Pulley question

[toolguy]

I decided to improve my Delta 9" disk/6" belt sander. It suffers from a lot of vibration which I've put up with for many years. I thought I'd upgrade to a larger/heavier machine but that hasn't happened. So I got the idea to change the belt to a link belt. (Let's not get into a debate on the merits of Link belts here. I like them and they have made big reductions to vibrations on machinery where I've used them.) I pulled the covers off to discover Delta uses a ribbed belt with like pulleys on this unit. I pulled the pulleys off and went to a transmission shop. They matched the sizes and off I went with 2 nicely machined 1/2" V groove pulleys. I go to put them on and behold, they don't want to go on the shafts. I have checked them with a micrometer and they seem to be the exact size of the old pulleys. I oiled the holes and shafts and have filed edges of the shafts to ensure I don't have any burrs. They seem to be fine. I haven't resorted to blasting them with a rubber mallet yet. Is this a common problem? Is there a "trick" to getting snug fitting new pulleys on shafts? Any thoughts to resolve this issue will be appreciated.

Neil

[Joe]

Two things you can do...

1. Thoroughly run a file around the shaft to make sure that all areas of the shaft are really clean and bump/burr/muck free. Repeat on the inside of the pulley with a round file. Be careful not to totally ruin the parts... If the shaft has a keyway (which it should!) make sure the keyway is fully clean and that the key is inserted all the way. If the keyway has a "ramp" towards the back portion, the key may walk up and jam the pulley. Try keeping the key out until the pulley is already on if you can (keyway has to extend to end of shaft).

1. Return the pulleys and/or ream them out slightly larger.

Regards, Joe Agro, Jr.

or near NJ and ride a Motorcycle: Life? eMail me!

[Wilson Lamb]

[Teamcasa]

Evidently they are not the same size. If cleaning all the burrs, keyway size and height are correct, then the hole is too small.

Dave (Who won't bother with the link belt issue)

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[Greg O]

Are you certain that the shaft and new pulleys are the right size? I question whether this sander is made "over seas" and may be metric. Greg

[Greg O]

Is this the sander? Model 31-695?

it is then the shafts are definitely metric. Greg

[toolguy]

That's it! Thanks for pointing out my oversight. They measured the old pulleys and assumed they were 5/8". When in fact they are 16 mm shafts. The 5/8" pulleys they sold me are about 15.8 mm. Back to the store!

[No Spam]

No need to use hammers or open out the holes. Just stick the pulleys in a pan of boiling water for ten minutes - they will fly on easily.

[LRod]

...Never to be removed.

[max]

Emery paper on the shaft and heat the pulley. It will expand a couple of thousandths max

[Joe]

Should he ever need to remove the pulley, the heating process might have to be repeated... I'd suggest getting it the right size to slid on at room pemperature the first time.

Regards, Joe Agro, Jr.

or near NJ and ride a Motorcycle: Life? eMail me!

[Backlash]

Oh, the pulley can be removed, all right. I have worked with machinery drive coupling halves of 1,400 lbs weight, with a 12" bore, 24" through the hub, with a 2" square key. They are heated and installed with a .002 inch of shrink fit for each inch of shaft diameter, being .024 undersize in this case. Whenever removal is necessary, heat and a puller is used, same as most cases, just a hell of a lot bigger hydraulic one. Hopefully the pulleys one has aren't potmetal In any case anti-sieze compound should be used for this type of mechanical assembly. It makes installation and removal much easier, and reduces broaching of the bore. In general, keys should be pre-fitted by marking the "top" of the key to retain orientation. Fit the key to the shaft by dressing key and shaft carefully with a file to match, then fit key to hub using same method. Fit hub to shaft by polishing with abrasive cloth, considering whether it will be a shrink or a slide fit. Mark top of key of a slide fit with magic marker and attempt to install pulley over it. Alternately, key height can be measured with the proper tools. If it doesn't go, file the top of the key to remove scratch marks left by the hub until it does. The height of the key should normally be the only factor left at this point, barring unseen complications. This is a tried and true millwright technique that works. I hope this can help someone along the way.

RJ, Millwright foreman of days gone by.

"LRod" wrote in message news: [e-mail]...

[Greg O]

Nope, when you heat a ring shape, such as a pulley, the hole will get larger. Greg

[Richard Cline]

Is that because the air in the hole expands more than the metal and forces it to be bigger?

[bridger]

the hole isn't part of the metal. it's where the metal isn't. look at it like this: say you have a piece of wire. you heat it, it expands and gets longer. now say you bend it into a circle. you heat it, it gets longer. the corcle gets bigger, both inside and outside diameters

[Ken]

Cooling the shaft does work. The mechanics, at the utility where I worked, sometimes wrapped the shaft with dry ice to cool it. A simpler approach is to follow the coupling and bearing manufacturer's recomendations. Instead of the 1 to 2 thousanths of shrink per inch of shaft that mechanics seem to hold sacred, machine it for 1/2 thousanths shrink per inch of shaft with a minimum of 1/2 thousanth as per mfg. recomendations. They also recommend that the coupling, bearing or whatever be heated in an oil bath to 300 to 350 deg F. It's a lot better for the metal than a torch or the shock of a superhot coupling suddenly being slamed onto a shaft that has been frozen with dry ice. With the smaller shrink fit this heating is more than enough to let it slide on easily. It comes off more easily too. I switched to that approach and never had any problems. Warning: Following mfg. recomendation could lead to more serious illnesses like reading instruction manuals.

Ken

[Richard Cline]

Yea but when you heat the wire, it gets thicker. That means one side would move toward the center of the circle.

Dick

[Morris Dovey]

Let me offer another way to think about the problem:

Let's look just at the atoms that make up just the inner surface of a ring. As the ring is heated, these atoms move farther from each other. As they move farther from each other, the circumference of this inner surface increases - and so, then, must the diameter.

[Robert Bonomi]

Wrong! counter-intuitive as it may be, that is *NOT* what happens.

Simple disproof: Consider a _square_ of metal. With a square hole in the middle of it

When the sides of the square expand, the top/bottom move further apart. The part of the sides that are against the top/bottom, expand exactly as much as the top/bottom do. The part of the sides against the hole _also_ expand. When the top/bottom of the square expand, the sides move further apart. The part of the top/bottom that are against the sides, expand exactly as much as the sides do. The part of the top/bottom against the hole _also_ expand.

There's another simple proof:

take a _solid_ chunk of material and draw a circle on it, to "represent" the 'hole'. Now heat it up. what happens to the size of the drawn circle?

Now, for the_hard_ question: Does it make any difference if you cut along that drawn line, before or after you heat the material?

Just cut along the line, leave both pieces where they are, and heat. Hmmm. the center circle gets bigger. yet it still fits in the outer piece. The hole _must_ get larger, too.

[Old Nick]

On Tue, 29 Mar 2005 21:42:07 -0800, Richard Cline wrote something ......and in reply I say!:

But it expands the same proportion both lengthwise and widthwise. So the length increases by far more than the width. Hence the hole gets bigger, because it's effectively a wrapped round side of the rod..

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