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How much runout is acceptable?

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Forum topic by TheDane posted 03-21-2010 06:39 PM 3169 views 0 times favorited 4 replies Add to Favorites Watch
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TheDane

4997 posts in 3130 days


03-21-2010 06:39 PM

Topic tags/keywords: question drill press steelex forstner joining

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!"


4 replies so far

#1 posted 03-21-2010 08:55 PM

It may come down to the ever-debated issue of: do you really get what you pay for? I don’t know what quality the Steelex name carries (although their 14” bandsaw seems a somewhat chintzy in photographs…please correct me if I’m wrong). Maybe a better “name brand” would offer more quality, such as Freud Forstner bits.

I’m a CAD designer,CNC machinist, as well as a woodworker, and I don’t believe .020” to .040” run-out is ever acceptable when you’re trying to get a precise fit between parts. I personally have never yet needed a very precise fit when dealing with my Forstner bits. I do know that mine are very “cheap”, but I never measured the run-out either. I think I paid $10 for a brand new 16pc set…

If you need a guaranteed .625” hole, get either a metalworking end mill that is able to make plunge cuts straight down, or maybe a counterboring bit at the .625 diameter. These should be ground beautifully straight, and unless they’ve been dropped or damaged, the only run-out you’ll get is whatever your drill press may have in it.

If you can get away with not needing a flat-bottomed hole, you could even find a quality twist drill bit that would be very accurately sized and have no run-out.

Accuracy is non-optional in metalworking tooling, so I don’t understand why accuracy in woodworking tooling should be considered any less important by some manufacturers.

I hope this helps!!

-- Lane Custom Guitars and Basses

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CharlieM1958

16244 posts in 3685 days


#2 posted 03-21-2010 09:12 PM

When you say the chuck tested okay, I assume you checked the runout on the outside of the chuck. Did you by any chance test the runout with a different type of bit, just to make sure there is no problem with the chuck jaws holding the bit correctly?

-- Charlie M. "Woodworking - patience = firewood"

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TheDane

4997 posts in 3130 days


#3 posted 03-21-2010 10:51 PM

Yes … I tested for runout on both the spindle and the outside of the chuck.

I have a set of Freud brad point bits … I checked the 3/8” bit from that set for runout: zero.

The 6 smaller (1/4” thru 7/8*) Steelex bits have straight shanks … the 10 larger (1” thru 2 1/8”) bits have hex shanks. I wouldn’t be surprised if the shanks didn’t set properly, but the straight shanks … ?

The thing that really blows me away is the cheapo bit from the big box down the road is dead on!

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

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TheDane

4997 posts in 3130 days


#4 posted 03-21-2010 10:54 PM

kunk—Good idea … thanks!

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

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