Dumb question on R8 (i think) spindle

[Toolmaker51]

Won't get reliable measure with a caliper. Also unlikely undersize per se, more that is burnished from riding in quill housing, not all have hard chrome plating. That will affect bore AND quill diameter riding through opening, at variance to what never exits. The tolerance/ allowance between them is not 'tight' by definition, it's minimum clearance with remainder taken up by lubricant. Mill spindles are sized to hold sufficient bearing size, and a lot of surface area to the housing.
It's why milling is best best performed with retracted quill. It's why drill presses make crappy milling machines.
Spindle or quill, never ran into a knee mill needing heat. Since they haven't built-in cooling, those tolerances would not result in a sweet running machine.
I doubt 3 of a hundred people can insert a quill free hand, maintaining perfect axial alignment. Cup the lower end in a short, faced off, section of tube on piece of printer or wax paper right on the mill table. Use both axis to 'find' centerline and raise carefully with the knee, twisting paper if need be. Until spindle has entered housing, roughly equivalent to one diameter, there really is little assurance of correctness. ie, 10% in = 90% probability of misalignment, halfway in is 30 to 50% and so on. Entirely dependent on physical sizes involved. Some might freeze spindle.....and risk condensation in non soluble lubricant, Sticky as hell, no lubrication.
It is possible towards the end to have problem when lower bearing retainer enters; dirt in mating faces, retainer over tightened, set screw protruding or too tight, incorrect bearing fit to bore, among others.

 

[rwm]

Which way did you pull the quill out? Are you saying you can't reverse the process now? It has to fit, unless you are mis-aligned as Toolmaker suggests.
Robert

 

[r-mm]

Hello from many years later! My knee mill project took a back seat while I tiled my garage and did Many Other Things. I finally got back to addressing the spindle mystery... by ponying up and buying the Grizzley part which has since gone from $300 to $400. Last night I pressed the old spindle out of the quill, pressed the bearings onto the new spindle and then went to snug the bearing retaining nut only to find that it appears to be 18TPI on the Enco and M35-1.5 on the Grizzley. The two are rather close and I hope I didn't damage the new one - I think I mistook roughness in the threads where the set screw is drilled for the fact that the threading is in fact different. Luckily a M35-1.5 bearing retaining nut appears to be a commodity so I ordered one for Friday delivery. The new quill is longer in ways I do not believe will effect anything: eg the nose and the splines. I may need a new drawbar, which is fine since the old one was ugly. Grizzley offers thew drawbar at a fair price ($25)

You can see that an R8 collet fits the new spindle much better than the old (no surprise there, thankfully). The new one does have a set screw to locate the collet.

Hoping to make some chips this year!

 

[RaisedByWolves]

I did my best to feel all around inside and could find no key/pin or evidence of one previously having lived in there.

A friend pointed me to many threads with people saying they prefer R8 with no key. Is there a trick to getting the drawbar to tighten and not spin the collet/spindle?

Hold it with your fingers?

I hate finding a machine that still has the key in it.

Keep a 7/16-20 tap handy and clean your collet threads regularly.

 

[rwm]

Not surprised that the new one is all metric. I recently found out that you don't need the set screw and probably don't want it in there in the rare case that you spin the taper. I have been running for a year without one.
Good job on this. Welcome back from vacation!

 

[Dabbler]

I hate finding a machine that still has the key in it.

@RaisedByWolves I have the same sentiment when I have to put the key back!

 

[r-mm]

Received the new nut, it fits. Can you all please advise me on two things. I replaced the angular contact bearings with Nachi 7207B but do not believe I added any grease. Am I supposed to pack a new bearing with grease? My next question is how to set the pre-load Presuming that is the correct term for what I am doing with my new metric nut.

 

[r-mm]

It's generally done by temperature. A setting that results in the bearings warming up after 30 minutes and fill speed, but not too hot too hold your hand on. For mine, I like it to reach about 130-140f after 30 minutes of use.

That said, unlike a lathe, these preload nuts are a pain to be adjusting multiple times, on the fly.

For my cnc mill, I went as tight as I could get the nut with my bare hands, then picked a spot on the outside edge of the nut and tapped it about another 1/16” in the tightening direction.

After 30 minutes @4000 rpm, it was at 130°. I could have got a little tighter, but runout was under a ten thousandth, so I left it alone.

Okay I KNEW we'd discussed this sometime years ago...

 

[Dabbler]

Robin Renzetti covered properly greasing annular contact bearings in one of his videos... I can't remember which one! DON'T follow Abom79's advice on this - he was waay wrong.

HW machine has a great video showing exactly how to grease these bearings - at the 5 minute point:

 

[r-mm]

Thanks for sharing that video very useful. The only thing that surprised me is how tight he went with the nut. On my machine the nut sits on top of the back to back bearings not on the upper bearing, however I believe it is ultimately doing the same thing.