Relief in Tapers

The cylindrical portion has to be a clearance fit to allow insertion and removal. There doesn't seem to be a readily available specification for the socket since the the R8 taper was proprietary to Bridgeport.
 
There's no law out there that says you have to have full contact of the taper in a given length.

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Thanks fellas.
So a question for the guys with experience both with MT tapers and R8s, which of those two designs is the most repeatable?
 
Tozguy said:
Thanks fellas.
So a question for the guys with experience both with MT tapers and R8s, which of those two designs is the most repeatable?
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They are all good!

My preference is R-8 for mills, or if the mill is big enough, NMTB 40 or 50. Thirty is too small for me in my opinion.
Any of the Morse tapers for drilling, live centers, etc.
I do not care for B & S tapers or Morse tapers for milling machine spindles. I've had my share of them over the years, they just don't hold up to a R-8 or NMTB 40 or 50 tapers in my opinion.

Ken
 
Economy during manufacture is one reason to undercut tapers, roughing is fast and finishing is slow. If making a 4" long taper of which only 1" on each end is finish ground that leaves 2" that may be left as roughed or forged, this is a considerable savings in finishing run time. For example a Morse taper tool with a fully ground taper ground at 10 seconds per inch = 40 seconds per operation. An undercut would allow 1" of grinding at 10 seconds, .5 seconds to rapid 2" then 10 seconds to grind the final inch for a total of 20.5 seconds. 19.5 seconds per part saved, For 2000 parts this is close to 11 hours less spindle time.
 
I think "wreck" got that one right. Plus grinding wheels and machines are expensive. I've run B&S slide angle grinders that grind 2 / 3 dia. at the same time finishing a face (shoulder). The wheel is 8" wide and dressed with a diamond following a cam.

Jim
 
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There are a large number of "specifications" for the R8 shank floating around but I have never seen one for the socket. R8 tooling was proprietary to Bridgeport and, to my knowledge, they have never released a specification. Without a specification from Bridgeport, any dimensions have to be obtained by reverse engineering which might explain why some of the aftermarket tooling doesn't fit.

The dimensions that I have had trouble with are the width and depth of the keying slot. I had to rework the slot depth on some of the collets in a set that I bought some thirty years ago in order to fit my mill/drill. I don't know if the issue was with the collet of the mill/drill socket.

Given the popularity of the R8 tooling, it seems strange that one of the manufacturers hasn't released a "straw man" specification for the shank and the socket.
 
A fair percentage of Chinese R8 collets have keyways that are too shallow to fit many existing mills. The only real way to address the issue is to get to the pin that protrudes into the spindle and modify it. On some mills it is easy to get to the head of the pin, which is often a dog point screw. On other mills, it is a big job, involving disassembling the head to get to it. The collet keyways are difficult to modify because they are hardened, and would need to be fixtured somehow so a grinding wheel dressed to the correct width could cut the keyway deeper, likely on a surface grinder. When you buy a set of Chinese collets, see if they all can go easily into the spindle, with no dragging on the pin. If not, send them back to the seller. A tight fit of the pin in the keyway can cause runout issues.

Edit: There can also be problems with the width of the keyways being too tight for the pin. Same techniques to address that.
 
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