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# 3D modeling of a gear train

## 3D modeling of a gear train

(OP)
I'm not sure what happened, but I had posted a question here a while ago. I received an email notification that someone had responded, but I have not been able to find the response, so.......I thought I'd try again.

I am interested in modeling in 3D, a gear train. I have in my head that I'd like to build, probably out of wood, a gear train. I'm thinking 3 stages, each stage with a 5:1 ratio. The driving gear will have 40 teeth and the driven gear will have 8. The 8 tooth gear will be hard coupled to the next 40 tooth gear which will drive the next 8 tooth gear which is hard coupled to the final 40 tooth gear. The final 40 tooth gear drives the final 8 tooth gear which is hard coupled to the output shaft.

Because I'm building out of wood, I suspect these gears will be large in diameter.

I thought it might be a time saver if I modeled these gears and worked out the dimensions and created drawings (to be used as 1:1 templates) for cutting out the parts. In addition, I thought it would be great if I could build this virtual gear train, move the first driving gear and see all of the other gears move. So I have been in search of a 3D solid modeling program that will let me do this. And here's the final requirement.....the CAD program either needs to be free (since this is a hobby project) or VERY inexpensive.

I have looked at FreeCAD but I don't think that program will allow me to move the 1st gear and then see all of the other gears move (according to the constraints I enter). I have looked at SketchUP Make (which is a great program), but again, I don't think I can get the constraint based motion. Others have recommended Fusion 360 but I don't see a free version and the purchase costs I've seen are high (maybe I'm not looking on the right spot). I am not a student so an educational copy is not an option for me.

I have recently discovered OnShape and it looks like this program will give me what I need (although I have not really used it much yet). The only downside side is that OnShape is only cloud based (I believe) and all of the designs done with a free account are available to the public (which perhaps is a good thing so others may be able to look at my designs and provide guidance). I'm so used to working from a local hard drive that working exclusively from the cloud is a big change.

### RE: 3D modeling of a gear train

(OP)
Yes, I am familiar with involute gears. Many of the CAD programs I've looked at so far have an involute gear design tool built in or as an extension. SketchUp, FreeCAD, and Onshape have these gear design tools. Perhaps other programs have a tool like this.

Since I will be fabricating my own gears by hand, I may opt to simplify the tooth profile....not sure yet.

### RE: 3D modeling of a gear train

#### Quote:

I may opt to simplify the tooth profile
Then you don't fully understand the importance of involute gear teeth.

Lots of crappy gear models with "simplified" teeth out there to copy. Some have been the source of tens of thousands of dollars in rework and warranty and customer dissatisfaction. "Simplified" gear teeth make life quite complicated.

### RE: 3D modeling of a gear train

I do gear train layout on a macro level first. Usually start in 2D with circles representing pitch and outer diameter of each gear. This makes it simple to drag gears around until I find the right place. Then fatten gears up to corect thickness and depth and finally add teeth.

### RE: 3D modeling of a gear train

If you're thinking of 3 sets of gears within the same frame then each subsequent gear from the first needs to be a bit smaller then its predecessor in order not to foul the shaft from the first gear.

If this is a hobby project, why not just draw it using paper and pencil / drawing implements?

Or cut it out of cardboard if you want a moving version?

3D looks great, but sometimes previous ways can be just as good and a lot quicker....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: 3D modeling of a gear train

Or just buy some meccano gears....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: 3D modeling of a gear train

(OP)
OK thanks.

Yes, I have seen a bunch of simplified gears online. All of these are "hobby" grade gears and probably used at low speeds.

### RE: 3D modeling of a gear train

#### Quote (LittleInch)

If you're thinking of 3 sets of gears within the same frame then each subsequent gear from the first needs to be a bit smaller then its predecessor in order not to foul the shaft from the first gear.
Not necessarily. You can arrange a stack of identical reduction gears in a train and they don't interfere (I've done it). Just depends on placement.

### RE: 3D modeling of a gear train

(OP)
LittleInch: Yes, I understand what you are saying. Since this is a hobby project, I am actually trying to figure out several things.

1. I'd like to know how to model in 3D and move parts in an assembly to see how all of the other parts move. So the modeling part of this project is to get familiar with virtual machine design. I'm sure I would use those new found skills for lots of other ideas/projects.

2. I plan to make the gears myself (to see if I can) so that's why I am not buying the gears.

3. The gears will be spread out from one another so as to not collide with the other gear shafts.

4. I'm planning on loading the gears so cardboard won't do. I considered prototyping in cardboard and might do that as a first test.

### RE: 3D modeling of a gear train

If you can tie this hobby in with a school you can get the Student Version of AutoCAD Inventor for free. My son's robotics team uses it for designs with lots of constrained parts.

Z

### RE: 3D modeling of a gear train

So far as I remember Autocad Inventor isn't modelling the gear train, it is modelling two circles rolling against each other with the nominal gear ratio defining the angular speeds. The teeth are there to look pretty. If that is the case, what have you really simulated?

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

### RE: 3D modeling of a gear train

(OP)
Thanks zappedagain. Unfortunately, all of my kids are grown and out of school so an educational copy is not available to me.

I have taken a closer look at AutoCAD Inventor and it looks and sounds pretty good. I may try their 30-day trial.

### RE: 3D modeling of a gear train

(OP)
Thanks GregLocock. Yes, I am looking for a package that will actually simulate the motion (by doing the math). At this point, I don't need FEA or any other analysis tools. Just looking for a way to build a digital prototype.

I'm thinking that it will be easier and faster to make iterative changes on the digital prototype as compared to a physical one.

Interesting...

### RE: 3D modeling of a gear train

I'm with Tick, stay away from an 8 tooth, it's not enough teeth on a circle, it's just too coarse. Also, best practice is to avoid combinations that are even divisors of one another. You can set up some weird harmonics or undesirable wear patterns. Probably not critical if this is just a hobby thing or you're not planning to go into production and sell them.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

### RE: 3D modeling of a gear train

All that work to make an arc, you're better off using the string-unwinding-from-spool method to get it right.

### RE: 3D modeling of a gear train

Or use a software package where you can define a curve using a formula and get exactly what you're looking for.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

### RE: 3D modeling of a gear train

(OP)
Yes ornerynorsk. I agree, 8 teeth may be too few. I won't know until I make 'em and try them out,This is another reason why I wanted to model them and move them on the computer.....just to see what the meshing looks like.

TheTick: Ever see a video using the unwinding string to get the arc right? I might want to try that.

JohnRBaker: The last link I placed in this thread outlines a method for approximately drawing the curves. I might try that out.

For people who like to tinker with 3D parametric programs, there is a way to get a semi free version of Solidworks. Join the Experimental Aircraft Association It costs $40 per year, and a free "Maker " version of Solidworks is a member benefit. Now if you like building home built aircraft that's even better. But for the rest ,don't say I told you. B.E. You are judged not by what you know, but by what you can do. ### RE: 3D modeling of a gear train Tick, Just because you're right doesn't mean he's not wrong. Sometimes you just have to let folks work on digging their own eyeballs out with a grapefruit spoon. Even when they get done they won't be able to see that it was just a waste of time. Happy Friday. ### RE: 3D modeling of a gear train In the Gear and pulley engineering forum we discussed the methods/programs/calculations of creating the involute tooth in CAD, years ago. There was also a Lisp program (for ACAD users) to do it, it can be probably still located by searching that forum; it is not that much of problem to calculate the coordinates of points on that curve (Excel, the Open Office or Libre Office can be used and trigonometry is all math one needs) and then use it in a script to create a spline through those points. I did it even in an ancient ACAD LT. In UG (at work) we used GRIP programs to create nice 3D gears more than 10 years ago just by entering the few basic gear data. And it was done for effect only, not for 3D manufacturing. To use the 3D printer with modern, fast computer to create an arc-shaped gear tooth approximation is - well, let's be polite - strange... To create working gear train needs some knowledge of gearing. The theoretical shape of the gear flank is just a fraction of the whole problem. ### RE: 3D modeling of a gear train One other problem you might consider: A 1:15 speed increaser is damn near impossible with precision metal gears and super-precision bearings in jig-bored plates. With hand-filed gears, or even gears made in a real gear shaper, in wood, it probably won't even move. Mike Halloran Pembroke Pines, FL, USA ### RE: 3D modeling of a gear train Did I miss a meeting, again? Mike Halloran Pembroke Pines, FL, USA ### RE: 3D modeling of a gear train Sorry, my bad, and even worse. Mike Halloran Pembroke Pines, FL, USA ### RE: 3D modeling of a gear train The only time I've seen wooden gears used 'successfully' is in old windmills. I think getting 125:1 is quite feasible with this sort of arrangement, in a single stage, but obviously the big gear will be seriously big, and the efficiency will be shocking. On the other hand you can build it with a saw and a chisel. Cheers Greg Locock New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? ### RE: 3D modeling of a gear train tried this? http://woodgears.ca/gear_cutting/index.html Looks to be exactly what you need from first glance. I rather think that wood mill above is more like 1:125, not 125:1. Kind of a big difference. Remember - More details = better answers Also: If you get a response it's polite to respond to it. ### RE: 3D modeling of a gear train (OP) Greg, thanks for the pic. The old designs are brute force but they worked. I think they have a certain elegance. LittleInch, Yes, I am familiar with this, thanks. Matthias is reasonably famous for his gear design tool. If you look at his YouTube channel, you'll find a number of projects using wooden gears that his has made. ### RE: 3D modeling of a gear train For about$300 bucks, you can buy a kit for a 3D printer from micromark, then you could design and print your own bits quite easily.

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