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Author Topic: Arbor bearings  (Read 2608 times)

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Offline bandmiller2

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Arbor bearings
« on: December 25, 2007, 06:36:50 AM »
Is their any reason  2 7/16 pillow block ball bearings should not be used on a light duty circular sawmill??Production mills use roller brgs.[$$$$$]is it a safety thing or a longevity thing??I would put a safety u bolt over the arbor near the fast collar in case of brg. failure.Whats the track record of ball brgs. on arbors I'am sure some have used them.Thanks to all have a good day with family.Frank C.
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Offline Firebass

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Re: Arbor bearings
« Reply #1 on: December 25, 2007, 01:43:17 PM »
I've done allot of machine work in our local industrial sawmill and I have seen them used for Barkers, Saws and most everything.  I too think they look a bit light compared to the old Babbitt castings,  but I think they are fairly tough.  I personally wouldn't use them on a saw arbor only because to me it's like using all-thread.  If I didn't own a machine shop I'd do it in a heartbeat and the U bolts is a good thing.

Merry Christmas
Firebass

Offline KGNC

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Re: Arbor bearings
« Reply #2 on: December 26, 2007, 01:33:08 PM »
Bandmiller:

There is a place for both types. For the same size the roller bearings will carry a heavier load. It all goes back to contact area of the bearing. The roller has a lot more contact between the races then a ball. The roller bearing is also more suited for shock or impact. But the ball bearings generally have a lower friction coefficients.

Most of the pillow block roller bearings are really double row tapered-roller bearings. This is a good choice if you will have a thrust load on the end of the shaft. But they are not the best choice for high speeds since they have a high friction CF. Most circular saws applications are not considered high speed.


Don't know of any real safety differences between the two. The results will be about the same for either if they fail.
Hope this helps.

Offline Ron Wenrich

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Re: Arbor bearings
« Reply #3 on: December 26, 2007, 05:09:21 PM »
I think a lot depends on how big of bearing you are getting.  I've seen and used mills with ball bearings, but it is usually a fairly wide bearing.  Your saw speed should be somewhere in the 500-550 RPM range.  The biggest problem with bearings is that you can get too much grease in them.  That will cause it to heat up.  You'll also want a sealed bearing, so no dirt gets in there.

I have only heard of one bearing failure and that was due to hitting a dog on the return, which shattered the saw. 

Are you using a wooden husk?
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Offline KGNC

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Re: Arbor bearings
« Reply #4 on: December 26, 2007, 05:46:52 PM »
Ron:
The "wide"  ball bearings are usually double row ball bearings. They have two sets of balls in the housing.

I spent a lot of time spec'ing bearings over the years. But most times it was someone else's money so I'd just picked the best one for the job (within reason). Very seldom do people complain if the bearings last too long.

Offline Firebass

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Re: Arbor bearings
« Reply #5 on: December 26, 2007, 07:56:02 PM »
@ 500 RPM Brass Bushings would last a life time if properly Lubed.  :)


Offline bandmiller2

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Re: Arbor bearings
« Reply #6 on: December 27, 2007, 05:41:16 AM »
Ron, the mill I'am looking at is a lane#1on wood.What I will probibly do is make up the husk out of rectangular steel tube,carrage also of steel,but with wooden ways.
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Offline Ron Wenrich

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Re: Arbor bearings
« Reply #7 on: December 27, 2007, 05:48:52 AM »
There's nothing wrong with a wooden husk, as long as its in good shape.  The big deal is your mill foundation.  I've seen some that are pretty lame, but work amazingly well. 

I was just wondering about the need for the U bolt over the arbor.  I don't think its necessary. 
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Offline bandmiller2

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Re: Arbor bearings
« Reply #8 on: December 27, 2007, 06:22:46 AM »
Ron,wile your on the wire,what is the normal size relationship of shanks to the plate they fit into.What I have is a 6/7 ga.48"3 pattern headsaw,the shanks are 8 ga.thought they were supposed to be wider than the plate.With that heavy a saw i will probibly have to use at least 5/16 bits.Ron probibly don't need the U bolt but if the saw breaks the bearing and climbes out of the cut you know right where its headed.Thanks Frank C.
A man armed with common sense is packing a big piece

Offline Ron Wenrich

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Re: Arbor bearings
« Reply #9 on: December 27, 2007, 04:51:04 PM »
No, I don't think you want them wider than the plate.  I run a heavy saw, a 7/8, and my shanks are a #8.  I would think a real wide shank would rub on the log and cause friction on the rim.  If you've ever seen a hot rim, then you know how impressive the twisted steel looks, until it cools down. 

You're clearance on the saw comes from the lead.  The shank serves 2 purposes.  One is to hold the bit in place, and the other is to hold sawdust in the gullet.  When the shank gets worn, it will allow dust to spill out of the sides.  I've had some pretty thin shanks that have worked OK.

I wouldn't go with the wide teeth, either.  If you need some extra width, you can swage the tooth.  But, if you're saw is adjusted right, you won't need that extra width. 

I've sawn at least 1 million logs.  I've never had a saw break a bearing.  And I've wrecked a couple of saws.
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Offline eamassey

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Re: Arbor bearings
« Reply #10 on: December 27, 2007, 11:32:10 PM »
A word about pillow-block bearings. . .  there are many different types out there.  Those cheap ones you see advertized are usually Chinese, light-duty, and ball bearings.  You can buy 2 inch pillow blocks ranging from $20 each to $250 each.  The price is not the only thing that is different.  But, the fact is that the $20 bearing will work OK in lots of applications.  However, for the primary bearings for a saw head, I would use roller-bearing or spherical-bearing pillow blocks, and only some with very strudy looking castings.  (My personal preferred brands are Rexnord, Link-Belt, and SKF.)  If you can find some used pillow blocks, you may be able to get some high dollar ones for $10 or $15 each.  I will use used pillow blocks in a critical place, if--- they are the type that I can tear down, clean, and fully inspect (I am looking for cracks, chips, brinelling, spalling.).   The bearings books detail the load and rpm capability of most bearings.  One more thing, many pillow blocks in industrial use are not sealed bearings-- just shielded.  "Shielded" allows for some contamination, but purge well when re-greased. 


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