prepping pittsburgs

[randyt]

By our slip roll we have a pile of heavy gauge straps, an inch or so wide by a few feet long. When fabbing radius fittings we smack one of these straps in each piittsburg. After rolling the metal the straps are knocked out. This prevents the pitts from being flattened down and now is much easier to hammer the fitting together.

[pricer]

We have tryed this as well. It seems to work well. I had an idea a few years ago about machining some sleeves to slip over the rolls that would be ajustable like a box brake. You could just slide the collars over to make a path for the pitts without mashing it. Don't know if this will work or not, never got around to trying it.

That is a great idea! I have a machine to do it but it is a pain in the ass. Randy, I'm going to try this one this week. I'll let you know how it comes out. Now this is brain power in motion! Bob

[bordontn]

Bob.......I think that if you look closely the rollers don't flatten the pittsburg
seam.It closes because the radius on the outside is larger than the inner part..Your pitts. is close to 1/8" thick>When you roll the wrapper it can't stretch so it closes.
Your pitts. is the same length front and back.The spacers you mentioned would help
give the proper curve to the metal between the pitts.The strips of metal are your best bet. When you form a wrapper the pitts determines the curve..The metal between never has the same radius as the pitts. We used to put a shim of cardboard between the pitts..If you notice when you form a radius throat the metal
wrinkles some.. bordontn

[drslater]

I have used banding straps for this purpose. The straps have a memory and return to the flat after rolling. This allows the straps to be removed easily and are also easy to drive into the pittsburg because of their hardness.

Another technique is to pre-roll the throat and heel fills prior to running the pittsburg. This works great on larger fittings.

[kodie]

preroll wrapper first then run pitt. and lift up as it comes out . will not work on throats

[tinman101]

adjust the bottom roll just enough to grab your wrapper piece and over roll it a little bit. Then use a pair of nippers in the open position, hook the raw edge and open the pittsburg.The extra roll will automatictly return to the proper radius.and the cheek
fits good.Then go to town knocken it together.Another easy way on big elbows is roll it over the edge of the bench, then open the pittsburgs as above.A third way on really big elbows is to lay it on the floor, step on the pittsburgs with both feet and from the end of the piece pull up towards yourself backing down the piiitburgs a little at a time until you have a good radius.Then open the pittsburg as above. It works like a charm. tinman101

[fogcrawler]

Randy,
I had to do that yesterday...
Made a large ogee fitting.
Ran 'em through the machine and realized very quick that I didn't form my wrappers in the flat first... Oops.
took some 24 ga strips, plugged them into the grooves and it worked fine, except it took a few extra minutes.
My shop foreman showed me that trick... Forming, wrappers, cheeks and throats in the flat first before doing the locks.
The pittsburg machine will flatten the sheet again but there is some memory of the bend forming left in there, 'cause they go back into the bend with little effort.

[rothalion]

I use copper strips to gain some space the are mallable and provide just the right clearance.

[Tets11]

I just run my pittsburgh in the burring machine after it is formed and it opens it up beautifully.