9 inch Ford differential in 1/3 scale

[gbritnell]

Gentlemen,

 Here's today's update. I turned the ring gear from 12L steel. I then chucked it in my dividing head and trued it up. The proper indexing plate was installed for cutting 36 teeth. Having learned a little in cutting the pinion gear I decided to first remove some of the stock with a .025 slitting saw. I made 2 passes which cut down the side of each tooth. With that complete I installed the special made gear cutter and started making teeth. Although it was a larger diameter it didn't pound as much as the pinion because it was mounted closer to the chuck. By the time I finished cutting the teeth the cutter seemed worn out because on my reset pass it was still dragging on the tooth. There wasn't much I could do until the cuts were finished so I slowed the speed down and kept cutting.

 When I got through I pulled the cutter and it was in bad shape. I think I had tempered it a little too much and the cutting edge had worn back from the face. What to do? I have a couple of 32 D.P. involute cutter one being a #2 which has almost the same involute radius as the one I made. When I was doing my layout I ascertained this because I thought maybe I could use the 32 D.P. cutter.
I took the gear off of the dividing head and cleaned up 4 teeth. The dull cutter had raised quite a burr on the teeth. With a nice clean tooth profile to go from I put the ring gear back on the dividing head and mounted the 32 cutter. I set up one side of the tooth perfectly flat in -Z- and then slowly moved the cutter into the space until I established my total tooth dimension. I then recut all the teeth, first on one side then the other. The involute cutter was a little wider near the small end of tooth so it took a little extra stock off but the rest of the tooth form looked quite nice, and much smoother than with my home-made cutter.

 After I had all the teeth cut I dismounted the gear and test fit the pinion to it. The fit was very loose and the teeth on the ring gear were bottoming out in the pinion teeth. At this point I had nothing to loose so I mounted the ring gear back on the turning arbor and recut the face angle, taking small cuts and fitting the pinion to it. After taking about .012 off of the face the 2 gears seemed to mesh very well.
That was enough for one day so I put everything aside until this morning.

 This morning I cleaned up all the teeth on the ring gear. I then made a test fixture to mount the 2 gears to see if the centers and fit were as they were supposed to be. By adding shims behind both of the gears I brought them out to their correct engagement positions and with a little fine tuning of the shims obtained a great fit with only about .003 backlash.

 The ring gear teeth aren't the pretties things to look at but they work great so now I can move on to the other parts.
gbritnell

[steamer]

Thanks for that George...I'm going to look into that "standard cutter" vs custom cutter dimension thing...but that looks great!

Can't argue with success!

Dave

[gbritnell]

This is a video of the metal gear running together. I had to put my 3 corner scraper up against the pinion gear when rotating it backwards because there is nothing to keep it from moving forward and binding up against the ring gear. It just the natural thrust against the gear moving it.
In the full sized differential the gears are adjusted with shims on the pinion housing and by moving the ring gear from side to side with threaded bushings until a perfect tooth wear pattern is developed. I will do the same thing but with the fixture I was able to determine a base line for my shim dimensions.
gbritnell
<a href="https://www.youtube.com/watch?v=fW5wzl9lGaM" target="_blank">http://www.youtube.com/watch?v=fW5wzl9lGaM</a>

[vcutajar]

Bravo George.   

Vince

[Jo]

Nice and the way you did it doesn't look any more difficult to do than any other bevel gear

Jo

[steamer]

George,

Not that I need to tell you how to suck eggs.....( you are the master model engine maker here for sure! )

I don't usually draw the temper on small cutters...I've never had one break...but I've had soft ones get smoked because they were too soft.

Anyway....I think the cutting edge gets plenty hot enough during use to draw the temper..."right there" ....at the cutting edge.....

JMHO

 

Dave

[b.lindsey]

Beuatiful and well thought out as always George. Thanks for allowing us to follow along.

Bill

[ScroungerLee]

Nice save George, I am glad it worked out.  In the video is the noise indicative of anything funky?

Lee

[gbritnell]

Hi Lee,
Yes, it's probably because they're not a perfect match, involute wise. I plan on running them together with some very fine lapping compound. That should take the high spots off. I was very happy that there was no tight spot, loose spot conditions. With the lash set as it is they rotate very smoothly or should I say evenly. This type of gear making was a great learning experience. When trying to make precision gears the home shop is generally not the place for it. I have made spur and miter gears that run very smoothly but with those you can use factory made involute cutters.  From the first calculating steps, the cutter and mandrel making, through the aid of fellow builders, to cutting the plastic gears and now with the metal ones I probably have almost 40 hours. If it didn't take so darn long I might even try to make another set but who knows if they would be any better than these. Another consideration is the size. Most of the gears we make in the home shop are probably no larger than 1.500 diameter and this ring gear is 2.700 diameter.
gbritnell

[steamer]

Hey George,

As you pointed out...a 32 dp cutter in the 47 tooth range will have the same radius as the gear cutter...and a same pitch cutter in the 22 tooth range would cover the pinion....approximately....I'm concerned about the form...but it can't be too bad...it works!

The numbers I ran where for 20 PA gears....

Dave

[Don1966]

George that is some bit of work you have done. I can relayed to the amount of time involved.
Is it my understanding that 14.5 degree pressure angles are no longer made by manufactures and they now make 20 degree pressure angle. When you cut your gear do you tilt you mill or the RT and at what angle? Also at what angle are your bevel gears versus the pinion.

Don

[gbritnell]

Hi Don,

 It's pretty hard to explain the whole thing so I'll try to summarize. In the Live Steam article on making skew gears the author presents all the formulas for creating skew bevel gears. With the help of Dave (Steamer) I created Auto Cad drawings of my desired gear set.

 The gears are actually 20 pressure angle. When I cut mine I made the appropriate cutters for the job but knew that the profile of a certain involute cutter would match my tooth shape (close). After I realized that my cutter had worn to the point that it wasn't cutting well I figured I had nothing to lose, except a whole lot more time, so I got out the 32 D.P. #2 gear cutter and mounted it up. I then trimmed the existing teeth to get as close as I could.

 My mill head was set square and my dividing head was rotated on the mill table to the angle that was calculated in the formulas. This would give the proper angle to cut the teeth off of the center line.
Believe me, and Dave can attest to the fact that a tremendous amount of time went into the calculations for this type of gearing by Mr. Hiraoka. Although the formulas work well for their intended purpose when it came to what I was doing it stretched the limits of the numbers, diameter, centerline offset, tooth size etc.

 I certainly would have wished them to come out 'perfect' but with any gear type other than spur gears the home machinist can only approximate the tooth forms and as I said this one was way beyond what I have ever done.

 I have to make some plain old bevels gears for the spiders and at this point I am looking forward to them. They should be a 'walk in the park' compared to these monsters.

 The biggest thing about this part of the project was the learning aspect. I enjoy learning something new every day.
gbritnell

[steamer]

Kozo certainly did put some work into that .....that's for sure....



I made up the spreadsheet using Kozo's article...and since I do stuff like that all the time..it only took me 3 or 4 hours to do in excell...I was sick anyway...and it took my mind off my condition...so it was a welcome break......but as I used quite a few of Kozo's drawing images as part of the spreadsheet....I have not made it a "public" document.   Kozo's article is readily available through Villiage press.   If your making skew bevels....get it, as there is a lot of instruction in there you won't get any place else.

Can't wait for the rest of the rear end build George!.....got the popcorn going!

Dave

[gbritnell]

With the gears cut I am able to move on to whittling aluminum. I started with a piece of 4 inch diameter aluminum (6061) You might wonder why I went with round as opposed to square when I set about somewhat squaring it up anyway. First I had a piece on hand and second it saved a little by already having the corners knocked off.
After cutting a chunk and facing it to thickness in the lathe I moved it to the mill to square it up to the required dimensions. I cut one side, rotated it 180 and cut the opposite side. My habit to make pieces square is to clamp them very lightly in the vise and while holding my square tightly I rock the piece until it butts up against the square. I then tighten the vise.

[gbritnell]

With the overall dimensions of the block set I used my edge finder to find center. My readout has a nice feature for doing this, touch one side, touch the other and hit the 1/2 button.
The flange depth was cut, the corners were knocked off and the holes were drilled and tapped.