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  • #16
    deleted
    Last edited by Mcgyver; 11-30-2021, 06:31 AM.
    in Toronto Ontario - where are you?

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    • #17
      Basically, two flat belts on one pulley is not a great idea. If it is crowned, then both of them will try to reach the peak of that crown. In short, both of them will want to run on the center. They will rub against each other and probably produce dust of whatever material they are made of.

      Can you make it work? I really don't know. Perhaps you can. I suspect it will take a lot of effort and you may need to make two, three, four, or more versions of each pulley before you can get it to work - after a fashion. You could easily spend double or triple the cost of a flat belt in the metal needed to make these pulleys.

      If I were going to try this, I would make the pulley about 3 inches wide with two 1.5" wide sections, each with it's own crown and a valley between them. In theory, that can work. Each belt would try to ride on it's own crown, leaving about a half inch clearance between them. But I would not try it.

      I have no experience on matching the size of two flat belts. I do know that vee belts are sold in matched sets. But then again, many will say that is not necessary if you just use the same part number. A bit of break-in and they are then all the same size.

      Perhaps there is a pulley design which can make the two ride close to each other. I do not know. Bented's design looks good until you realize that the belt must enter and exit the channels he has created. And those channels have sharp corners - 45 degrees, but still sharp. That is a point of wear for the edge of the belts. There is going to be dust there. And the edges of the belts are going to wear to a rounded edge which will start to fit that 45 degree angle. Sooner or later is may start to climb it. And once it starts climbing, the self steering mechanism that keeps the single flat belt on a crowned pulley, will rapidly pull it over the top of that edge flange. At that point, if you are lucky, the belt will break. If you are not lucky, the pulley or it's shaft will.

      You can get a serpentine belt at any auto parts store that is a lot stronger and can transmit a lot more power than the old fashioned leather belts. I got one for my SB lathe. It is about 1" wide (25mm?) and it works perfectly on the original, crowned pulleys on the lathe. I have never had it slip. I believe it cost about $20 and after about 15 years of use, it still looks perfectly new. It will probably outlast me. I run it with the flat side against the pulley and the grooved side to the outside. It seems to work better that way. I did have to disassemble the headstock to install it but that was a good thing because I discovered the oilers were worn out and their springs were starting to scratch the spindle bearing surface.
      Paul A.
      SE Texas

      And if you look REAL close at an analog signal,
      You will find that it has discrete steps.

      Comment


      • #18
        Hmm. Like everything I try there is a lot more to it than I thought.

        You can get a serpentine belt at any auto parts store that is a lot stronger and can transmit a lot more power than the old fashioned leather belts. I got one for my SB lathe. It is about 1" wide (25mm?) and it works perfectly on the original, crowned pulleys on the lathe. I have never had it slip. I believe it cost about $20 and after about 15 years of use, it still looks perfectly new. It will probably outlast me. I run it with the flat side against the pulley and the grooved side to the outside. It seems to work better that way.

        I was advised in another thread that the 1 inch wide steps on my small lathe were only good for transmitting around 1/3 hp. This setup is much bigger so I assumed the 1" belts on there own would not suffice.

        These belts I have are composite. 2 different materials with a steel mesh band in the middle. Seriously strong and seriously grippy.

        @ Paul A......What size is your setup that's running the 1" belts?

        If I can get away with single 1" belts that's great!
        Last edited by Jonesy; 11-30-2021, 07:07 AM.

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        • #19
          The Smart & Brown model A lathe uses a 1" wide flat belt with a 1 1/2" hp three phase motor and the primary from the motor is a single 1/2" wide vee belt. As the lathe is about 73 years old, I don't fully tension the flat belt, prefering to let it slip before anything breaks. I can take a 0.020" depth of cut in 2" diameter mild steel before the belt slips which is plenty for me. The flat belt is two speed and both double pulleys are crowned, but the bottom one also has outer flanges, probably only for making changing the speed easier as the belt never contacts the flanges while running.
          Last edited by old mart; 11-30-2021, 02:44 PM.

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          • #20
            Originally posted by Jonesy View Post
            Trying (as always) to work with what I've got. And I've got tons of 1" composite belt.

            The pulleys arn't made yet. I can make straight flanges no probs (but not to Bented's standards!).

            There will be an idler / tensioner on the ouside of the belt(s) on the slack side to give more contact on the smaller pulley. Maybe this will help with keeping them in place on pulleys with straight flanges.

            I know this is doing it the hard way but I always do everything the hard way. Makes life more fun. Buying is boring.

            @Bented.... is that design for 2 belts side by side?
            Can you make the pully with two separate center crowns, one for each belt, rather than the side edges? Neat thing about what you're doing is that if it doesn't work you can always start over. Thanks for sharing your experimenting experience with us.

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            • #21
              Re Old Mart's post about .02DOC into 2" diameter. A quick check of a couple of online calculators suggests that the power needed to make such a cut is only using around 0.13hp over and above what is needed just to keep the lathe turning*. I suspect that it's not unreasonable that just to turn the lathe over without making any cuts likely takes the better part of 1/4HP. And he mentioned that he leaves the belt slightly slack out of concern for the safety of the breakable parts of the lathe.

              So all in all I'm thinking that the previously mentioned figure for 1" belts being able to transfer around 1/3HP sounds about right. So with two belts you'll be able to transmit 2/3's hp.

              But power transfer for flat belts is also highly dependent on the contact area of the pulleys. 2" pulleys won't have a lot of contact area. You mentioned using a tensioner to aid with getting more wrap around the 2" pulley. I'd say that's a good idea if you can't use a larger diameter. But in the end and even with the maximum possible wrap around where you might have 2/3's of the pulley diameter in contact I can't see your 2" pulley with dual belts moving more than maybe 3/4 HP? Is that going to be enough for your intended use?

              Perhaps instead of looking at the motor and assuming that you need to use all of the power you might look at what the job itself would require much like Old Mart has sort of done with his use of a slightly slack belt to limit the power transfer. In your case will the machine and operation you want to run NEED more than the roughly 1/3HP that a single belt can transfer?

              _____________________

              *-Figures I used for the HP needed for the cut were DOC - .02", feed rate .004"- RPM 100 giving a Metal Removal Rate of 0.1. And from a reference I saw on another forum I used a power/in^3/minute of 1.4 to get the 0.13hp needed to make the cut described.

              Old Mart- Just using your figures. Not intending anything other than it got me wondering if there was an easy way to find out how much of an extra load you were causing with such a cut. I hope that you find the numbers pleasantly interesting. It does appear though that you're using maybe 1/4 to perhaps 1/3 of the power you could be getting from the motor.... which is fine. We hobby home machinists use what is handy for parts and safe for the machines. And if you're using a VFD with the motor for variable speed it would certainly give you some extra oomph when running at lower RPM's.
              Chilliwack BC, Canada

              Comment


              • #22
                Jonsey, you're killing me bud. I'm gonna have to stop reading these threads or something.

                Machining can be a fun hobby with a minimum of investment if one invests a lot of time. But, a miserable one with no investment. All this work to save, $20-40? I bought 13' of 2" belt for my camelback from McM for $30. Thirty dollars. By the time you've chucked your stock to make your custom pulley of dubious usefulness, you've already surpassed that mark. I'm sure your country has an equivalent supplier.Just get the right thing. Put your time into battles worth fighting.

                I've been where you are. I'm not yet to the buying new machinery phase, but I'm heading towards it.
                21" Royersford Excelsior CamelBack Drillpress Restoration
                1943 Sidney 16x54 Lathe Restoration

                Comment


                • #23
                  Originally posted by Jonesy View Post
                  Hmm. Like everything I try there is a lot more to it than I thought.

                  You can get a serpentine belt at any auto parts store that is a lot stronger and can transmit a lot more power than the old fashioned leather belts. I got one for my SB lathe. It is about 1" wide (25mm?) and it works perfectly on the original, crowned pulleys on the lathe. I have never had it slip. I believe it cost about $20 and after about 15 years of use, it still looks perfectly new. It will probably outlast me. I run it with the flat side against the pulley and the grooved side to the outside. It seems to work better that way.

                  I was advised in another thread that the 1 inch wide steps on my small lathe were only good for transmitting around 1/3 hp. This setup is much bigger so I assumed the 1" belts on there own would not suffice.

                  These belts I have are composite. 2 different materials with a steel mesh band in the middle. Seriously strong and seriously grippy.

                  @ Paul A......What size is your setup that's running the 1" belts?

                  If I can get away with single 1" belts that's great!
                  Belt width by itself has zero to do with the power it can transmit. How much power can a #8 wire transmit?........Right, without voltage, you have no idea.

                  Power transmission has to do with belt tension and belt speed. Belt width AND MATERIAL affects how much tension the belt can have. The pulley size and rpm affects belt speed, and how well the belt can transfer power into the pulley or out of it.

                  Ideally, the belt should have full tension on it just where it comes off the driven pulley, or begins to wrap onto the drive pulley, and can have zero tension where it begins to wrap on the driven, or comes off the driver. Friction allows the grip on the pulley, but depending on belt stiffness, too small a pulley may not allow the belt to wrap so that it works.

                  The higher the belt speed, the more power it can transmit. In any given setup, the belt and pulley can stand only so much tension before the belt is damaged, or the pulley slips. For 1 HP, you need 33,000 ft-lb per minute. The product of tension and movement has to equal that.

                  For one HP, and 1000 fpm for belt speed, the usual 1" leather belt can transmit about 1 HP. That's with 33lb tension of drive, and the 1000 fpm, or 33,000 foot-lb/minute. When you reduce anything, the power transmitted is reduced.

                  With a 1750 rpm motor, and a 2" pulley diameter, the FPM is about 900. Not bad. With 37 lb difference from tight to slack side tension on the belt, you have your 1 HP.

                  You have 1.5 HP, and 1400 rpm. So, you need 49,500 ft-lb/minute. At 1400 rpm, the 2" pulley gives 730 ft/min. That means you need about 68 lb difference of tension across the pulley.

                  The question is whether the belt will wrap and grab the pulley enough to get the 68lb difference. If you can get that OK, then 1.5 HP is no issue (assuming you can arrange the drive to get the speeds you want without losing capability later in the drive).

                  The reason that the 1" belt is not good for more than maybe 1/3 HP is not at the motor side, but later in the drive, where the FPM is much lower so that it would take an enormous tension to transmit the full 1 HP.
                  Last edited by J Tiers; 12-01-2021, 12:29 AM.
                  CNC machines only go through the motions

                  Comment


                  • #24
                    Originally posted by The Metal Butcher View Post
                    Jonsey, you're killing me bud. I'm gonna have to stop reading these threads or something.

                    Machining can be a fun hobby with a minimum of investment if one invests a lot of time. But, a miserable one with no investment. All this work to save, $20-40? I bought 13' of 2" belt for my camelback from McM for $30. Thirty dollars. By the time you've chucked your stock to make your custom pulley of dubious usefulness, you've already surpassed that mark. I'm sure your country has an equivalent supplier.Just get the right thing. Put your time into battles worth fighting.

                    I've been where you are. I'm not yet to the buying new machinery phase, but I'm heading towards it.
                    MB.... for me this is the most fun bit... seeing what I can get away with from my assortment of stuff.

                    Apart from the tiny initial outlay for the pile of rust that used to be a lathe I've got £0 invested in this.... just a large amount of elbow grease.

                    My projects have nothing to do with money, and I've got no important machining jobs lined up.

                    To be perfectly honest I don't even need a lathe, and now I've got 2.

                    My tinkering is my hobby... keeps me out of the house and in the shop.

                    Like I said.... I'm having fun.

                    Comment


                    • #25
                      J Tiers

                      Wow. Thank you for all that info. I've read it a few times and I think I need to read it a few more times!

                      Comment


                      • #26
                        I second/ third the car poly v belt approach. They're dead cheap, grip very well and don't take a set. You can even make the pulleys to match off you haven't made them yet

                        Comment


                        • #27
                          Well, here's more reading:

                          https://www.plantengineering.com/art...f-belt-drives/

                          This looks like a very solid engineering document:

                          file:///C:/Users/Owner'/AppData/Local/Temp/0000007871.6026PTB-en-0612.pdf

                          Another:

                          https://www.mitsuboshi.com/english/p...V836-E_jis.pdf

                          Without reading in depth, it seems to me that you guys are a bit too pessimistic about the power capabilities of flat belts. But then, a lot depends on the pulley size and linear speed or RPM of the pulleys. And then there is the percentage of wrap. Many variables. That first reference above had a statement about flat belt being rated at 150 Hp per inch. That sounds high to me, but it may refer to operation at the very top end of the speed range. I am not sure how you de-rate it down from there as the speed decreases.

                          In answer to the OP's question, my lathe is a SB-9. It has a 1/2 Hp motor and the speed is reduced with a standard vee belt before the pulleys with a flat belt. Frankly, I am a bit worried that it won't slip if something jams or gets caught up in it. I don't know what will give, but I seriously doubt that it will be the serpentine belt. I would bet on the vee belt to be the weak link in the chain. I have seen vee belts slip many times but not on my lathe.

                          There is a lot on the web if you just search. And read!
                          Paul A.
                          SE Texas

                          And if you look REAL close at an analog signal,
                          You will find that it has discrete steps.

                          Comment


                          • #28
                            Originally posted by Paul Alciatore View Post
                            ...............

                            Without reading in depth, it seems to me that you guys are a bit too pessimistic about the power capabilities of flat belts. But then, a lot depends on the pulley size and linear speed or RPM of the pulleys. And then there is the percentage of wrap. Many variables. .........................
                            Well, Goodyear was just as "pessimistic" as I am. I have a belt drive book from them that explains the flat and V belt operation and limits.

                            Essentially, the belt wrap and friction determine the amount of tension difference that is sustainable around the pulley. Static tension affects that, and belt type affects the allowable tension before permanent "set" in the belts.

                            After all that, belt speed then sets power.

                            I have never seen 150 HP per inch figures, and I'd like to see how they get that. Seems VERY high. Requires high belt tension and high belt speed. REALLY high.
                            CNC machines only go through the motions

                            Comment


                            • #29
                              He only has a 1.5 Hp motor and that is 1/100th of the 150 figure I saw. As I said, it does sound high and I must wonder if it was a typo or was referring to something else; heaven knows what.

                              But 1.5 Hp is not all that far (3X) from what I am running (0.5 Hp) and is also around the numbers I see in other tables, again depending on torque and speed etc. I don't know, but it sounds like it may work. He wants to work with what he has so I suggest giving it a try.

                              Anybody know what loads these serpentine belts drive under the hoods of our cars and trucks? Alternator, power steering, AC: it all must add up to a few Hp. Or what?

                              Here's a quote from Wikipedia: "In a modern automobile, the A/C system will use around 4 horsepower (3 kW) of the engine's power, thus increasing fuel consumption of the vehicle."
                              https://en.wikipedia.org/wiki/Automo...r_conditioning

                              And another quote, "An alternator takes about 1 HP for every 25 Amps of power. At full output, a 100 Amp alternator will need about 4 HP. For a long time, most alternators don't operate at full output."
                              https://homex.com/ask/how-much-hp-do...lternator-draw

                              So, ONE serpentine belt under my hood could easily be transferring over 5 Hp, perhaps as much as 8 or even 10. And, unlike the old vee belts, they seem to last almost to forever.

                              OK, I know the multiple grooves with a wedging effect will provide a lot less slippage than a flat belt, but still, all he wants is 1.5 Hp.

                              Yes, I say give it a shot.
                              Paul A.
                              SE Texas

                              And if you look REAL close at an analog signal,
                              You will find that it has discrete steps.

                              Comment


                              • #30
                                Originally posted by J Tiers View Post

                                Well, Goodyear was just as "pessimistic" as I am. I have a belt drive book from them that explains the flat and V belt operation and limits.

                                Essentially, the belt wrap and friction determine the amount of tension difference that is sustainable around the pulley. Static tension affects that, and belt type affects the allowable tension before permanent "set" in the belts.

                                After all that, belt speed then sets power.

                                I have never seen 150 HP per inch figures, and I'd like to see how they get that. Seems VERY high. Requires high belt tension and high belt speed. REALLY high.
                                When I looked it up, the 150hp figure (if it wasn't a typo) was in conjuncture with a belt speed of 20,000 fpm, which sound pretty high to me
                                'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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