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What's the deal with R8's?

taiwanluthiers

Cast Iron
Joined
Dec 6, 2016
Location
Xinjhuan District, New Taipei City
I notice people talk about R8 tooling a lot, and I know that's what the Bridgeport mill uses.

When I was shopping for my mill (which is a NT40 taper) I asked about R8 and they never heard of it. The 40 taper is superior to R8 in every way. Has positive drive keys, doesn't lock up, and is completely interchangeable with BT40 CNC tooling (just take the pull stud off and extend the draw bar a bit).

So my question is, why doesn't mini mills use something other than R8? Why not NT30 taper (which is pretty close in size to R8 except it's got all the benefit of NT40 because it's a scaled down version anyways). In Taiwan, all the mills use either NT30 or NT40 tapers, nobody here uses R8 unless there's an import Bridgeport Series 1 that made it to Taiwan... even then I'm sure someone will have it converted to NT30 too, because if you show up to a tooling store looking for R8 tooling here they will look at you like you're from Mars or something.
 

GregSY

Diamond
Joined
Jan 1, 2005
Location
Houston
Because mini mills are already garbage so why would they use a better holder?

Because at some point Bridgeport settled on R8 and it became THE holder of choice

Because R8 holders are simpler, and therefore cheaper.
 

L Vanice

Diamond
Joined
Feb 8, 2006
Location
Fort Wayne, IN
Forty years ago, I had a small Taiwan-built horizontal mill with a 30 taper spindle. I had trouble finding cutter arbors for it, though my vertical mill had an R8 spindle and I had/have lots of R8 tooling. At the time, I had the impression that 30 tapers and larger were common on modern horizontal mills and R8 was the most common spindle in vertical mills except some of the older or smaller ones. I guess that is no longer true.

Larry
 

neanderthal mach

Hot Rolled
Joined
Dec 18, 2008
Location
princeton b.c.
R8 would be almost for sure much more common in North America than anywhere else. Judging the value or usefulness of any tooling based strictly on where your located and your own personal experience as the only benchmark for what would be best for everyone else in the world is a bit arrogant. Yes there's no question the various 30 and larger tapers would be better in almost every way. But R8's are still so common in N.A. because of the amount of tooling built and sold since it was first invented and the shear volume of all the tooling owners still have.

Since we have it, then buying any new mill makes more sense as an R8 machine than anything else. So those new R8 machines keep being built. And my mill was also built in Taiwan, so no there not ALL NT30/40 in that country. I'm at best only a hobbyist and I'd still loose at least a couple of grand trying to replace what I have tied up in my R8 tooling. There were also more than a few accessory heads built in only R8 as the drive taper. And so far I haven't yet found anything I wanted or needed that wasn't still made in R8 and usually for fairly cheap even for N.A. built tooling.
 

TDegenhart

Diamond
Joined
Mar 26, 2011
Location
Geneva Illinois USA
Don't know why the makers of the original BP's chose an R8 over other systems but for the 1/2 hp spindle it was probably more than adequate. Not so with the 2 and 3 hp heads and marginally the 1 hp.

Tom
 

Peter S

Diamond
Joined
May 6, 2002
Location
Auckland, New Zealand
One of the nice things about R8 collets is they give you maximum space under the spindle. I find that pretty useful at times, and my mill has a 4"? riser block as well. For example using a dividing head with its spindle vertical. Not just milling cutters, you can hold say a stub drill in a collet when it's tight for space.

This also puts the cutter as close to the spindle bearings as possible.

I would guess both of the above are useful on a mini-mill (not sure what a mini mill is, but they sound even more floppy than a BP).
 

taiwanluthiers

Cast Iron
Joined
Dec 6, 2016
Location
Xinjhuan District, New Taipei City
I'm not sure how floppy the original Bridgeport is, but in Taiwan all the Bridgeport Series 1 clones use NT30 spindles... My mill is supposed to be in the same class as a Bridgeport Series 1 but it's a lot heavier. Has box ways for both the Y and Z axis. I think there is another model the company who made the mill produces which uses the exact same body casting but it was a universal mill, as in it has both vertical and horizontal milling capability (except mine doesn't). I was actually going to buy a Bridgeport clone from the dealer and he kept recommending this one that I now have, saying I'd be far happier with it than the BP clone that he considers junk. It was like 150% more than the BP clone too.

I think R8 is good for mini mills but for a full sized machine like a Bridgeport I find it really limiting. Perhaps it's perfect for the Series 1 with its wimpy motor, but anything heavier, like Series 2, Lagun FTV4, etc. it's very limiting. Those machines should be using 40 taper spindles.

Right now I'm in the process of buying a Victor 16x40 lathe from the same dealer. There are LOTS of those floating around in Taiwan...
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matt_isserstedt

Diamond
Joined
Dec 15, 2003
Location
suburbs of Ann Arbor, MI, USA
In my mind its because that's all that machine can handle. Its no metal hogger, just a thing that's extremely flexible as in swissarmyknife. Best practice is to pull the internal key to avoid a much bigger problem.

Save your big positive drive shanks for something that can throw out a stream of metal and still make a gleaming finish.

The R8 does have the disadvantage of having no dead-length. I think I could live my life with a 3/8" and 1/2" R8 collet only.

Its a big step forward over the ancient MT2 drawbar collets which had to be beaten out since they locked so vigorously due to the low taper angle.
 

taiwanluthiers

Cast Iron
Joined
Dec 6, 2016
Location
Xinjhuan District, New Taipei City
Have a friend who owns and runs VMC's.

He told me to avoid BT30 like plague. Because if you take a heavy cut that wimpy pull stud on the BT30 can snap on you, resulting in BIG DAMAGE to the machine. Not as much of a problem on NT30 as the draw bar is much beefier compared to a pull stud...

He even thinks if it were possible he's go with BT50.

A bit off topic... but why doesn't anyone make ER50 chucks for even BT50?
 

matt_isserstedt

Diamond
Joined
Dec 15, 2003
Location
suburbs of Ann Arbor, MI, USA
It holds the collet while you tighten the draw bar until the taper starts holding. No drive torque on keys: motor shaft, drive axles, or collets is a general rule. Keys align, not drive.

My thought on the R8 drive key is that if something goes wrong and the key gets sheared (wiped) you have a big old mess in a place you can't easily access. So the only solution available is basically full on Neanderthal: beat it back apart with more massive lumps of steel. Not good for the drawbar, drawbar threads, collet, spindle tube nor the spindle bearings.

Contrast that with removing the internal R8 drive key and then having a problem where the collet slips/spins in the spindle tube. Sure a hardened part got wiped on a hardened part for a couple of revs but the collateral damage is considerably less in my thinking.
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
.......................

Its a big step forward over the ancient MT2 drawbar collets which had to be beaten out since they locked so vigorously due to the low taper angle.

Unless you have a drawbar that will eject the collet as you unscrew it. Best thing I ever did with a small horizontal that uses MT3 tooling. Pops the collet out without hammering or fuss.
 

taiwanluthiers

Cast Iron
Joined
Dec 6, 2016
Location
Xinjhuan District, New Taipei City
CAT40 and BT40 seems to be the same, except the pull stud thread is different. I don't know how to convert a NT40 spindle to say BT40 though... not sure how the pull stud mechanism works. It would be great if possible though as it'd be like a power draw bar.
 








 
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