A flathead V-8 engine

Gentlemen,
I thank you for the gracious responses. One of my enjoyments is designing and building engines. The other is sharing it with builders and modelers like you.
That being said here is the next installment in the build.

The bellhousing was quite a piece of machining. I start with drawing and metal in hand but have no way of knowing what the time involved will be. I know what my general plan of attack will be but naturally things change as the process gets going.
In this case I started with a piece of 6061 aluminum round bar 5.75 inches by 2.25 long. The first step in machining elaborate parts like this or any other is to start with the inside shapes. The reason for this is quite simple. If you machine the outside there is generally no place to chuck or locate to because of the shapes of the surfaces. Once the inside is done you can use a vise, clamps or fixture to do all the outside machining.
I gave myself some layout lines and chucked the blank in the 4 jaw chuck. Once centered on the layout lines I bored the center hole and then roughed out the extra stock with a heavy boring bar.

The part was then moved to the rotary table to finish the inside. As with all my contoured parts I make up a step-off chart to form the radii. The rotary table was centered, the zeros set then the part was mounted, centered and clamped. I went in with a .50 diameter ball mill and started stepping off the shape. Once complete I switched over to long 2 flute end mills to cut the inside shape of the clutch area.

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I forgot to mention. While doing the inside shape I drilled all the mounting holes, some for the screw clearance and some for tapping. The tapped holes would be used to mount the housing to the fixture plate for all the outside machining.

With the part screwed to the fixture plate the rotary table was put back on center and the previously bored center hole was indicated true. I had given myself some rough layout lines as a guide but this is just for roughing the heavy material off.

I had to make two step-off charts for the outside radial shape. The first cuts were for the radius on the top of the two ribs that are cast into the full sized bellhousing. These go from the transmission flange to the top outer mounting flange. Once the first cuts were made the part was removed from the table and the steps blended smooth so that layout lines could be applied as a guide for cutting the second radius. There is no easy mathematical way of doing it because as you work your way down the radius the contact point with the layout line changes.

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One of the nice thing about machining with a part on the rotary table is that you can dial up all the different angles without having to move and reclamp the part like you would normally do if it was just clamped to the mill table. The piece was slowly whittled away, stepping into corners and working down the previously roughed shapes. An endmill with a small radius was then used to clean up around the mounting flange and provide clearance for the mounting bolts.

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The area for the starter needed a boss added so this was turned and threaded then lightly pressed into the housing. From the inside I securely fastened it with a special made aluminum screw.
The other area that needed finished is where the clutch throwout arm enters the housing. I set the bellhousing in the mill vise and cut out that window. All that remains is filing, burring and polishing.
Here are some pictures with it mounted to the rear of the block.
gbritnell

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I admire your patience in the step-over work. I never developed the knack for it for some reason. I think it would be nice if you'd elaborate just a little so some who may not really understand how that's done. I'd say they would gain new appreciation for your already outstanding work.

I know I appreciate you showing your work, and so does the rest of the group.
 
In response to Tony's question about how I step off a shape I will try to explain it as simply as possible.

When I served my apprenticeship as a metal patternmaker, late 60's, our shop did a lot of repair work on patterns and coreboxes. We had some duplicating machines that would be set up for doing large areas but when a small area needed to have the weld brought back to the original surface or a small patch needed to be machined they were all done by the step off method.

Each of the old timers on the mills had their own little reference books that had standard radii calculated using standard ball end mills. These books were very valuable considering all the math (trigonometry) had to be done by long hand. There were no calculators at that time.

The process went like this. You take a given radius that needs to be cut and add the radius of the desired cutter. You then calculate the distance of the step that will give you the desired cusp (height of material between cuts). Once you have that then you continue with that same angle of step to give you the numerical coordinates (X or Y and Z) you need.

You might think, "why step something off when you could just tilt the mill head or put the part on a sine table and cut it?" Well sometimes the area in question is a pocket that has no angular access, meaning you have to go in from the top so stepping is the only way.

I have attached a document showing both internal and external calculations.

With today's technology and CAD programs it makes it fairly simple. Take you part curvature, add the radius of your cutter, set up your step spacing, do an array of the radian and then add coordinate dimensions.
The hardest part is paying attention to where you are on you chart. Over, down, over, down, over, now where was I?

gbritnell
 

Attachments

  • SINE-COSINE DRWG.pdf
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This is amazing!

My first experience with auto mechanics was when I was about 8-10 years old and my Dad had a 1950 Ford Coupe with a flat head. This was circa 1960 or so. My Dad, one of his good friends, and I replaced the engine with a new short block. I'm not saying I did much except hand them tools and maybe turned a few wrenches. But, I remember, for me, it was so much FUN!! So this thread is really brings back fond memories of those days!!

Dave
 
George, your work continues to leave me in awe. Keep the pics coming, I am thoroughly intrigued!
 
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