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Drunken pulley

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Martin Dowing15/04/2021 13:53:57
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355 forum posts
8 photos

I have one old machine which has a pulley problem.

Hole for axis is not true to tthe plane on which transmission belt works and this results in wobbling.

Pulley works with V-belt and has 5 inch diameter and a "total runout" of wobble is 2mm (~1/12 inch).

Distance between centers of both pulleys is 10 inches and second pulley has a diameter of 1-1/2 inch.

Quite annoying situation.

Would you leave it as it is or repair faulty pulley by drilling larger hole, soldering in or loctiting core and drilling it again?

Does such a wobble affect bearings causing faster wear or can it be ignored?

What about expected wear of transmission belt?

Many thanks for any comments.

Emgee15/04/2021 14:10:17
2195 forum posts
272 photos

Martin

You don't say what rpm the drive is but if an electric motor most likely 1425 rpm, this will create a fair bit of heat into the belt which in turn will conduct to the spindle being driven via the pulley.

If you have the means it would be straightforward to bore and sleeve the pully and re-bore to suit the driven shaft.

Emgee

Pete White15/04/2021 14:17:09
149 forum posts
16 photos

I am not a perfectionist but it would irritate me if the pulley had an head ache and would have to fix it with a bonded in bush bored correctly to the rim, I would not drill it !

I am guessing that the machine doesnt run 24/7 ? so would not worry about wear issues myself, belt will last for "ages".

Others may have different thoughts, as just seen above heat issues ?

Pete

 

Edited By Pete White on 15/04/2021 14:17:44

Edited By Pete White on 15/04/2021 14:20:29

larry phelan 115/04/2021 14:33:09
1115 forum posts
14 photos

That would drive me nuts ! even looking at it.

I would bore it out and fit a sleeve to be bored [not drilled ] to the correct size.

Not that big a job and at least, you know it,s right

Howard Lewis15/04/2021 15:32:18
5545 forum posts
13 photos

If there is enough metal outside the present bore, I would make a bush, turning the OD and the bore without disturbing the work inn the chuck. In this way, OD and bore will be concentric.

Choose the OD to keep a sensible wall thickness for both e bush and the boss of the pulley.

Bush length should be same as that of the boss of the pulley.

Measure the OD that you have produced.

Now e get into the Catch 22 land if the pulley is part of the drive to the lathe!

The pulley needs to set in the chuck, or under a milling machine so that the rim of the pulley is square to the required axis. Bore the pulley.

If you are going to Loctite the bush into the pulley, bore it no more than 0.003" (0.075 mm) larger than the OD of the bush.

If the intent is to make the bush an interference fit in the pulley, bore the pulley to 0.0005" SMALLER than the OD of the bush.

If the pulley is alloy, don't overdo the interference, for fear of cracking the pulley!

The bush goes into the freezer overnight. Before taking the bush out of the freezer, put the pulley into a pan of water and boil it for at least 10 minutes.

You may want to make up a simple puller, as a "Just in case". A length of studding (M8? ) and two large washers and nuts.

Then remove the bush from the freezer, and then the pulley from the hot water and press the two together. If you are lucky, the bush will just slide into the pulley. If there is any resistance quickly thread the studding through the bush and pulley, Have spanners to hand. (Fit one washer and nut to studding, in readiness first! ) then fit the second washer and tighten the nuts to pull the bush into the pulley.

If the pulley bis locked to the shaft with a grubscrew, you will need to use the existing tapping as a guide to drill and tap the bush.

Hopefully, by now you will have a pulley that runs true, and is ready to refit.

Howard

Martin Dowing15/04/2021 19:31:29
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355 forum posts
8 photos

Thanks for comments, all of you.

It is also very annoying for me and I will bore hole and install a bush like all of you are suggesting.

Martin

Edit:

Howard,

I will fit bush easy  -  have access to liquid nitrogen if needed.

Tried few times and interference fit is very nicely made.

Loctite or that. I am considering loctite because pulley is made of cast iron and interference fit could crack it.

Pulley is not from lathe. Just 50 years old pump. There is a belt guard so it would not be seen while working. Still very annoying.

Martin

Edited By Martin Dowing on 15/04/2021 19:56:33

not done it yet15/04/2021 21:06:22
6438 forum posts
20 photos

Pulley is not from lathe. Just 50 years old pump. There is a belt guard so it would not be seen while working. Still very annoying.

Been in use 50 years? How long does the belt last (or how long has it lasted)? You are suddenly starting to worry about it?

Power and belt section might be important factors to consider - presumably it is not a thick section and very low power? Leave well enough alone. It’s not broke so don’t need fixing. Put the guard back over, where it was, and carry on.

Robert Dodds15/04/2021 21:23:51
301 forum posts
55 photos

Martin,

Are yo sure the wobble is in the pulley and not due to the shaft that it sits on being a bit bent?
At least check the shaft for concentricity before boring out or modifying the pulley
Bob D

Hopper15/04/2021 23:11:03
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5505 forum posts
137 photos

There are applications where pulleys are at 90 degrees to each other, such as tranferring drive from a horizontal shaft to a vertical shaft. Yet others run the V belt crossed to reverse direction of rotation between two shafts. So 2mm runout on a pulley is not going to cause any kind of unacceptable belt wear. The belt is rubber. It bends and flexes. It's on a 50 year old pump that has been running just fine. Leave it alone.

If it were the drive on your lathe, you might have cause for concern about vibration being transferred to the turning job and surface finish patterns etc.

But if you just want to do the job for the sake of doing it, make sure as Bob D says, the shaft is straight, unburred and unworn first. And check the pulley rim is not bent or warped. Then fit an undersized bush and bore the ID out to final size after fitting, setting the rim of the pulley true on the faceplate first. Those bushes don't always press or shrink in dead straight and true.

Martin Dowing16/04/2021 07:57:01
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355 forum posts
8 photos

@not done it yet.

It was left in my dad's shed and forgotten.

Seen daylight again only recently.

@Robert.

Definitely pulley.

Other pulley fit on this shaft doesn't wobble but I need this pulley for something else.

@Hopper,

Pump was not used for very long time, possibly for 40 years, so I will have to test it after running it for an hour or so.

But thanks for your remarks. There is a belt guard, so it doesn't annoy my eye once covered.

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