Dialing in parts that are 6" away from the face, I have a weird runout problem. Every second rev, I get about .0003tir, then it will roll perfect for a rev. The high spot is always in the same location when it shows up. Logic would tell me that I've got a bad roller, but I find it highly unlikely that the cage rotates at exactly half the rpm. Its a Kingston HJ-1700, which seems to be regarded as a decent machine as far as imports go. New SKF bearings are In-stock from the manufacturer for a reasonable price of $360, although we weren't able to ID what precision class they are. Is it worth trying to improve, or am I just expecting too much?
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.0003 run-out. Do I need spindle bearings?
- Thread starter Ksracer
- Start date
- Replies 22
- Views 5,698
Milland
Diamond
- Joined
- Jul 6, 2006
- Location
- Hillsboro, New Hampshire
Sometimes there's another element that can influence the spindle, like a spur gear that's constantly engaged. If there's a two-one ratio in the gears, and there's a stuck chip in one of the tooth gullets, then it's possible it could push the spindle over every second revolution.
You can check the geometries of your spindle bearings and see if there's a constant ratio there, but usually such things are not integer ratios.
You can check the geometries of your spindle bearings and see if there's a constant ratio there, but usually such things are not integer ratios.
iwananew10K
Diamond
- Joined
- Sep 12, 2010
- Location
- moscow,ohio
.0003" six inches out???
most would be ecstatic...last thing I would be thinking is spindle bearings.m
what Milland said about debris in gears or chppded tooth.
most would be ecstatic...last thing I would be thinking is spindle bearings.m
what Milland said about debris in gears or chppded tooth.
CarbideBob
Diamond
- Joined
- Jan 14, 2007
- Location
- Flushing/Flint, Michigan
Since you have seen the cycle yes it is bearing runout.
Kudos here, few "get" this bearing problem and action.
One can map the cage run but it sort of changes 2-3-2.5-3.5-4..... sometimes it is a exact rotation.
We map such in our workheads and will add blank revs to bring them back into alignment.
$360 seems oh say way cheap for spindle bearings inside this tolerance. I'm more used to 3-10 times this price.
Do you need better than where you are running? You will get highs and lows but only the highs count.
A spindle rebuild to get into the microns in rotational repeatability is not something for the faint-hearted.
All great to measure such and I applaud that but do you really need better?
You may be chasing something that will make no difference and a rebuild very well could end up just the same or worse.
Bob
Kudos here, few "get" this bearing problem and action.
One can map the cage run but it sort of changes 2-3-2.5-3.5-4..... sometimes it is a exact rotation.
We map such in our workheads and will add blank revs to bring them back into alignment.
$360 seems oh say way cheap for spindle bearings inside this tolerance. I'm more used to 3-10 times this price.
Do you need better than where you are running? You will get highs and lows but only the highs count.
A spindle rebuild to get into the microns in rotational repeatability is not something for the faint-hearted.
All great to measure such and I applaud that but do you really need better?
You may be chasing something that will make no difference and a rebuild very well could end up just the same or worse.
Bob
jrmach
Titanium
- Joined
- Jun 9, 2012
- Location
- Boise,Idaho USA
Ever so slightly out of Tram?
The parts guy examined the bearings and they have a suffix code that ends in 4p. I'm kind of going out on a limb and assuming that's a P4 class, which according to Skf's website is an ABEC 7. I'll confirm tomorrow when they reopen.
I'm dialing rifle barrels co-axialy into the spindle prior to cutting the chamber using 2 locations 1.5" apart. Do I "need" better? That's debatable. Do I want better?.Yes. Plus the odd runout makes it a very tedious job to get it as close as I can.
Thanks for the info.
john.k
Diamond
- Joined
- Dec 21, 2012
- Location
- Brisbane Qld Australia
Runout that repeats every second revolution is typical of tapered rollers,the cage rotates at that rate......but not with higher grade bearings........neverthe less,as mentioned unless there is a noise as well ,probably best left alone.
CarbideBob
Diamond
- Joined
- Jan 14, 2007
- Location
- Flushing/Flint, Michigan
Yes a P4 is mostly a 7.
To reliably beat this number 6 inches out you will need 9s and a clean room..... Read the specs and do the math. Mount arrangement and distance does count.
However there is getting lucky.....
Now I'm going to ask the hard question, how many spindles have you rebuilt? Hand scraped retainers and lock nuts? Comfy with 1/10 micron indicators?
You are not at the nose but a bit out there in space. Lever or moment arm. Everything is multiplied.
A new $600,000 end mill grinder will run a six-sigma just inside half your number so perhaps you are asking a lot..
Bob
To reliably beat this number 6 inches out you will need 9s and a clean room..... Read the specs and do the math. Mount arrangement and distance does count.
However there is getting lucky.....
Now I'm going to ask the hard question, how many spindles have you rebuilt? Hand scraped retainers and lock nuts? Comfy with 1/10 micron indicators?
You are not at the nose but a bit out there in space. Lever or moment arm. Everything is multiplied.
A new $600,000 end mill grinder will run a six-sigma just inside half your number so perhaps you are asking a lot..
Bob
EmGo
Diamond
- Joined
- Apr 14, 2018
Then you better go buy a different machine because you're not going to get it with that one.
They should require a license for people to buy tenths indicators
Thanks for the perspective. Yes, it looks like the arrangement would multiply the error 3-4 times. I've worked for a few years on industrial pumps and turbines and such, so I'm no stranger to precision work, but not to this level. I'm not asking for .0000 runout when I'm done, just that it's repeatable every rev. Seems like I'd better consider the fact I could very well make it worse.
Honestly this is were good old plane, fluid or air bearings start to come into there own.
Bearings are available in higher than your P4 grade sure, but any errors on the spindle - housing distort them and then come into play. New bearings could possibly better it, equally they may well not better it.
$360 sounds cheap for a set of lathe spindle bearings too. Especially from a OEM.
Bearings are available in higher than your P4 grade sure, but any errors on the spindle - housing distort them and then come into play. New bearings could possibly better it, equally they may well not better it.
$360 sounds cheap for a set of lathe spindle bearings too. Especially from a OEM.
I just wanted to update the thread. I checked run-out on some other machines and decided I had room for improvement. My spindle has 2 opposing tapered rollers spaced about 4" apart on the nose end, and a third support bearing on the 12" long spindle extension exiting the back of the headstock. For the sake of simplicity, all measurements were made with the support bearing REMOVED, so it didn't influence or mask the run-out in the main bearing set. Before the rebuild, I had .0004 Tir on the nose of the spindle taper, that included ~.00015 of run-out that only repeated every second revolution. The end of the spindle extension had .0015 TIR, with .0005 non-repeating run-out.
The old bearings I removed had a lot of radial scoring, but I didn't see any indentations from debris. They were standard bearings, not precision class. I replaced them with identical off the shelf SKF bearings keeping everything as clean as I could, and set the preload to 15"lbs of rotational drag.
After the replacement, I had .0007 TIR on the spindle nose, but I couldn't detect any NON-repeating run-out with a tenths indicator. On the extension, I had .002 TIR, again with .0000 NON-repeating run-out. In other words, the indicator comes back to the same spot every rotation. So overall run-out on the spindle went up, but the NON-repeating run-out that was causing me problems dialing parts in is essentially gone, or at least undetectable with my measuring equipment. Thanks for all the help and insight guys, I wish my TIR would have been less after the rebuild, but since I never use anything mounted directly in the spindles taper, I'm satisfied with the results.
The old bearings I removed had a lot of radial scoring, but I didn't see any indentations from debris. They were standard bearings, not precision class. I replaced them with identical off the shelf SKF bearings keeping everything as clean as I could, and set the preload to 15"lbs of rotational drag.
After the replacement, I had .0007 TIR on the spindle nose, but I couldn't detect any NON-repeating run-out with a tenths indicator. On the extension, I had .002 TIR, again with .0000 NON-repeating run-out. In other words, the indicator comes back to the same spot every rotation. So overall run-out on the spindle went up, but the NON-repeating run-out that was causing me problems dialing parts in is essentially gone, or at least undetectable with my measuring equipment. Thanks for all the help and insight guys, I wish my TIR would have been less after the rebuild, but since I never use anything mounted directly in the spindles taper, I'm satisfied with the results.
Milland
Diamond
- Joined
- Jul 6, 2006
- Location
- Hillsboro, New Hampshire
Thanks for the update! Always appreciated.
motion guru
Diamond
- Joined
- Dec 8, 2003
- Location
- Yacolt, WA
You can adjust your clamping of the part to compensate for a repeatable 0.0007” runout, but when you have an odd size roller in your bearing, it affects runout every other revolution + the actual location of this runout drifts as the bearing race skids. You can’t adjust for this runout and therefore it is worse than a repeatable runout of twice the magnitude that you can compensate for.
Thank you for putting that into words that are easy to understand. I thought it was inferred when i stated I wasn't mounting anything in the spindles taper, but I guess I should have been more specific for the keyboard butchers.
thermite
Diamond
- Joined
- Sep 21, 2011
Not that there is any easy fix for it, but every second revolution, exactly, signals that the machine-tool's designer screwed the pooch on bearing selection. Can't quite get to "hunting tooth" ratios of a good geared setup, but even so, one repeat in MANY more than just two is more common. Also partially self-correcting, because it IS odd.
moonlight machine
Diamond
- Joined
- Nov 19, 2007
- Location
- marysville ohio
Did you get the P4 bearings? Is it a 7?
strokersix
Hot Rolled
- Joined
- Jul 25, 2009
- Location
- NW Illlinois USA
I have this periodic runout on my lathe too. A little worse than yours was. In my case I believe it is the outboard bearing because I can dial in to zero if I am close to the inboard bearing. 6 inches out can never get closer than .001 or so. Bearings had been replaced by previous owner presumably less precision bearings.
The ONLY time this has been an issue for me is when dialing something in on the 4 jaw. Never had any problem accomplishing tasks required. Not trying to do super precision work. Shaft and bearing fits are no problem.
The ONLY time this has been an issue for me is when dialing something in on the 4 jaw. Never had any problem accomplishing tasks required. Not trying to do super precision work. Shaft and bearing fits are no problem.
DMF_TomB
Diamond
- Joined
- Dec 13, 2008
- Location
- Rochester, NY, USA
i suggest you measure 10 to 100 other lathes and see what is normal.
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also check bearing tightness. obviously a loose bearing if gearing gets tight in spots at certain rotations the gears will shift or push on spindle and cause bearing is loose spindle moves.
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i have seen lathe spindles you could grab chuck and move them back and forth .001" (some require more pressure than others to move), often bearings are kept slightly loose cause at higher rpm they get hot and tighten up. not good if spindle seizes
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dynamic spindle position that is at high rpm with oil moving in bearing the spindle picks up and shifts slightly to side. hard to describe. but many a bore just done on a horizontal cnc indicates this even when no tram error. sure amounts are measured in .0001" but i have seen .0005" shift before. basically what you get at slow rpm is not always the same as what you get at high rpm
.
also check bearing tightness. obviously a loose bearing if gearing gets tight in spots at certain rotations the gears will shift or push on spindle and cause bearing is loose spindle moves.
.
i have seen lathe spindles you could grab chuck and move them back and forth .001" (some require more pressure than others to move), often bearings are kept slightly loose cause at higher rpm they get hot and tighten up. not good if spindle seizes
.
dynamic spindle position that is at high rpm with oil moving in bearing the spindle picks up and shifts slightly to side. hard to describe. but many a bore just done on a horizontal cnc indicates this even when no tram error. sure amounts are measured in .0001" but i have seen .0005" shift before. basically what you get at slow rpm is not always the same as what you get at high rpm
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