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  • Cogged belts

    What sort of tension is necessary on a cogged belt drive?

    I have a motor drive with a cogged (tooth) belt and I'm thinking it's a tad loose...but it's now running so smooth and quietly I hate to screw with it again.

    If I adjust the motor position to the limits of it's travel but with no extra force the belt is quite snug. Slacking it up a bit so that I can squeeze the two sides of the belt in about an inch each runs quite nicely but I don't want to jump the belt teeth either.
    Len

  • #2
    Really tight. They dont do any good if they are loose. We usually set ours so you get a "twang" when you pluck them. Of course this depends on the application too. If it is a tiny little motor or only bushings instead of bearings it might not be so tight.

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    • #3
      Originally posted by macona
      Really tight. They dont do any good if they are loose. We usually set ours so you get a "twang" when you pluck them. Of course this depends on the application too. If it is a tiny little motor or only bushings instead of bearings it might not be so tight.
      Wow, thanks for posting that, I had no idea they should be that tight! I had the motor off my surface grinder to convert it to delta windings and clearly haven't put the belt back on tight enough then (toothed belt).

      Pete

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      • #4
        Originally posted by PeteF
        (toothed belt).
        Pete.
        When you say toothed belt, do you mean a cogged vee belt or a timing belt? One has teeth on the pulleys, the other just plain vees in the pulleys.

        Example of a cogged vee belt here.
        http://www.bosch.com.au/content/language1/html/4662.htm

        Regards Phil.

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        • #5
          Phil, I mean a toothed belt, yes also called a timing belt, but that's just one application for them. I fiddled with the tension a few times and thought the tension I had it at provided the least amount of vibration, but I don't think I tried it as tight as you're suggesting. I would now like to experiment more with this, as you know any vibration is bad in this application so the smoother I can get it the better. It's a much smaller and wider version of one of these anyway.

          Pete

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          • #6
            Go out to your vehicle and check the tension on the serpentine belt. The tensioner should be putting an appropriate amount on the belt. I realize that's probably a v-ribbed belt, but for a similar width and thickness of carcass, the tension would probably be in the same ballpark for a toothed belt. I agree- it should not be loose at all. You should be able to hear the pitch rise as you pluck it while tightening, and you'd want to have it in that range at least. That's pretty vague I know, but it's something you can get used to. If it doesn't 'sing' a little at least, it's too loose.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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            • #7
              Originally posted by PeteF
              I don't think I tried it as tight as you're suggesting.
              Pete. It wasn’t me suggesting that, That was Macona.

              This is on the drive from the motor to the rear of the grinding wheel spindle? Fairly small bearings in the front of the motor. I cant see the need to tension it until it twangs. Its not like its going to start jumping teeth. I wouldn’t be putting that kind of radial load on what should be a precision spindle.

              On axis drives, going to ballscrews I might do that, it reduces tooth creep on the pulleys.

              Regards Phil.

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              • #8
                There are a lot of different things that come into it but span is an important one and I can't imagine it being anything over 16" here so I would not recommend any twang, as the span grows the tension can decrease abit but unless this was designed with this drive setup it can be hard on your bearings to run it really tight. From your description I would shoot for about twice the tension you currently have or max 1/2" deflection when squeezed together in the middle.
                Opportunity knocks once, temptation leans on the doorbell.....

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                • #9
                  Originally posted by Machtool
                  Pete. It wasn’t me suggesting that, That was Macona.

                  This is on the drive from the motor to the rear of the grinding wheel spindle? Fairly small bearings in the front of the motor. I cant see the need to tension it until it twangs. Its not like its going to start jumping teeth. I wouldn’t be putting that kind of radial load on what should be a precision spindle.

                  On axis drives, going to ballscrews I might do that, it reduces tooth creep on the pulleys.

                  Regards Phil.
                  Oh sorry Phil, I knew it started with an "M"

                  I'll take another look at the belt tension when I get a chance. I have to strip the machine slide and get all the grease out somebody kindly put in there, so will have a chance to experiment then. I basically figured that the teeth on the belt would prevent any slipping, so there was no real need for it to be super tight, unlike a V-belt which would slip. Having it a little looser would also help to isolate the motor from the spindle a little better too. When I was experimenting with the tension that certainly seemed to be what I was finding, but again, didn't try it super tight so not sure how that would go.

                  Pete

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                  • #10
                    You would really have to have the belt super tight before you would come even close to the radial load on a spindle. You will probably break the belt first.

                    If you are running standard trapezoidal belts like MXL, XL, and L series belts know that they do run a little noisy. Thats one of the reasons for HTD belts and why they are used in spindle drives.

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                    • #11
                      I just finished installing a new timing belt of the "toothed" type on a Nissan Xterra yesterday. The belt has an automatic tensioner spring that tensions the belt before you lock the tensioner down. When finished I was curious as to how tight he belt was. I found that the tension was much like the same type of belt used these days as a final drive on Harley Davidson motorcycles. A good test, the same one I performed yesterday on the Xterra, is to attempt to twist the belt 90 degrees. You should feel high resistance when you get to the 90 degree point.
                      Technically, Harley uses a gauge to measure resistance to deflect the belt a specific distance to insure correct tension. I believe the numbers are 10 pounds and a deflection of 3/8", but am not certain.

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                      • #12
                        Originally posted by macona
                        You would really have to have the belt super tight before you would come even close to the radial load on a spindle. You will probably break the belt first.

                        If you are running standard trapezoidal belts like MXL, XL, and L series belts know that they do run a little noisy. Thats one of the reasons for HTD belts and why they are used in spindle drives.
                        So decently "snug" would be OK then?
                        It's the main drive belt on my lathe but the v-belts for the stock speed reduction slip long before that belt will suffer damage.

                        Thank you all.
                        Len

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                        • #13
                          +1 for the 90 degree twist, that's the way I learned it and it works.

                          Cheers,

                          Benta.

                          Comment


                          • #14
                            In order to give an accurate answer one should be aware of several factors that come into play when asking how tight any belt should be.

                            Some of these factors are, span between pulleys or sprockets, load to be transmitted, rpm range of drive and driven members, belt width. Is the belt dive to be used for registration as in a stepper motor drive?

                            Lastly, belt drives are somewhat forgiving in nature. As long as one is reasonably close and uses a bit of common sense one should not be overly concerned radial bearing load.

                            I've included a link to a pdf file that discusses some of the issues involved in timing belt tension.

                            http://www.sdp-si.com/D790/PDF/D790Tech.pdf

                            Remember this is not a definitive guide for everyone's particular situation, just a guide to illustrate some of the parameters involved.

                            Personally I've always used the "1/64" deflection per inch of span" rule combined with an educated feel with good results. I know, vague as the day is long.
                            Home, down in the valley behind the Red Angus
                            Bad Decisions Make Good Stories​

                            Location: British Columbia

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                            • #15
                              Originally posted by firbikrhd1
                              A good test, the same one I performed yesterday on the Xterra, is to attempt to twist the belt 90 degrees. You should feel high resistance when you get to the 90 degree point.
                              Surely that will be highly dependant on the width and span of the belt? In my case it's a wide belt and the two pulleys are sitting right next to each other; there's no way I could twist the belt, even a small amount, unless the belt was stupidly loose. With something like a motorcycle final drive I can well imagine this would be a valid test, but basically unique to that particular application. Conversely I used to use these as precision drive belts in electronic equipment, and you'd be able to turn those little suckers several times yet their tension was quite high.

                              Pete

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