Custom gearboxes

[Hangtight]

I needed a project to learn Fusion 360, and I wanted a gearbox for a bullpup build...

 

 

 

 

ICS split gearbox upper, Retro Arms motor cage, a couple of aluminium plates and some 3D printed parts. Just finishing off the last few details. And yes, I know it looks like a V6 gearbox, but this one has a microswitch for cycle detection so it'll work with a BTC Chimera or a G&G ETU with remote microswitches for the trigger and selector.

[Davegolf]

You clever ba$tid!

 

As Ali G would say, Restecp

[Hangtight]

If it works properly, I'll be making all the files available for free, just in case anyone else wants one. And maybe do a version that's a direct V6 replacement, if anyone wants to get rid of the funky trigger mechanism?

[Samurai]

Nice one!

[Hangtight]

Done.

 

 

 

 

[Davegolf]

I like that you've disconnected the cutoff micro switch from gear contact. Good job!

[Davegolf]

Oh draw in a pinion peep hole

[Davegolf]

I'm getting carried away but this would be pimp with stainless side plates and thermally stable engineering composite centre bodies mmmmm

[Hangtight]

If I can find a local place that will do small quantities of laser or water jet cutting then the stainless might happen. Plan B is I get the files out, in which case the material of choice is aluminium! The infill is going to be 3D printed, as is the cutoff lever. It'll either work or it'll break. Because of the gear placement the cutoff lever was the only way I could get the switch to be operated at the release point. The switches are similar to the type used on BTC Chimera trigger boards and are good for over 100,000 cycles.

I've found some RC drone threaded stand offs that will key the two sides together and provide a thread for bolting the halves together. The plates will be bond to the infill.

Now I just need to build something round it.

[Hangtight]

Just for you...

 

 

[Davegolf]

Awesome, so nice to see what's going on when building a box!

 

Even if you can't find a place local the company I use for water jet courier for a tenner.

 

Because you want the most precise cut finish and I'm assuming you want to avoid machining processes I would say get them laser cut rather than water jet and cut to the highest finish, fast/coarse laser leaves less than desired cut finish which would make bearing fitment meah.

 

Alignment of all parts is critical as is making sure nothing can walk.

 

If you use SS plate you can thread one side and CSK the other negating the threaded standoffs.

 

Put a few straight dowel pins through to key all parts together.

 

I don't know what 3D composites are available, but Nylon66 for example is hard as but is so sensitive to temp change, like a couple of degrees C can grow a thousands of an inch, enough to ruin a nice shim job.

 

Im looking forward to a precocked P90

 

 

[Hangtight]

I'm tempted to see if I can find a cheap AUG or P90 and attempt to model a drop in replacement gearbox.

The side plates are 2mm thick, and the engineer in me is troubled by a threaded engagement less than the thread diameter.

PLA is pretty temperature stable... Certainly no worse than pot metal.

I was going to go with water jet cutting if I can find it locally due to the accuracy and cleanness of the cut, particularly on holes. The bearing holes are 0.1mm undersized so they can be reamed to the correct diameter with perfect alignment.

[ImTriggerHappy]

Use a press fit insert for the side plate and check your inbox.

[Hangtight]

Didn't think of Nutsert/Rivserts. And I've got some dowel pins kicking around somewhere...

[Davegolf]

Yep I like at least thread diameter for tapping depth too!

 

I take it back use the threaded standoff, studlock one side in.

 

Can you get turnbuckles that small?

That way you could have left and right hand thread to stop the wrong part coming undone.

 

2mm SS will be stiff, nice!

 

If the dowels were like a pastry rolling pin they would locate everything and be contained / retained by the side plates.

 

Going to make a reaming jig up?

 

Soz I like design thinking 

[Davegolf]

And I'm jealous of 3D software. Never had the time to learn it yet

[Hangtight]

Get yourself a copy of Fusion 360. It's free if you register as a Start Up /hobbyist. My next challenge is to get some drawings out of it to get a couple of parts made, then I need to learn to reference parts to each other, so you can change a key dimension or move a part and the model keeps all the relationships so everything still lines up!

I've only spent a couple of hours a few evenings a week, and things are starting to come together. The trick is to keep learning and not fall into bad habits.

[Samurai]

I got a very good quote from these guys for 10 pieces of 2x2cm steel parts. They do any quantity. Never got around to order them though.

https://www.lasermaster.co.uk/

[brandyyyyy]

hey can i get the 3d data from you build?

[jackd787]

Hey, just wondered if you ever got this produced?

im thinking of producing a custom gearbox and wondered what the production costs were like.