Machining Stuff,,The Law of finding center

The Cynic in my head is screaming at me. he must be heard...

(edited) I think Those super tight and techie ultra tolerances are much more nominal than actual.

You can throw the dial indicator measurement off by more than .006 just touching it to use it.
Theoretically you could say if you had .002 clearance between the pilot shaft and the bearing and the ****** hole was offset .010 that you have .008 interference causing preload on the pilot shaft by the bushing...but wait...
Look at the nose of your crank with the engine running...
Flexes don't it ?
It doesn't turn true, neither does the rear because the crank is whipping and distorting with every power stroke.
feel your input shaft... it has some play doesn't it?
it will flex and move around as well.

There are someplaces where such strict tolerance is essential, the trick is knowing what counts and what is muffler bearings. I guess it depends on how tight the ****** parts and pilot sahft bearings are
Check this out:
nominal:
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the academic technitians will argue who's the best all the way down as tight as you can measure which may be fart far awayfrom what would have done the job.
Where do you draw the line to meet functional requirement?

actual caveman tech:

...from the HAMB technical archives.
http://www.jalopyjournal.com/forum/showthread.php?t=315269&highlight=caveman+bellhousing

 

that might be an idea as well ,,would then just need to make mounting holes in teh GM bell

 

Although +.006 and -.001 is .007 tir I would agree with the guy in the vido that is is well within useable standards. How is wing going to get this close or even within .030 tir just laying her plate on the bellhousing? Of course some people never owned a torque wrench. Never measured a bore and felt the the resulting product was good enough. Fine. Some others feel that anything worth doing, especally if you are doing it for fun, is worth doing right. Your choice. If you turn your bearing retainer .122 to fit the Chevy "big hole" look first to be sure your not screwing it up by making that diameter smaller than the snapdia. into the trans. Per '64 Ford transmissions (before they went to the duel bolt patteren) had the .100 smaller dia. You can either find a per '64 retainer or turn yours to fit the early bellhousings. As did I to fit my Packard bellhousing.

 

All supers***ions aside, it is as impossible to do something right
Right is a concept not a reality... but it is possible to fail or succeed.
I'm in no way criticizing the quality of the work, I'm just being geek.

 

I spent 33 years as a toolmaker and an A&P with a major US Flag carrier. I hope you are in some other line of work.

 

That's pretty cool and No, I don't make tools or work on an aircraft carrier. I could...time, There isn't enough time.
Construction...Journeyman carpenter. It moves at a little faster pace with easier tolerances but it's still applied science.

If he bolts his trans on and it don't come off, the car goes down the road manufacturers and the ****** doesn't wear out or break isn't it done correctly?
Like setting up ring and pinions... after you know what your doing...what the end result needs to be... then the dial indicator is obsolete and slows you down for that purpose.
Take setting up a ring and pinion by hand for example...
You can use hand tools and marking compound and do it by feel without the crutch. The crutch is your teacher
Some things can be taught out of a book but there's a higher method for anyone willing to take the next step.

 

Were it mine, I would take a piece of 3/4" plate (steel for a steel or cast iron bellhousing, aluminum for a cast aluminum bellhousing), big enough to get the bigger of the two bolt patterns on, chuck it up in my lathe, and turn a boss 5" in diameter and ~3/16" tall.

I'd then lay the bellhousing on the table of my Bridgeport (engine mounting face down) with gage pins in two opposing holes a****ed to one edge of a t-slot to align it with the X axis, and indicate the trans mounting face to check it for flat.

If it wasn't flat, I'd take a skim cut with a face mill to make it flat. If it's already flat, I'd find center on the registry bore (big hole), and set my machine zero there (X & Y at the center of the big bore, Z at the old trans mounting face).

You can find center either with a co-ax indicator, or a good edge finder (touch off one side, set zero, move one axis to touch the other side, go back half way via the dials or DRO, then using the other axis, touch one side, set zero, then touch the other side and go back half way, then reset both zeros). I prefer the co-ax, because it is more precise.

Once it's on the table, flat, and centered up, I'd bore the big registry hole out to 5" to make a very tight slip fit (or maybe a thermal slip fit) on the boss you machined into the plate. I'd then mate the plate to the bell and clamp it into place.

Now the plate and the bell are concentric about the transmission mounting bore (and your machine zero). It's a simple matter to move the machine around to drill and countersink the holes to mount the adapter to the bell housing, and drill and tap the new transmission mounting holes (all the way through both pieces).

While this is all still mounted, I'd return the machine to zero and drill the center out of the adapter plate using the biggest drill I owned. Once the hole has been opened up, I'd then step the ID out with a boring head until I had a bore with a nice slip fit on our transmission registry ring.

Then I'd take a face cut on the trans mounting face of the adapter, 1/2" up from the old trans mounting face (to account for the extra half inch of input shaft on your Packard trans), check it with an indicator to make sure it was flat, and call it a done deal.

If you had your **** really wired straight, you could have already dialed the bellhousing in relation to the engine crank before all this started and found how much and in which direction the dowel holes needed to go.

If they needed to move much at all, it would be very easy to weld up the existing dowel pin holes beforehand and then bore new ones in the right place while it was set up in the machine.

Without the proper tools, this will be a difficult project to do accurately. You could "eyeball" it and get it close enough to function decently, but you may also end up with an adapter that kills transmissions too.

The only good way to lay out the center of the circle is to use the perpendicular bisectors of two non-parallel chords.

An easy way to ensure perpendicular is to use the 3-4-5 method.

Lay a straight edge on the big hole and clamp or tape it down, not across the center of the hole, off to one side. The inside edge of this will be our first chord.

Find the mid point of the chord and make a mark. (This is easily done if you had the presence of mind to use a ruler as the straight edge. ) Then move 3" down the ruler and make another mark.

Now, measure out and mark two lengths of string, one 4" long, and one 5" long. Hold one end of the 4" string on the mid point mark you made on the chord. Hold one end of the 5" string on the 3" point you marked on the chord. Then hold the other end of both strings together and pull them tight. The axis along the 4" string is exactly perpendicular to the axis of the chord (or ruler in this case). Lay another straight edge along this axis and clamp it down. We've now divided the circle exactly in half.

Move around the circle about 80 degs and do this again with another set of straight edges and your strings.

When the two bisector straight edges cross is the center of the bore.

This method is only as accurate as your ruler reading eyes, and the stretchyness of your string, but it'll get you close.

Boring a hole this big accurately and without a boring head, milling machine, or lathe is anyone's guess though.

You might get close enough with a hole saw for the Packard trans registry bore, but I'm at a bit of a loss as to how you machine a circular boss to fit into the chevy bellhousing hole with a drill press. Any setup that includes a boring head or ad-hoc fly cutter is likely to end in failure and s***ches.

Sometimes, you just need to use the right tools, ya know?

 

Let's pretend for some crazy reason I want to put a dodge ****** behind a pontiac 400 and I'm going to build a bell from plate or attach a ****** plate to an existing bell....
figure it has 3"mains..I might get some 3"od tube. have a bushing made to fit the input bearing retainer snugly and centered inside the 3" tube and there's where the hole in the fabricated bell needs to be.
Just an example...
You can also have something made up that bolts to the back of your crank and locates the hole. Theres a million and 1 ways get it done servicably if not the NASA method

 

Heres what id do if I didnt have a bridgeport.
Clamp the bell housing to the the base of my drill press, use a dial indicator chucked into to my drill. Dial it into center, (making adjustments to the bell housing to get it center). Bolt down the adapter plate to the bellhousing. Drill a hole large enough to get the input shaft in. Remove the adapter plate, slip it over the trans input shaft. Mark the trans bolt holes and drill them. Then Id take the crude adapter plate to someone with a mill, and have them make the hole to my needed size.

You might need to use something like a clear plastic template to locate your transmission to bellhousing bolts for drilling.

 

I still have not seen how Wing is going to locate her spacer on the bellhousing. Eyeball I guess. Snap string won't be much help. The bar through the main bearings would be nice, Pretty much the same idea as the snap rings used by Packard and Chevy and recomended by myself, clod that I am. Ford and Chrysler, Toyota and VW all use that method as do all the other manufactures I ever saw. Millions of cars do. But carpenters being presision craftsmen that they are don't. After all the drywall guys can cover up most anything.

 

If you have the real estate on the bellhousing, that would be the way to go. Of course barring weakening any of the structure of it.

I've turned down bearing retainers to fit bellhousings before and I've made up spacer rings if the hole in the bellhousing was too big.

Bob

 

Words to live by


can we get back on track here?

I am positive at least a dozen hambers here have the ability to do this swap without consulting NASA. Yes, if those guys had the parts right in front of them, the ideas would flow much quicker.

 

RichFox; do you mean how "locate" as to find out where the plate needs to be, or how to keep it there?

If you mean how to keep it there after it is centered, why can't pressed in dowels from "adapter to bell" do the job?

 

I think I covered the dowels on an eariler post. However had I wanted to ask "How will the plate be held in place?" I would have. I wanted to know how she was going to locate that place. I think that was what she was asking at the begining of all this. Plenty of ways have been suggested. I'd like to know which one got the nod.

 

me too.


I only asked because "locate" could mean either....in garage language

 

to be honest ,,just so much info,,( thanks all ) lil overwhelmed,,reading it all understanding about 1/2..first thing is to borrow a few proper tools and measure stuff..gonna transfer patterns of each piece onto one surface and start a mock up.. I'm sure that with all teh info,,I can get this done and it will work right..


Though I will say,,the cutting the retainer or bell hole to fit each other ( which im guessing would then pu things in alignment regardless ) and shortening input shaft.. Seems a very simple direct route...

anywho,,thanks again all ,,and will be working on this over the weekend

 

Looking from herre, it looks like you could:

Bore the Chevy bellhousing .125

Shorten the Packard input shaft 1/4"
You may have to have the splines ground back - on a precision grinder - to match the Chevy pilot hole depth.
You may need a new crankshaft bronze pilot bearing as well, but that's easy.

Check to make sure the Packard retainer where the throwout bearing slides fits ok.

You may luck out and find that the Chevy throwout bearing fits or a proper size bearing fits the throwout arm or you may have to adapt the Packard arm or more than likely modify the Chevy throwout arm to fit a Packard size bearing.


Plugging the bellhousing trans mount holes and drilling to a new pattern may be required.







Take a look at the combination square set here: http://www.rockler.com/product.cfm?...utm_medium=se&utm_campaign=V9128&cookietest=1


Note the center finder head on the far left.

With the center finder, 2-3 lines scribed on a circle will locate center fairly well, but not as good as a dial indicator will.

Just a fwiw to make life easier in the future.

It may seem expensive, General makes a pretty good one, probably for much less $$, but don't faint when you see the Starratt combination square set price....

 

Since you lose the locating feature of the front bearing retainer, it would have to be "pinned" in 2 places. Still not the best way to go for long-term reliability.

Bob

 

A thought on this...layers and layers needing to be centered. How about a sort of short tube made to press onto the register at front of trans, long enough to go through adapter plate and into the flathead bell? Seem like it could be made to diameter of largest hole if hole is big enough, other hole or holes centered and bored out to match. That way trans snout would register all the pieces with no need to pin, they could just be bolted together.
Bellhousing then needs to register to engine if not going back on a flathead...

 

I thought this was going on a SBC? Anyway i thought of offering to make a step ring to do what Bruce is suggesting. One could be cut out of 1/2 inch 6061 in an hour or hour and a half. that would locate the spacer she has now for pinning to the bellhousing. But I think the decesion has been made to do this without machine shop intervention. So be it.

 

Yes it is SBC ( used the flatty bell just as an example of teh center finding thing )..and no decissions have been made or anything cast in stone,,you guys dumped a ton of iinfo here,,lot of reading and rereading ,,,wanna understand and look at all ideas offered ,,lotta info to process

 

It is an interesting problem and junkyard ingenuity will prevail for a solution. Try to lay out a side view of the cross sections of all components on graph paper in scale first. I cheat and do it all in CAD.

If you can drill and tap the SBC bellhousing and have the holes fall out in strong enough sections, that would be great. You may find a cast iron truck bellhousing to be best for that.

If the front bearing retainer is too small for the bellhousing, make up an adapter ring to fill the gap. If the retainer is too big, take it off and have it turned to fit.

All of which means machine shop access. Who here is in your area that could help?

Bob

 

Another thought...tech archives, someone did an interesting tech (caveman was in the ***le) on making an adaptor from scratch.

http://www.jalopyjournal.com/forum/showthread.php?t=328096&highlight=caveman&showall=1

 

Have 2 very good machinist's I use for stuff I can't do ( and don't have teh machines to do ),,I just like to do as much as I can myself,so when I do go to them I can say..here I need you to make me this,,and this is what its for..and give them templates or whatever.. Instead of ...I have this problem can you make something to fix it ?

and they are good cause if I don't have it all right they point things out

 

More caveman tricks...

tip: Wiki Iteration and heuristic
I had another idea
A way to center something in it's variance fairly accurately.
imagine your Bell bolted on the back of the engine, the pilot bearing in place and the adapter on the ****** and inserted into the bell. You would need to have everything pointed up and down with the ****** straight up in the air so gravity doesn't throw off your measurement.

clean the back of the bell and color it with machinist die or something you can scribe. The mess is going to have some play to it.
If the bell facing is perpendicular to the crank centerline, As you move the ****** and adapter around on the face of the bell it should remain parallel to the crank line even though your taking it out of alignment with the centerline.
To find center, move it towards 12:00 till it stops moving and mark the 4 sides of the adapter on the back of the bell. you now have zero play in that direction. do the same for 3:00 6:00 and 9:00 positions.
You should end up with a large square and a small square scribed out on the back of the bell.
The adapter position for center of crank will be when the adapter lines up with a third square created by scribing it's lines halfway between the lines of the larger and smaller square.

A carpenter can measure a room and divide the number but when you take the half number and measure it out from both ends of the room to center it is 2 lines not 1 because of error.
You measure more times.. A point between the lines will be exact center by logic even though you failed at finding it directly.


The center of something is a combination of the average of it's extremes and the average of it's mean.
Human ingenuity has discovered a way to measure something beyond the accuracy of your tools with functionally accurate results. repe***ion.

 

Just waller out the mounting holes it"ll line up!

 

A micrometer has threads in it. these threads are not exactly the same distance from each other and they have play between them. It becomes accurate because there are many threads. It is easy to measure an inch.

Bubba is a blacksmith about to become a machinist cuz he's a hard worker and good at cipherin'
He makes some rod stock
he makes a chisel out of rod stock
he takes a rod and hammers a 3 sided thingamajiggy out of it
He takes the chisel and cuts teeth into the 3 sided thing. Now he has a file.
He makes a bolt by measuring out an inch starting at the end on a rod with his measurer.
Then he marked out 1/10" marks on one side of the rod along a line.
Bubba started filing a groove spiraling from the end to one inch through a new 1/10 mark every orbit around the rod.
He made 2 almost the same, best as can be done by hand. they look rough but he has faith.
He takes the other rod and chisels a couple grooves opposite each other with sharp edges in it along it's length.
Now bubba has a bolt and a tap both with a thread pitch of 10 threads per inch. He punches a hole in a 1/2" plate and runs the tap through it. now he has a sloppy old handmade ugly bolt and nut.
His bolt and tap had ugly crooked old threads but the plate"nut" seems to have straighter and more even thereads. This is because every thread in the tap contributed to the threads in the nut. Iteration...it is the average by repe***ion of all qualities of the sloppy tap
Good for measuring right???
Not yet
Everything is still pretty sloppy so he punches a hole through a 2" block of steel. He made another nut a little bit smaller and cut some grooves accross it's threads. He used this one to make a new bolt and a new tap with pretty threads.
He made alot of them because now it was easier. All he had to do was turn it to cut threads, he hung up his file.
He used the new tap to thread the 2" block for the pretty bolt which now fits pretty good and screws in and out smoothly.
The threads are still a little geometrically imperfect but a theoretical 10 threads per inch x 2" means he has a total of 20 threads in engagement. The sum of the imperfect pitch of each thread divided by the number of threads gives an average thread pitch which is...excactly 10 threads per inch even though each thread is imperfect...Teamwork!!!
Now Bubba marks the bolt with a witness mark.
He draws a clock on the end of the block but this clock has 10 hours in it.
Starting with the witness mark at any point on the 10 hour clock, as Bubba rotates the bolt 1/10 of a rotation and lines the witness mark up with the next clocking mark...the bolt moves a perfect 1/100th of an inch into or out of the block. he mounts this block in a frame that will not flex and now he has a micrometer. He builds other tools including a drill with a clockwork gearing driving a screw that shuttles a cutting tooth along the rotation and he begins to make more and more perfect screws gears etc.
By doing simple things over and over again you can reach "perfection" which is basically the ideal you are trying to attain. carefull repe***ion will keep returning smaller and smaller variances but there is a point of limited returns. there is simply no need to continue the process beyong the engineering specifications of what is being built

Iteration is either doing something over and over again like taking the result of an equation and plugging it back in and doing it again...or it is trying every possible combination over and over again in every way possible to come up with a field of results. In this case the individual threads meet each other in every way possible within the constriction of a plan and a perfect execution with no tolerance for fail is the result

 

Sorry, you lost me after the 6th paragraph. What are you trying to say?

 

ok,,again thanks to everyone for there input,,advise and help,,I do have to say much of this kinda went over my head,,as it seemed things got complicated ,,then those things got complicated,,then those things got argued .........so um


yes I need to find proper tools to do the job right


I like to do as much as I can myself,,it would be swell to have a small machine shop or hell all the right tools to just "do" but I don't and most others I don't think do

Those who do I sometimes think loose sight of other "hand" ways to do things as they are fortunate enough to have the machines to just up and do


so
1: yes it needs to be on the money to work right,,be safe and last
2: certain tools will be required


Based on all the info I have read ( understood ) here is a basic theory I have come up with



Things that come to mind:

1: If bellhousing hole is what lines up input shaft then it would stand to reason.

a: cutting down the retainer to fit bell hole

b: enlarging bell hole for the retainer
( which in this case is one 1/8 of an inch )

Seems would both achive the same thing and both be correct.

2: The adapters are 1/4" thick to shorten shaft lenght for seating in pilot hole.
No changes are made other wise to the input shaft. Therefore it would only make sense that if you remove a 1/4 " from the shaft ( which the adapter would be doing ) then it should all fit and be the same,had an adapter been used.


Last matter of concern would be where the bolt holes would fall out for the trans....

after all that,,what is it tht dictates what throw out bearing is used? Can I keep the Packard one ?

and I guess that depends on if it will match up to the fork.

if thesplines match then can I go with the chevy Clutch and Plate ( as its a Chevy flywheel.

Then lastly but seems straight forward pilot bearing ,,find one that fits

so this is my backyard no fancy tools take on the overview

I could be wrong on many levels,,lol who knows,,but this is where I think Im gonna start..have a few extra parts I can sacrafice to check this theory and if it works,,horray for me,,if not,,,on to more complex ways

 

Hi little wing...looks like you got it, hope it works out for you.
The's prolly a selection of throwout bearings that will fit the ******. The closer to the clutch fingers it sits the sooner the clutch will release when you push the pedal but it has to not touch the clutch when driving or it will wear out fast.
You can mix and match pressure plates and discs. the pressure plate needs to bolt to the flywheel and the friction on the disc needs to be pretty close to the size of the ring in the presure plate and the disc needs to spline up with the ******.
A packard throwout bearing of the same length as the chevy one should put it in the right place for the chevy fork to work it in the chevy bell. there are also different length clutch fork pivots that screw into the bell to play with. I put a hays steel billet flywheel in my pontiac with a lakewood bell and had to add some length by splicing to my clutch pivot so the clutch would work right and the arm would not bind against the arm hole in the bell. It took a few tries to get it right.

It's a fictional story about Bubba and how he manufactured something accurate by hand out of nothing by applying his mind and using simple methods. I based the story on how a micrometer works (the relationship between the threads and the clocking position of the screw) and what makes it so accurate(repe***ion of application).