Metal / Plastics Work

I need a custom gearbox for this upcoming project and because of the torque involved, I'm certain they need to be aluminum or steel components. Preferably aluminum.

The problem is I don't have any metal shop equipment or access to said machines. I knew this guy who used to design small aluminum brackets, then send the designs to China and have them shipped back in bulk. But I have no experience drawing mechanical blueprints.

* What are a few good companies to order aluminum or plastic part designs from?
* What form do they send the design in? Is there some kind of industry-standard CAD program?
* What if your design has missing information? Does anyone warn you?
* How do they charge? Is it by dimensions or number of cuts?

A gearbox is about the hardest common place mechanical item to design/make. It takes expert skill to make one and designing one as your first venture into drawing blueprints is similar to starting out by designing an FPGA board and programming it as your first project. I can guarantee you that your design will fail when you get it back (similar to PCBs!)...and it will cost a lot more than PCBs.

There is no set way in how they charge you. It depends on the material, how easy it is to machine, and what exactly you want done to it, and how much machining you want done to it, and how much material needs to be machined. It's all over the place.

CAD programs are also not free (ones that can design things like gearboxes anyways). Downright through-the-roof expensive I would say. Just like OrCAD or Altium eMachineshop is the only one I know of with free CAD that is permanently linked to their service and no other (like PCBExpress...or was it EXpressPCB?), but I'm not sure you can design something like a gearbox with it.

If you really want a custom one, either learn the trade (obvious time disadvantage there, not to mention lots of little projects to build yourself up to a gearbox) or hire someone to do it for you (expensive, but it would easily cost you the same in mistakes, and far more time on your part).


What do you need? Can you not find anything like it from battlebots gearboxes (like http://www.robotcombat.com)? Those things already cost like $500 a piece and though they aren't mass produced, they aren't singleshot (and thus cheaper) like yours will be either.

Guys like http://www.rc4wd.com might also design and build it for you...at a price.

What's your budget? FOr something like a gearbox the size of your first, it could easily be $600 in machining costs and maybe 3x that for design labour (wild guess). I got a quote for a pair of solid RC axles from them (no custom gears involved like your gearbox will likely be) as $600~1500 (something like that), and they were not charging me for all the design labour involved.

Only expert-level skill? Too bad. Well, the gearbox is only one of many components I'm going to need. The rest is stuff like rods, hubs and pivots. This other guy was ordering extruded aluminum brackets at 19. The design processes seemed easy enough. I had the impression he was using some kind of proprietary software, but it sounds like OrCAD is the industry standard.

Say I get eMachineshop and eventually OrCAD... Is there a standard format that I send to the extrusion company? I mean, we Electrical guys have the netlist and the Gerber file. What do Mechanical guys use?

So far my budget is $0. Literally. I'm just giving myself a head start so I'm not stuck trying to figure it out later. If $600, yeah I'll probably have to substitute. Unless I can rent some time in someone's machine shop or something, I'll need at least a few custom parts. I guess I could also lookup a few companies and go straight to the info source.

hi digitan,
Looks an interesting but expensive project.

Found this:
https://www.engineersedge.com/gears/gearbox-design.htm

lotsa links on that page, look at the link at the bottom of the page.

You could, probably still can, buy off the shelf gears etc...

DigiTan said:

Only expert-level skill? Too bad. Well, the gearbox is only one of many components I'm going to need. The rest is stuff like rods, hubs and pivots. This other guy was ordering extruded aluminum brackets at 19. The design processes seemed easy enough. I had the impression he was using some kind of proprietary software, but it sounds like OrCAD is the industry standard.

Say I get eMachineshop and eventually OrCAD... Is there a standard format that I send to the extrusion company? I mean, we Electrical guys have the netlist and the Gerber file. What do Mechanical guys use?

So far my budget is $0. Literally. I'm just giving myself a head start so I'm not stuck trying to figure it out later. If $600, yeah I'll probably have to substitute. Unless I can rent some time in someone's machine shop or something, I'll need at least a few custom parts. I guess I could also lookup a few companies and go straight to the info source.

Click to expand...

Yes, there is a standard format (several I think). But since I don't specialize in it, I can't remember what they are. (OrCAD is PCB program so you won't need it). If you look around this webpage, you'll quickly figure out what some of the extensions are:

**broken link removed**

THere's also at least 3 others, but I can't remember what I was trying to look for when I came by them and so I have no idea how to back track my steps to find them because I am not the soberest right now. Better luck tommorrow morning.

Have you considered belt drives? Those are much easier to pull off on your own.

EDIT: Eric is right, if you want to go gears, your best bet it to buy gears off the shelf and make all the pulleys axles mount into "slots" so you can adjust all of their spacings, since the tolerances are seem to be what hardest part about getting a gearbox right in the first place. It'd definately be a lot easier than having to design each gear. I'd still triple check everything though. But if this is sufficient, you might be able to get away with doing nothing but designing "slots" in sheet metal which you can definately do in eMachineshop, assuming you can get the appropriate gears, axles, etc.

Like this gearbox:
http://www.geology.smu.edu/~dpa-www/robo/trux/index.html

Now that I've typed it out it doesn't seem to so bad, at least for single gearboxes where you only have simple spur gears on a single plane. Maybe I was thinking of more complicated with gears in multiple planes with combination gears? or machinging the gearbox yourself? The required tolerances definately come into play there if you machine it yourself.

Re: Standard formats for CAD

DXF and DWG are very common for 2D designs. Import and export between CAD programs works reasonably well, but is still prone to unintended changes.

3D is a different story.

As for machining, I would stick to the shafts, frames, levers, etc. I would buy pre-made gears and adapt to my design or design in accord with what is available. John

Are you very sure you can not buy a gearbox that will work? Could be there are sources you are not aware of. What are the torque, size, and weight specs.

Look for old copier machines at inorganic rubbish collections.
These yield gears and sometimes powerfull DC or stepper motors with complete gearboxes, chain drives and beltdrives.
Also a good source of transformers etc.

Cost zero !

Used drills and power screwdrivers have some pretty decent gearing and you can often pick them up cheap at thrift stores etc. I've seen some neat things done with the right-angle gears out of old angle grinders too.


Torben

Yeah, I can get the gears from other website and surplus shops, but eventually I'll need my own shafts and frames. And improvising seems to only go so far. For the time being, it looks like eMachine pretty much solves both the design and manufacturing problems.

well not much info provided but don't forget your trusty (and relatively cheap) 15 speed bicycle. Use a pillow block for drive bearings (can also be found cheap/ free at junque yards) and you'll have a ton of torque with a fairely nice gear range. Plus it may give you extra marks on the excentricity scale

Just curious: I checked out eMachineshop. Just how similar is that interface to AutoCAD?

You're asking me? I've only ever drawn two 2D circles in AutoCAD so I have no idea.

D'oh! Well I guess I can look for AutoCAD youtube videos.

I am a consulting engineer - used to work for a large manufacturing company (Kodak). People who need things designed come to me and I provide anything from reports, calculations, drawings, specifications, etc - sufficient information for whoever will take care of the next steps. For your project, an hour of my time would cost you at least $100. Once the idea was developed a designer, at a lower rate of pay would produce drawings, etc.

If this is a one time effort you might go straight to a machine shop - but before you do I suggest you develop the design to the extent that you can as they are unlikely to spend time without payment.

Keep in mind that for a mechanism like this you'd consider the manufacturing process and your design would have to match with that.

Some questions that seem relevant:

A. How much power, torque, etc.
B. RPM
C. How will you lubricate?
D. Cyclic or constant load?
E. One direction or both?
F. Are shafts parallel, perpendicular, any offset, etc?
G. What about vibration, noise and other things that affect the type of gears?

I'd do as others have suggested and look for a premanufactured gearbox - unless your needs are so simple that a local machine shop could throw something together for you. If your needs are really basic it would seem that someone with a home shop could develop something - possibly someone with a robotics background. You might find some help from local robotics enthusiasts - got to be a common problem for them.

All of the above is guesswork as I know very little about your needs other than "gearbox".

DigiTan said:

D'oh! Well I guess I can look for AutoCAD youtube videos.

Click to expand...

The people at www.engatech.com may be able to help you. They use the leading 3D CAD program, Solidworks.