9 inch Ford differential in 1/3 scale

[gbritnell]

Gentlemen,

 When I started this project I posted a question on trying to make gears for it. As the originals are hypoids I wondered if it was possible to create such a thing in the home shop. With much investigation I concluded that it was almost impossible so the  next step was to try and make offset bevel gears or skew bevels.

  I was put in touch with a fellow that helped me out with some calculations and then our own Dave (Steamer) made me a spread sheet. Thanks Dave.

 Using all of the numbers I set about making up the cutters, mandrels and such for cutting the gears, from Corian first. Well I ended up with a pinion and gear that resemble what I want but it was by trial and error as a couple of the dimensions didn't make any sense. I am at the stage now where I am trying to figure out if an off the shelf involute cutter will produce the desired tooth shape I need. The cutters from the build article have 1/2 of the involute shape and 2 passes need to be done with the cutter being flipped over to create both sides of the tooth. My assumption is that these cutters have an involute curve so why wouldn't the proper numbered cutter be capable of doing the same thing with the 3 step method for cutting miters and bevels?

 Here are a couple of pictures of the project. The first 2 are of the full sized differential. I cleaned and disassembled it to make a set of drawings. The 3rd picture is of the ring gear that I cut from Corian. I'm at the point where I have to make up a fixture to mount the 2 gears at the proper offsets to see if they will mesh properly. This part of the project is going to be the most time consuming. I know how to sculpt a hunk of metal into a recognizable object but getting these gears right it a whole new ball game.

gbritnell

[Dan Rowe]

Very nice looking skew bevel gear George 

I am looking forward to watching this build.

Dan

[pgp001]

I have a set of sketch drawings for a gadget that my late father designed.
It will convert a Myford lathe into a spiral bevel gear generator.

He never built and tested it, but the concept is good.

Phil

[b.lindsey]

Oooooh...another great project to watch and learn from George. So in the end do you expect to have the engine, transmission, drive shaft and differential all mounted together? Looking forward to this as I do with all your builds!!

Bill

[vcutajar]

George

This looks to be another of your projects where I will be learning lots of new things.  Pulling up a chair.

Vince

[ref1ection]

I wish my first attempts were as photogenic. This should be a very interesting build again George. I'll be watching with interest.

Ray

[Jo]

I am watching with great interest 

Jo

[Mosey]

I'm hanging on to the rail...let er rip!

[steamer]

George,

the instantaneous radius of the tooth can be approximated by the( ( base circle diameter)/2) x sin (pressure angle)

The challange will be to cross reference the commercial cutters with the actual required radius....but there must be a match out there somewhere.

Gail Graham has a nice spreadsheet that can do this....but I don't want to volunteer that without him speaking up on the subject.

Dave

[Don1966]

George I would follow any of your threads, I learn from every one of them. I am pulling up a chair so get after it bud. It will be interesting to see how you go about doing it. And I have never made a bevel gear so hopefully I will learn how.

Don

[zeeprogrammer]

Oh  yes. I'll be watching too!

[gbritnell]

Gentlemen,
I think I have made some progress. I guess it's just a matter of trusting what you're doing and not worrying about what the parts look like. By that I mean I was mentally comparing what I knew a bevel gear tooth looked like and just couldn't wrap my head around the convoluted shape that I was getting.
Anyway, I'll start more or less from the beginning.
The first group of pictures are the cutters and arbor. These type of cutters are detailed in Ivan Law's book on gear cutting. I started by making the tool buttons to cut the involute shape on the cutters. There were 2 sizes, one for each of the pinion and gear. The pinion cutter was no problem as the O.D. of the button was .155 but the large profile has a radius of .695 and I only had a piece of 1.25 drill rod. I had already made up buttons for a previous attempt and the large one from that set was .565 so I plotted out the cuts to make using that button. With the tools at hand I cut a couple of 1.00 discs from drill rod, faced them to thickness, drilled and  reamed .312 and mounted them on an arbor to cut the profiles.
Trying to cut the large involute profile necessitated putting my lathe in the slowest belt speed and putting it in back gear. I would say it was around 50 rpm. Getting down to the final profile was hard even at this speed because just as you lingered for a second at the finish dimension it would want to chatter. The trick was to approach the finish dimension and just before the chatter started, back off the tool. I got a minute amount of chatter which didn't hurt anything.
The discs were then put in the mill to have the sides cut down to produce 2 cutting edges, one for each side of the tooth. This cutter only has the involute on one side and 15 degree clearance on the other.
After the milling was completed they discs were hardened and tempered.
gbritnell

[gbritnell]

I had posted the ring gear previously so this is a follow up with the pinion gear. I started out by mentioning how odd the tooth form looked after cutting. As you can see it seems to have a pronounced hook to the tooth. That's  because of the angle of intersection with the face. If you look down the tooth it has the proper profile. Another thing to remember is that these teeth are 20 pressure angle teeth so they are of the stub form compared to 14-1/2 degree tooth form that I'm more familiar with.
The first 2 pictures show the small and large ends of the gear with the tooth shape. The large end has a pronounced boxy look to it because of the tooth form but as you will see it seems to fit quite nicely into the ring gear tooth cavity.
The next 4 pictures show the engagement of the pinion to the ring gear. Another note here is that the back and the front of the pinion stick out beyond the inner and outer diameters of the ring gear because the working area of the tooth is on a line across the face of the ring gear.
gbritnell

[gbritnell]

I know I can speak for myself and I'm sure there are quite a few others out there that just can't wait till all the parts are made to try and fit things together to see how they work. With that said I chucked the pinion in the lathe and held the ring gear against it to see if all the hours of calculating, tool making and cutting proved out. As one can imagine I was overjoyed at how well the to gear ran together. Now if I can get the metal ones to do the same I will be doubly thrilled.
gbritnell
<a href="https://www.youtube.com/watch?v=up1-lQm_32c" target="_blank">http://www.youtube.com/watch?v=up1-lQm_32c</a>

[steamer]

Glad that's working out for your George!

Dave