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Crowned Pulley Specs?

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  • Jim Stabe
    replied
    Originally posted by sasquatch
    Jim, great build on the MGB, very nice fabrication,,a lengthy build for sure, but looks like you have it all covered.

    Thanks for that interesting build site!!
    Thank you! Seems like most of the big fabrication tasks are done but the littany of medium and small stuff goes on forever. Maybe when I retire at the end of the year...

    Jim

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  • gwilson
    replied
    Re: Harris's post; I have noticed that the pulleys on my toolpost grinder are a LOT more crowned than the pulleys on my Elgin bench lathe.

    Leave a comment:


  • sasquatch
    replied
    Jim, great build on the MGB, very nice fabrication,,a lengthy build for sure, but looks like you have it all covered.

    Thanks for that interesting build site!!

    Leave a comment:


  • jdunmyer
    replied
    Jim,
    You're correct, it isn't that big a deal.

    I found through bitter experience that a half-decent crown will keep the belt on and tracking UNTIL you load it enough to make it slip a bit. She'll pop right off then. If you get it aligned properly, it'll stay on, even if you do push things a bit.

    Leave a comment:


  • Jim Stabe
    replied
    You are making more of this than you need to. I just put the pulleys for my 2 x 72 in the lathe and hit the sides with a file and tried to make both sides the same. The belt seemed to move a little easier than I wanted so I hit it again and it was fine. Don't need to make a science project out of it.

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  • j.bain87
    replied
    It's real simple to work out how much crown you need, divide the length of the pulley by 3.
    Centre section is left flat, taper each end about 1/8" to the foot, done hundreds and never had one come back because it didn't do what it was meant to do.
    Works for any size, from a foot long to 6 foot long, just do them all the same.

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  • Forrest Addy
    replied
    How much crown? Shouldn't one of the factors be the elasticity of the belt's tension material?

    Leather is flexible and thus may require largish crown proportions to track properly. Synthetic belt materials with glass or steel tension (so-called "high modulus") elements may track well enough on pulleys intended for leather belts but may suffer wear or degration if mated to pulleys having significant crowns. In effect only the center portion of suck a synthetic belt is actually under tension. Therefore: recognizing industry practice as a product of evolution and experiment it would seem a subtler pulley crown be employed for synthetic belting.

    I can't recall any dimentional details of the conveyor pulleys I machined back in the day in El Paso (um, 1971, I think. I was visiting my sister then and took a short job to keep me occupied Sis and Bro were at work.) I took over a running job so I had nothing to set-up. Just run parts. There wasn't much crown but it may have been 1/8" taper in a couple feet.

    I do remember the lathe was a relic with the head and tailstock built up a couple of feet to increase the swing to maybe 5 ft. The chuck had a groove machined in it so the 1" roller chain wrapped in even pitches to mesh with a couple dozen dowel pins driven and spaced to approximate sprocket teeth. The chain drive was driven from a worm gear that was in turn driven with a cone pulley from a 10 HP motor. Everthing was bolted to timbers and scrap iron. Gawd! It was crude! But it worked.

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  • lakeside53
    replied
    Both belt sanders I built track beautifully with a single 1 degree crown tracking wheel. Tiny crown... and mine are 0 to 6000sfm.

    Tighten your belt tension. I can push mine off track if I man-handle it. Unlike KMG, no springs involved in mine so tension can be set to whatever I want.

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  • Shuswap Pat
    replied
    Belt tracking

    So once you guys figure out how much is enough for 'Crown' I will be watching. My next question -I am building a 2 x 72 belt sander - similar to a KMG. It has one 'FLAT' drive wheel, one'CROWNED' tracking wheel, and 2 'FLAT' idler wheels. I fire it up, set the tracking (belt speed 4000 sfpm), start to grind and the belt wanders to one side. Relive the pressue, and it returns to the center.

    I was looking at the 'Radius Master' site - (Australian company) - they have a beautifull machine, and claim no belt drift!

    What could their secret be - Kangaroo Snot?

    Patrick

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  • LES A W HARRIS
    replied
    Text Book of Advanced Machine Work.


    From: Text Book of Advanced Machine Work. Robert H Smith, M.I.T. 1910~1912~1915, Google download.

    Section 4, Pg,28.

    TURNING PULLEYS.
    60. The taper or crowning on the face of pulleys, ranges from
    ¼” per foot for large pulleys to ¾” per foot for small pulleys.

    2 pages further into the section, a drawing for a 5" pulley, gives 1/2" per foot,
    with a 1-3/8" face width.

    Cheers,


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  • mickeyf
    replied
    I would guess that an absolute minimum of crown is best. Especially after hearing about the 8' wide belts. The greater the arc, the less contact between the belt and the pulley, presumably reducing power transfer. This is my intuition speaking, not science, so may be wrong.

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  • lakeside53
    replied
    I made 1 degree "crown" on my 2x72 belt sanders. Two linear tapers meeting in the middle and a short "flat" area. Nicely rounded in short order by the belt.

    Less is better for the belts. Doesn't take much to make them track, but you don't want to put a center curve in the belt. Needing more than 1 degree is probably trying to compensate for some other tracking error.

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  • Shuswap Pat
    replied
    As I still try to figure out the easy way to make a true radius crown - all the literature I have read suggests 1/8" per foot on the diameter (taper) - on a 2 foot wide roll, the center would be 1/8" larger than the ends.

    We used to do 'Slow down Belt' rolls, they are 5-6' wide, 12 1/2" diameter. They would get a trapazoidal crown - tapered ends, 1/3 flat in the middle.

    These belts were about 8' centers, so they were almost as wide as long. We always managed to get them to track.

    My challenge is always to come up with the 'Manual way' to show some of the 'CNC' guys what a real machinist can do.

    Patrick

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  • sasquatch
    replied
    Re: A few wraps of Duct Tape:

    Now,, i bet Red Green NEVER thought of that one!!

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  • jdunmyer
    replied
    I've put a few wraps of duct tape in the center of a flat pulley in order to form a "crown" of sorts. It worked fine. Belt was 6" wide, handling about 12 Hp.

    Electrical tape didn't work very well, if the belt slipped at all, the tape would wad up and come off.

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