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Best way to make a pulley for round belt

Inspired by Nick, I'm going to make a tramp oil skimmer for my mill. I've scrounged a length of 7mm dia. PU belt that I'm going to use but I don't have any pulleys, so I plan to turn up a pair. I'm going to use Delrin and need to cut the correct profile which is a shallow flat sided V groove 7.2mm wide at the top with a 3.4mm rad at the bottom; obviously I won't need to be too accurate as the power transmitted is negligable. I was thinking of cutting this in 1 hit by grinding a form tool for the correct profile but I'm not sure if that's the best way; I seem to remember reading up on cutting V belt pulleys somewhere but can't find the article any more. Any hints as to the best approach? Martin

Reply to
Martin Whybrow
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Naw, just plow in, it's only Delrin.

10,000 rpm, 10 ft / im feed, back of a garden rake for a tool - priceless

. Regards,

John Stevenson L Stevenson [ Engineers ]

Reply to
John Stevenson

I just used a V-shaped lathe bit. The angle was 60°. But I found out that you will need to transmit *some* force. When you let sit the PU-belt for a while under tension, it will get deformed and then will slip. So you need a bit rough surface. I made mine out of aluminium and will see wether sand blasting them cures the problem. Some radial scratches with a scriber solved the problem for now. :-)

Nick

Reply to
Nick Mueller

Professor Chaddock recommended a 30° included angle for the round belt pulleys on the Quorn. I used this angle for the pulleys on my cobbled together toolpost grinder and it seems to work. You may need a bit more tension if the belt is slipping after deforming when stationary.

Mark Rand RTFM

Reply to
Mark Rand

Oh sorry! It was 30°. It slips with all the oil on the belt. If I would tension the belt more, it only would be deformed more and I'm fearing a too big radial load on the tiny gearbox of the motor. So it's best not to use a too slippery material for the pulleys. Maybe CI would be better or an even sharper angle than the 30°

Nick

Reply to
Nick Mueller

That explains the rake embedded in my shed roof then...

Reply to
Steve W

Some of our tramp skimmers use a poly timing belt with a smooth steel pulley that just hangs in the belt loop to tension it. A piece of plastic rubbing against the smooth side of belt to scrape along with a troth to catch the oil and that is a skimmer.

Another design I tend to like has two smooth pulleys that are on motor outside the sump and on a spring loaded extension below the sump. Between them an endless loop of plastic runs. This way the plastic scraper can scrap both sides of the belt.

Wes

Reply to
Wes

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