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Alistair Hosie
03-15-2007, 07:43 PM
what are the advantages over belt drive and direct motor drive.I know some people argue that a belt can slip and this can save a motor from burning or damaging a workpiece or tool ,but recently I downloaded two different designs for a small belt sander linisher and one was direct drive with the bottom wheel directly driven from the motor and the other was belt driven there must be an element of favouritism of the designers here what do you guys think Alistair

aboard_epsilon
03-15-2007, 08:11 PM
the belt design plan was done probably to gear up or gear down the motor ...

with a sander the belt will slip ....and your hardly likly to get into trouble with it .like a lathe or a mill.


All the best..mark

BadDog
03-15-2007, 09:00 PM
Several things come to mind. Gearing, clearance/location (do you really want that motor righter there next to your work surface, getting int he way, and catching grit?), common/on-hand frame style, slip, vibration isolation (though probably not critical for belt grinders), and so on.

wierdscience
03-15-2007, 10:04 PM
Belts are less effecient than direct drive for one and direct drive eliminates parts, no pulleys or belts to contend with.

BadDog
03-15-2007, 11:53 PM
Can you quantify the inefficiency? I know there is some, but isn't it negligible for a properly designed belt system? Certainly it’s simpler, as long as it has a face mount (most don’t) frame, long shaft, is sealed and not in the way of work maneuvering. Baring a face mount frame, it’s still doable with a Lovejoy or something, or shaft extension, and a carefully designed and/or adjustable mount for alignment, but now the complexity is creeping back in. I dunno, maybe I’ve just got blinders on, but I like the belts to get the motor well out of the way for full access, and also at least somewhat protected from grinding crud. Belts also givey you easy gross speed adjustments, but I plan to run my grinder with a VFD so it's mostly a moot point for me...

wierdscience
03-16-2007, 01:31 AM
Belt effeciency varies as to type,v-belts are around 96%,poly-vee 97% and flat belts 98%,but that is under ideal conditions which won't always exist over the lifespan of the belt.

Vee belts are lumpy and cause significant vibration unless you use the link type Fenner belts.

You can extend the case bolts on most motors and use them as a pseudo-face mount design if you like.

My own favorite is to use face mount motors.They are 20% more money,but that is more than canceled out by not having belts,pulleys and extra motor mounts and labor to build those mounts.Face mount means one pilot bore and four bolt holes in the machine's frame which can be done easily.

BadDog
03-16-2007, 03:41 AM
My lathe's double spindle belts, at $8 each IIRC, have no perceivable "lump". I know they are pieced, and have no idea the practical limit, but they seem more than up to the chore of driving my lathe spindle, much less a belt grinder. And I recall reading that in some applications, particularly with single phase motors, belts are actually used to isolate the spindle to dampen motor vibrations from telegraphing through.

On a personal note; I also have never understood how “Fenner” belts, which are just a series of lumps, can run more smoothly than a normal belt. I know that’s the general opinion and I’m not denying they do, never checked or tested it, but intuitively it just seems counter intuitive. :D

And I’ll gladly trade even 5% inefficiency to get that motor down below, well out of my way, and away from the abrasive swarf.

Not trying to be argumentative, just debating the point...

I’ll give you the simplicity and compact design, assuming the proper long shaft face mount frame is available. Of course you loose that, at least in part, as soon as you start having to make extensions and adapters. This might be more compelling if you wanted to have a small self contained unit that’s easily moved around as one poster noted on his grinder. And also I’ll give you that there is some small improvement (negligible for this purpose IMO) in efficiency as well as maybe smoother running, maybe. But again, situational modifiers aside (such as needing a mobile platform) I think the remote motor wins in the more important (to me) categories of usability and (potentially) isolation from harsh environment. Then again, maybe I’m just biased because of having grown to completely DISPISE my bench grinder due that that @^@#% motor ALWAY being in the way of how I want to present the work piece to the stone... :D

Your Old Dog
03-16-2007, 05:20 AM
By making it a three wheel grinder you can use direct drive and still keep the motor away from most of the dust. It also allows you to use 72x2" belts much easier then with two wheels. The 72 inch belts last quite long. The Wilton Snag Wheel Grinder is built that way and it worked great for me. Sure wish I still had it.