Variable speed V Belts- Angle ?

Somewhere I read the angle on a metric variable speed belt is 22 degrees. If so, this makes no sense whatsoever based on my measurements of metric belts. I've got a pretty accurate high end dial type protractor and I'm measuring 76 degrees (or 14 if you change orientation, which I presume is where 22 comes from) on most. I did measure 72 on the most extreme angle one (or here again, 18 if looking at it another way)

So, where did the 22 degrees some from ??

Also, I measured one brand new inch type variable belt and the angle was only 83 degrees (or 7) !

Also interesting in this is that nobody that sells the things can answer the question of angle ! I've talked with four different companies, including AMetric and Motion....and they can't find the angle specs. AMetric is supposed to pull one out and actually measure the angle of the V, but a day later they have yet to do it.

Another thing....say I need a belt 33 x 8 x 800 mm....but all I can find is 33 x 10 x 800. Would the 10 thickness one work fine with the only result being that the top of the belt might project out 2 mm from edge of pully set at extreme end of speed spectrum ? (this on the theory that the 800mm length is the inside length, not the outside length)

22° sounds familiar:

Attached is a picture of the CVT belt on my 'unmentionable' which bizarrely captured the size while in motion 925 long (mid-line length, I believe) 22° and 30mm wide [edit] this is actually 22mm wide & 30° angle

However, looking at my fairly accurate 3d models of the CVT sheaves for the same device, I see they measure ~13° (26° when doubled), and the sheaves for another Vehicular CVT measure 24°, so I understand your confusion

The V angle will change if the belt as the belt is tightened around a radius, so perhaps the 22° is a nominal value of the relaxed or straight belt?

I doubt the thickness will make any difference though the thicker one might not ride around the small diameter of the pulley so well. Mine does this even though it is the correct thickness, just a different make. To set up the pulleys I adjusted the adjustable pulley so that the belt was riding right near the top edge then adjusted the motor mount so that the other end was right at the bottom of the spring-loaded pulley. This gave me full range both ways 1:3/3:1

My lathe uses a 22x8x(26)x750 belt. I guess this means 22 degrees, 8mm thick, 26mm wide and 750 long.

Bill, I have a spare set of pulleys and belt that I want to fit to my 1952 milling machine. I don't suppose you have any more details or photos of that setup you could send me?

Bill, I have a spare set of pulleys and belt that I want to fit to my 1952 milling machine. I don't suppose you have any more details or photos of that setup you could send me?

Click to expand...

Hi Peter,

Yes, PM me with your email address and I'll send what I have. (there are a few more pictures etc. at http://billtodd.dyndns.org/drillmill

AMetric gal finally calls back and sez "they" tell her there is no angle ! I ask who is "they" and she admits warehouse guys, so I tell her they are wrong and try again. But then they probably don't know a protractor from a monkeys ass so I can't trust what they come back with anyway.

Sorry to cause any more confusion, but I've just measured two metric CVT belts and that size is 22mm wide 30° V angle (same angle measured on a Hardinge drive belt).

Bill

An included angle for v belt section varies according to bend radius. That's why they can't answer your question. You have not specified the bend radius.

I think you also will find sheaves have different angles according to pitch diameter to match the belt angle.

the angle is what the sheaves are supposed to be, NOT the belt itself. measuring the belt's angle just adds to all the confusion.

there used to be a nice metric variator belt list in PDF form, i believe from optibelt, that listed the angles and other than a couple of oddballs in the really narrow sizes like 13mm everything was 27 deg. i can't for the life of me find it now and their new updated site is totally worthless.

An included angle for v belt section varies according to bend radius.

I think you also will find sheaves have different angles according to pitch diameter to match the belt angle.

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True, but the (few) sheaves I've measured have been pretty well straight cones

Looking at the Gates Catalogue there are various angles of multi-speed belts from 22° to 36° spread across a range of sizes

Billtodd said:

Looking at the Gates Catalogue there are various angles of multi-speed belts from 22° to 36° spread across a range of sizes

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Yes, this is what I recall as well. I investigated this a long time ago, wanting to build my own variable sheaves, and found that belt V-angle varied according to width. That is, less wide belts (like 10-12 mm) tended to have a steeper wedge, maybe 30° or so, and wider belts like 22 or 28 mm tended to have a flatter wedge angle, like 22° or 26°. I don't know why.

This angle is in fact quite distinctly specified, but you really have to read the fine print and diagrams. I think I found most of the info in the Gates catalog, as Bill Todd suggested above.

So Milacron, you're on the right track. I'm sorry I can't answer exactly right now, but there is merit to what you've been thinking, and to what some of the guys have been saying. You just need to really dig into it and read the fine print in the catalogs.

You might as well stick with Gates or Lovejoy, since they pretty much set the standard.

.

Edit & Addendum:

Milacron, upon rereading the original post, i see you're only asking WHY the angle is 22°. ??? I have no idea why.

And,

Milacron said:

Another thing....say I need a belt 33 x 8 x 800 mm....but all I can find is 33 x 10 x 800. Would the 10 thickness one work fine with the only result being that the top of the belt might project out 2 mm from edge of pully set at extreme end of speed spectrum ? (this on the theory that the 800mm length is the inside length, not the outside length)

Click to expand...

Yes, but it seems only 1 mm projection from the edge, since you'd be measuring the radius. Not likely to matter.

.

SKF Power Transmission -- OptiBelt < search belts, tech info & more.

Cheers
<jbc>

Here, check this out.
Multi-Speed Belts:

Example: Belt No. 2326V310 designates:

Top Width in 16ths of
an Inch: 23/16" = 1-7/16"
Sheave Angle in
Degrees (26)
Pitch Circumference to the
Nearest 10th inch: 31.0"

First two digits indicate top width in sixteenths of an inch.
Next two digits designate sheave angle, in degrees, that the
belt is designed to fit. Last three or four digits indicate pitch
length to the nearest tenth of an inch.

Thanks to Billtodd. I am also aware from such nice information. Your suggestions are very nice and it also helpful for me.