Advice on Belt Tensioners

Hi Guys,

I just wanted to tap into the wonderful font of knowledge that is this forum! I am fitting a belt to my home-made grinder and at the moment the motor is just free standing. This provides (sort of) reasonable tension on the v- profile drive belt. I want to up the tension a little because it is a smidge low but I still need to be able to release the tension quickly to change the speed (stepped pulleys). What would people suggest?

Should I go with a spring system? Should I go with an off-set leaver type thing? Should the tensioner wheel be on the outside or the inside of the belt? I am assuming it should be on the non-drive side of things but I am willing to be corrected on that by someone more experienced!

I will try and get some pictures up tomorrow if needed. The set up is very simple, machine on top of the bench, hole for belt, motor on the floor.

Many thanks in advance,

Barney

What I have done on several motor powered tools is to bolt the motor to a plate, then weld or bolt a hinge to one side of the plate so the motor and pulley can pivot in and out of the V belt. You can use a bar with a slot and clamp bolt to set tension and hold it in position, like an alternator mount on a car. Or slot the motor plate opposite the hinge the other side of the motor and use a length of threaded rod through the plate. A wing nut with lock nut above it can be used to adjust the tension. A heavy spring over the threaded rod under the plate helps lift the motor and keep it balanced while tension is adjusted.

Just my $0.02 worth - your mileage may vary. Good luck with your grinder.

Hi this is one from my album of the Vee Belt clutch on my wood lathe

More pics in my album may be what you are looking for

Not too clear thethe clutch lever goes just over centres and on to a stop that can just be made out in Pic  1

Edited By oldvelo on 12/04/2018 04:42:10

Edited By oldvelo on 12/04/2018 04:48:29

On most of my motor set ups I use the motor weight on a pivoting base to tension the belt. The 10" circular saw has a spring added as the 1.5hp motor isn't heavy enough to prevent belt slip.

Ian S C

Thanks for the replies, I'm not sure the hinged motor idea is going to work that well because the motor is HUGE, a big old 3Hp brute of a thing. I would prefer to bolt it down solidly to the floor and have a separate tension arm I think. Thanks for those pictures Oldvelo, I will check out the rest of your album on the subject!

Hi Barney, once you decide on how it will be secured, to get the correct belt tension as with most things these days there is now an APP for your mobile phone that can tell you when the belt - any type of belt is correctly tensioned

all you do is pluck it like a guitar string - the phone listens to the vibration, calculates its hertz frequency and translates it to tension/force

app is called Gates Carbon Drive and is free, I was a little sceptical at first but it does work, the belt manufacturers list what the correct frequency needs to be

Try it and see

cheers

If you do fit a tensioner pulley put it on the non-drive side of the belt and near the smaller pulley. This gives more wrap round the small pulley. A good source of tensioner pulleys is old car cam belt tensioner pulleys.

I used a Volvo Amazon handbrake lever with ratchet mechanism as a belt tensioner on my Portass Dreadnought lathe. The motor is fixed to a sturdy plate hinged at the back of the lathe. Easy to set the belt tension and lets me change speed on the go without starting and stopping the motor.

Regards,

Mick

Love the re-purposed handbrake lever!

Plenty of good stuff here, thanks! I stopped by the local garage today but they didn't have any suitable wheels in the scrap box. The scrap merchants come round so often these days you need to be lucky to get what you need! Hopefully something will come up soon. Love the name Dreadnought for a lathe as well!

I know, this old chestnut again. How do you tell what the "non-drive" side of the pulley is, as mentioned by Gordon W above? Thanks - Bob

If the rod which provides the tension was telescopic, it could have a spring between the halves to allow more tension without overdoing it. It is difficult to see exactly how the system works, so I'm guessing.

Robert

The belt direction will provide the info you need, the drive belt will be pulled by the motor pulley on the drive side between pulleys, so the non-drive side will be the other leg of the belt.

Emgee

I've used a cable tensioner to good effect, I modified it to push against the back of the lathe and on to the motor countershaft and it can be tightened or loosened in a second to move the belt over

Hi Bob, quite simple really, as belts can only pull and not push, it will be as shown below and if the driving pulley is reversed, the drive side and the non drive side will change places.

Regards Nick.

The slacker side, when running.

In many cases, the weight of the motor, pivoting about a shaft provides sufficient tension.

Faced with a choice between a ratchet or a screw tensioner, the screw gives the better chance of getting the right tension..

Excess tension should be avoided, (usually about 10 mm flex , half way between the pulleys should be adequate ).

Excessive tension merely puts extra load on both sets of pulley bearings, which will shorten their life.

Wherever possible, run the tensioner on the back of the belt, to increase the angle of wrap around the pulleys.

Howard

Hi, I have modified my lathe with a spring tentioner for the direction I use 99% of the time(F). The purpose was to give the lathe a soft start, it works great. I give it slack in such a way at standstill the springed pulley press down on the belt top side right around the middle. Now if you start the lathe that 1st second the belt moves up from the drive torgue it provides a soft start on the gears(Chuck weight counter). I have no problem parting off, it will break the parting tool tip off you feed it wrong, so far no problems.

For reverse(R) I need to do the same from the bottom. Still working on the idea to have both together in one go with two pulleys, I think its possible but tricky.

Edited By Chris Mate on 31/05/2022 21:36:01

A couple of thoughts:
A - If you use a tensioner as suggested above by Vic Newey, and it used in compression (pushed to gether) rather than tension, don'have it unscrewed very far. The threads tend to be rather wobbly (cheap mass production) and a sudden collapse is possible.
B - If you add an extra pulley rather than moving the driver and driven apart, use one with the same V profile and add it inside the belt. V-belts don't like being bent the wrong way. Yes, I know Howard says the opposite ...
Arrange it to be held against the belt by a spring, and then speed changes are easy.

Have fun - Tim

Edited By Tim Stevens on 01/06/2022 21:23:56

Reading what Tim says, automotive V belts are usually tensioned by moving the dynamo or alternator outward. This has two advantages; it tensions the belt and increases the angle of wrap around the pulley of the generator.

For just a two pulley set up, an outside idler increases the wrap around the pulleys decreasing the risk of slip.

(One way of holding a pulley to slacken the retaining nut, is to wrap a belt around the pulley, as closely as possible, to maximise wrap. )

If a V belt is incapable of flexing, it is not much use Very often, because of torsional vibrations, they flap, and survive for long periods..(I have seen such violent torsionals, that the belts actually turn over! )

Polyvee belts,often in serpentine runs in automotive use. are often tensioned by an idler running on the back of the belt.

Howard