Dumb question on R8 (i think) spindle

higgite said:
Wobbly, I think you’re afflicted with the same malady as me. I was confusing rwm with r-mm until I finally noticed that rwm’s spindle pic didn’t match r-mm’s pics. ;)

General question, does it seem to others that the sheared set screw in r-mm’s spindle is awfully far up in the spindle for an R8 guide pin/screw? I have a bench mill, not a knee mill, but like Jim F, the guide pin/screw isn’t nearly 3-1/2” from the end of the spindle. Mine is more like 1-5/8”. Is it common for the pin to be recessed as far in as r-mm's on, say, a Bridgeport or similar spindle?

Tom
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Well @higgite thanks for being kind about it! Now I need to go back in the thread and figure out which pics belong to the OP...

Nonetheless, a rubber impression like casting might further identify what the issue is. Or use a 0.75" rod which should always fit and see if it goes into the spindle cavity at least 4". And measure the taper. Maybe just use a wad of modeling clay and press it in and compare with your R8 taper. Oh, please check that what you think is an R8 actually is one.
1610911893419.png
 
The dimensions of the drill chuck arbor in post 28 look pretty darn close to the dimensions for an R8 according to that drawing.
At 29.9mm/1.18” the nose of the spindle is not sized for an R8 collet.
It has to be a different taper.
 
To get the clay out mostly intact, I'd use some all thread, a washer and a couple of nuts to hold the washer. Size the washer around 3/4" OD. Slightly oil the inside of the spindle to act as a release agent. Put the washer assembly in about 1.5". Sort of hold the all thread centered and pack clay in around the rod to fill the cavity. Might have to make a simple spider to get it roughly centered. When packed full of clay, pull the rod out of the spindle and you should get a decent impression of the inside of the spindle.
 
DavidR8 said:
The dimensions of the drill chuck arbor in post 28 look pretty darn close to the dimensions for an R8 according to that drawing.
At 29.9mm/1.18” the nose of the spindle is not sized for an R8 collet.
It has to be a different taper.
Click to expand...
Although the two in the picture are similar, they aren't the same at all. I can tell from the picture that the arbor taper is longer than the R8 taper. My eyes aren't good enough to estimate the taper angle. My R8 looks exactly like the one on the left, and is really close to the drawing. I'd bet the taper angles of the spindle and the R8 are different. That might account for the R8 not going in as far as it should. Only way to know is to measure it somehow.

If the clay method isn't suitable, one could cut off the back of a collet (so there's no interference due to length possible) and blue the collet taper. Then push into the spindle. It will be very obvious if the tapers are different. Shoot, why bother. Just blue the R8 now and see what transfers.
 
I see two different situations that may have happened:
1- It is actually an R8 spindle that is just somewhat poorly made and designed. There isn't really a 'standard' for R8, so I could see a cheap importer just putting the pin were it was easy to fit/machine, and not cutting the taper deep enough.

2-It is some oddball taper that is close enough to an R8 to be reasonably effective with an R8 collet in it. The previous owner, thinking it was R8, used R8 tooling (including that drill chuck!) with it.

I'd guess #1.
 
I didn't see the similarity in the names!
The pin in my R8 spindle is 3.1" from the nose and engages the straight part of the collet.
Robert
 
rwm said:
I didn't see the similarity in the names!
The pin in my R8 spindle is 3.1" from the nose and engages the straight part of the collet.
Robert
Click to expand...
The pin really could be just about anywhere along the slot, so that seems ok.
 
On my collet, the length of the taper is 1.038". That's the length along the surface. Can you measure the length along the surface of the spindle taper? According to the drawing above, it should be r = 1.015"/cos(8.25) = 1.026" minimum.

If you put a ground rod against the spindle bore, and measure the distance from the rod to the edge of the spindle taper, what is that dimension (y)? If we know both y and r, then the angle of the taper is arcsin(y/r). If you have the correct taper it will be 8.25 degrees. If r isn't long enough, you know the spindle taper wasn't bored fully. If you have measured this already, my apologies.

PXL_20210117_205928257.jpg
 
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