-sized hole. I spot-checked several of the other Steelex bits, and all exhibit runout between 20 and 40-thousandths.
So the question is: How much run-out is acceptable?
BTW … I ran over to the big box, and bought a 5/8” Forstner bit (cheap house brand) that produced a perfectly-sized hole, so my project didn’t suffer. But that sort of defeats the purpose in buying a 16-piece set that I thought was better quality than the house-brand at the big box.
-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"