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Power Transmission/ lathe belt design

Discussion in 'Woodturning Discussion Forum' started by Roger Chandler, Jan 1, 2018.

  1. Roger Chandler

    Roger Chandler

    Joined:
    Nov 26, 2009
    Messages:
    504
    Power Transmisson/ lathe belt design

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

    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.
    TNarrow 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!
     
  2. john lucas

    john lucas

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    Location:
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    Have had lathes with both V and flat belts. Never had a problem with either one. The lathes I have had with flat belts have small V's in the pulley and match the small V's on the belt so tracking isn't a problem. Other than that I can't answer your question.
     
  3. stu senator

    stu senator

    Joined:
    Apr 5, 2011
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    Location:
    Long Island
    Power transmission by belt or chain drives is by the difference in tension between the drive side vs the slack side. This load is the bearing load. If the tension on a belt at rest is so high as to cause excess bearing load the design is NG or the belt is NG

    Stu
     
  4. Richard Coers

    Richard Coers

    Joined:
    Aug 14, 2009
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    426
    Location:
    Peoria, Illinois
    I designed belt drive systems on Caterpillar track type tractors for a part of my career. Horsepower transmission is calculated on first the driven load, then contact area (number and size of belts on tractor design), and percentage of wrap contact with the pulley. Percentage of wrap contact is not an issue with wood lathes, we basically have 180 degree contact. So then the design is based on contact area and load. Load is highly variable based on personal cutting methods and material size. I've not found any lathe manufacturer that has designed for a maximum effort. Any lathe can be stopped with a heavy cut on the max diameter blank. Ask guys who do coring with high friction loads. Coring a 20" blank can easily stop a machine. Finally contact area. A single v belt will not have the rubber contact area of a poly v belt. V belt manufacturing has gotten better, but in the past, the method of manufacturing would often have a bump or issue in the belt. This induced a vibration. Poly v belts have never had that issue based on manufacturing and thin cross section. With more contact area, you need less tension. Wasn't it a Jet issue for a while where they recommended only the weight of the motor for proper tension. That recommendation came out after some bearing failures due to excessive belt tension on a long cantilever shaft. Now your mention of flat belt is fine, but I've never seen a pure flat belt on a wood lathe because of speed. Again the seam was part of the issue. Old lay shaft driven machinery did just fine on flat belts because of lower speed applications and very large diameter pulleys. Many metal lathes do just fine as well. Today you can buy man made flat belts with a vulcanized seam. Each of those is custom made. I can see a wash on v-belts and poly v, IF the v-belt is of high quality. As mentioned, none of them can handle all the torque that can be applied by an aggressive user. I'm certain all the manufacturers use a slipping belt as a safety feature. Super high loads that could be successfully driven, put the operator at higher risks. There are stories far through history about metal lathe accidents. Accidents where the operator had to be cut out of the machine as it would not stop and the limb of the operator was wrapped around the chuck or part.
     
  5. Roger Chandler

    Roger Chandler

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    Nov 26, 2009
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    Thanks Richard for this helpful information.......much appreciated!
     

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