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  1. #91
    Quote Originally Posted by Robin Hewitt View Post
    I have never found a pulley separation calculator that got it right.

    This one has it right. Proven a couple of times. Also drawing circles with pulley external dimension / teeth/ as per specs, connecting circles with straight lines at tangential points, deleting unnecessary and using CAD to calculate total length has proven spot on, even for a couple of pulleys where small to none adjustment was necessary.
    project 1 , 2, Dust Shoe ...

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  3. #92
    Lee Roberts's Avatar
    Lives in Wigan, United Kingdom. Current Activity: Viewing Moderator Control Panel Has been a member for 9-10 years. Has a total post count of 2,545. Received thanks 161 times, giving thanks to others 652 times. Made a monetary donation to the upkeep of the community. Referred 10 members to the community.
    Sweeeet find Boyan, I couldn't get my head around it all when trying to work this out, this point and click link is great!

    .Me
    .Me

  4. #93
    That calculator matches the sheet called "Belt Length" in mine:

    http://www.mycncuk.com/threads/5848-...g-belt-lengths

    Looks like there's a slightly discrepancy on the sheet where I did it the other way round. Perhaps I should have worked out the formulas myself, not copied the nearest source...It's two circles and two lines, how hard can it be!

    I think the problem here is more the tolerances on the pulleys and belts - they're not much, but enough to require a small amount of center distance adjustment to get the correct tension.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  5. #94
    Just had a go...



    Anyone want to check it?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  6. #95
    Exactly. There is some small adjustment necessary as pulleys go bigger. So you should include the correct pulley formula in that calculations to begin with.

    Here bellow is a screen snip from the parametric pulley i draw. The formulas are correct for any tooth count HTD 5 pulley

    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    project 1 , 2, Dust Shoe ...

  7. #96
    Just checked, the mess I just posted correctly calculates the total perimiter for what I drew.

    Silvaski - your formula there is helpful for drawing the pulley, as it includes the correction (0.57mm) for finding the difference between the pitch diameter and the actual pulley diameter. However for calculating the center distance and belt length, we only need the pitch diameter (D=N*p/pi).

    Looking at the javascrip on the website you're using (http://www.product-config.net/catalo...r_functions.js), we can see the following:

    Code:
            theta = Math.asin((pitchDiameterA - pitchDiameterB) / (2 * englishDesiredCD));        costheta = Math.cos(Math.asin((pitchDiameterA - pitchDiameterB) / (2 * englishDesiredCD)));
            desiredBeltLength = 2 * englishDesiredCD * costheta +
                    Math.PI * (pitchDiameterA + pitchDiameterB) / 2 +
                    theta * (pitchDiameterA - pitchDiameterB);
    Their expression for theta is the same as my alpha.
    For the overall belt length, the 2*CD*costheta is the same as my formula for 2*L, they just used trig not Pythagoras.
    The expression pi*(D+d)/2 matches my formula - they've just factorized it and used diameters not radii.
    The last item, theta*(D-d), is the extra length to account for the small angle of belt that is used due to the difference in pulley diameters. Again, if you re-arrange my formula then this term falls out. You can see if pulleys are the same size, i.e. d=D, then that part of the equation is zero.

    So their formula is identical to what I just derived.

    Then they round to the nearest integer teeth belt size and use some crazy looking formula to back-calculate the center distance.

    Code:
    v = 4 * beltLength - 6.28 * (pitchDiameterA + pitchDiameterB);        centerDistance = (v + Math.sqrt(v * v - 32 * (pitchDiameterA - pitchDiameterB) * (pitchDiameterA - pitchDiameterB))) / 16;
    Whatever floats their boat...
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  8. #97
    What's up gang , I'm in London on holiday and just ordered a nice vice from rdgtools and some clamps for this upcoming machine , at least make use of the free shipping haha.

    Anyone got suggestions on useful things to get from the country but not so heavy?

  9. #98
    A DTI to square up the vertical face of the vice jaw to the spindle (swinging finger type rather then vertical plunge type), plus some parallels to raise work up in the vice but keep it parallel to the base of the vice.

    And sorry about the rain over here, it's supposed to be summertime.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  10. The Following User Says Thank You to routercnc For This Useful Post:


  11. #99
    Quote Originally Posted by routercnc View Post
    . . . . some parallels to raise work up in the vice but keep it parallel to the base of the vice.
    .
    Thanks for that routercnc, as a lay man I've often wondered about the purpose of these "parallels" that folk keep on mentioning, but hadn't yet got around to finding out. Now their purpose makes total sense, and here's a video.
    .
    Machining Tips: What Are Parallels Used For? https://www.youtube.com/watch?v=nlLVEXXlFnY
    .
    Cheers, Andy

  12. #100
    Quote Originally Posted by routercnc View Post
    A DTI to square up the vertical face of the vice jaw to the spindle (swinging finger type rather then vertical plunge type), plus some parallels to raise work up in the vice but keep it parallel to the base of the vice.

    And sorry about the rain over here, it's supposed to be summertime.
    Thanks I already got those covered before. no worries about the rain so far it hasn't bothered us and the weather overall is a step up from the humidity and heat lol. although it's quite fascinating how it alternates between cold and hot during the day and even both at the same time!
    do you feel its like that or are we imaging it cause we are new to the place?

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