rkcarguy wrote: ↑Tue Nov 27, 2018 11:23 am
Doug_Edwards wrote: ↑Tue Nov 27, 2018 12:52 am
rkcarguy wrote: ↑Mon Nov 26, 2018 11:49 am
I've posted this before, but I feel a needle bearing is a poor choice for our application. The small diameter wheels spin faster @7mph than a cars wheel on the freeway, and the speed is way too fast for such tiny little needles. They are typically used on things that pivot, not rotate, or for instance the floating side of a centrifugal clutch or motorcycle clutch basket(only has to spin at ~idle until the clutch locks up).
I pulled out my Torrington catalog on needle and roller bearings. A 7/8 dia axle with a 3/4" long bearing has a limiting rpm of 5500 rpm. The basic capacity of the bearing is 3600 lbs. If you run this bearing at 5500 rpm with a 6" driver, you would be traveling close to 100 mph. How fast did you want to go? Fwiw, if you use a similar roller bearing, the limiting speed would be over 300 mph!
I'm using needle bearings in my Climax trucks. I figure I will not be running more than 5 miles an hour, although the limiting rpm is close to 7000 rpm. I put hardened bushings on the axles for the bearings to run on. The bearing load was over 1000 lbs per bearing. I think I am covered. I Used 1045 ground and polished shafting for the axles and lineshafts.
Regards,
Doug
I would question the 5500 rpm, is this greased? Oil bath? Size of the needles? A bearing with larger needles more in line with a Timken would certainly hold up better. I am curious though, and would like to know what the needle bearing size is that you are using. I'll calculate out the RPM of the needle based on the diameter when the axle is going 5500 rpm and we'll see how far into the stratosphere it is.
Another issue is that needle bearings have next to nothing for tolerance for torsional twist, so if your trucks or chassis is twisting at all as you navigate uneven track, the needle bearings are going to fail in short order.
Question it all you want, but the numbers come straight out of the Torrington catalog. If you are interested, I pulled the numbers from data for bearing number BH-1412. I looked but did not see any mention on the size of the needles in the bearing. I would guess for this bearing that they are 3/32 or 1/8. The catalog makes no mention of oil for lube, only grease.
From my notes it looks like I am using the B-812 bearing in the Climax. Basic dynamic capacity is 2130 lbs per bearing, for a total of 25,560. Torrington states if you halve the load, you increase the life by 10 times. My loco weight is 1/50th of the total maximum load. Bearing life is not even a question.
Journal boxes on most locomotives should be able to rock with axle movement. The Climax is no different in that respect, although Climax used more clearance between the journal box and the pedestals that they rode in than what rod engines can use.
One loco that I am familiar with was built in the early 70's with needle bearings on the rods and axles. Over 6000 actual miles with no bearing changes. That is not the only one in the hobby built that way. Hard to argue with success like that.
Regards,
Doug