Power Transmisson/ lathe belt design

[Roger Chandler]

Gates 7M750 PolyFlex Belt - This is the belt on the G0800 lathe - there is a description below..

This Gates Polyflex belt is a power transmission V-belt for transmitting greater loads at higher speeds on small equipment. It is made of a polyurethane compound for resistance to fatigue, wear, ozone, and most environmental conditions. Its precise casting method eliminates layers and overlaps for smooth running and low vibration. It has a ribbed backing for lateral stability and reduced bending stress on small diameter pulleys. The 60-degree angle of the belt provides greater support to the tensile section for an even load distribution and improved wear. The working temperature range is -65 to +180 degrees F. This belt is suitable for use with machine tools, computer peripherals, medical equipment, library equipment, small appliances, blower drives, and woodworking machines.

The trapezoidal shape of the belt's cross section wedges into the groove of a similarly shaped sheave or pulley to provide traction and alignment. This wedging action increases as the load increases, providing higher torque transmission and minimal slippage. V-belts are standard for belt-driven power transmission and can be used in single- or multi-belt systems for increased carrying power. They are found in drive systems in the automotive, agricultural, textile, printing, mining, and office equipment industries, among others.

The Laguna Revo 2436 has a flat poly V ribbed belt that fits into grooves in the pulleys, like we a accustomed to. On the videos I have seen no one has mentioned any issues at all with the G0800 not having good power transfer.

I have been doing some research, but find little info that I can easily digest, so perhaps knowlegeable machine specialists or engineers can speak to the differences or efficiencies of the two types of power transmisson belts used on the two lathes mentioned above. Here is some info I found related to power transmission by belts on pulleys.


The use of flat belts has decreased as most modern industrial equipment has built-in drives or uses V-belts.

The main disadvantage of flat belts is their reliance on belt tension to produce frictional grip over pulleys. The high belt tension required to transmit power often shortens bearing life. Another problem with flat belt drives is their failure to track properly.

If equipment bearings are adequately sized, tensioning requirements should present little problem to the drive. Because flat belts are quite thin, they are not subjected to high centrifugal loads and thus operate well over small pulleys at high speeds in ranges exceeding 9,000 FPM.


Narrow V-Belt

Narrow cross-section V-belts transmit up to three times the horsepower of conventional V-belts in the same drive space, or the same horsepower.
Three cross-sections of narrow V-belts are available, as shown in Figure 18; again all sizes are nominal.

Figure 18: V-Belt Cross-Section

Narrow V-belts provide savings in drive space with narrower sheaves, shorter centers, smaller sheave diameters, and reduced sheave weight which may help decrease bearing loads. Greater speeds can be handled by this type of V-belt; up to 6,500 FPM.

Narrow V-belts have a narrow cross-section, but they sit deeper in the sheave groove than a conventional V-belt. Concave sides are commonly used which makes for more uniform belt wear.
The radius relief minimizes corner wear and the arched top helps prevent dishing and distorting of the tensile member.

A poly V-belt is a single unit with a longitudinally ribbed traction surface. As shown in Figure 26, the ribs mate with sheave grooves of the same shape. These belts offer power transmission capabilities of standard V-belts and the flexibility of flat belts. Uniform engagement of the belt into the sheave grooves and complete support of the tensile member eliminates differential driving and equalizes belt stresses.


Poly V-Belt Advantages

• Reduced belt thickness permits use of smaller sheaves.
• Lighter, more compact drives are available.
• Speed ratios of up to 40 to 1 are available.
• Center distances are reduced; space is saved with no loss in horsepower.
• Even distribution of pressure over all parts of the drive surface provides uniform loading.
• Smooth running, good response to shock loads.
• No belt turnover, smooth tracking.

Okay [sorry for the long post] I am thinking it is basically a wash on power transmission belt design, as both designs seem to carry the same loads, and if I am reading correctly the reason for a 7M750 belt might be because as load increases the torque increases [makes sense with large wood on a really big lathe?] and they both have even load distribution on the pulleys..........

Can you think of an advantage of one design over the other? Okay, I admit, I might be a little bit deep into the weeds here with this, but I am a stickler for performance, and understanding design parameters and rationales is something that helps me make good decisions!

[Brice Rogers]

Hi Roger, It will be interesting to follow this thread.

Automobiles switched to flat vee ribbed (serpentine) belts a while ago, but they had other driving factors, like the percent "wrap" on a pulley, and the total parts count. Flat belts seem to work better than traditional Vee belts in some respects for smaller diameter pulleys.

I suspect that with the G0800 if you get a huge catch that the narrow vee belt may be more likely to Squeal than the Laguna flat ribbed belt. But, maybe that is a good thing for the life of some components. On a catch, something has to give. If it is the belt, it is probably the lowest cost replaceable item.

I suspect that at the end of the day that either belts will work okay. That one may have theoretical advantages over the other but both will work fine.

[Roger Chandler]

The info above states that the narrow V belt [if you notice the larger pic of the ribbed design on top for lateral stability] has greater torque as speed increases.
Related to catches - I honestly don't have one very often anymore, unless I am inattentive or something [now that I've said that, I've likely jinxed myself, and will get one every time out for a while! ] but I don't think that will be an issue at all in any meaningful way for me.

According to the information I read, the narrow V is easier on bearings. Might be good for heavy wood blanks.

[Dennis Ford]

The biggest difference is flexibility, the poly V belts are very flexible and will wrap around smaller pulleys without losing grip on the pulley. The narrow V belts are easier on bearings than traditional V belts, not sure if that also applies to poly V belts.

[Bill Dufour]

A big advantage of flat belts is that they can be spliced and mounted over a pulley like a lathe spindle without dismounting the spindle. People use old auto serpentine belts and lace the splice like a leather belt. Or they use the link belt for vee pulleys.
Bill

[carl mesaros]

Hello again Roger. My Laguna 2436 has the V- Polyflex belt. In 2-1/2 years it has given me no trouble. If I have a catch the belt will squeal slightly but not near as easily or loud as my Jet 1642 did. I seem to remember reading that the Polyflex belt was used in the auto industry.

[Bob Bergstrom]

I not sure the belt design would be a decision breaker. I don’t think a catch would be a good test. I core some good size bowl blanks on my 3 hp Robust and it often sequels and on occasion is overloaded and shuts down. I would think Bret English chose the rib belt for the same reason he chose many other components. He wanted the best that would be best on a wood lathe. I suggest calling him as he would be highly qualified to give the correct answers. Also see if customer service at Grizzly and Laguna can help. I spent a morning at the Robust plant and he walked me through the entire process.

[Jerry Bruette]

The flat belts in your post are the type used on old factory machines that used line shafts and on old farm implements, saw rigs, thrashing machines etc.. They are no longer used on modern machines and have been replaced by V belts. They required alot of tension to prevent them from slipping. They also had problems tracking and staying on the pulleys under a heavy load and that's why some flat belt pulleys were crowned.

The "narrow" V belts in your post are actually what's called a wedge belt. The angle of the V groove is steeper than a standard A, B, or C belt. They transmit power better but can wear the groove faster.

The flat belts have no problem going around any size pulley, but the V belts tend to bulge on the sides when wrapping around too small of a pulley.

This is where the micro groove or as you call them poly v belts come into play. Because the V's are smaller they don't bulge as much as a full size belt and because there are several of them on the belt they can transmit as much power as a full size belt, and still wrap around small diameter pulleys. Sort of like bending a multi stranded wire versus a solid wire of the same diameter. I suspect they were developed for the automotive and small appliance industries where a belt is required to wrap around one or more small diameter pulleys.

When using full size V belts it's fairly easy to see when the grooves are starting to wear and get out of spec., it's harder to see when the grooves on a micro groove pulley are starting to wear out of spec.

But I'd guess that as a hobbyist or even a professional turner you'll never wear out the grooves in your pulleys, I've seen industrial machines that run 24/7 for many years before the grooves get out of spec. and the pulleys need to be replaced.

I think that any smooth sided belt would serve very well for driving a wood lathe, and provide the safety of slipping should you have a catch or other type of incident.

Sorry for rambling on about belts.

[Mel Fulks]

Not a turner, but when I was a kid I worked in a turning and furniture building shop. The lathes had the old flat belts,I think they were leather. They worked well on the beefy old lathes ,some of which were Babbit. We had to keep pine resin on the belts. They lasted for many years and I don't remember them being under a lot of tension. They were really large lathes, the story was the biggest one had originally been powered by water.