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andy_b
10-22-2008, 01:29 PM
i posted a few weeks back about this UP mill/drill i picked up. it has a Frejoth motor on it (not Feioth), and after doing some searching i think it is an old Acra mill/drill (the motor has a 1978 manufacture date). it is your standard two-belt, three-pulley design.

i noticed the spindle gets very warm after a short time and was reading prior threads on spindle bearings and related topics. if i just turn the mill on for a few minutes and run it without making any cuts, the lower spindle still gets hot, so it isn't due to heat transfer from the endmill. i have no idea what speed it is running as there are no speed charts on the mill, but it is probably on the third-highest speed or so. i have never operated a mill/drill, so i don't know if my machine is louder than it is supposed to be, but it doesn't sound like rocks are rolling around in the spindle when it runs, and the spindle turns smoothly, but it doesn't spin as easily as the spindle on my old lathe.

this mill sat in the former owner's garage for several years before i bought it. it was never powered up the entire time and the garage was unheated/uncooled. there is no rust on the machine anywhere. is it possible the bearings just need to be relubed?

i have gone through Tim Reidhead's Bridgeport spindle rebuild, and it looks pretty similar to what i'd have to do for my mill/drill.

http://members.cox.net/tangoromeo/mill_upgrade.htm

any other tips or ideas? i went through many pages of old threads (especially the more recent ones), but if there is a certain one that contains all this info and i missed it, feel free to redirect me.

andy b.

lazlo
10-22-2008, 03:24 PM
Andy, it sounds like either the bearing pre-load is set too high, or more likely, that the grease on the tapered roller bearings is old and cruddy.
Assuming your Acra mill/drill is like any other Chinese/Taiwanese mill/drill, you can drop the spindle out, clean and re-lube in about 1/2 hour - 45 minutes.

After you re-lube with some clean NGLI 2 spindle grease, run it for awhile and if it still gets hot, you'll want to reduce the bearing preload a bit.

derekm
10-22-2008, 07:02 PM
but whats too warm for a bearing? if you look in the threads in here its above 90C. Greases are commonly rated to 120C+.

All of these temps are not warm but hot to the hand...

andy_b
10-22-2008, 08:01 PM
it isn't getting over 100C, but i bet it's close. i wouldn't be able to grab the lower spindle ring in my hands and keep my hand on it for more than a second. if it got this hot after running it for an hour taking heavy cuts, i wouldn't worry, but the fact it will get this hot after a few minutes with no load at all on the spindle, just spinning, is what concerns me. i have never ran the mill more than a few minutes so i don't know if it will get to a certain temperature and just stay there, or if it will just keep getting hotter.

i think i'll try re-greasing the bearings, run it, and make an adjustment to the preload if needed. besides, it's supposed to rain saturday by me, so this gives me a good indoor project. :)

i'll report back what happens.

andy b.

derekm
10-23-2008, 03:31 AM
it isn't getting over 100C, but i bet it's close. i wouldn't be able to grab the lower spindle ring in my hands and keep my hand on it for more than a second. if it got this hot after running it for an hour taking heavy cuts, i wouldn't worry, but the fact it will get this hot after a few minutes with no load at all on the spindle, just spinning, is what concerns me. i have never ran the mill more than a few minutes so i don't know if it will get to a certain temperature and just stay there, or if it will just keep getting hotter.

i think i'll try re-greasing the bearings, run it, and make an adjustment to the preload if needed. besides, it's supposed to rain saturday by me, so this gives me a good indoor project. :)

i'll report back what happens.

andy b.
try measuring the temperature to be sure
Btw After you have regreased you need to let it get rid of the excess grease while its doing that it will get hot.

oldtiffie
10-23-2008, 06:53 AM
Andy, it sounds like either the bearing pre-load is set too high, or more likely, that the grease on the tapered roller bearings is old and cruddy.
Assuming your Acra mill/drill is like any other Chinese/Taiwanese mill/drill, you can drop the spindle out, clean and re-lube in about 1/2 hour - 45 minutes.

After you re-lube with some clean NGLI 2 spindle grease, run it for awhile and if it still gets hot, you'll want to reduce the bearing preload a bit.

I'd go along with that lazlo.

But I think I'd slacken off the pre-load first and see what if feels like. I'd strip it down as well just to see that there was no spalling on the bearing balls, rollers or races and if in doubt, replace them. If the mill hand-book (if you have one) doesn't give the pre-load I'd suggest having a chat - in person, phone, email - or on the web, with the bearing vendor or manufacturer for guidance on initial setting for the pre-load.

If a "strip-down" is required, I'd barely put any pre-load on it, see if it is smooth and if so "run it in" at no load for 10>20 minutes and see how it sounds. After stopping, see how it "feels". If OK, set the pre-load and check again. If OK, put a cutter in and try it out.

I keep wondering why the mill was left aside and not run. I wondered if it had anything to do with the spindle bearings.

If re-packing the grease, use the correct grease and the correct amount - too much grease can almost be as bad as none at all.

derekm
10-23-2008, 09:07 AM
My Background -
My first job involved computer simulation of bearing lives of vertical inline directly coupled pumps with roller, taper roller, spherical roller, angular contact ball and deep groove ball bearing races.

later : Commissioning 10Kw to 30Kw Radial Fans for pollution control on steel and cement works as well as paint treatment ovens.

So i have literally over the years spent weeks looking the SKF data books (but none recently I use the web site)

Some facts:
predicted bearing life at zero load is zero (well close enough) -
Upper Operating temperature limit of bearings is the minimum of the lubricant and the bearing. (this usually means the lubricant)


Note the ISO Standard reference temperature for bearings is 50C above ambient. thats 70C or 158F SKF link (http://www.skf.com/portal/skf/home/products?maincatalogue=1&lang=en&newlink=1_0_46)

And of course "A temperature peak may occur during the initial start-up of a grease-lubricated bearing. Therefore the bearing may have to be in operation for up to 10 to 20 hours before it reaches the normal operating temperature."

So 70C ~ No problem

But too low a grease temperature can be a problem. If you trawl around the SKF site you will see you shouldnt run the bearings below 20C for too long on standard grease.

For standard greases the green zone is from 20C to about 120C and the red zone is above 175C skf-link (http://www.skf.com/portal/skf/home/products?maincatalogue=1&lang=en&newlink=1_0_106)

remember 70C/158F feels very very hot indeed to the hand but thats just normal temp ~ measure the temperature

Why not back off the preload?. Because in a mill you are presenting a varying radial axial load and if you dont have enough preload you can get a zero load condition on one set of the bearings - not good and at speed very badSkf link (http://www.skf.com/portal/skf/home/products?maincatalogue=1&lang=en&newlink=9_0_30)

lazlo
10-23-2008, 03:03 PM
But I think I'd slacken off the pre-load first and see what if feels like. I'd strip it down as well just to see that there was no spalling on the bearing balls, rollers or races and if in doubt, replace them. If the mill hand-book (if you have one) doesn't give the pre-load

Agreed, although if it's an old Mill/Drill, it wouldn't be a bad idea to pull the spindle and clean it up, just for peace of mind.

The spindle preload wasn't described in any of the Mill/Drill manuals I could find -- I had to go by the instructions posted on the Yahoo Mill/Drill group. I started off with light preload, and kept increasing until the quill sleeve on the outside of the tapered bearings got pretty hot after running for 30 minutes or so.

The problem I had with the manufacturer's preload recommendation is that they specify the preload in ft/lbs, and the preload nut on the Mill/Drills are one of those pin spanner nuts, so it's not a simple task to convert foot pounds to torque on that castle nut.

andy_b
10-23-2008, 10:14 PM
man, i need to get my head out of my anus.
i'm sitting here reading through the replies some more, and i just realized i have a temp sensor i use to measure the head on the nitro engine on my radio control truck. i'll fire the mill up tomorrow and take several measurements over a five or ten minute span and see what it shows.

also, the reason the mill sat for so long was just that the guy never got to set it up. the previous owner worked with a friend at a small gun shop. his friend had the mill and would do some small gunsmithing projects on it and eventually bought a larger mill. the guy i bought it from bought it from his friend to do the same. he brought it home and put it in his garage and wanted to eventually move it into his basement. the garage only had 110V outlets, and the motor was wired for 220V so the guy never fired it up in the garage. jump ahead a few years and the guy decided it would be too big of a hassle to move it to the basement. then he and his wife were in a traffic accident and recently got out of the hospital. he and his wife are moving out of the area to live with a daughter of theirs, so the son was helping sell things off after the house was sold.

anyway, the mill looks to be in very good condition, except for this "hot" spindle thing (which maybe isn't as hot as i think, but i'll know soon enough).

andy b.

J Tiers
10-23-2008, 10:37 PM
Some folks may be missing part of the point........

Yes, bearings get hot.

But they should not get real hot real fast...... if it can warm up that much in just a few minutes, the rate of power input to the bearing sounds way too high.

A client has a bearing that he wants to run at high rpms, probably 20 times higher than the mill drill will ever see. THAT bearing has a break-in cycle (although I already know that isn't their problem) which they have to do to reach high speeds.

But the slow spindle on a mill-drill, going maybe 3000 rpm, should not be so fussy. And, it should not get hot enough to scald you in a few minutes......

Added note:
The first speed of the break-in cycle which I mentioned, is well above mill-drill speeds.......

oldtiffie
10-24-2008, 06:40 AM
But I think I'd slacken off the pre-load first and see what if feels like. I'd strip it down as well just to see that there was no spalling on the bearing balls, rollers or races and if in doubt, replace them. If the mill hand-book (if you have one) doesn't give the pre-load I'd suggest having a chat - in person, phone, email - or on the web, with the bearing vendor or manufacturer for guidance on initial setting for the pre-load.



Agreed, although if it's an old Mill/Drill, it wouldn't be a bad idea to pull the spindle and clean it up, just for peace of mind.

The spindle preload wasn't described in any of the Mill/Drill manuals I could find -- I had to go by the instructions posted on the Yahoo Mill/Drill group. I started off with light preload, and kept increasing until the quill sleeve on the outside of the tapered bearings got pretty hot after running for 30 minutes or so.

The problem I had with the manufacturer's preload recommendation is that they specify the preload in ft/lbs, and the preload nut on the Mill/Drills are one of those pin spanner nuts, so it's not a simple task to convert foot pounds to torque on that castle nut.

lazlo,
the torque to be applied can be at the loading ("castellated") nut (indirect) or to the shaft (direct).

If you want to apply it to the castellated nut "C" spanner, just fit a male or female 1/4", 3/8" or 1/2" square to the handle of the spanner, measure the distance from the centre of the shaft to the centre of the fitted square and set to torque using the pics/scans in these links, 1>4 are for general information - there is no number 5 - and 6 and 7 are specific to this instance:

http://i200.photobucket.com/albums/aa294/oldtiffie/Torque1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Torque2.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Torque3.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Torque4.jpg

(There is no No. 5)

http://i200.photobucket.com/albums/aa294/oldtiffie/Torque6.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Torque7.jpg

oldtiffie
10-24-2008, 07:59 AM
For derekm:

Derek,
that SKF reference you posted at:
http://bbs.homeshopmachinist.net/showpost.php?p=388940&postcount=7
is a very good read.

Many thanks.

andy_b
10-25-2008, 03:31 PM
oldtiffie,

you're a crazy man. :) i am not sure why you posted photos of head tightening specs and old torque wrenches, but you certainly always post interesting things.

anyway, i guess i'm a big pansy because i took my spindle temperature readings and this is what i came up with. the readings didn't seem correct as i was taking them, so i started taking readings of the back of the spindle and then the spindle bore to see if the shop lighting was affecting the IR temp sensor i have.

Minutes--Front----Back-----Spindle Bore
0-------65.8F
1-------73.7F
2-------86.4F
3-------94.3F
4-------99.6F
5-------102.8F
6-------104.1F
7-------100.1F
8-------97.9F-----109.2F
9-------95.8F-----106.9F
10------96.3F-----107.8F----120.2F
11------95.4F-----104.2F----118.8F
12------94.1F-----103.3F----117.9F
13------92.1F-----102.3F----116.9F
14------92.3F-----103.6F----116.6F

i then filled a cup with the hottest water from my faucet and put a meat thermometer into it which gave a reading of about 155F. when i aimed the IR temp sensor at the water it read about 127F, which is about what i expected since the water is very reflective (the IR sensor reads best on dull objects, black is best). when i put my hand in the water, it was HOT, and i'd say yes, it felt hotter than my spindle.

SOOOOOOO, i guess i don't have anything to worry about. i did find it interesting how the spindle temp went down after a certain warm-up period.

i'm thinking i'm not going to do anything to the spindle for now and just run it as is. what do you guys think?

andy b.

J Tiers
10-25-2008, 04:33 PM
Temps go down when the grease "channels" and gets out of the way of the rollers/balls.

Those temps are no problem. use it.

lazlo
10-25-2008, 05:32 PM
Yeah, you're fine Andy -- fire-her up! :)

oldtiffie
10-25-2008, 06:10 PM
oldtiffie,
.................................................. .

you're a crazy man. :) i am not sure why you posted photos of head tightening specs and old torque wrenches, but you certainly always post interesting things.

andy b.

Thanks Andy.

Dat am de troof.

I posted it mainly for the the last two pics as they were mainly for lazlo for using a torque wrench with an extension - in his case with the torque wrench on the end of a "C" spanner" - to get the torque applied at the castellated nut. The math is pretty easy once the principles are known. But its easy to get them wrong and to make a mistake.

There are two common ways to set or measure the torque due to friction and end-loading on the spindle bearings:

1.
the indirect method of/by applying the torque to the pre-load setting nut as lazlo mentioned; and

2.
the direct methods (2) of/by applying the torque wrench to the spindle directly either to a nut on the spindle or one in the chuck.

a.
the first measures the torque required to start the spindle moving. This measures the "break-away" torque (the torque due to "stiction" that is required to get the spindle moving); and

b.
the second measures "dynamic" friction - the resistance of the spindle to continued turning due to friction, grease, and bearing pre-load.

The method/s used are usually as advised or recommended by the machine or bearing manufacturer.

I showed the torque wrenches as there are basically two common types: the "clicker" and the "dial" types, but again the math and principles are the same. I prefer the "clicker" as I can both hear and "feel" it when it "goes off" whereas I have to actually see the dial type and that can be difficult at times (under a car or in poor lighting etc.).

I posted the old torque settings for standard bolts and nuts (US and UK) as there has been some discussion at times and a bit of different advices. I have had that "clicker" that came with those tables for a long time. It had the settings for some very old vehicles as well as the basis for the sequence of fastening, in this case cylinder heads, but applicable to almost anything.

I am very pleased that the spindle and bearings are OK as it has been a good learning experience and a very good outcome in a very good thread.

Well, I must be off back to the asylum as they are coming for me!! But "they" have a problem too as "they" think they are "in charge" - but they're not - 'coz its "us" wot izz!!!

And dat am de troof too!!

derekm
11-17-2008, 07:22 PM
This information found in the SKF site I thought would be generally useful since its relavent to the OP and "troubles" of my own detailed in other posts
LINK (http://www.skf.com/portal/skf/home/products?maincatalogue=1&lang=en&newlink=9_0_76)

A grease lubricated high-precision bearing will initially run with a higher frictional moment. If the bearing is run at high speed without a running-in period, the temperature rise can be considerable. The high frictional moment is due to the churning of the grease and it takes time for the excess grease to work its way out of the contact zone. This period can be minimized by applying a small quantity of grease distributed evenly on both sides of the bearing during the assembly stage. Spacers between two adjacent bearings are also beneficial.

The time required to stabilize the operating temperature depends on a number of factors the type of grease, the grease fill, how the grease is applied to the bearings, the bearing type and internal design, and the running-in procedure.

Bearings typically work with minimal lubricant when properly run-in, enabling the lowest frictional moment and temperature to be achieved. The grease that collects at the sides of the bearing will act as a reservoir and the oil will bleed into the raceways to provide efficient lubrication for a long time.

Running-in can be done in several ways. Wherever possible and regardless of the procedure chosen, running-in should involve operating the bearing in both a clockwise and anticlockwise direction.

Standard running-in procedure This is the most common running-in procedure and can be summarized as follows:

1. Select a low starting speed and a relatively small speed increment interval.
2. Decide on an absolute temperature limit, usually 60 to 65 C. It is advisable to set the machine with limit switches that will stop the spindle if the temperature rise exceeds the limits set.
3. Start operation at the chosen initial speed.
4. Monitor the temperature by taking measurements at the bearing outer ring position avoiding peaks, and wait for it to stabilize. If the temperature reaches the limit, stop operation and allow the bearing to cool. Start again at the same speed and wait for the temperature to stabilize.
5. Increase the speed by one interval and repeat step 4.
6. Continue increasing the speed in intervals, allowing the temperature to stabilize below the limit at each stage. Proceed until this is achieved for one speed interval greater than the operating speed of the system. This re-sults in a lower temperature rise during normal operation. The bearing is now properly run-in.

This standard running-in procedure is timeconsuming. For a medium to high speed spindle, each stage can take anywhere from 30 minutes to two hours before the temperature stabilizes. The total time for the running-in process could be 810 hours.

Short running-in procedure
An alternative solution to the one mentioned earlier, reduces the number of stages and shortens the overall running-in time. The main steps can be summarized as follows:

1. Select a starting speed approximately 2025 % of the attainable speed for grease lubrication (see product tables) and choose a relatively large speed increment interval.
2. Decide on an absolute temperature limit, usually 60 to 65 C. It is advisable to set the machine with limit switches that will stop the spindle if the temperature rise exceeds the limits set.
3. Start operation at the chosen initial speed.
4. Monitor the temperature by taking measurements at the bearing outer ring position until the temperature reaches the limit. Care should be taken as the temperature increase may be very rapid.
5. Stop operation and let the outer ring of the bearing cool down by 5 to 10 C.
6. Start operation at the same speed a second time and monitor the temperature until the limit is reached again.
7. Repeat steps 5 and 6 until the temperature stabilizes below the limit. When the temperature peak is lower than the alarm limit, the bearing is run-in at that particular speed.
8. Increase the speed by one interval and repeat steps 4 to 7.
9. Proceed until the bearing is running at one speed interval greater than the operating speed of the system. This results in a lower temperature rise during normal operation. The bearing is now properly run-in.

Although each stage may have to be repeated several times, each cycle is just a few minutes long. The total time for this running-in process is substantially less than with the standard procedure

oldtiffie
11-18-2008, 12:54 AM
Thanks Derek.

That was a good informative read.

darryl
11-18-2008, 01:55 AM
I thought I'd bring this up because no-one else has. The spindle will heat along with the bearings and will expand . This could easily affect the pre-load, and it depends on the bearing configuration. If two preloaded bearings are placed close together, this effect is minimal, but if the bearings are any significant distance apart the preload will lessen. Over a period of time the heat from the bearings will transfer to the spindle, possibly resulting in a lower preload, thus easing the heat being generated by the bearings. I can say by this deductive reasoning that the bearings could initially get fairly hot, then settle down to a lower temperature after a period of running. If the housing containing the quill heated up as much as the spindle, the change in preload would probably be zero, but the housing has so much more mass to conduct heat away so the potential remains for the preload to lessen after a period of running.

Note that one effect of the heat buildup is that the cutter position will change slightly. You might start by taking say, 10 thou off a workpiece, then without changing anything you find that later on 12 thou might be coming off.

I'm not discounting the effect of the grease on the heat being generated, but I can't say it's all because of the grease. It will certainly be wise to use a proper amount of grease, and that's probably less than what a person might think is the right amount.

I guess I should add in a disclaimer- I'm not a bearing or spindle engineer, and what I'm saying is simply what makes sense to me, coupled with a few things I've learned about all this (mostly from this forum). My own direct experiences with preload come from doing the wheel bearings on the 4x4. Set by the book they pretty much ran cold, but I didn't like that they had a discernable play. Going up a notch at a time, I stopped when I could detect the beginnings of some heating, and left it at that. Never been a problem. Granted we're not talking high precision spindle here, but similar type bearings anyway.

derekm
01-24-2009, 01:59 PM
Some folks may be missing part of the point........

Yes, bearings get hot.

But they should not get real hot real fast...... if it can warm up that much in just a few minutes, the rate of power input to the bearing sounds way too high.

.....

Not according to SKF....

See
http://bbs.homeshopmachinist.net/sho...40&postcount=7
http://bbs.homeshopmachinist.net/sho...40&postcount=17