First attempt at a gearbox

[dbb-the-bruce]

Below are some images of the model/design I put together for an attempt at a windup gearbox. It does nothing other than prove that I can build this sort of thing.

The flywheel will allow me to get a sense of how much force the geared down spring can provide.

Two 12:1 gear sets in a row, the final flywheel will spin at 144 X the mainspring unwind. The gears are rather large for the assembly - at this point the smallest cutters I have are M1. If this goes well I'm going to probably get a set of 48DP cutters.

Regarding the gears, I know that a 6 tooth pinion is really pushing it. I looked at a number of approaches to the pinion gears, including pinion wire ($$!). My conclusion was that I'd try to do it on my desktop CNC first. If I can make decent small tooth count pinions with the CNC it will provide a lot more design freedom for future projects.

The model doesn't have any shafts in it yet. I have not put a lot of thought into that. I don't have a great sense of how hefty they need to be or how to handle the bearing interfaces. From the research that I did do, I picked up two tips - first that the shoulders of the shafts should be relieved to reduce friction on the frames and also that (at least for clock work) the pinion holes in the frame should have a slight taper. The tapper allows for reaming to a precise fit and also provides minimal surface contact on the pinion.

The plan is to start cutting gears today.

Any thoughts or tips on the gear train etc. greatly appreciated. Again, the primary point of this project (at this stage) is to learn and prove I can do it!

-Dave

 

[dbb-the-bruce]

CNC Pinion gears!
M1 - 6 tooth. Each gear is .315 max diameter.
They appear to mesh with the other M1 gear I previously cut.


Still need to take exact measurements and see how close the CNC came out. I did not make any attempt to measure the actual cutter diameters prior to machining. I'm sure they are close but probably off by a few .001

Next step is to cut them out and face the back sides. Then figure out how to get them into a working gear box.

-Dave

 

[dbb-the-bruce]

Progress!
I got the frame plates done and the spring assembly mounted. The mounting screws for the spring are 2-64 - lucky that I already had a tap for them

The spring assembly has registration pins for its original mounting. Amazingly, I managed to get both the mounting holes and the registration pins holes dead on. Really pleased with the fit. Bottom plate has a cut out for the spring assembly to pass through. Drilled a starter hole and then opened it up to about an inch with my boring head. The side lobe was drilled and then milled the straight sides.

Getting the pillar (frame spacer) shoulders identical was a pain. After much fussing, I finally got it to where the space between the plates only varies by .0015. I lost about .005 from the cad design - but no big deal.

You can see the pins I put in the top plate to align it to the bottom when I finally get the shaft positions accurately located. That waits until the gears are mounted and done - "depthing"

Next step is to make the main / spring shaft. I need to put a nub/hook on it to pick up the center of the spring. I've got a bunch of pinion wire on the way, not sure how that's all going to work out - mounting and holding the gears on tiny shafts......

Man there is a lot learn with this!

Enjoy,
Dave

 

[rwm]

Those gears look great! Keep it coming...
R

 

[Mitch Alsup]

In just a few years you will be competing with ClickSpring !!

 

[dbb-the-bruce]

In just a few years you will be competing with ClickSpring !!

I've got to say that I did go back and watch a bunch of his videos - really glad I pined the frames at the start.
I don't really know where this is going, I've wanted to make complicated mechanicals since I was a child. Right now it's just trying to get to the point where things are easy - in the sense that I know how to approach stuff and have it come out decent.

 

[dbb-the-bruce]

I cut the big gears today and cleaned up the pinion gers, really happy with how they came out.



The large gears are close to 3" dia. I made an arbor from 1 1/2 1018 - man it took forever to hog out the arbor shaft down to 1/2 to fit the largest collet on my dividing head. I made it with a press-fit center that can be replaced and turned to whatever shaft/hole size I need for future work. Super glue was used to hold the blanks on the arbor. The recesses on the arbor face help the glue set better. The second blank was just centered on the pin and glued to the first. This approach worked really well - doing more gears is going to be easier.

I also cleaned up and faced off the small pinion gears.



These gears are barely .3 inch diameter. Was fun to figure out how to hold them. I ended up using a 5/16" collet, catching 2 teeth on each segment of the collet. I also turned a tiny washer out of .025 plastic shim stock that just slipped over the outer diameter of the gears and allowed me to register the "flash" waste to the face of the collet with .025 to spare. It was then easy to turn the flash/waste down to the root diameter of the gears ( .140), take a really light face cut and then finish the center hole.

It's actually starting to look like something!



Still waiting on pinion wire to arrive.

-Dave

 

[dbb-the-bruce]

January was crazy, but I did make some actual progress. Got my pinion wire and went through several attempts to get the first two gears mounted and running true.

The spring/drive gear was tricky for two reasons. first it needs a small hook/nub to catch the hole in the spring. First attempt at that I managed to snap a 2-64 tap off in the pinion shaft. The other screw-up was that I located hole for the shaft opposite the spring with a small punch pushed through the spring assembly - but the assembly isn't sitting perfectly flat on it's plate. The shaft was miss-aligned by about .010 in both X & Y. I ended up making a floating bushing in an oversized hole and secured the bushing once I had the gear/shaft trued up.


I also had to do the second gear mounting twice. First time was with a very small shaft (.06) and I couldn't get the gear to stay mounted true. The second attempt was with a .108 shaft better fit and used wicking Loctite (green). There is only a total of about .025 clearance for both sides of the second large gear. Truing it up and setting it square to the frame was challenging. But definitely worth the effort/experience. It's pretty clear to me now how important it is to get everything as true and square as you possibly can. I'm pretty happy with this as a first attempt.


Finally, I made a little key for winding it up. I kind of got ahead of my self and soldered the tab onto the shaft before I thought about shaping it. Next time I'll make it a little fancier. I used color matched solder for brass and I tapped it threw before assembly because I didn't have a bottoming tap. I think it came out pretty good - was afraid that the solder job would muck up the threads.


And finally, it actually does something!
View attachment gearbox-med.mp4

A full wind on the spring really gets the gears spinning and when the spring is completely unwound the gear inertia back-drives the wind up. Next up is to add a final stage with a flywheel and a clutch. I may also try to make the gears open with spokes to lighten them up and reduce inertia.

Having fun and learning a lot. Glad I'm not invested in what it's going to be just in the making of it.

 

[brino]

Excellent, it looks very clean.....and clocky.......

I used color matched solder for brass

I did not know that exists!
I will have to look it up.

Thanks for sharing this with us.
-brino

 

[dbb-the-bruce]

I did not know that exists!
I will have to look it up.

A little pricey but a little goes a long way. It's also on the higher end of the temperature scale which makes it a little more difficult to solder with (like hard silver solder or hotter).

Sheet Solder for Brass, Bronze, Copper and Yellow Gold-Filled - RioGrande

www.riogrande.com