Tooth belt pulley drives

[rotarysmp]

Hi Bob and Art,

Good work you are doing here.

It would be great if the standard toothed belt systems would be supported:

XL
HTD
AT
T
etc

Regards,
Mark

[Greolt]

I'll add my name to this request. 

Greg

[vandal968]

I want to second, er third, this excellent suggestio n.  I'd heard about Gearotic, but haven't had a need for gears so-far.  I do need several timing belt pulleys and I came to this site specifica lly to see if Gearotic can make them.  The list of suggested types listed above is perfect, but I'd also like to see GT2 added in both 5mm and 2mm pitch (my current applicati on).  GT2 5mm is basically interchan gable with XL although they are slightly different tooth forms and the pitch is off by a hair.

cheers,
c

[ArtF]

Hi:

  Well, XL's it seems can be made by the involute generator, two examples are in the library
in the latest 1.64 version. If I can get informati on on the specs of the other types I dont have
a problem with adding them to the developme nt list. Its possible many types can be made by
playing with the spur gear generator s parameter s as the XL series were.
  But if not, perhaps just an additiona l setting or maybe even a new page would be possible for
those types of pulleys. For many types of these things its a matter of finding the specifica tion. I suspect it wouldnt be difficult to simply add a coupel more controls to allow them to be made, and
then storing them in the library. Library files can be shared and posted, so we could build a library of special gears here and Ill add them to the release so everyone can use them.

Art
 

[ahford]

I believe machinery's handbook has the spec on all of them.  I'll look it up when I get home, although I only have the 26th ed.

[ulihuber]

Hi,

I am convinced that HTD would be a really good option because most machines have these pulleys due to their better precision and almost no play. And larger HTD wheels are in the price range of this wonderful new software.

I did, however, not find any good spec for these wheels, not even in the patent documents ...;-(

Uli

[ArtF]

Uli:

  A lack of specs is the typical problem you face. Even the gears we currently have were a bitch at times due to infomrati on that was conflicti ng, or diofferin g specs, or a simple lack of documenta tion.
  Its a normal thing it seems in the gearing world..

Art

[John S]

5mm pitch HTD is easy as it can be done two ways, one is to drill a series of 1/8" holes on the pitch circle diameter and then turn down to the OD to produce the shape, second way is to use a 1/8" ball nose end mill or slot drill and cut it in the vertical just using the 4th axis as an indexer.

I am not sure on the other pitches, I really need to call in the bearing company and grab a few to measure what diameter fits best.

John S.

[BobL]

Hi John:

 Thanks for your post. I was just curious as I looked at one of these today and noticed a slight tooth width change from top to bottom. When I insert the belt on pulley you see why angle is nessessar y and how well it fits and rolls when spun. Now if I was to cut one of these using the theory of drilling a series of holes on the pitch circle like you said, would results be round edges and would that matter for backlash or early belt wear verses cutting it vertical on the 4th axis?

Cheers
Bob

[John S]

Bob,
Cutting one of these by either method I have described will produce sharp edges which is to be avoided and I usually go round the pulley afterward s with either one of those scotchbri te wheels or give it some big licks on a rotary wire wheel.

This has two effects, it removes the burrs and blends the finer edge details into one another and makes for a smoother profile.

John S.

[ulihuber]

John,

I tried several ways and was not satisfied by the popular advices for making these pulleys. The reason is the uneven bending of the belt which happens almost only in the spaces between the teeth. This is not dramatic for really big pulleys, but as you make them smaller you'll see that either the belt does not lay on the teeth of the pulley or the belt teeth do not slip into the puley valleys easily.

You need to break the edges of the pulley teeth. Here is an example of a pulley I designed in Autocad years ago. But what I did was not based on a proper calculati on - just try-and-error. However, it runs fine on the Z axis of my machines for years now.

Best regards
Uli

[BobL]

Hi Guy's;

 Since I'm new to all of this belt and pulley talk, I thought I would detail some of the abbreviat ions to help me better understan d the conversat ion in case no one dared to ask. From my research I found:

HTD = High Torque Drives,
T =  Timing pulley,
XL = Extra light duty pulley for tooth drive belts types,
L = Light duty pulley for Cogged belts type,
H =  heavy duty pulley for tooth belt type,
XH = Extra heavy duty pulley for Cog belts type,
XXH = double extra heavy duty pulley for tooth belt type.
GT2 = Newer pulley types with excellent registrat ion which exceeds HTD and trapezoid al belt capabilit ies according to info

Reading onward I also found tips on optimizin g your configura tion by altering sizing which goes something like this.Use as large of a pulley diameter as possible to give the best performan ce with high periphera l speeds. This will minimize the bending stresses in  belt and will allow for narrower belt.  It is preferred to select a belt width which is less than the diameter of the smaller pulley. The wider the toothed belt, the higher the possibili ty of edge stresses occurring in the case of inaccurat e assembly. This could cause abrasion and impair the smooth running of the belt. In marginal cases it may be better to select a larger pitch rather than a wider belt. Finally, wherever possible, try to use standard belt lengths. Special lengths cost more and are slower to get when ordered in.

Cheers
Bob

[Dan]

Nice summary on timing belt drives, Bob.

One thing you missed about using largest pulleys possible is that the larger the pulley diameter the less tension in the belt is required to transmit the same torque and consequen tly less load on the shaft bearings.

Oh... and what about MXL belt drives...

Dan

[ulihuber]

Just to add at the HTD side:
There are some different belt types with teeth that are not the usual half-circle shape. They look more parabolic and they have a little grooving un the top.
These belts run on the same pulleys. They are just optimized for higher speed/lower noise because no air is trapped in between teeth and pulley.
Interrest ing patents are:
EP 0 309 653 A2
DE 28 54 052 C2
DE 28 55 748

What I did not understan d...why is the shape of the pulleys nut published by Uniroyal or Continent al ? They  are focussed on belts not on pulleys and should have vital interrest in pushing the use of belt drives.

Uli

[John S]

Some body said they are in Machinery Handbook but I did a search in V28 and came up blank.
Mind you I often do that in that book, time to replace the door stop ?

John S.