[MVHPV]

I cross posted this in OpenSource Software forum , but applies equally here. I need a CAD program solely for designing 2 sprockets. The problem is finding one which has tooth profiles, specifically, Gates Poly Chain in 8mm pitch. I'd rather not spend $900 for software just to design 2 sprockets. I've search here, and Googled elsewhere with no firm candidates. Any suggestions/guidance would be greatly appreciated.

[RICHARD ZASTROW]

There are dimensions available in the Gates on line catalogs and engineering pdf's.

Dick Z

[BurrMan]

You can go here and configure your specs and download a model for it:

http://www.gates.com/designview/inde...ocation_id=866

[MVHPV]

Thanks guys. Been there, and when clicking through the "Partview" feature for both specs & cad files, I stumbled across this:



Not all samples displayed the above, but both the 30 and 71 grove (among others) in the 8mm pitch x 12mm width, did. Needless to say, because of the critical nature of the profile, I'm a little dubious because of the warnings.

[BurrMan]

Never downloaded a model to see that pop up. It would certainly be a deal breaker!

Maybe call that number in the disclaimer and see if they have a solution to offer for designing these.

[blowlamp]

This DXF is a 5mm pitch pulley straight out of CamBam after being scaled by 1.6 to get the 8mm pitch you're looking for. Is that any good?

Picture is of the same DXF after extrusion in ViaCAD.

Martin.

[MVHPV]

blowlamp,

Sprocket grove profiles are critical and must match the belt designed for it. Grove pitch is only one of the criteria. See examples below.

Your example looks much like this:



The Poly Chain profile I'm seeking, I believe, looks much like this one:

[BurrMan]

Here's a step file of a gear I downloaded from that site, just for giggles.

It was this one: 8MX-30S-12

I included the 2d spec sheet they publis, and all the numbers seem to jive. COuld the disclaimer be just a protection scheme? How can they publish stuff as "the engineering specs and data, and say it's not a true representation?

Maybe they just want to sell them to you instead of have you make your own.

This model matches the data.
Maybe someone experienced in this area can comment on the model.

Surely you will want to confirm things before destrying some machine though...

[MVHPV]

Attached is what I suspect is the original patent for the Gates GT (Poly Chain) profile:

[MVHPV]

Surely you will want to confirm things before destrying some machine though...

Absolutely. The belts arn't exactly expendable either. I bought two @ $50 each... wholesale.

[blowlamp]

Oh, I see now.
It does beg a few questions and observations though. My first being:

1/ Why is the standard form not suitable?
2/ Is the CAD drawing just a representation or is it to be used for manufacture?
3/ If the design is patented, would it be legal to make your own anyway if done commercially?

If you intend to make this profile, I think it might be quite an involved process even if you can draw the proper tooth form.
In your second drawing there are a couple of corners (that look important) in the root of the tooth, that can't be taken out cleanly by normal endmilling because of the cutting tool radius. That probably leaves form tools or possibly laser cutting, although I'm not sure how suitable a laser-cut surface would be for running a belt on.

Martin.

[RICHARD ZASTROW]

Thanks MVHPV, The patent drawings supply many answers. Looking at the date of the patent raises a question; Is this the CURRENT form?

Gates' latest form, GT 2 has a form similar to a gear, an involute on the sides of the groove.

One other thing, if you can buy the sprockets, why go through all the effort to draw and make your own? Just curious.LOL

Dick Z

[MVHPV]

1/ Why is the standard form not suitable?

Among the many dozens I've seen, what is a 'standard' profile?

2/ Is the CAD drawing just a representation or is it to be used for manufacture?

Not sure what you mean. While Gates seems to offer the exterior dimensions in CAD drawings, I'm not convinced the drawings accurately represent the profile. But I could easily be mistaken.

3/ If the design is patented, would it be legal to make your own anyway if done commercially?

Cutting one or two prototypes for an experimental project wouldn't likely be an issue. But I certainly wouldn't mass produce any or try to market any.

Looking at the date of the patent raises a question; Is this the CURRENT form?

Dunno. That's the reason for seeking a CAD program which may have the profile included in it's library.

One other thing, if you can buy the sprockets, why go through all the effort to draw and make your own?

Therein lays the problem, Gates doesn't make the sprocket I need - specifically, the mounting is completely different, and I'd prefer 7075 aluminum. Yes, Gates offers "made to order" customs, but I'm guessing the costs would be beyond my budget. I also have access to local CNC should I need different ratios (a strong possibility).

[BurrMan]

In your second drawing there are a couple of corners (that look important) in the root of the tooth, that can't be taken out cleanly by normal endmilling because of the cutting tool radius. That probably leaves form tools or possibly laser cutting, although I'm not sure how suitable a laser-cut surface would be for running a belt on.
Martin.

The flat is a true flat, so a simple index on a rotary should cut it.

[BurrMan]

Still looking for a sprocket expert that can confirm the model as "true" or not. If true, no need any software as the models are available. I dont know enough about them to say if it is just a "toy model".

Anyone?

Beuller.....Beuller??????

[blowlamp]

MVHPV.

The reason I posted the file produced by CamBam is because I believe it will allow you to easily produce pulleys for use with timing belts that are commonly available.

If the CAD drawing was only intended to represent the basic form of the pulleys I was going to suggest that you don't go to too much trouble in getting an exact shape. Conversely, if the drawing were to be sent to a CAM system for manufacture, it would need to be accurate.

BurrMan

That would remove some but not all of the material in that area, a little would remain on each curved section near the root.

Martin.

[BurrMan]

That would remove some but not all of the material in that area, a little would remain on each curved section near the root.

I am assuming that the sides come off of the assembly. A straight pass over the top.

[MVHPV]

The reason I posted the file produced by CamBam is because I believe it will allow you to easily produce pulleys for use with timing belts that are commonly available..

The Poly Chain GT is available in over 29 different belt lengths spanning 4 different widths - that equates to 116 individual sizes. Bare-in-mind, that's counting only 8mm pitch. Doesn't seem too uncommon or unpopular to me. http://www.vbeltsupply.com/8mmpolychainseries9274.html

Also...

The Poly chain exhibits the highest efficiency of any currently available belt drive, short of roller chain. Crap!... now i'm beginning to sound like a salesman.

Question Blowlamp,

Does CamBam specify manufacture's profiles, or just one or two generics?

[blowlamp]

The Poly Chain GT is available in over 29 different belt lengths spanning 4 different widths - that equates to 116 individual sizes. Bare-in-mind, that's counting only 8mm pitch. Doesn't seem too uncommon or unpopular to me. http://www.vbeltsupply.com/8mmpolychainseries9274.html

Also...

The Poly chain exhibits the highest efficiency of any currently available belt drive, short of roller chain. Crap!... now i'm beginning to sound like a salesman.

Question Blowlamp,

Does CamBam specify manufacture's profiles, or just one or two generics?

Well I never did doubt that there would be a selection of available products, but the fact remains that the The Poly Chain GT tooth profile is not as common and is going to be harder to machine than the HTD tooth form because of its shape.

I've just checked the CamBam documentation which says the pulleys are made to the HTD5 form. See here: http://www.cambam.co.uk/docs/tutorials/profile-new.html

This might be of some help See here: http://www.roymech.co.uk/Useful_Tabl...ing_belts.html

Martin.

[easymike29]

Therein lays the problem, Gates doesn't make the sprocket I need - specifically, the mounting is completely different, and I'd prefer 7075 aluminum. Yes, Gates offers "made to order" customs, but I'm guessing the costs would be beyond my budget. I also have access to local CNC should I need different ratios (a strong possibility).

Assuming you can buy an existing sprocket of the correct diameter and pitch, any competent machinist or toolmaker with an optical comparator can document the profile by sectioning the sample.

Gene