topic Re: gear to box modelling concept in Fusion Design, Validate & Document Forum

gear to box modelling concept

TimelesslyTiredYouth — Tue, 17 Feb 2026 20:03:56 GMT

Hi, I'm trying to design just a simple prototype for a larger design so I can understand the concept of gears before I implement it, but when figuring out how to convert the rotary effect of a gear to a sliding effect, in order to push something like a box forward, I got confused. Can anyone help me? the screenshots below and file should explain the issue at first glance.

I basically want to get the 2:1 gear ratio to spin and push the box forward, but I get confused with how I'm meant to make the turning force into a sliding motion, I think I'm meant to add a line of teeth into the side of the box, but even then I'm confused.

Kind regards

Ricky

Re: gear to box modelling concept

TheCADWhisperer — Tue, 17 Feb 2026 21:10:14 GMT

@TimelesslyTiredYouth

Components

Joints

Rack and Pinion

What you are naming Base Circle is actually Root Circle (and should be dimensioned).

Reference: Giesecke et al

More information to follow later...

Re: gear to box modelling concept

scottprater — Tue, 17 Feb 2026 21:31:40 GMT

Hey Timeless, no teeth required.

Step 1) You need to convert your design into a Hybrid design. You can't define joints/motion between the bodies of a single component.

Step 2) Create some new internal components for each of your bodies (after you make the internal components, you can just drag and drop the bodies into them).

Step 3) Define your joints (revolute for gear, slider for box), then use the Motion Link tool to define the relationship between the two.

-Scott

Re: gear to box modelling concept

Drewpan — Wed, 18 Feb 2026 00:44:40 GMT

Hi,

I am a little confused as to what you are trying to achieve and how you are

modeling it. There are a few ways to translate rotational motion to linear

motion. Probably the most common way would be with a Rack and Pinion

system.

There is a couple of ways to make it happen. Either the Rack is fixed and the

gear rotates along the rack and the linear motion translates to the movement

of the axle. The other way is that the axle is fixed and as the gear rotates the

rack is moved linearly.

In the image you have provided, what is missing is the rack for the gear to move

the box in and out.

In terms of how to get fusion to do this then as mentioned by @scottprater what

you need to do is set up a motion link between the gear and the box. As the gear

Revolute Joint rotates X degrees the Slider Joint on the box moves Y distance.

This principle is almost identical to setting up a screw with a threaded rod and

nut.

Cheers

Andrew

Re: gear to box modelling concept

MichaelT_123 — Wed, 18 Feb 2026 01:13:33 GMT

... look how a piston in a combustion engine works. Keywords: crankshaft, camshaft.

Re: gear to box modelling concept

TimelesslyTiredYouth — Thu, 19 Feb 2026 10:04:19 GMT

Thank you all for your replies.

@Drewpan now that I've seen what you've written, I believe the right way for me to prase my issue is, "I'm trying to design a rack and pinion system, where the axle is locked in place and the rack is being moved back and forth; my issue lies with the fact that I don't know how to make perfectly shaped cone things on the rack for the gear to spin on"

@TheCADWhisperer I used the spur gear add-in. I'm still learning how gears work and how to design them, in this case, I'm just looking at the concept of a "rack and pinion system" as I wanted to finish a project I wanted to use this for quickly, but if you have any advice on designing gears and rules, and tolerances I should follow, I'll happily hear them as I'm in the process of trying to understand how to design gears, understanding tolerances, ratio's and torque.

@scottprater, your such a lifesaver😂, I recently came back to fusion and I saw the part design, hybrid, so on so forth after updating fusion and i was so lost, I chose part design hoping for the best and I was severly confused when I couldn't make joints or components, seeing only joint motion when i used the pop up search bar.

SO my rephrased question really should be :

"I'm trying to design a rack and pinion system, where the axle is locked in place and the rack is being moved back and forth; my issue lies with the fact that I don't know how to make perfectly shaped cone things on the rack for the gear to spin on" - what's the correct design process for this? and to know the correct dimensions for designing the inner cuts, do I have to know the exact dimensions of the gear it's linking to, preventing me from using the spur gear ad in?

Kind regards

Ricky

Re: gear to box modelling concept

Drewpan — Thu, 19 Feb 2026 11:23:37 GMT

Hi,

So I am still a bit confused about these "cone things" you are referring to. Also I said

that a Rack and Pinion is ONE method you could use. A Worm Gear system would also

work. In terms of learning about gears a very good place to start is Wikipedia (where

90% of what you read MIGHT be true, but in this case it is quite comprehensive and

a good place to start). https://en.wikipedia.org/wiki/Gear

In term of modeling you have a couple of work flows. You can do what most designers

do and download what you want from the McMaster-Carr cattledog and scale it and

insert it. Or, you can re-invent the Wheel and design one yourself. The former is easy

and the latter is a learning process. It depends on how much time you want to spend

on this Project. As a student Mechanical Engineer I know the Basics of Gears and various

Systems and I can design my own if I need to but in many designs you really want to

use the cheapest method which is Off The Shelf components. Designing your own may

be an accomplishment but will be very expensive in time spent and custom fabrication.

Even if I was designing my own I would still try to use OTS components where I could to

keep costs down.

Ok, so we are going on a Learning Exercise. I would still use the various Tools like the

Gear Plug-ins. If designing a gear was easy then everybody would do it. As @TheCADWhisperer

has already alluded to in his diagrams - a "simple" gear is actually got quite a lot of

physics and mechanics under the hood. The correct terms describe very specific things

that exist for a reason.

So this learning exercise - how far are we taking it? Do you actually have a problem to

solve or is it just a theoretical? A problem to solve will involve what is going to provide

motive power to this system? What Gear Ratios do you need and why? Torque v Speed.

How much power do you have available? Do you want the gear system to move fast or

slow? What are the mass limits of the load? What materials are we thinking of using?

Will we need to lubricate and maintain the system or is it one off? What efficiency do

you need? These are a few simple questions that come to mind just thinking about the

basic design parameters, let alone what the design might actually look like. What I am

trying to say is don't start modeling anything until you have a Goal and a Plan how to

achieve the Goal. Once you have these then you can tackle the design and the workflow

should simply - flow.

I am not sure where you are in your learning journey but there are some very good free

books about machines and mechanisms. I like machines and engines and so just simply

seeing how problems were solved historically can give you ideas on how to solve various

problems. I saw a diagram of a Scotch Yoke in a book and was impressed and fascinated

at the same time. If you don't know what that is - Wiki is your friend.

Start of defining your Goal.

Make a Plan.

Think about what limitations you might have - small spaces etc.

Decide what materials you might use.

Consider the limitations of the materials - 3D Printed PLA works

great but I wouldn't trust my life with it.

Ask a friend to look at your design and discuss it in case you forgot something.

Take a Deep Breath.

Decide if you are ready to start actually Modeling.

Cheers

Andrew

Re: gear to box modelling concept

TimelesslyTiredYouth — Thu, 19 Feb 2026 12:04:02 GMT

Thank's for the reply @Drewpan , these topics I'm exploring right now aren't entirely related and I have already planned for this project, i.e., PETG, one of lubrication, mass load limit of 50g, fast moving (thats why the 2:1 ratio), these were just a few topics I mentioned for context with me trying to learn about gears in general.

Anyway, I've mainly solved my issue using your first post (I started again with a hybrid design)

and all I have left to do is work out how to add joints, as it seems to have changed since the "parts, hybrid designs, assembly, ect..." update, or I could just be thick.

I've attached the file below if you think my workflow, or anything I've done is wrong that needs to be brought to my attention,

Kind regards

Ricky

Re: gear to box modelling concept

scottprater — Thu, 19 Feb 2026 14:22:21 GMT

Hey Timeless,

You're doing good so far! Joints haven't changed at all actually since the update, so you shouldn't have any problems making your motion link. Just be sure to "Unground from Parent" any parts you want to move (like your SPINNY GEAR!; I would ground your SPiiny tiing! instead). Because your parts are already positioned correctly, you can use "As Built" joints just to define the motion they should have (slider and revolute for the box and gears, respectively; make sure all of the parts are joined with your SPiiny tiing! base plate).

-Scott

Re: gear to box modelling concept

TheCADWhisperer — Thu, 19 Feb 2026 16:49:05 GMT

@TimelesslyTiredYouth

(view in My Videos)

Re: gear to box modelling concept

TimelesslyTiredYouth — Sat, 21 Feb 2026 16:53:21 GMT

I'll model some "real world" holder for the sliding box, and post it here thank you!

@scottprater , yes i did realise after what seemed like a year that I forgot to ground my base, once I did this my model wasn't spinning the base and keeping the gear in place. It's the math that got me in the end. I realised that I need to multiple the angle of the little gear by 2 (360 *2) in the dialogue box so that the gear teeth would line up, and don't get me started on the gear to the rack because I thought the math was just the pitch circle diameter multiplied by PI which gave something like (48*PI) in the dialogue box, the gear teeth still refused to line up

Kind regards

Ricky

P.S I've 3d printed this now and it works a charm, I'm just continuing questions so I can further understand gears, and more importantly motion links within fusion so I don't make the same mistakes further on.

Edit

I've attatched the file of everything I had done up to this point before I saw the new comments, I'll attatch the changes on a new comment for @TheCADWhisperer

Re: gear to box modelling concept

TimelesslyTiredYouth — Sat, 21 Feb 2026 17:07:23 GMT

It's a bit rushed but I'm presuming this is what u meant by a box to hold it:

Re: gear to box modelling concept

TheCADWhisperer — Sat, 21 Feb 2026 17:26:54 GMT

@TimelesslyTiredYouth wrote:
It's a bit rushed ...

Re: gear to box modelling concept

TheCADWhisperer — Sat, 21 Feb 2026 17:33:47 GMT

Re: gear to box modelling concept

TimelesslyTiredYouth — Sat, 21 Feb 2026 17:47:59 GMT

OK, yes I saw the overlapping bit I've fixed it. Thank you for help with the maths ! so it's diametrical pitch circle mulitpled by PI for distance when converting from rotary to linear motion?

Kind regards

Ricky

Re: gear to box modelling concept

MRWakefield — Sat, 21 Feb 2026 23:45:42 GMT

If you want to get a good understanding of gears there's a really good document here: https://qtcgears.com/tools/catalogs/PDF_Q420/Tech.pdf

Hope this helps.

Re: gear to box modelling concept

TheCADWhisperer — Sun, 22 Feb 2026 00:27:59 GMT

@TimelesslyTiredYouth

Just thought I would add to the discussion that to validate rotational/rotational motion and rotational/translational motion - you do not need the actual gear geometry.

Think of it as a Rolling Cylinder on Cylinder Joint and a Rolling Cylinder on Plane Joint for the motions.

Re: gear to box modelling concept

MRWakefield — Sun, 22 Feb 2026 15:36:12 GMT

One other thing to mention: In this configuration, the 2:1 ratio between the two gears will have no effect on the amount your box moves. It will only affect its direction. To achieve a 2:1 ratio you will need to use a compound gear. ~~I seem to be unable to paste images into my replies otherwise I would've inserted one to show you what I mean.~~

EDIT: managed to add the screenshot: