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Advice on Belt Tensioners

Trying to make a belt tensioner for a v-belt drive

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Barnabas Taylor12/04/2018 01:26:32
30 forum posts
8 photos

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,


Jeff Dayman12/04/2018 04:03:06
1850 forum posts
45 photos

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.

oldvelo12/04/2018 04:39:19
230 forum posts
51 photos

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

Ian S C12/04/2018 10:22:33
7468 forum posts
230 photos

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

Barnabas Taylor12/04/2018 10:24:40
30 forum posts
8 photos

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!

Trevorh12/04/2018 10:58:02
302 forum posts
87 photos

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


Gordon W12/04/2018 11:56:32
2011 forum posts

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.

Mick Dobson12/04/2018 22:04:12
21 forum posts
10 photos

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.




duncan webster13/04/2018 00:42:18
2733 forum posts
40 photos

Love the re-purposed handbrake lever!

Barnabas Taylor13/04/2018 03:15:41
30 forum posts
8 photos

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!

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