Machining Stuff,,The Law of finding center

Ok,,all you smart people with protractors and such

Is there a universal law or rule in Machining to what is center ?

Making an adapter so need to know a few things

Like am I close with this diagram ,,is center measured from the center of the bolt holes or.............

 

Center is found by dialing in the transmission pilot bore.

 

is'nt the center where the input shaft set by that bolt pattern since thats what lines up the trans, so the input shaft goes where its suppose to ?

I have to make another pattern over the bell pattern

 

Put a square around the circle then X the corners

 

You can't find center using those bolt holes (irregular pattern). Dial the hole like pete1 said. Making an adapter plate, I would first outline it on a template, then transfer from the template to the work piece.

 

Are you finding the center of the trans bore or center of the holes?
To get the holes center get some transfer screws. Screw them in leaving only a small amount protruding. Then stick your plate on bellhousing and tap with a deadblow. (if the holes are not tapped, use a transfer punch) Drill your holes in plate then bolt up plate to bellhousing. You can flip over and scribe the trans bore onto plate from the inside. To find the exact center you must indicate the trans bore.

 

you know what's way easy?
first, lay the thing upside down and transfer the hole onto a piece of paper
then take a ruler (not a measuring tape) and see what the longest line is you can draw through that circle (that would be, if you circle has a diameter of 3", then 3" would be the longest line you can draw).
then do that again. where they cross is dead center.
good thing is, you don't need to have those lines crossing each other at a 90 degree angle. anything is fine.
longest line through a circle will ALWAYS go through the center, so two longest lines will ALWAYS cross each other in the center.
to make sure you did it right, pull a 3rd, 4th, line. they should all cross at the same point.

then of course there are other (more mathematical) ways. but this is easy, fast, and fool proof.

 

Surly ya'll know how to find the center of a circle. Your not even close. http://www.mathopenref.com/constcirclecenter.html Hope this helps. Good luck!

 

ok well I know the size of each circle,,just trying to find center for both as one hole will be bigger than teh other...Will sit down with info give and return

Thanks

 

You probably already checked it but; Make sure the donor transmission input shaft is long enough to reach the engine pilot bushing, including the thickness of your adapter.

 

I guess it depends on how accurate you want to be.

You could bolt the Bellhousing to the engine, put a dial indicator on the crank or flywheel and see how much the hole is off center from the crankshaft centerline.

Or you could just measure the diameter of the hole in the bell, make a shoulder on your adapter plate that fits it, and chuck the plate in the lathe on that shoulder.

At that point you only have to push the center off the tailstock into the plate to find the center ( or drill it)


I'm no machinist, but those are some of the things I'd try...

 

Take a comp*** with a pencil on one end and draw a bunch of arcs using different spots of the outer rim as your center pivot. That should get you really close.
Justin

 

Hmmm, I've seen something like that thing in the center,... but I just can't place it

 

I knew you old dudes would say that. I had " No comments from the peanut gallery" but decided to delete it.

 

using the 2 crossing diameters is just as acceptible, just matters whether you have a right angle device ,or a comp*** and straight edge laying around.......both just as accurate.

interesting link though,thanks.......brought back math cl*** memories

skull

 

been watching too much star search, lol


skull

 

The input shaft of the transmission must be concentric with the crankshaft within .006" or you'll have shifting problems and pilot bushing wear.

 

If I really wanted to know where those bolt holes were in relation to center, I would mount the bellhousing as you show it. Put a couple of bolts in the top two holes and square them with the table. Clamp it down. Indicate the center of the pilot bore. Set your zeros. This is eaiser if you have didgetal reed outs. Pitch out and up to the top holes and mark down the measurments. Do the same with the lower holes. Now you have a map of the bolt pattern that you can transfer to anything and not worry about lining stuff up and using transfer punches. You do have a mill?

 

first step get a dial indicator,,,thanks again everyone

well that is not the bell I am using ( just used it for my theory/question )

I have diagrams of both bell patterns with the correct measurement ( have a bunch of those diagrams if any body needs one )

No ,,no mill ,, Drill press and friends with teh proper tools and machines,,im sure I could give them the info and ask them to make it for me,,but I'm stubborn and like to do as much as i can myself

 

Not as elaborate as other methods, but when I read this, I instantly knew what he meant.
This is good, common-man thinking.

 

what is the adaptor for?maybe someone has one already and can foward the specs to you.

 

Packard Transmission to SBC bellhousing

 

Set the cover face down - clamp it to a pc of aluminum & use transfer punchs to set your bolt patern.

While your still clamped up - set up in a drill or mill & indicate in your bore.

After you find ( zero ) with the indicator - put a punch in the collet or chuck of mill/drill & pull it down till you make a punch mark.

Use the center mark in your plate to make a center bore - use bore as center for the SBC patern & rev transfer punch from block.

Now you have all the points you need for an adapter - with no math.

 

I read every suggestion and all I got out of it was a big headache and a desire to never try to do this. Isn't this why god made machinists?

 

um ..thats what this hobby is all about learning ,,and the more you learn the more you can create

 

I made a simular adapter to put a (don't laugh) Pinto transmission behind a Lotus 907 engine. Firist I had to know the diameter of the pilot hole in the Louts bellhousing. It was bigger than the Pinto bearing retainer. The bearing retainer snaps into that big hole in your bellhousing and locates the input shaft on center with the crankshaft. If properly made. The bolt holes only hold it on, thek do not locate it. Since on the Lotus/Pinto deal the input was ...614 longer than the bellhousing was tall, I made a spacer with a collar turned to fit snuggly into the bellhousing and bored through in the same set up to fit the bearing retainer of the Pinto trans. Then I layed it on the trans and transfered the bolt holes through and drilled clearance holes. Then I layed the spacer on the bellhousing and drilled it to the same hole pattern. So I could have done that with out using the mill but i did have to use the Lathe. Now might be a good time to get your buddy to teach you some simple machining

 

What makes you think machinist dont get head aches trying to figure this stuff out.LOL

 

You are on the other end of the country from me. If anyone around here is stuck trying to do the same thing, I have done a few and am pretty much retired, so you could come here and learn something.

 

is the trans bearing retainer larger or smaller than the bellhousing hole? maybe you dont need an adapter. maybe all you have to do is turn the bearing retainer down to fit into the bellhousing, if you do because of the length of the trans input shaft then ok, even still it would be hard to make a hole in an adapter for the bearing retainer without a lathe, and if your going to have that hole done on a lathe then they can also turn down the other side to fit snug in the bellhousing.