Art & Inspiration Ford 9" differential in 1/3 scale

Gentlemen,

This is the 3rd part of the 1/3rd drivetrain, the differential.
As I had mentioned in one of the earlier threads every year prior to winter I pick out a couple of projects to get me through the long cold months. Last year was the construction of a Ford 9" differential.
It started with the Wednesday night get together of our car group. While sitting and BS'ing I noticed a 9" center section sitting in a plastic bucket in the corner of my buddy's shop. I went over to check it out and found that it was complete so I asked my buddy if I could 'borrow' it for awhile. "Sure, take it as long as you need it."
It went home that night and in the following weeks got dismantled and scrubbed clean prior to taking dimensions from all the parts.
With dimensions in hand I started making detailed drawings with the requisite changes to make a working miniature. By changes I mean metal wall thicknesses, bolt sizes and dimensions to accommodate standard parts like bearing and seals.
Knowing that full sized diffs have gears know as hypoids I started the investigation process to find out just exactly what they are and how they're made. What I found was the manufacturing process involves extremely complex machinery, more than what most gear shops can handle and certainly not in the realm of home shops.
At this point I started investigating possible alternatives to make the ring and pinion gears for without them the project was dead-in-the-water.
What I found was a series of articles published in some old magazines I had for the construction of offset bevel gears or skew bevels. The author compiled all the information to make this type of gearing from making the cutters through setup and final machining.
The next job was to convert his Algebraic equations into something I could use. In scaling the 9" down I wanted to keep the centerline offsets as close to scale as possible. In posting what I was doing on a model engineering forum a fellow stepped up and made me a spread sheet whereby I could plug in gear pitches, offsets, tooth counts etc. and come up with working dimensions.
With some hard numbers I made up some cutters and decided to cut the first set from Delrin to prove out my numbers and setups.

 

The gear blanks were made up and the gears were cut. For any of you fellows that are familiar with cutting gears or just gear geometry in itself these gears needed 2 cutters for both the ring gear and the pinion as only one side of the tooth could be cut at one time. Once all the teeth were cut then the blank would need to be rotated the proper amount, the mill head shifted and the other cutter installed to do the other side of the tooth.
gbritnell

 

Here's a link to the plastic gear set being run together to prove out the mesh.
gbritnell
http://youtu.be/up1-lQm_32c

 

Everything worked out great so at this point is was on to the metal gears. Not having the ability to harden them I decided to make the ring gear from steel and the pinion from brass figuring if there was any significant wear it would be much easier to replace the pinion than to have to make another ring gear.
The blanks were made up and cut, first the pinion. These shots show the setup and the final gear. The teeth look skewed because of the nature of these gears being offset from the centerline.

 

Because the ring gear was made from steel it required some initial gashing to remove some of the stock prior to cutting with my home made tooling.

 

Once the gears were finished I made up a fixture to mount the gears with the proper spacing and offset to see how well they would run together. As with a full sized diff there is provision to shift the ring gear and shim the pinion to get a good smooth engagement.

 

Here's a video link to the metal gears.
gbritnell
http://youtu.be/fW5wzl9lGaM

 

There were a great many steps in cutting the diff housing so I'll skim over the main steps.
I started with a block of aluminum for the center section. I calculated what I needed for size and roughed down a piece of round stock to the overall dimensions.


From there I stared by roughing the internal shapes and putting all the main holes and drilled and tapped holes in.






Here's the inner cavity with the bearing blocks installed.

 

Just wow !

 

The next step was to set up a rotary table to finish the inside curves and the radii on the mounting flange.



This was followed by another setup to profile the caps and bore for the bearings.

 

The next step was to step off the ring gear clearance. A mathematical step-off chart was developed using AutoCad and with a ball mill the large radius was milled out.




The part was then flipped over and a new setup was made. to bore for the pinion housing, drill and tap the holes and start whittling away some of the outside stock.

 

From here the part got some layout lines so I could have a visual reference to the stiffening ribs and bosses. Although everything was cut using digital readouts and calculating cutter diameters it didn't hurt to have a line to see that you weren't going too far. Too much work at this point to have to start over.

 

Moving from one side to the next, excess material was slowly cut away. At this point it's starting to look like something familiar.








Although the steps look quite large in the pictures you have to consider the overall size of the part. Usually if I have an area that's large enough to get at with files to finish I will make the steps larger. If it's a tight area where I have to get in with burs and stones I'll make the steps smaller.

 

Here's a shot of the inner cavity with the pinion hole bored through.

 

Now comes the start of the finishing work. The area that's going to get worked on gets a coating of ink. This make it easier to see the high spots as you're working them down. Using
files, burrs and an assortment of riffler files the contours are all worked down until they're smooth.

 

With many, many hours of hand work the bumps and warts are all smoothed down until it looks like a tiny casting.

 

With most of the grinding and polishing completed it was time to do a little more machining on the outside of the case. For those of you familiar with a 9" there is a recessed area below the pinion. On a casting this area is cored out but on a part cut from solid it requires a different setup to undercut the area.

 

And finally a finished differential center section housing.
gbritnell

 

Well that's enough to digest for now. Stay tuned for all the inner parts, bearings, axles, spider gears etc. etc.
gbritnell

 

You are my new best friend. This is cool.

 

My eyes are stuck crossed now......

 

Double Wow!! Just incredible work. Thank you for sharing your craftsmanship

 

Really nice - I have this urge to reach out and try to touch it for some reason.

 

You sir are awsome. very cool.

 

Incredible! nice work

 

Once again, incredible work. Thanks for taking the time to document and post. It would be interesting to see your shop.

 

Wow, that is really cool! Nice work!

 

Hi 1964countrysedan,
My shop's not very sophisticated. I'm attaching a link to a short video of my shop. The only thing different is now I have a medium sized knee mill rather than the round column mill in the video although I used the round column mill on my T-5 build.
gbritnell
http://youtu.be/K7_O2jPpmEg

 

I wished you lived next door !!!!

 

You, sir, are either an artist or a psychopath because your work is just crazy.