Camming section rambling
Posted: Thu Sep 05, 2013 2:21 pm
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.
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.