New Build 1000x600x200mm (newbie)

[Boyan Silyavski]

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.

[Robin Hewitt]

This one has it right.

I have book marked it and I will give it a try next time I set a pair of pulleys.

It took me a while before I could bring myself to mount pulleys with absolutely no possibility of adjustment, but now I can't imagine why

[Noplace]

Quick question gentlemen, on my long axis I have a motor ballscrew setup for each side, what is the best way to align & make parallel both rail blocks/side plates/etc before attaching the gantry pieces and make one of the motors a slave? should I get a long machinist square? I don't have one that would reach all the way to the other side atm but would that suffice anyway?

thanks!

[Lee Roberts]

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

[Jonathan]

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.

[Jonathan]

Just had a go...



Anyone want to check it?

[Boyan Silyavski]

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

[Jonathan]

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:

        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.

v = 4 * beltLength - 6.28 * (pitchDiameterA + pitchDiameterB);        centerDistance = (v + Math.sqrt(v * v - 32 * (pitchDiameterA - pitchDiameterB) * (pitchDiameterA - pitchDiameterB))) / 16;

Whatever floats their boat...

[Noplace]

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?

[routercnc]

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.