Measuring V belts

A recently acquired machine is fitted with a V belt (I think A size) that seem rather wide for the application. I'm considering changing it to a narrower one. (I think this will be (Z section). What is the collective advice on ensuring I order the correct length? Should I measure the existing belt and do some mathematical gymnastics or would it be better to I make a calculation measuring the two multi-step pulleys?

Plenty of guides like this one **LINK** on the net.

Yes I agree but at what point along the V side do I measure the pulley diameter?

I would recommend a link belt, the proper red fibre ones which are available from RS (though cheaper suppliers may exist!). You only need to know the approximate length as you can adjust the belt and they give smoother drive, and on machines like the Myford you can avoid major dismantling to fit.

BTW older Myford use A section belt and if you buy link belting for the Myford often this gets supplied, but the new big bore lathes use Z section I believe and A section is too big as you mention. Also the plastic link belt is too stretchy.

On the basis that the belt will normally sit down in the V such that the top edges are vaguely level in use I would use the outer pulley diameters minus 2 belt thicknesses (ie this will give the pulley inner diameter) to calculate the inner length of the required belt. Belts are defined as Section x length. Which machine are we talking about?

Edited By KWIL on 30/01/2017 09:53:26

Hi all, working out the correct belt size is a forgotten Black art........nothing worked for me properly.......

Found it easier in the old days to take the machines and yes 3 ton Tractors as well to the parts place to get the correct belt....

Now the nice people let me take a dozen belts and take back the 1's that don't fit........I'm doing this about twice a month..........my parts place is 15 miles away........it's less stressful this way, well for me........

not the answer u want but hey, ho.........clogs

Are you changing the pulleys? A Z section belt will not fit A section pulleys! It may drive when you first fit it but it will very soon end up trying to drive on the bottom of the pulley and it will start slipping

Most of the online belt calculators are set up to work from the outside diameters of the pulleys.

Or you can wrap a flexible tape measure or dress maker's cloth tape measure around the outsides of the two pulleys following the path of the outside of teh belt. Then deduct about an inch from the measurement, because belts are actually sized by the 'cord" measurement (aka pitch measurement, aka datum diameter), which lies a bit below the outer surface of the belt. How much below depends on the size and profile of the belt. That's the way it's done around here anyway. It works for me.

Easiest way is to take the old belt to the belt shop and ask for one the same size as this.

Edited By Hopper on 30/01/2017 11:48:53

This belt length calculator is easy to use and covers various belt sections:

**LINK**

Most manufcaturers seem to specify the Inside (nominal) length.

Thanks for all the input. The machine in question is a Dore-Westbury mill. The belt width that's currently fitted seems to be wrong on three counts.

a) Wisdom from elsewhere suggests the 1425rpm 1/3HP should be sufficient yet the stiffness of existing 1/2" wide (A section?) belt seems to sap an awfully large amount of the power available.

b)The existing belt rubs on the side of the larger/adjacent step on the multi-step pulley.

c) The existing belt seems to sit quite high within the V groove.

I'm rather taken with the suggestion by Clogs and see if a local supplier will let me have a few on a Sale ot Return basis.

Perhaps there is another Dore-Westbury owner lurking here that could give "chapter and verse".

I have just bought a Dore Westbury Mk11.

It came with all the plans and books and I have just looked it up. The book says it is a M 46 V belt,

Googling that produces 10 x 6 x 46" Z or 1168mm. They seem quite cheap on eBay so I will get on and order one and report back as mine looks and sounds knackered. I don't have a belt supplier that I know of to go to 'borrow' any from.

Edited to add £2.35 inc p&p  we will see what turns up!

Edited By Phil JOHNS on 30/01/2017 16:04:32

I've used beltingonline previously for timing belts and pulleys. Quick - and reasonable prices.

They have a handy v-belt identification page.

Hi, the may help.

Regards Nick.

A bit more delving a little earlier reveals a very faint A43 on the current belt. This confirms my original speculation of an A type belt to be correct but also suggests the horizontal arm on the Dore-Westbury Mk1 is shorter than its later brother owned by Phil JOHNS. When I'm back in the workshop, using the information gleaned here, I'll measure the length that I need in a Z section belt and try to find a local supplier. I'm hoping I can get the calculated size plus one size up and down on an SOR basis to find which one is best.

I didn't want to go though the trouble of measuring pulleys and center distance and then doing the calculations so I fitted a link type belt to my bandsaw. The belt whipped so violently and vibrated enough I thought the saw would destroy itself. Don't repeat my mistake.