Shaft problems.

Grower · November 22, 2013, 04:01:00 AM

Hello again, I am still having shaft problems. This is the fourth time between the two main pulley shafts that we have had bearing failure. Whats causing these problems? We have a reliable engineer in town and they appear to have made a great job of fixing things. The shaft diameter is 1 1/2" and this time we are using special bearings with waterproof seals. Is it the sideways pull the problem? If it is how do the sawmill manufacturers solve this? Thanks.

Grower · November 22, 2013, 04:04:48 AM

https://forestryforum.com/gallery/albums/userpics/17673/shaft.jpg

Ron Wenrich · November 22, 2013, 05:57:09 AM

I'm far from being an expert on these things. I worked in circle mills, so our belts only drove the saw directly. We didn't have to worry about the tension in the blade while putting tension in the belts. Usually when we had bearing failures it was either from not being heavy enough with our bearings or shafts, or we had an alignment problem.

When you put tension in your pulley system to tighten your belts, how does that affect the band pulley? Seems to me that you can't put the same amount of tension in both sides, since rubber stretches more than the metal. That would put a lot of stress in that bearing.

bandmiller2 · November 22, 2013, 07:21:10 AM

The first thing that comes to mind is too much tension on the bands,that is a high load area.My homebuilt bandmill uses 1 1/2" shaft and bearings and I've replaced them once after many years of service.Most of the pillowblock bearings we buy now are of pacific rim origin.Try to find some US made bearings lower your tension a little and lube with good high pressure grease. Frank C.

5quarter · November 22, 2013, 09:27:15 AM

Side load always puts wear on bearings...Frank gives good advice. Also, bearings are rated by rpm; Make sure those are high rpm bearings. here's a good source online:
http://www.nskamericas.com/cps/rde/xchg/na_en/hs.xsl/innovative-830.html
Also try Cooks saw Mfg.
Some mill designs put less side load on the shaft bearings than others. Factory bearings may be inadequate for long life on your mill, especially if you're running higher than recommended tension. also make sure your shaft is running true; even the slightest deflection of the shaft will shorten bearing life.

PC-Urban-Sawyer · November 22, 2013, 02:29:19 PM

Guys, Grower is located in New Zealand. Not sure how much good the sources in the U. S. will do him...

Herb

drobertson · November 22, 2013, 04:37:16 PM

Sounds like a few possible issues, Load being one, contaminants being one and then vibration, the last being lubrication. This is all contingent on the correct bearing being used from the start, it sounds like if engineers are on it, the right bearing is in place, hard one to call not seeing the equipment or conditions, hope all works out for you, david

Grower · November 22, 2013, 06:30:05 PM

We tension the blade using a vernier caliper, the blade stretches 4.5 thousandth of one inch every 5 inches. Much less than this and we get wavy cuts. The engineer fitted 2 new bearings of a different type with waterproof seals and they have no locking collars, they both have 2 grub screws and are part of the inner bearing, they screw straight onto the shaft from the bearings themselves, the front bearing was locktited in place at the engineers. We are also from now on going to use a special high load grease (NZ$35/tube). The bandsaw wheels were balanced at the start and there is no vibration from them at all. We are just reassembling it all now and it looks good, but it did last time too.

submarinesailor · November 22, 2013, 08:46:23 PM

Is it possible that you are placing a side load on the bears by locking them both to the shaft with the "grub screws"? It seems to me that locking them both to the shaft would not allow for any thermal expansion. As I see it, when the mill runs, the shaft will pick up some heat from the belts and the blade. With this heat, you will get some thermal lengthening of the shaft. This expansion could place some side load on both of the bearings because they are locked into place.

To me the better way would be to place a thrust bearing, rated to take a load in both directions, on the blade end and a regular roller/ball bearing on the belt end. And don't lock the roller bearing tothe shaft, thus allowing the shaft to move. It won't come out because the thrust bearing would be locked to the shaft. If it wasn't, it could not do it's job of taking thrust (movement) in both directions.

I just found this on the web: http://www.sirfrt.com.au/wikis/imrt/images/7/75/-43_OH_Fan_Brgs_Part_1.pdf. It illustrates exactly what I was speaking of. Check it out. I also fond this document: http://www.sirfrt.com.au/wikis/imrt/images/1/12/SRB_SIRF_National_CM_Forum.PDF. I think some of you will enjoy reading it.

Bruce

Grower · November 22, 2013, 09:23:33 PM

This is on the idler pulley end so there are no belts to interfere. We now have it up and running again perfectly. The pillar blocks are a P208, I see cooks use, or sell P205's. The bearings tend to run cool and I done see the shaft picking up any heat from the 24" pulley, it runs as cold as charity. The first shaft destroyed the bearing when it flew to bits as the shaft it was on wasnt tight enough.

https://www.ntn-snr.com/catalogue/fr/en-en/index.cfm?page=/catalogue/home/industry&method=pa.productdetail&id=P208

https://www.ntn-snr.com/catalogue/fr/en-en/index.cfm?page=/catalogue/home/industry&method=pa.productdetail&id=P205

5quarter · November 22, 2013, 11:43:12 PM

PC...I saw that. I'm sure he can order quality bearings from any number of online sources that will ship to NZ. I just wanted to give him an idea of what to look for.
Grower...That's great news. I would inspect it after every run to see if there is any change or degrade in the assembly. also check for excessive heat. Also, don't over pack the bearings with grease as it can cause nearly as much damage as not enough.

Grower · November 23, 2013, 12:14:50 AM

There are plenty of fellas down here who sell good quality bearings although it is cheaper to source them directly from the US, some people do that. The grease we are using is Rocol Molybond TPG450 or something like that, I will have to empty the new greasegun before I can tell anyone whats on the actual cartridge, the gun is to be used ONLY for greasing the bearings and blade guide rollers. I just cut up 2 more logs and the blade, even with just a trickle of coolant running on it is stone cold. Maybe I'm "making progress on the progress by ultrafine tuning the fine tuning." She cut well! 8)
https://forestryforum.com/gallery/displayimage.php?pid=146835

Grower · November 24, 2013, 09:34:51 PM

The second set of bearings on the drive side has just gone, the front one. Where to from here? It hasnt done that much work.

Den-Den · November 24, 2013, 09:42:11 PM

Is there any chance that the bearings have experienced impact load; (such as being hammered onto the shaft) this is the fastest way to make bearings fail.

Grower · November 24, 2013, 09:46:17 PM

No, the engineers press them on.

Grower · November 24, 2013, 09:53:41 PM

The new ones we only just installed are also warmer than I would like.

mikeb1079 · November 24, 2013, 10:12:46 PM

so the new bearings lasted only a day?

also, what kind of mill are you running?

Grower · November 24, 2013, 10:14:36 PM

The bearing that just collapsed wasn't really hot or anything and it hasnt moved on the shaft at all. The ball bearings can be seen hanging in there with the naked eye.

Grower · November 24, 2013, 10:16:21 PM

No, longer than a day, a couple of months maybe, this one is the bearing at the front of the drive pulley and now its irritating me. The shaft looks good its just the one bearing. Its on a bandsaw with a 5 metre 1 1/4" blade.

Grower · November 24, 2013, 11:49:48 PM

As you can see there is plenty of sawdust about, the bearing is still tight on the shaft. I want to know what is causing this problem. Maybe some sort of sawdust guard?

https://forestryforum.com/gallery/displayimage.php?album=1910&pid=146968#top_display_media

https://forestryforum.com/gallery/displayimage.php?album=1910&pid=146969#top_display_media

beenthere · November 25, 2013, 12:40:20 AM

Is this the shaft you are having problems with? (copied from your gallery)

You can also copy pics from your gallery and paste them in your posts if you'd like.

I'd make a guess that your bearings are not aligned with your shaft and causing their early demise.

Lay that problem squarely in the lap of your engineer. He/she should be able to figure out what the problem is that causes the early failure.

Have you had the shaft out and mic'd for tolerances and such?

Grower · November 25, 2013, 02:02:44 AM

That is the current one yes, the other side has been fixed twice in that it is now on its third set of bearings. The third set are about to go into this one. We have a top engineer on the job and yes everything is mic'd out. I don't understand why I am having these problems. The inner bearing shell cracked on the shaft on the last cut I could feel it wasnt right half way through the last board.

submarinesailor · November 25, 2013, 05:45:47 AM

Has any of the engineer's had or performed a laser alginment or vibration analysis on these bearings? If not, I would recommend both.

Bruce

bandmiller2 · November 25, 2013, 06:00:10 AM

Grower you mentioned the engineer pressed the bearings on the shaft and they seemed to run hot.Most pillowblock bearings are designed for a slip fit on the shaft that's why the have the grub screws to lock them on the shaft.I believe their too tight on the shaft,running hot,and that's leading to their early demise. Frank C.