Need help extruding teeth onto a curved surface

[Anonymous]

Hi,

I am attempting to project a sketch onto a curved surface.

The curved surface is the 3D pulley which is a cylinder. The sketch of one of the teeth from the belt which goes onto the 3D pulley is shown in the first picture. 

I am having trouble with this because the teeth are not curved, so as soon as I click extrude (second picture) there is a gap left between the teeth design and the pulley. I wish to eliminate the gap between the teeth and the pulley by curving the teeth onto the surface of the pulley so that it curves onto the surface and is not "straight". Would I have to redesign the sketch or is there a feature you would recommend using in order to do this? Thank you.

[mcgyvr]

You can't work that way..

Obviously the belt (rubber or whatever) is going to deform so that tooth profile is basically incorrect for the pulley..

You need to sketch the correct profile for the pulley not the belt.. The pulley manufacturer will have that information..

Or just download a model of the pulley all finished.. 

[blair]

I've attached a PDF file that will help you out on your gear design. You need to add your minor diameter.

https://www.geartechnology.com/issues/0584x/geardesign.pdf

If that doesn't work, this website will create a proper CAD file that you can use.

https://geargenerator.com/#200,200,100,6,1,0,0,4,1,8,2,4,27,-90,0,0,16,4,4,27,-60,1,1,12,1,12,20,-60...

[Anonymous]

I decided to modify the teeth design slightly at where they curve on the bottom. This allowed me to extrude this sketch and it now looks similar to what is required. However, the gap between the teeth is now too large.

I need to have the diameter of the pulley match up with the number of teeth around the pulley and the gap between teeth in the design. This pulley is then placed onto a belt with the matching teeth dimensions.

In order to perform these calculations, would the links you sent me help?

Basically the trouble has been converting the teeth sketch from a 2D orientation to a 3D orientation with a curved surface.. 

 

[blair]

Yes, it should, especially the second link. You need to remember that the number of teeth on the sprocket determines the diameter. 

[johnsonshiue]

Hi! I think this case can be done easily using some help from Surface Modeling. Please attach the part here so forum experts can help comment further.

Many thanks!

[Anonymous]

Here are the details of the files I attached.

The "gates" file is the file of the belt, from which I traced over and copied and pasted into sketch 3 of the "pulley sketch" file.

As annotated in the pulley file, the required width of the teeth is .248, which I have correctly.

After making a circular pattern of 5 teeth, I made a sketch under Extrusion 2 which connects the base of the two teeth. However, this gives a rough edged pattern which of course would not fit well with the teeth of the belt, and gives a .10" distance between the teeth as annotated. We need the distance between each tooth to be .068" as shown in the gates file.

The OD of the pulley is .510" (which I prescribed) and for 5 teeth:

(Width of tooth+gap between teeth)*# of teeth= OD * pi

(.251+.068)*# of teeth = .510"*pi

# of teeth = 5

Therefore, the width of the teeth should be .251, # of teeth should be 5, OD should be .510 and width between the teeth should be .068.

Currently, it is .10.

Therefore, I am going to delete Extrusion 2 and find a way to make it .068. However, at the end, the gap between the teeth should be .068 and not .10 which I am not able to get because the pulley is a curved surface, but every other dimension is currently correct.

I hope you can assist me in finding the error, but I think it is .10 simply because the pulley is a curved surface and the teeth are not straight, but again, I need it to be .068. I think the reason it ends up as .10 is because the teeth are not curved, so I am not taking that curve versus straightness factor into account for my calculations. Probably need to start by modifying sketch 5 under Extrusion 2 because that does not work. Hope that helps.

[johnsonshiue]

Hi! There are multiple problems in the part. The sketch has overlapped segments. Proper constraints are not applied. It is just not the most robust way to build a parametric model. I tried using surface modeling workflows but the poor sketch led to more problems. In the end, I just use the existing geometry and find the quickest solution.

I personally think you want to spend time understanding sketch constraints and how to simplify geometry. Never complicate the geometry than necessary. It makes it hard to edit down the road.

Many thanks!

[swalton · Accepted solution]

You might have better luck if you configure and download the pulley you need from someone like Misumi.

See: https://us.misumi-ec.com/vona2/mech/M1000000000/M1002000000/M1002030000/

Even if you want to learn to make your own, having a copy of the correct geometry should help.

[Anonymous]

The teeth details on the belt are very specific. I tried altering the design by changing the arcs at the bottom of the teeth, assuming that the teeth dimensions were not as important in the bottom as at the top. Then I restrained the distance between the teeth at the top to be .25 which is required. However, when combining the belt & pulley assemblies in solidworks, something just seemed really off, like it didn't match up.

I just feel like it's hard because the pulley is a curved surface, but the teeth on the belt are straight. So it's hard to account for the curvature on the surface of the pulley. The reason I had to change the sketch of the teeth was because of the pictures I pointed out in my previous posts. But basically, nothing matches up the way I want it to. But I will keep trying, because it could be the smaller details.

Also, thank you guys for your help. I really appreciate the input, although I wish I was smart enough to just figure it out.

[Frederick_Law]

Get the belt and roll it so you get 5 teeth in a circle.

The reason you can't buy a pulley with 5 teeth is because the belt not supposed to roll that tight.

All belt has a minimum belt radius.

Smallest pulley from Gate is 22 teeth.

Idler is 3" minimum.

Take a look at the manual.

https://www.ahrinternational.com/PDF_catalogues/Gates/polychaindesignmanual17595.pdf

Part of P.102:

[Anonymous]

The number of teeth that I am designing will vary for the diameter of the pulley that I am making.

So for this case, I made a 0.375" diameter (currently) not counting the teeth, which gives a .25" distance between the teeth.

I will also try out the cases with 7, 9, ... 15 teeth and we'll print out models of all of them.

The pulley in itself can range from a .75-1.5" diameter model because this pulley is placed on a sensor and acts as a "wheel" that goes on the belt. The width of the belt is 21 mm, so I made the width of the pulley .85" so it fits onto it.

However, looking at the gates.ipt file, how would you rotate this so that it is curved? That is really the only problem I am having. One of my colleagues suggested that I try working backwards by making a larger circle and extrude cutting the features.

Really I wish I could just make the belt curved and copy paste the features so they perfectly match up instead of having to guess work the diameter, # of teeth, and everything. But I will try using your formula to see if I can be more accurate.

[blair]

The pitch distance of the bars on the belt is your pitch-distance for the teeth on the sprocket.

[Frederick_Law]

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@Anonymous wrote:

The number of teeth that I am designing will vary for the diameter of the pulley that I am making.

So for this case, I made a 0.375" diameter (currently) not counting the teeth, which gives a .25" distance between the teeth.

You're using a 8mm/0.315" pitch belt and you want to wrap it around a d0.375" pulley?

You don't see any problem with that?

0.25 distance between the teeth.  How many 8mm pitch 4mm wide teeth fit into 0.25"?  1.587?  You got belt with 0.587 teeth?

[Anonymous]

Hey.

Yeah I know about that. I calculated the pitch distance/circumference and number of teeth for the calculations. Just having trouble with Inventor. Going to try what my colleague suggested and then attach the file if it still doesn't work!

[Anonymous]

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You're using a 8mm/0.315" pitch belt and you want to wrap it around a d0.375" pulley?

You don't see any problem with that?

0.25 distance between the teeth.  How many 8mm pitch 4mm wide teeth fit into 0.25"?  1.587?  You got belt with 0.587 teeth?

Yes. 

.315" pitch*5=1.575~=(.375+.134)*pi=1.599

When I said the diameter of the pulley, I said that doesn't include the teeth. When including the teeth, the height of the teeth is .134. So the total circumference is 1.599 of the pulley+teeth

The reason I'm having to use a 1.599 circumference rather than matching it up however is to account for the curvature. If I made it the same, then it would be even less. Therefore, I worked backwards and adjusted the dimensions until I got a .25" distance between the teeth.

Just to clarify, there is a .25" distance between each tooth, and a .067" width of each tooth, which gives the .315" pitch.

I calculated all of this before doing this so I don't think the calculations are a problem. Also if you would like you can see my drawing it does fit 5 teeth in there. I wish I had an updated version but it keeps screwing up and I'll get the updated file ASAP.

[Anonymous]

Here is the updated file.

The diameter is currently .37" for the pulley not counting the teeth. I annotated this. It gives a .25" gap between the teeth which it should be. However, the bottom gap between the teeth is messing up. So all I tried to do is change the sketch for the teeth. But then it wouldn't help because changing the sketch messes up the calculations. So I just don't know... maybe someone could help me work around this? I just really need help fixing the bottom part where it curves. See attached screenshot. Appreciate all the help!

[TheCADWhisperer]

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@Anonymous wrote:

However, when combining the belt & pulley assemblies in solidworks,..

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What does SolidWorks have to do with this design problem?

This is a math and geometry problem at it's foundation, not so much a design problem.

Once you have the proper math/geoemtry - you can easily set up a spreadsheet driven iPart to return desired number of teeth.

Before I start - this appears to be a school assignment, where is your teacher?

From your files - it does not appear that you are getting proper instruction.

The first lesson in learning Inventor (or SolidWorks) is how to constrain a line.

Your instructor should have covered this topic long before giving an assignment like this.

If you stick around and answer questions and follow instructions - I will walk you through the process.

When is the assignment due?

[Anonymous]

Hey.
This isn't a homework assignment. I'm working to design a pulley to go on
an actual belt in a press room. I'm an intern.
I was having trouble but then someone I was working with told me to work
backwards, and extrude cut the sections that are the gaps rather than
extruding the teeth out. So currently will try that.
I used Solidworks to make an assembly because I do not have access to
Inventor Professional but only LT which does not allow one to make an
assembly. But I did have access to SW from my school. Therefore, I used
that to make an assembly instead.
If there are any suggestions you could make I would of course appreciate
them! I am just a beginner.
As for the cuts, I'll try it out this way, and hopefully it takes care of
the problem in the last screenshot. Thanks for your help. And also youre
right it's a math problem

[Frederick_Law]

You need some technical reading:

http://www.sdp-si.com/PDFS/Technical-Section-Timing.pdf

http://www.brecoflex.com/products/pulleys/design-guidelines/

http://www.pfeiferindustries.com/timing-belt-pulley-pitch-diameter-outside-diameter-charts-i-12-l-en...