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Old 10-07-2007, 09:10 PM   #1
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pillow block help

I'm working on a new project with the impending deer season. I need a rough cut mower for up at the farm, but I refuse to shell out that much good money for what is essentially some steel, a Briggs, a few pulleys, and a belt. Therefore I have drawn up my own plans and I will post pictures as it happens....

But I need a little help real quick. Is a pillow block like this ok foir a vertical load? The vertical load would just be the weight of the blades, drive hub, shaft, and pulley. I'm used to tapered bearings so this set screw business is new to me. There would be three bearings supporting the shaft as I have the mower drawn up now.



If I needed to add some of those set screw lock collars to make it more secure that wouldn't be that big of a deal, but less rotating mass and $$$ is always appreciated, especially given that my engine is an old 28ci iron liner Briggs single rated at only 12 hp.
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Old 10-08-2007, 06:31 AM   #2
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Re: pillow block help

Not sure. But have you looked into getting a mower blade spindle that is designed for such use? They come in similar bolt patterns and have the shaft built in. Not sure how much they are since all the ones I have had replaced were under warranty. But after buying that bearing assembly and finding everything else, it might be easier to buy the complete assembly. Or you could always look for scrapped mower decks and probably find an assembly that still has some life in it. Just need to find a lawn-mower graveyard...
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Old 10-10-2007, 10:53 AM   #3
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Re: pillow block help

Two of those on a shaft with some distance apart would work. The rule of thumb on a standard bearing like those (verses an angular contact bearing which is 50/50) is 10% of the load can be linear, the majority is radial load. Regular mower deck spindles use those kind of bearings (standard roller bearings with seals) so I think you are OK on that. You are going to have to figure out how to keep a blade on the end of that shaft and keep the bearing locks tight though. A set collar with dimples under the set screws with locktite works well to control end movement w/o haveing to rely on the bearing locks to do all the work. 1" shaft size would be a good starting point, any smaller and you will bend it, stress proof steel would be ideal but you won't find that just anywhere. An old front wheel drive car hub is stout and could be reasonably adapted to work, they have timkens in them, are well sealed, are short and can be had for next to nothing off an old junk car. Lawn mower blades are heat treated steel and not just a piece of flat steel with a hole in it so don't make your own blade unless you make it out of steel thick enough to make up the difference. Just imagine what would happen if you halved a blade and it went flying through the side of a house or car, nothing would be spared from the carnage. After it's all thought out it would probably be easier to buy a spindle and adapt it to your home made mower. You would have your standard blade mount, your pulley mount and a flange to mount to your deck. sportyrick
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Old 10-11-2007, 02:52 AM   #4
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Re: pillow block help

Thanks for the replies. I have my plan crudely sketched out. I looked into other alternatives such as using an automotive hub or old mower parts, but the auto hub would be difficult to adapt and the mower parts are either not stout enough (this might not be either, but atleast it's cheap and commonly available stuff) or are pretty spendy.

The blades will be made of 3/8 high carbon steel so I think I should be ok there. I don't plan to mow a lot of saplings down so hopefully it will hold up. The breakaway blade design also saves a tremendous amount on the blades and everything else. Basically, the blades are mounted in double shear with a single thick grade 8 bolt holding them in place. Centrifugal force is enough to drive them out (especially with a small weighted section on the end) so that they effectively cut, but should you encounter anything too large they can fold back. By folding back they also change from a hacking axe type motion more to a knife type slice to get through stuff. The design seems to work very well for Agri-Fab with their rough cut stuff.

Any idea what ratio they turn the blades at on the commercial stuff relative to the crank speed? I can go look at a dealer if all else fails, but maybe someone has a rough cut sitting around they could take a peak at?
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Old 10-17-2007, 01:08 AM   #5
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Re: pillow block help


The bearing you show a photo of is known as a flange bearing around here.
A pillow block is the Omega shaped housing. Local terminology may vary, I suppose.

I'd be leery of using three bearings on one shaft. It's generally not a good idea, as it is unlikely that you will get all three lined up perfectly, and then the bearings will force the shaft to flex with every revolution, leading to fatigue and breakage. Don't ask me how I know.

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Old 10-17-2007, 12:01 PM   #6
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Re: pillow block help

The design has already changed to using only 2 bearings, but thank you for the input. I am currently fighting with trying to get an exhaust flange for a 28 cubic inch Briggs so I can get some sort of muffling device on there. The WIDE open exhaust is ok in the yard for waking the neighbors, but beyond that it isn't good.
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