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Pulley/Belt choice - Drummond

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Peter Lord08/11/2018 09:26:34
8 forum posts
5 photos

Hi,

I have just got my dad's old Drummond round bed lathe out of storage and with the help of Keith Long I have got it running after dismantling it to fit a new belt.
Because I'm stuck for space, I'm not gearing down an AC motor but I am driving the lathe from a 600W DC treadmill motor which has variable speed from about 100 - 3000 rpm. This works really well.

As you will know, the Drummond has a 3-step crowned pulley. The treadmill motor came with a Poly-v pulley which is meant to fit a ribbed belt.

In practice it does work but the ribs are getting flattened as they pass over the crowned pulley and there is quite a lot of vibration.

Has anyone managed to get this configuration to work?

I was thinking about changing the 3-step crowned pulley for a Poly-v type. Alternatively I could change the motor pulley to a wedge or even a cogged timing belt type? Which pulley/belt configuration is best?

If anyone has a workaround for this I would love to hear it.

Thanks

Peter L

Michael Gilligan08/11/2018 09:45:50
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20113 forum posts
1044 photos
Posted by Peter Lord on 08/11/2018 09:26:34:

[ ... ] I was thinking about changing the 3-step crowned pulley for a Poly-v type. Alternatively I could change the motor pulley to a wedge or even a cogged timing belt type? Which pulley/belt configuration is best?

If anyone has a workaround for this I would love to hear it.

.

"No Contest" Peter ... Poly-v wins

That said, you may get a useful improvement by simply machining the crowns off the pulleys.

MichaelG.

Hopper08/11/2018 10:59:27
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6220 forum posts
322 photos

It's possible the belt is not the source of your vibration. I have run my Drummond M type for years with a poly-V belt running on the original crowned pulleys designed for flat belts.Never had a vibration problem. I run it with the V grooves inwards in the normal manner. Seems to work fine on the old pulleys and grips better than the original flat belts ever did.

You could try flipping the belt over and running the flat side on the pulleys, see if the vibration changes.

What rpm range is the vibration worst at?

Have you tried putting the belt on a different pulley so the motor runs at a different rpm range? I would think the largest pulley on the headstock spindle would be best; get that motor spinning as fast as possible to smooth it out.

Be careful not let the headstock spindle run at much more than 800rpm or those old plain bearings could burn out.

Edited By Hopper on 08/11/2018 11:01:15

Edited By Hopper on 08/11/2018 11:02:28

Michael Gilligan09/11/2018 09:54:42
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20113 forum posts
1044 photos
Posted by Hopper on 08/11/2018 10:59:27:

It's possible the belt is not the source of your vibration. I have run my Drummond M type for years with a poly-V belt running on the original crowned pulleys designed for flat belts. [ ... ]

.

idea Having just seen the photo that you posted on another thread **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=138978&p=1

I have realised the important distinction !!

You are running the belt on a pair of crowned pulleys; so it will behave like a flat belt

But Peter has a treadmill motor with a poly-v pulley [probably quite small diameter], so the dynamics of the drive will be very different.

MichaelG.

Ian S C09/11/2018 10:09:02
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7468 forum posts
230 photos

The Poly - V Belt should be OK as long as it is set up to run on the top of the flat belt pulley;s crown, if it is to one side or the other it will creep up the pulley, then slip down causing extra wear and a variation(small) in speed. Ideally the lathe pulleys would be replaced with Poly - V pulleys. In the space on the headstock you might fit 5 or 6 speeds.

Ian S C

Michael Gilligan09/11/2018 10:15:39
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20113 forum posts
1044 photos
Posted by Ian S C on 09/11/2018 10:09:02:

The Poly - V Belt should be OK as long as it is set up to run on the top of the flat belt pulley;s crown [ ... ]

.

... but, in Peter's current configuration, it will also flex across its width at every revolution [because the drive pulley is 'flat' and the driven pulley is 'crowned'] ... The numbers will be tiny, but this may be the source of the wear and vibration.

MichaelG.

Peter Lord09/11/2018 10:33:54
8 forum posts
5 photos

Hi,

I think the best and easiest solution to my problem would be to replace the poly V pulley on the treadmill motor with a plain "U" profile aluminium pulley for a flat belt. I could invert the ribbed belt so its flat side runs over the pulleys.

I have looked for such a pulley on the internet but have come up blank.
Of course I could make one on the lathe if it was running. A "catch 22" situation!

Maybe someone would like an engineering job and make one for me?
I can supply dimensions. Just name a price.

Hopper09/11/2018 11:02:59
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6220 forum posts
322 photos

It's a rubber belt. It's flexible. It's unlikely to cause major vibration. I'd look elsewhere first.

Edited By Hopper on 09/11/2018 11:22:43

Michael Gilligan09/11/2018 16:25:50
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20113 forum posts
1044 photos
Posted by Hopper on 09/11/2018 11:02:59:

... I'd look elsewhere first.

.

... I will be interested to know what you [or Peter] discover.

Please do note that my suggestion was offered with the cautious qualification 'may'

MichaelG.

Peter Lord09/11/2018 17:32:19
8 forum posts
5 photos

Hi,

Does anyone know where I can buy a pulley like the attached ?

poly v pulley.jpg

Peter L

Robbo09/11/2018 18:54:17
1504 forum posts
142 photos

poly v pulley.jpg = **LINK**

Ian S C10/11/2018 10:47:45
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7468 forum posts
230 photos

Vibration, check the bearings are properly adjusted, headstock, and jackshaft, and motor. Keep the speed down, Hopper says 800 rpm or less, a lot of work can be done at 400 rpm, or less. Use SHARP HSS tools, when this lathe was built model engineers used carbon steel tools, now there's a hint, carbon steel tools run at about half the speed of HSS.

Ian S C

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