Measured my mill's runout with a digital indicator

Not a good test for the runout of the spindle, although it's a reasonable test for the runout of the 7/16" shank. That it is eccentric by .0003" is not a guarantee that the spindle runs out the same amount. It could be more, or less. Maybe even none, at all. You must check the mill proper, not any added devices, in order to determine runout-----and even then your reading may be suspect unless you can find a ground surface that has not been used. Even running an indicator on the inside taper can lead to erroneous conclusions due to uneven wear. When you're looking for tenths, it's hard to not introduce non-existent error.

Harold

I was going along with what you wrote until this part. If the taper has uneven wear then it has runout.

Wes

The device (the taper) has runout------the spindle (bearings) may not have. What I'm talking about is the faithfulness of the bearings, not the condition of the taper in the spindle. There's a difference. You have to be able to properly identify what the problem is when there's runout. Checking the taper is no different from checking something held in the taper with a collet or end mill holder. Yes, you get a deviation, but from what? It very well may not be the bearings, and that's the point. You certainly wouldn't want to replace bearings in a spindle that ran true, but the taper did not. By testing an area that is ground concentric with the bearing seats, you can ascertain which one is the problem. Do I have you back following me now?

Harold.

I understand you. There are a number of factors that can lead to run out. Bent spindles, bad bearings, nasty tapers due to crap that isn't cleaned out, bell mouthing, tooling, ect.

Then there is how something indicates statically vs performs dynamically where real world loads are applied.

I fix cnc machines for a living at a factory. When I go out to a machine I always wonder what did the button monkey do to it this time or is the machine fine and the operator is the problem.

As the machines age finding a good ground spot is getting increasingly hard to do ;)

Respectfully,

Wes

snip-----

That I understand!

My world is completely different from yours, too. I've never been exposed to anything CNC----so I'm still stuck in the old world. :-)

Harold

This is a bit embarasing but today I was tramming my recently aquired bridgeport when I found something I had not noticed before.

This was triggered by noticing that when I looked at something uncle had milled it looked like the trailing edge of the cutter had dragged on it.

So I placed a nice big flat inner bearing race I picked up from a spindle rebuild on the floor of my vise and checked tram. Perfect as far as my indicator would show.

I scratched my head and on impulse, pushed directly up on spindle. CLUNK. Looking down at indicator that was held by a chiwan indicol and touching my bearing race, I see 0.005" movement.

I try to tighten the nose cap (loosen set screw) but it doesn't move. I unscrew it and knock out the quill expecting to find rubbish for bearings.

Luckily that is not so. The bearings seem okay and are loaded. So now I wonder why I didn't notice it at first, what is out of spec, did the former owner spin a bearing in the quill, ect, ect, ... Did actually oiling the spindle periodically wash out some gunk that was cementing the bearing pack in place.

So later this evening after I get up, I am going to make a shim to give the nose piece a bit more reach and hope life is good again.

Wes

Well that isn't the smart thing to do since it would interfere with the labyrinth sealing.

Sorry for hijacking your thread Iggy but it fit in.

Wes

Wes, the lathe looks awesome. Like an old steam engine.

snip--

sorry to hear of your spindle woes, but it appears you have a solution in mind.

I am somewhat troubled by the statement that the cutter had dragged on the back side of the cut. It should, but just barely, which I'm sure you understand. If nothing else, the peaks should be reduced as the cutter crosses them. Cross hatch is a sure sign of a spindle that is dead perpendicular. If you're getting a full cut on the back side, sounds like the spindle is, indeed moving up and down. How about a report when the job is finished?

Harold

Yes it seemed to be the solution. Uncles old lathe did the trick turning down the nose cap. If I had driven in to work, I'd have been upset since it took two attempts to get the recommended 0.008" gap between nose piece and quill.

Uncle was cutting with a 1 3/8" inserted endmill. The endmill was way wider than what he was cutting. Uncle wouldn't take my suggestion to crank up the speed to 1000 rpm or so, said it will just throw chips further.

So I think the leading edge of the cutter took a cut and deflected up, the trailing edge was able to catch a bite as the spindle assembly fell back down.

Without adjusting tram after the repair I get this.

Wes

That's what I'd expect to see. Lookin' good! :-)

I've never screwed around with the spindle on my BP---my hat's off to you for recognizing the problem.

Harold

I'd like to say that I noticed on the very first cut. It took a few times before my brain finally kicked in. :(

At least it did eventually. :)

Wes