Flat belts

[Jonesy]

Well I am giving it a shot. Absolutely nothing to lose.

I will keep it very simple to start. Single 1" belt from motor to C/S, and a single 1" from C/S to lathe. I crowned the C/S steps quite heavily and it's now sanded and varnished. Actually quite nice to look at.

Will make the large pulley next and crown that as well.

Seems to be contradicting theories both here and in internet searching regarding whether to crown the drive wheel, the driven wheel, the largest wheel, the smallest wheel, all wheels or no wheels.

In old VHS video recorders (I was a TV / Video engineer for years) the capstan flywheel was uncrowned and the motor pulley was heavily crowned. In other equipment it's the opposite.

The step pulley on one of my lathes is crowned slightly. On the other it's dead flat.

Seems experimentation with crowns and pulleys is the only way to find what works for my setup, and as I said earlier, that's what I enjoy.

[old mart]

Other factors are oil contamination causing slippage and there are also belt dressing products which can be used to increase the friction between the pulleys and the belt. I would go for steel or cast iron pulleys rather than aluminium for a flat belt and crowning the pulleys is essential. There are dimensions available for the crown, in Machinery's Handbook. I have just looked in my copy and there is plenty of info, as expected. They recommend crowning of 1/8" per foot of pulley width.

[The Metal Butcher]

Guys.

We used flat belts for like 80 years straight, and then in low use through today. This isn't some obscure science. Just look in the machinery's handbook.

I will say that my 2" belt on my drill press will slip before the 1hp motor stalls. It does have substantial speed reduction though. So 1.5hp with a 1" belt... good luck. Without rubber or high speeds I'd say not possible.

[J Tiers]

As mentioned, the friction, affected by belt tension, is very important, as is the belt speed, which affects the needed differential tension in the belt.

I do NOT think 1.5 HP is impossible with a 1" belt. It is obviously and clearly "possible", given the right conditions of speed, tension, friction, belt wrap, etc..

The important question is whether your particular situation has those conditions.

The primary drive belt, with the highest belt speed in the system, is the one most likely to be OK. If you can get your 68 lb tension differential, you have the power capability, per the quickie analysis above. The belt type you have (and the structure) will determine if you can do that.

If you look at the belt info in the Goodyear book, it has figures for power capability vs belt width and belt thickness (single ply, double, etc). Why? Obviously width increases frictional area and capability in proportion.

Belt thickness is (with leather particularly) a measure of the allowable static tension*. More tension means more friction and more power capability. But thickness also means that small pulleys cannot be used, the pulley must be larger than what can be used with a single ply belt, which wraps better.

* There are two tensions involved. "Static" tension is the tension applied between the pulleys when the belt is not moving. It transfers no power, but it makes possible the dynamic tension.

Dynamic tension (differential tension) is the difference between the tight side tension and the slack side tension when running. That is the tension which is actually turning the driven pulley and transferring power.

Usually, the dynamic tension does not exceed the static tension, because if it did, the slack side point of contact with the pulley would start to creep around the pulley, reducing the contact area. At some point as that happens, the belt will slip.

That is a little more complicated, because belts stretch. Static tension is taken by both the slack and tight portions of the belt. But dynamic tension is taken by the tight side, adding to the static tension, and subtracting from the slack side static tension. So, the belt will stretch a bit on the tight side, and the effective length gets longer there, while relieving tension on the slack side means it will "spring back" a bit. Probably not all the way in the short time a section of belt is on the slack side, belts commonly require a bit of time to fully recover from tension. That "unknown" affects the behavior of the belt.

[BCRider]

.....Seems to be contradicting theories both here and in internet searching regarding whether to crown the drive wheel, the driven wheel, the largest wheel, the smallest wheel, all wheels or no wheels.......

The step pulley on one of my lathes is crowned slightly. On the other it's dead flat.

The old belt sander I've got was a bear to get to track until I ground/sanded the drive pulley with no belt on it so it was a straight cylinder. Then the sanding belts tracked easily from then on.

If you look around at any number of belt grinder projects on YT or pulley sets sold for such projects you'll find that all the pulleys are flat but for one. The only machines I've seen with dual crowned pulleys seem to be bandsaws.

[J Tiers]

...................... The only machines I've seen with dual crowned pulleys seem to be bandsaws.

ALL the lathes I have seen with flat belt drives from the countershaft have had both the countershaft AND spindle pulley crowned.

You can use just one crowned pulley, and it does seem that most bench belt sanders do that. But I notice that those also have a tracking adjustment which tilts the wheel, as do all the hand-held belt sanders.

I see no DISadvantage in having both crowned, unless you have a shifting arrangement such as fwd/rev that involves shifting a belt across two pulleys. The crown would tend to fight belt shifting, but it can still be done.

If both belts are crowned, the adjustment for alignment only needs to be approximate, and the wheel tilt is not at all critical. Old time farmers did not need a theodolite to align the pulleys from tractor to implement, just get it close and go.

[old mart]

I already mentioned that the Smart & Brown model A lathe has both pairs of pulleys crowned with non contact outer flanges on the lower one to avoid having the belt falling off the pulley when the balt is slackened to change speed. The lathe has a 3 speed gearbox driven by the motor which drives the lower pulley which is 2 speed. Having backgear gives a total of 12 evenly spaced speeds from 35 to 1430 rpm in the earlier models and 50 to 1800 rpm in the later models with the revised and much improved backgear.

[BCRider]

I wonder if there's a relationship with the crowning to length of run with the belt? Or the width of the belt to the run or some other factor I know that my combo disc and belt sander was super fussy and would not hold the tracking for long at all until I cylinder'ized the one pulley. Yet bandsaws with both crowned hold tracking for months at a time.

I recall that my father's large and very old flat belt lathe did not have any crowning on the cone pulley of the headstock. And that was a 3 inch wide belt. And from using it a lot I had lots of time to notice that sort of thing. But if modified to a shorter belt "rear drive" setup versus the overhead shaft setup I suspect it used originally perhaps the shorter run demanded that one of the pulleys be a flat cylinder?

[Jonesy]

I wonder if there's a relationship with the crowning to length of run with the belt?

But if modified to a shorter belt "rear drive" setup versus the overhead shaft setup I suspect it used originally perhaps the shorter run demanded that one of the pulleys be a flat cylinder?

My plan is for exactly that... a shorter belt "rear drive" setup.

Glued up all the discs for the large pulley this evening. 15" approx to be turned down to 14.5". Got to machine a boss to center it on my small wood lathe outer faceplate in the morning, as the inner centers have only got 6" clearance, so 12" diameter max, and also need to machine a boss to fix it to the countershaft which is 25mm.

Getting there... slowly but surely.

Something like this..... with a quick tensioning method for the belt at the top and a sprung tensioner (off one of my scrapped cars) on the slack side of the motor belt.

[J Tiers]

That is the exact physical setup of the Logan, and most older Southbend. A V-flat combo for motor (like SB also) and a flat belt with both crowned, for the short belt to the spindle.

Belt length should not be a factor... but belt type probably is. Sanding belts do not typically have much stretch, especially the ones on hand held belt sanders. Leather and rubber drive belts do. Crowning may work better with a belt that has some stretch.

[old mart]

I had mentioned in post #32 that Machinerys Handbook recommends a crown height of 1/8" per foot of pulley width.

[Jonesy]

Today I hooked up the motor and counter shaft to the Chekko and it moved under power for the first time in an unknown number of years. My home made flat belts and wooden pulleys surprised the life out of me.

The main drive belt from the motor was a slight let down though, as my scarfed joint, although good on the inside, was a bit lacking on the outside and bumps slightly as it rides inside the tensioner pulley. And the joint was not quite as straight as it should be, but it proved the principle. No amount of doctoring the joint was going to fix this. I could move the tensioner to the inside but this would reduce the wrap around the smaller motor pulley.

Before I finished this evening I glued up a new belt, sized to run with no tensioner pulley to hopefully smooth it out.

But, all belts tracked beautifully, including across the 3 step pulleys.

The drive assembly weighs a considerable amount. As a test I just used it's own weight to tension the step belt and it works great. A real unexpected bonus not having to mess around making a tensioner. When I put the lathe to some real work I'll find out if this method will suffice. If I have to make tensioner so be it, but it'll be tensioning the bracketry rather than an idler on the belt.

All-in-all, this is working out every bit as good as I could have hoped. Hopefully get the new belt on tomorrow and grab a few pics.

[jmm03]

pictures would be good...

[MrWhoopee]

I wonder if there's a relationship with the crowning to length of run with the belt? Or the width of the belt to the run or some other factor I know that my combo disc and belt sander was super fussy and would not hold the tracking for long at all until I cylinder'ized the one pulley. Yet bandsaws with both crowned hold tracking for months at a time.

I've been dealing with tracking problems on my Craftsman 6x48 combo sander. The tracking adjustment is crude and touchy. Once I do get it tracking properly, pressure on either side of the belt will cause the belt to creep (iirc towards the opposite side) and the belt will not come back to center without applying pressure to the opposite side or readjusting tracking. I've tried wrapping tape on the center of the upper roller to increase the crown, but it did not seem to help. I haven't looked at the drive roller to see if it is crowned. Suggestions welcomed.

[Jonesy]

I've been dealing with tracking problems on my Craftsman 6x48 combo sander. The tracking adjustment is crude and touchy. Once I do get it tracking properly, pressure on either side of the belt will cause the belt to creep (iirc towards the opposite side) and the belt will not come back to center without applying pressure to the opposite side or readjusting tracking. I've tried wrapping tape on the center of the upper roller to increase the crown, but it did not seem to help. I haven't looked at the drive roller to see if it is crowned. Suggestions welcomed.

I feel your pain.

Before diving into my lathe project I abandoned a 6 x 48 vertical sander project because no matter how much I played with the crown(s) it just would not behave. Just like you, once it ran true it would wander off if I sanded anywhere but in the centre of the belt. The shop bought 3 x 36 at work does exactly the same. Abandoning that was one of the best desicions I've made. Chucking the carcass out for the scrappy was a real moment to cherish.

Good luck with yours.