Thinking outside the cup ......

bruce991 · Tue Feb 28, 2017 1:43 pm

Okay going to try again to walk the cup on inside T joint on carbon steel scrap. I always find my progression is jerky due to the cup not sliding as I wiggle. So got thinking has anyone tried sanding the porcelain to a bigger radius where it rides on the steel? To make the action more forgiving as you rotate and walk it.

Oscar · Tue Feb 28, 2017 3:06 pm

I think you'll have a hard time sanding an aluminum oxide cup with aluminum oxide sandpaper. You might need a harder material on the sanding paper.

MarkL · Tue Feb 28, 2017 4:32 pm

bruce991 wrote: I always find my progression is jerky due to the cup not sliding as I wiggle.

The cup shouldn't be sliding, the edge of the cup should be rolling along the surface. Jody gave a good analogy on one of his videos, he says it's like moving a heavy barrel across the floor. You tip the barrel one way and roll that edge a little ways, then you tip it the other way and roll it on that edge a little ways.

bruce991 · Tue Feb 28, 2017 5:54 pm

MarkL wrote:
bruce991 wrote: I always find my progression is jerky due to the cup not sliding as I wiggle.
The cup shouldn't be sliding, the edge of the cup should be rolling along the surface. Jody gave a good analogy on one of his videos, he says it's like moving a heavy barrel across the floor. You tip the barrel one way and roll that edge a little ways, then you tip it the other way and roll it on that edge a little ways.

Agree not trying to slide cup but rocking and rolling while watching tungsten sweep across, but I often find the progress on a joint I sometimes get stuck just enough to lose spacing, especially if steel has any surface issues. I think I also push a bit inward and shouldn't. As I am doing this I ask if the cup had a bigger radius where I am contacting the metal would I be getting a smoother movement forward as I rock and roll along. I guess the cup is not something I can modify from what I read above.

MarkL · Tue Feb 28, 2017 6:45 pm

bruce991 wrote: As I am doing this I ask if the cup had a bigger radius where I am contacting the metal would I be getting a smoother movement forward as I rock and roll along. I guess the cup is not something I can modify from what I read above.

Using a larger cup forces you to increase the stickout (or steepen torch angle), which can lead to other problems. I'm sure no expert, buy my experience is a #6 or #7 cup is about right.

Poland308 · Tue Feb 28, 2017 6:59 pm

It takes a bit of practice to get the rythem down to walk the cup. I use a 4 or a 5 for the root on pipe and then progress to a 6-7-or 8 for the fill and covers. Depends on pipe size and thickness. If I can get away with it I'll use a 6 for all of it most times.
Note the barrel analogy mentioned earlier.

Poland308 · Tue Feb 28, 2017 7:03 pm

: IMG_1634.JPG (66.26 KiB) Viewed 687 times

Here is an old pic I've posted before. Note the marks my cup left on the edge of the flange. Trails from walking the cup. That was a sch 40 carbon 4 inch slip on flange. Was welded in a vice just where it sat.

cj737 · Wed Mar 01, 2017 1:16 am

Carbon steel is more difficult to walk a cup on. The heat effects it and you get skipping and sticking intermittently. Less pressure than you're using, or more pressure on the back of the cup. Walking on stainless is butter smooth comparatively. And make sure you remove all the mill scale to aid your walking.