I ran my mill for 16 minutes at 3,000 RPM (I get email when my CNC jobs complete). It was machining a mold prototype for a kids toy. We will need to cast 18 of them that in wax, and the mold will be made from Aluminum. But I digress.
After I finished running for 16 minutes, I measured a few temps:
*) Inside the shop - 86 degrees
*) On the variable speed transmission on top -- 105 degrees
*) On the low part of spindle (at the QC-30 collar) 115 degrees. I am not sure if I fully believe this last measurement. The bottom of the spindle feels warm to the touch, I can hold it indefinitely, but it is not comfortable.
Would you consider this temp rise to be excessive?
The bottom bearing may..may be a bit dry. What provisions are there on your machine for bearing lubrication? Every Bridgeport Ive seen has luber for the bearings.
And no..its not bad at all. Im rather surprised that it was that low, from a 20-30 yr old machine.
My Gorton, run at 5000 rpm, wide open, will increase temps to 80' above ambient. This of course doesnt include..as yours doesnt..the cooling effects of coolant on the spindle as well as the cutter and work piece.
I rebuilt the spindle in mine about 6 yrs ago,...somewhere less than 30 hours of actual run time. Probably closer to 5 hours actually.
Gunner
One could not be a successful Leftwinger without realizing that, in contrast to the popular conception supported by newspapers and mothers of Leftwingers, a goodly number of Leftwingers are not only narrow-minded and dull, but also just stupid. Gunner Asch
You would be greatly surprised at how well heat transfer works .....
The same type that came out.
I dont recall what the number was. Shrug.
"A conservative who doesn't believe? in God simply doesn't pray; a godless liberal wants no one to pray. A conservative who doesn't like guns doesn't buy one; a liberal gun-hater wants to disarm us all. A gay conservative has sex his own way; a gay liberal requires us all to watch and accept his perversion and have it taught to children. A conservative who is offended by a radio show changes the station; an offended liberal wants it banned, prosecuted and persecuted." Bobby XD9
The varispeed runs hot, because the belts rub. That is normal, that's why they have air vents in the housing.
Yes. This temp rise in only 16 minutes at 3000 RPM does sound excessive. But, this is a series 2 machine, with 3 HP motor? (I'm trying to remember.) They usually have sealed, grease-packed bearings, which run a lot hotter at high speed than the oil-drip bearings used in many of the Series-I machines. This kind of heating is going to cause spindle growth, for instance, making it hard to hold fine tolerances on Z.
(I see in your reply to Gunner that it is a sealed-bearing unit.) One possible problem is somebody repacked the bearings with too much or the wrong kind of grease, or that coolant and swarf has gotten up in there. The oil-lubed Bridgeports depend on oil dripping down to flush contaminants out of the bearings. If your bearing seals are shot, contaminants could easily work up into the bearings (gulp). I think it is fairly easy to drop the spindle cartridge out of the quill. There is a setscrew that locks the bearing cap. You remove the setscrew and unscrew the cap. The entire bearing/spindle assembly may just drop out the bottom from its own weight, so be ready to support it. This should allow you to examine the seals, at the least, and the cleanliness of the inside of the bearing region. If filled with crap, you know you need to flush and relube, at the least. The bearings need to be filled with a known quantity of lube to avoid overfilling. If you have to replace the bearings, they may be a bit expensive. I know the bearing sets for the Series-I are quite expensive.
When reassembling, you use the dimple made for the setscrew to put the bearing cover back in the rght position, and then GENTLY tighen the setscrew to avoid warping the quill.
If you decide to take the bearing assembly apart, ask for advice, it is a bit tricky, and I don't know the sealed bearing version. The bearings need to be aligned a certain way and fitted with matched spacers. I know there are couple guys on here that know the procedures well.
Oh, the other thing to know is, how far does this progress? If the temperature just keeps climbing at this ~ 2 degree F per minute rate, you have a SERIOUS problem, and the bearings are going to blow shortly. If it levels off at 130 F and stays there, I'd still be a little concerned, but it isn't going to melt down right away.
What concerns me is the rate of rise, which is some measure of the heat output. My spindle gets hot, too, but it takes at least a half hour or more to get near this temp.
It is an Interact mill, it is not really a Series II equivalent.
It has a 2 HP motor that says "good for 3 HP for 30 minutes".
Yes, sealed bearings.
Jon, I think that for now, I will file your advice but will refrain from taking the head apart. It is just too risky. Just one stupid thing and bye bye CNC mill.
Another possibility is that the machine sat unused for a fair amount of time and the grease in the bearings hardened. The grease should reliquify ok, but certainly he should keep an eye on spindle temp for a while.
Yes, but it is a standard Bridgeport Ser-II BOSS head.
Yes, years ago, I was the same way, horrified at the thought of horribly messing something up. There ARE things that shouldn't be taken apart because the "springs will all fly out", but I am a lot bolder now. Of course, after doing a complete strip-down and rebuild on a 3500 Lb toolroom lathe, maybe I have earned the confidence.
Anyway, if the spindle temp levels off after a longer run, then I agree, it probably isn't a big problem. If the temp keeps going up, then you are going to have to investigate. You can get plenty of advice here from people who know these machines better than me.
I really don't trust ancient, hardened grease that may have contaminants in it in a set of expensive spindle bearings. I have experienced this "hardened grease" and I don't think it actually does ever liquify after that process happens. This machine could very well have the original 30 year-old grease in it!
Yes, Iggy should DEFINITELY watch the temp until he is satisfied that it does level off. I have a feeling with an ~30 F rise in only 16 minutes, that the limit temperature is going to be way up there. Now, that may be normal for the sealed bearing Ser-II head, but it will cause spindle growth that will be several thousandths of an inch. Especially because the ballnut is all the way at the top end of the quill in the BOSS head, a full FOOT above the spindle nose, the expansion can be considerable. Now, assuming the limit temp rise is 60 F (twice as hot as it got in only 16 minutes) and assuming the whole quill heated evenly (not possible) then it would expand .005". Assuming the quill had a linear drop in temp along the whole foot, the expansion would be .002". While not hideous, that could mess up precision work.
Fill them completely..and they will run very warm/hot
Gunner
"A conservative who doesn't believe? in God simply doesn't pray; a godless liberal wants no one to pray. A conservative who doesn't like guns doesn't buy one; a liberal gun-hater wants to disarm us all. A gay conservative has sex his own way; a gay liberal requires us all to watch and accept his perversion and have it taught to children. A conservative who is offended by a radio show changes the station; an offended liberal wants it banned, prosecuted and persecuted." Bobby XD9
Right, but how the HECK do you determine how much is 1/3rd? I guess the bearing manufacturer can calculate the exact volume of the bearing that isn't filled with steel, but I think this could be hard to do correctly in the field. Hmm, I suppose you could weight the bearing and then calculate the volume of the OD - ID and that would get you pretty close.
Nah..fill em full with a bearing grease press, then soak em in solvent, collect the grease, burn out the solvent with heat, and measure the grease volume. Then divide by 3 and voila!
Or make an educated guess like I do when packing bearings on machine tools.
Say!..you could use a grease gun and a needle and fill in between every third ball! That would do it!
Gunner
"A conservative who doesn't believe? in God simply doesn't pray; a godless liberal wants no one to pray. A conservative who doesn't like guns doesn't buy one; a liberal gun-hater wants to disarm us all. A gay conservative has sex his own way; a gay liberal requires us all to watch and accept his perversion and have it taught to children. A conservative who is offended by a radio show changes the station; an offended liberal wants it banned, prosecuted and persecuted." Bobby XD9
So, a recap is that the the outside temp of the spindle after 15 minutes running at 3K RPM, was 115F. (30 something degree F temp rise).
I have looked far and wide for the answer as to whetehr this is excessive.
According to someone at cnczone, he measured temp on the bearing and outside with a non-contact thermometer, and the bearing was 10 degrees hotter than the outside of the spindle.
So it was, say, 130F, being a little generous, or 54 degrees C.
Barden machine tool bearing catalog says that their spindle bearings can run at 100C.
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bearings are not Barden, but it is a good data point.
Another guy pointed out that Timken's roller bearing calculations assume a temp of 130 C for the service life calculations.
So, everything points to a conclusion that 115C on the outside represents a normal bearing operating temperature and is nothing to worry about. Since I use this mill for hobby purposes, I will back out a litle bit and will run it at 2700 or so RPM max.
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