What's so bad about R8?

Look, I've been machining stuff here in America for over 30 years. done lotsa work on Bridgeports with R8 collets. I have even modified a
horizontal mill I own to accept R8 collets. It was originally a Morse taper (I Think). That worked so well I did it for someone else too. Folks posting to this group speak of R8 stuff with derision. I'm willing to be educated. Thanks, Eric
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On Oct 1, 8:57pm, snipped-for-privacy@whidbey.com wrote:

Hear, hear. I reckon a quick slap with the drawbar spanner on R8 is way better than battering MT stuff out of a mill quill with a lump hammer. I've no experience of INT stuff but always presumed it was for bigger boys toys. So please clarify, where does the R8 derision come in?
Geoff J
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It's a system that seems to me to be strong enough for the small machines and small tools it runs on. It's nothing like as sturdy as the bigger INT series but then it isn't designed for taking the sort of cuts that machines fitted with those will be doing.
If I had a grumble it's that concentricity is not as good as with collet systems with a longer engaged length and I've never seen a machine that still had a location pin left in it. They snap off the first time a cutter jams. They seem to do bugger all anyway though so it's no great loss.
Theoretically concentricity is meant to be provided partly by the tapered end of the collet which is only about 3/4" long and partly by the top end being a tight fit in its sleeve 4 inches away. Unfortunately as the sleeve and collets wear this end doesn't do much and the bottom end can rock as it's tightened. That's the silly part of the design if you want to find one. You can't beat a long, narrow angle taper like a Morse for concentricity which is why later collet systems than the R8 look more like those. The R8 is unnecessarily long which wastes space but to no good effect if it's worn. You ideally need at least double the R8's length of tapered fit for good concentricity. A 3" long collet with 1.5" of taper and the rest for drawbar thread would save space and work better. Oh, hey, I've just designed an INT30.
I could also do without having to whack the top of the drawbar to free the collet every time I change tool. When I'm doing that frequently, like every couple of minutes when I'm cutting valve seats, it gets to be a pain.
But on balance I'm happy enough with it. My old Bridgie clone has given me 15 years of sterling service and the R8 hasn't stopped me doing anything I've needed to.
--
Dave Baker



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Greetings Dave, I bought my Bridgeport new in 1980. I make my living as a machinist and that mill has many hours on it. And the locating pin is still the original one. Though I have spun tools in the collet I have never had the collet spin. Also, I buy good collets and tools run very concentric. I'll check just how good it is tomorrow morning. I do see your point though about the short taper. However, the very common 5C collets also have a short taper and they run true and grip well if good collets are used in a machine with an accurate taper. Cheers, Eric
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    --FWIW I converted my Quorn to R-8 many moons ago; no complaints. I use them to locate work and so far I haven't had an issue with anything being out of concentricity. Be aware that many companies make R-8 collets and some are pretty bad. I've stuck with the good stuff and have no complaints.
--
"Steamboat Ed" Haas : "Hold on! we're passing
Hacking the Trailing Edge! : through the moronosphere!"
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There is a complete thread earlier on the history of R8, the pragmatic point being made was that if you were tooling up form scratch, R8 probably wouldn't be the first choice. The previous thread contained all the detailed technicals on R8. At the end of the day, if you are happy with your choices, why worry? Ignorance can be bliss.
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