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Yondering
04-12-2016, 05:53 PM
Looking for any suggestions or comments you guys might have here.

I recently brought home an older Jet BD-1336 lathe (belt drive, 13"x36", predecessor to the newer 13"x40") that was made in 1991 and has seen very little use. (I'm still scraping cosmoline off a lot of the parts.) Everything is tight and it seems to work well, but the spindle is a little stiffer to turn than I expected, and the bearings get warm when it's running. These are roller bearings BTW, I assume tapered roller since I don't see any thrust bearings.

The bearings don't get too hot to touch, I can hold my hand on either bearing housing without discomfort after 10-20 minutes of run time; I've read some say this is OK, but can't help wonder if the bearings are too tight. The spindle takes a little effort to turn, but it's hard to tell how much is the bearings and how much is drag from the large V-belt (it drags a little even disconnected). I did try to loosen the bearing preload (two large nuts on the back end of the spindle) but either I'm missing something, or something (bearing, pulley, etc) is stuck on the spindle, because the preload wouldn't release, even with some moderate hits to the spindle with a rubber mallet.

Any suggestions? Just run with it, or do I need to address this first? Anybody know if there's something else besides the large nuts that I need to do to loosen up the preload?

Thanks in advance

RussZHC
04-12-2016, 06:01 PM
The bearings don't get too hot to touch, I can hold my hand on either bearing housing without discomfort after 10-20 minutes of run time
to me that sounds very manageable...I know that sort of "test" is not infallible but often used/referred to...guess it depends a bit on what for you and that lathe's use is "long" before that next break

Is it possible the bearings, or more, the lube that was on the bearings during the last period of little use has solidified or thickened to a great degree causing drag?

Asked as I seem to recall the suggestion of flushing out bearings (in place) a couple of times and then re-lubing...don't know if that is possible in your example or how complex an op it is.

Joe_B
04-12-2016, 06:11 PM
Warm is OK, my lathe has tapered roller bearings and it is the same. It also has a little resistance to turning mostly from the belts.

Yondering
04-12-2016, 06:55 PM
Is it possible the bearings, or more, the lube that was on the bearings during the last period of little use has solidified or thickened to a great degree causing drag?

Asked as I seem to recall the suggestion of flushing out bearings (in place) a couple of times and then re-lubing...don't know if that is possible in your example or how complex an op it is.

I wondered the same, but was able to see the rear bearing after removing the bearing cover - everything looks like shiny bare steel. I couldn't see the actual bearing surfaces though, just the ends of the rollers, so varnish may still be a possibility. I drained and refilled both bearing housings with the recommended Mobil DTE Heavy/Medium oil.

Thanks guys, this is good to know. I mostly asked because my 12" Grizzly lathe I was using up till now runs much quieter, and the bearings never get warm, even at 2000 rpm, without suffering from any excessive runout. That made me wonder if the bearings in this Jet lathe are just tighter than they need to be, but I'm not sure how to loosen them up.

firbikrhd1
04-12-2016, 07:50 PM
Even the best bearing have some friction and friction causes heat. The stirring of the grease in the bearing alone can generate some heat. As long as you can hold your hand on it there should be no problem. Tapered roller bearings that are too loose can be a problem just s too tight can be.

RussZHC
04-12-2016, 08:51 PM
I think I understand what and the why you are thinking the way you are...MY biggest issue in situations like these is trying to make something perfectly functional "better" and even at 50+ y.o. I don't know that I have learned that strongly enough or often enough to know when not to or when to stop...

Richard P Wilson
04-13-2016, 02:48 AM
The manufacturers instructions for my UK built Denford 280, which has taper roller bearings, are that when correctly set, the bearing housing should be not more than 60 degrees C after an hour of running at top speed. The lock nuts on it are left hand thread.

BigBoy1
04-13-2016, 07:38 AM
A problem I discovered on my South Bend Heavy 10 which I rebuilt was the channels which lead from the oil cups to the bearings were blocked. Even though the oil cups were full, there was no lubrication getting to the bearings. Perhaps there could be solidified grease blocking the oil channels and little/no lubrication is getting to the bearings.

Yondering
04-13-2016, 12:31 PM
Thanks guys. Russ, I hear ya. I'm usually pretty good about leaving "good enough" alone, just wasn't sure if this was "good enough" given the difference in bearing preload from my previous lathe.

I did fiddle with it more last night, and was able to loosen up the preload a bit using a mallet and piece of wood against the back end of the spindle. (Probably not the best method, but I was careful to not damage anything.) I got it too loose at first, but tightened it back up in stages and went just a few degrees past snug. It definitely runs quieter now, and the bearings are barely warm to the touch after running for an hour. It cuts as well as it did with tight bearings too, so I'm pretty satisfied with the result.

Do any of you know if lathe spindle roller bearings are typically pressed on the spindle? I'm still wondering if they are supposed to be that tight on the spindle, or if they are gummed in place from old oil? It doesn't matter for now, but sooner or later I'll have to remove the spindle completely to replace the belt.

BigBoy1, thanks for the input, but these are roller bearings in an oil bath; not like the small South Bend lathes. (I have one of those too.)

RWO
04-13-2016, 12:58 PM
I have the same lathe. Don't forget you have 4 rubber lip oil seals on the spindle which will cause some resistance to rotation. The inner races are not pressed on as the preload is set by the dual lock nuts on the outboard end of the spindle. There is no need to remove the spindle to replace the belt. Get a Fenner Power-twist linked belt. It will run smoother and with less noise than a standard V belt. Mcmaster-Carr carries them if you need a source. http://www.mcmaster.com/#v-belts/=11ys2yo There are other sources on the net.

RWO

Yondering
04-13-2016, 02:47 PM
Thanks RWO, that's good to know about the belt. I wondered about those linked belts but wasn't sure if they'd hold up; I'll get one of those on the way. Love ordering from Mcmaster too. Do you happen to have the link type and belt length written down? I haven't measured my belt yet, and any markings were worn off years ago; it's in pretty bad shape.

Yeah, the rubber seal lips cause a little drag, but the drag on the spindle bearings was easily 2-3 times higher; when spinning the chuck by hand (with the belt disconnected and off to the side) it wouldn't spin freely at all, just stopped immediately even with a hard spin. After removing some preload it spins better now, maybe 1/2 turn or so free spin before it stops. I'm glad I fixed it; it seems to run better now.

johansen
04-16-2016, 01:57 AM
The usual rules for preloading axles and rear end differentials are tighten the preload till it takes xx foot pounds to break the static friction of the tapered roller bearings.

That static foot pound limit can be calculated if you have all the information you need (timken has all the math freely available in their books)
This friction is mostly the sliding friction at the end of the roller against the shoulder of the cone.

Once the fluid film is built up, given enough rpm, the usual numbers are about one tenth of that that static friction. but 1 tenth is still a fairly significant number.

RWO
04-16-2016, 01:32 PM
Thanks RWO, that's good to know about the belt. I wondered about those linked belts but wasn't sure if they'd hold up; I'll get one of those on the way. Love ordering from Mcmaster too. Do you happen to have the link type and belt length written down? I haven't measured my belt yet, and any markings were worn off years ago; it's in pretty bad shape.

I bought my link belt about 20 years ago. At that time, Fenner Drives was the only supplier. The package I bought is "B25-72 Powertwist Plus". It is for B and 5L industrial drives and is 72" long. That will give you enough belt to replace both belts, I think. I never replaced the motor belt on my lathe since it is still in good shape. The spindle belt didn't last but about 6 or 7 years after I bought the lathe, which prompted me to get the link belt replacement kit.

There are several sources besides Fenner now, including China. Apparently the patent has expired. I don't know who supplies Mcmaster with their version.

RWO

Yondering
04-16-2016, 06:01 PM
Great info RWO, thank you!