There really isn't _a_ standard for belts, or for pulleys.
The wisest course is to buy a length of pulley stock >for the specific belt profile you intend to use<, and machine it into a pulley.
Or just buy the exact pulley you need from someone who makes them all the time.
Like MikeHalloran notes, currently there are not standard types of timing belts. Every manufacturer now has their own proprietary tooth geometry designs, which each require a matching sprocket. Many years ago, the "standard" belt used a crude trapezoidal tooth profile. But I don't believe this type of belt is used much anymore. The good thing is that the proprietary belt designs provide much better performance than the old trapezoidal tooth belts.
If I were to manufacture a pulley based on the belt profile, will the pulley profile match? Will it have any sort of involute? or will it match the belt tooth geometry exactly?
Is the tooth geometry the same on a HTD belt that has a different pitch? Or different belt length? I'm wondering if one hob cutter can cut multiple different pulleys for different pitches and belt lengths.
In general, the pulley profile is not complementary to the belt profile with the belt's back glued to a straightedge, which is the easiest way to measure the belt.
The pulley profile usually but not always matches the profile of the belt when the belt is held to the curvature of the pulley.
This is further complicated because the real pitch radius of the belt lies in the plane of the cable reinforcement, which lies entirely outside of the pulley OD, and that some belts are designed to ride on the pulley OD, some are designed to ride on the teeth flanks, and I've found 'scrum' belts whose teeth are covered with something that looks like hair, and I don't know where the hell they ride.
Just buy the damn pulley stock, or the finished pulley; making your own is insane.
"Just buy the damn pulley stock, or the finished pulley; making your own is insane." quoted for truth.
Gates and Goodyear will make you a custom pulley for reasonable cost and lead time, plus you get the genuine article.
HTD designs are the closest thing I know if to being a "standard" and available from multiple manufacturers. I infer then that they are not strictly proprietary, but if you want a full warranty probably not an option.
company I work for makes these in a blue moon. we use a hob to cut the sprocket. I am sure for a one or two parts a mill will work easily. reverse engineering will work easily. but seriously buying them is surely easier. unless there is special circumstances. then making them is OK.
Usually the tooth profile is obtained from the belt manufacturer.
The prototype parts are then made using wire EDM and a little CNC.
Production parts are powder metal.
I'd give you an example tooth profile but they are all proprietary.
Can the tooth geometry be obtained from these belt manufacturers with a non-disclosure agreement? Do the manufacturers charge a fee to obtain the tooth geometry?
Good question.
Sometimes they will not reveal the geometry they use unless there is a contract for doing business.
There are usually 2 types of companies. The ones that only give you profile points (eg. excel sheet or stp file) so that it is very difficult to figure out the actual geometry, but you can still use the points to make prototypes for experiments.
Then there are the companies that give a profile drawing, sometimes the dimensions are 'estimates'.
However, if you are a Tier1 supplier it is usually not a problem.
Gates, for instance, shows you the belt profile along with the pulley drawings. It wouldn't be too much of a problem to construct the tooth based on that belt profile - you only need one.
From what it appears, there are many different tooth profiles for timing belts. Would it be correct by saying a given tooth profile is the same for two belts with different pitches? Or does the tooth profile also change with pitch length?
Ex: gates htd 3mm pitch belt versus gates 5mm pitch belt
Is the tooth profile same but the belts just have them spaced differently?
Also, on the flip side, 2 belts of the same pitch that have different lengths, are the tooth profiles the same? I'm leaning towards yes on this one but I want to learn all I can about timing belts/pulleys.
Would it be correct by saying a given tooth profile is the same for two belts with different pitches? Or does the tooth profile also change with pitch length?
Regarding your question about the difference in tooth profile between a 3mm and 5mm pitch Gates HTD belt, I believe they are similar to standard involute gear tooth profiles, where they scale in proportion to DP. Almost all of the tooth profile dimensions would scale in proportion to the ratio of pitch change, all other things being equal.
As for two belts of the same tooth pitch having different lengths, that would depend on what location on the belt section you measured the length at. Most belts and sprockets are measured based on a defined pitch location, and the offset from this pitch location to the outside of the belt can vary among different manufacturers.
did some looking today...you can download profiles from the gates website. Not sure if these are totally accurate, probably going to contact our gates salesperson and dig a bit deeper.
What are you designing exactly? If it's automotive I suggest you contact the belt manufacturer as well.
And remember to design mid-tolerance. Many drawings are low-side tolerance.
