Design from scratch

Mostly in my blog are about design software but now I’ll be discuss “how to design from scratch”, start from design purpose until become drawing that ready to machining or prototyping stage of course still involve software as a tool. For example I made some simple gearbox as our case. I will explain stage by stage in design:

1. Design purpose

Before starts everything we need to know what kind of design purpose or a case that become our target, in this example I’ll make a gearbox with input by motor 1800rpm, but I expect three option output 900, 1800 and 3600rpm so I could use it in more wide range ability from my motor.

2. Layout concept

Now begin to planning gearbox layout, but before that I’ve to choose standard component that available in the market, the most clearly part that needed are motor. I start with baldor motor 3hp 1800rpm (you can googling for available catalogue) that has detail frame dimension so this is our first guide to decide required space or dimension for gearbox.

As you know for common gearbox are consist of components that need to be designed such as Gear, Shaft, keys, Casing, Speed transmission also don’t forget other peripheral like bearing, screw, cap, rubber seal that will affect in overall design dimension.

3. Engineering calculation

In this stage we will face the core of design it self, how to make rough component spec base on equation or mechanical rule such as gear ratio, transmitted torque, overall load in every speed option. The result is we have data’s that will become our guideline to choose the right material and dimension each component (minimum spec).

4. Engineering Criteria

After runs for some calculation we can advance to choose what material that will be use and detail dimension with considering market availability, price, machining process, installation difficulties. Beside that our designs have to pass engineering criteria as perquisites to operate perfectly for example in gear are tooth strength and wear stress also in shaft have to pass moment and shear stress criteria. In this stage we have detail gear train as a core for gearbox design.

5. Peripherals component

Other supporting component in our gearbox can follow previously designed component, price are become main issue here since this is not our main focus so you would consider to us as many as common part and standard part that will be helpful for replacement and reduce price too. Sometimes there are also custom part that need to be created but don’t forget common part’s rule so can cut some machining price and time.

6. Technical drawing

Base on data in previous stage, we can start to make a technical drawing to translate our design so technician can follow what designer want, how precision the component is, how to assembly, what kind material that will be used. Of course don’t make mistake in adjusting tolerances or double dimension standard that will be confusing and become problem in assembling.

After those stage are completed, now can be advance in machining component and prototyping to test whether our calculated design are appropriate or not, just remember above step are made by theoretical aspect especially for mechanical component (gear and shaft) since I’ve neglected the effect from vibration and heat generated by high speed mechanism that will contribute failure in operating condition so any improvement are still open to make final design base on actual operational condition from our product.

There are several tips in engineering design:

1. For designer, experience and strong engineering background become main issue to make good design so never stop learning new technologies.
2. Always keep price as our consideration and benefit for any designed component, this will give value add in our design.
3. Remember that our design doesn’t end in a drawing paper, this will be applied and produced by manufacturing process so always be aware about how to process the component. Don’t make difficult shape that impossible to make and giving another problem when assembly.
4. Give as clear as possible information in technical drawing and avoid redundant item so not confusing everybody that read our design.

For technical drawing I use Pro-Engineer WILDFIRE 3 and collaborate with Vn4D for visualization, actually with Vn4D our analysis can be spread more wider from monitoring load and stress analysis in every component but I’m use it just for visualization purpose.

 

I also include presentation file and technical drawing for designed gearbox, this article are my thought about design engineering and base on my experience in my workplace (even though I’m not in design dept.) so maybe there some other opinion from experts in mechanical engineering design, I would be open minded to learn more.