For the bulge and jack marks, it’s all about the angle, if you dig the tips in that’s when you get that scaring on the glass (and bulging if you push the tips in really hard, but this can also happen if the walls are uneven, another thing that just takes practice)

When opening a tumbler, just be conscious of how you jacks are angled, you almost want the tips pointed toward your punty, so the blades edges open the cup rather than the tip. Lots of wax will also help the scaring.

Most importantly, just keep practicing! The fact your aware of what you want to improve on is the first step to actually improving it! You’ll get there, just be patient with yourself, and try to get better with each piece. And remember that a few jack marks are just the sign it was handmade, nothing wrong with that! Good luck!

I can’t seem to get my angle right. I either bulge out the wall or leave grooves from the points of the jacks. Lol and then I end up either not opening up the jacks enough or too much. Guess it’ll just take time. I appreciate the advice!

The best advice given to me was "Lift up and open your hands." Let the spring of the jacks do the work opening. Put your jacks deep enough so the tips of them are riding on the colder glass, this can help you keep the line that you have established on the pipe. If you are having trouble with the lip flaring out make sure you are keeping your blades parallel to the ground.

If you really wanted to you could open a tube on a blow pipe, neck it back down, and keep opening, but the best practice will be just to make cylinders. Hundreds of them =)

Watch some YouTube videos.   Bill gudenrath is a good one to watch.

That's the nature of the game. Just find a lot of videos of people using Jack's and copy them.

Do you happen to know of any good videos? Every video I’ve seen just kinda glosses over that step and doesn’t explain it thoroughly.

Turn fast, get it hot, and maybe watch the youtubes!

Match the shoulder, unless you want the shape to differ from that straight wall. The glass will make the same angle you hold your jacks.

When you put the jacks in, are you holding them at a 45 degree upward angle to match the shoulder of the piece first or just going parallel to the pipe? Asking because I’ve seen it both ways

Always make sure you’re on center first, then alternate between outside of the cup and inside with the jacks. Open them a little wider on the outside, allowing the walls to slide along the inside of the blades, then tighten your jacks a tad on the inside of the cup, using the outside of the blades. Your jack blades should be hot and well waxed, and try to keep the tips past where the glass is hot; this helps to keep the walls straight. And yeah, get it hot and turn it fast. Good luck!

Preheating and waxing the Jack's is helpful. Specifically heating the lip instead of the whole cup is better for control. Finesse over force if you want to avoid tool marks. Remove Jack's briefly when changing directions at the bench.

My issue was not putting the jacks far enough into the piece. I'd only go halfway in and get the bulge or the grooves that you're talking about.

Does anyone have any sage advice for learning how to use the jacks to open a tumbler? I have a lot of trouble with understanding how to do it properly. Is there any way to practice besides making a billion tumblers? Thanks!

Trouble with using the jacks to open a piece