Pulleys and pulley wheels?

I am just about to motorise my 30 year old (NIB!) linisher. Interesting that the lubrication holes for the bushes had not been drilled though!

However my problem is that there is a pulley on the driven roller. Now it is the same size as the belts used on the Myford, so what size belt am I looking at?

Second problem is that I need to put a pulley on the electric motor and arrange for the size of the pulley to give me the correct gearing. So that I get the belt speed correct.

Now I know that the nominal pulley size is not the OD of the pulley, neither is it the diameter of the bottom of the pulley groove. It is somewhere in between. People seem to be very coy about what the diameter of a pulley is. So how do you measure this diameter.

I appear to have, what I would guess to be a 1" pulley on the driven roller. This from past experience of sizes. I know it isn't vastly important to get the belt speed dead on the recommended speed, but it would be good to get it some where near!

As a matter of interest how would you define the belt size required for two pulleys a given distance apart, assuming you knew the "nominal" sizes of the pulleys? It isn't too important as I have long slotted holes for the motor mount, but I would like to know the methodology behind that calculation.

Apologies for my ramblings, for what is basically a simple question.

Regards,

Andrew.

Interesting that the lubrication holes for the bushes had not been drilled though!

Maybe the bearings are oilite type?

Andrew,

Try this www.calculatoredge.com/mech/vbelt%20length.htm

Regards,

Keith.

Hello Both!

I don't think the bushes are olite, they appear to be simple plain bearings of what looks like brass or bronze, certainly not got the honey comb appearance of an olite bush. Anyway, too late, I have drilled through them! A good job I had it apart and cleared out the grease in the bearings! Otherwise I would never have spotted the cock up!

Thanks for the link Keith. I did try Googling, but nowhere could I find the definition of size for a pulley! I must have waded through a lot of sites which simply repeated the fact it wasn't OD or base diameter. Very frustrating!

Thanks both,

Andrew.

Rule of thumb: Wrap a tape measure around the outsides of the pulleys in the route the belt will take and measure the distance around. Deduct one inch and that's about the length of belt you need. If pulleys are the same profile as the Myford headstock to countershaft belt, you will need an A profile belt. If they are are same as the smaller section pulleys on the Myford motor to countershaft belt, it will be an SZ section belt.

The exact point of measuring pulley diameter is, sometimes, the cord diameter which is where the cords inside the rubber belt lie, which is, sometimes, about a quarter of the way down the profile. But different manufacturers use different measurements. Some even use the OD, others the ID, others in between. And there are various standards, which various manufacturers tend to ignore. Hence the rule of thumb above and the need for adjusting slots on the motor!

The formula for calculating the length is complex as the wrap around the circumfrence varies with diameter of pulleys and centre distance. Much better to use the above posted calculator. There are also plenty of online pulley rpm speed calculators. You dont have to worry about where the pulley is measured, as long as both are meausured the same. EG, measure the OD of the one you have and calculate the size you need to get the desired rpm. Answer will be the OD of the pulley you need. It;s all proportional. Difference is only going to be a quarter inch or so due to the cord diameter thing so nothing to worry about. A 10 inch pully is a 10 inch pulley, even if it actually measures 10.3 inches or so. Close enough for a linisher I am sure.

Edited By Hopper on 15/07/2017 12:47:23

Andrew

At the quick and dirty end its probably easier to address the problem by using outside diameter of pulleys and outside diameter of the belt. Won't be dead accurate but I find it better than results from the proper calculators when fed with wrong numbers due to incorrectly specified components.

The proper calculator formulae use belt pitch length and pulley pitch diameter. Pulley Vee angle varies for smaller pulleys made to specification which doesn't help.

Effective belt length is the length about the effective outside diameter of the pulley sheeve at a specified tension and wrap as defined in the specifications. Which is rarely the actual diameter.

Inside diameter is frequently the one given as the nominal size printed on the belt. Probably chosen as being the easy one to measure. Put the belt on a pair of flat pulleys under suitable nominal tension and measure the separation. Add half the flat pulley diameter to the separation. Nominal length is double that result.

I'm not sure that the folk who make belts and pulleys really understand it either :- **LINK** . Frankly if I wan't that much of a headache I'd rather get it the old fashioned way via a bottle of Glenfiddich!

No great help with your pulley problem tho'. Get two of appropriate diameters and allow enough wiggle room to fit. When you get into the lower end of the market there is no telling what you will actually get in pulleys or belts. For one job I ended up with had three pulleys of very different diameters but same nominal size. A section, maybe 3/4" variation from largest to smallest. On another three different lengths of A section belt with same number covering three "proper" sizes. This went down really well as I trying to buy 4L section.

This link is helpful in converting nominal length to outside length :- **LINK** .

Clive.

Hello Hopper

Thanks for your time in setting out the answers to my queries. No wonder people are coy in defining the diameters of pulleys. Seems that standardisation isn't the manufacturers strong point!

Regards,

Andrew.

Hi Hopper try this link ...

http://www.beltingonline.com/vee-and-wedge-belts-213/v-belt-length-calculator-617/

http://www.beltingonline.com/

George.

We all know about standards. You can have as many as you want.

If the pulleys are the same as a Myford 7 Series, they are likely to be A section.

if you are in the market for a belt, take one of the pulleys to a supplier, and cheack a belt against the pulley.

A "B" section section will be much too big for an A section pulley, and a Z will fall down the groove.

The old belt is probably marked with the section and length such "A32" , which should tell you all that you need to know, unless you have changed pulleys, pulley sizes, or motor location.

Howard

Edited By Howard Lewis on 18/07/2017 12:52:16

Now I know that the nominal pulley size is not the OD of the pulley,

Maybe not quite, but for certain it is near enough for a large majority of applications.. Just how far down the pulley groove do new belts run? Not far is the answer! They don't make pulleys which have much wider grooves than the belt section they are designed for, as that's is just a waste of material. That is why V belts are sized on the outside of the belt, 'nest par' (or n'est pas in 'propper' french))? KISS principle in operation again, I think.

Not sure about the honeycomb bit. Porous bushes are generally quite shiny with a very slightly mottled colour. They are formed by sintering under enormous pressure, resulting in them taking up the polished finish of the die they are formed in.

I wouldn't be surprised if you have drilled a hole in a sintered bush but probably no real harm done in this case. Having said that, if I'm correct, you may find the oil now dribbles out of the bearing rather than permeating the bush itself.

Murray

PS: Here's an example of one. 12mm OD, 20-25% porosity:

Edited By Muzzer on 18/07/2017 14:12:02

Andrew if it is any help, my linisher has a 3 3/8 or 3 1/2 inch diameter driving roller, I cannot get at it to be more specific, the linisher has the same size pulley on the roller as the motor, so the ratio is 1:1, and the motor is 1425 rpm. This has served me well for 40 years or more, and seems to be around the right belt speed.

Chris Gunn

Bushmills is just as good for dealing with speeds,feeds,rates,dia,s belts ect,ect,and so on.

Thanks everyone you have all been a real help to me.

Muzzer that is quite a shock. All the olite bushes I have ever seen have been quite obviously porous, when you examine the ends of the bush. You don't need a magnifying glass to see that! If what you say is correct (no doubt you are right!), then what on earth have I been looking at all these years thinking they were olite bushes?

A puzzled,

Andrew.

Andrew,

According to the Myford S7 manual the belt from the motor to clutch is 33 1/2" and the counter shaft to spindle belt is 29 1/2". Both inside measurements.

I have just made a pulley for a new metric motor VFD conversion and found that this was Z profile. The countershaft to spindle belt looks like A profile.

Hugh

Andrew,

Details for v belts is found in the Tubal Cain's Model Engineer's Handbook section 13. The pitch dia l belive is the correct method of measuring belt size/length.

Hope this helps.

Hugh