Camming section rambling

[marknct]

No particular order.
During some of the demil operations they squished the CS area into a parallelogram. A 270* square can help you find this and correct it. You need one of the 3 piece square sets like Brown and Sharpe sell or 2 sets of the normal 90* head. This is the type with the groove in the 12" scale that the head locks to. With the scale on top you have the 90* heads facing each other or the protractor head set 90 giving you 2 perp edges and 2 parallel . A vise with a V jaw helps hold it while you apply more pressure than you like to move it back to true.
There is probably a lot of residual stress in this area from the torch cut. Taking a torch and lightly heating the area with a slow cooling might help if you need to build up the CS pads later. The heat from the weld dots will change this area making you angry without some stress relief.
Matching CS numbers is nice but I don't think it's a deal breaker. How the small piece fits in the groove is critical and lots of tiny burrs can exist from bouncing around in a box. You will need small files and triangle Arkansas/die stones to massage it. This can take a few hours in itself because the small piece should slide in with a light finger tap and the groove in the C needs to allow the flat surfaces to mate with rivet tension to the "I". There is a very slight taper on the tongue/groove which allows for a zero clearance assembly. I think this is why they are paired more then heights. There doesn't seem to be a flat surface on that thing to take measurements from. If you are worried about mismatched pieces set the top cover side of the camming blocks on a parallel arrangement and poke around with a height gage.
None of these seem to be truly square on the inside with a smaller dimension typical on the groove side of the C. Can't make this easy right?
Read the BRP manual on this area for some background.
Now it gets tricky if the CS isn't original to stub and will take some time. The CS needs to fit with essentially zero clearance to the recv.
They all measure roughly the same on the inside, some might fit your stub better. You are trying to use the existing pads as much as possible to reference the old centerline. This isn't a +/- .001 item here so don't get crazy with it. You are establishing the new centerline with your final CS placement which will be close to the original one. From this point you will align the nose piece and then the rear. Using a bubble level on this thing is kidding yourself, there isn't a good flat surface on the stub and the little bit you do find probably has nothing to do with the c'line. Keep in mind that new rails measure about .636" and the bolt head rail is around .628. A carpenters level isn't calibrated with a divided scale like a machinists level. Even then you won't find a flat spot long enough to get a real reading. I'm not saying this to be a dick or flame what people have done! I'm trying to point out potential shortcomings so you can decide how you want to proceed or help with trouble shooting.
More later.

[marknct]

So you've got your front half and the CS doesn't really fit up right. If you're going to make a shavings generator,hammer away. If not this might give you some ideas. First pic shows a flush fit of the CS to the rcvr with the CS pushed on as far as it will go. Make sure the weld seam isn't sitting high. The second shows a typical back view where the CS doesn't sit flush. This is caused by a binding distance of the trunnion stops and TOR, trunnion open rear.

[marknct]

Flip the order of the last pics, I never get that right.
Using the BRP drawings for this area you need to come up with your numbers. First is getting TOR. His typical value here is 3.100"
The bolts are only light finger tight, don't bend things. Notice how they fit against the edge, it's not always even. The rear is .75 wide, front 1.38.
Mic the parallels,1/8 is a nominal size and they aren't always the same thickness overall. Measure the thickness about where you will take the distance.

[marknct]

So that had a value of 2.824". The .75 par was .127 and the 1.38 was .126
So 2.844+.127+.126 = 3.077"
Now we need a TR stop value. Probably easiest with shims and we are looking for a comparison here more than a true distance. A piece of drill rod is best to find the edge, a drill bit might rest on a groove. Clean the shims you use, they shouldn't make crunchy sounds. The last shim should roll pretty freely under the rod so you have an idea that it's not being bent. When you mic the stack use about the same pressure that you felt with the stack under the rod. Mic the rod.

[marknct]

The shim stack value is .224" and the pin .125 for a total of .349". So 3.077 - .349= 2.601 for a TR stop value.
Now we need to see what the TR actually wants. Find a know good block and set the TR on it where the stops hit. Measure from the block to the back edge of the cam thingy.

[marknct]

That value is .495".
So 3.077 TOR - 2.601 TR STOP = .476"
Rought row.
.495-.476=
.019" short.
Expected accuracy is probably around +/- .005
So using a typical value from BRP 3.100-3.077=.023"
2.61TST - 2.601= .009"
More later.

[42rocker]

Nice info Thanks for sharing it.

Later 42rocker

[anjongni]

Nice photos. I wish I had your machinery and of course the knowledge you have to use it!......Phil