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Just a fun question.
I have been fusing for many years and obviously used running pliers all that time.

Often when I use the pliers I wonder what good that screw on the pliers does. When the pliers are in place to separate the glass, neither the pliers nor the glass knows where that screw is. The glass just reacts to the stress applied by the pliers.

Why the screw?

The screw should be adjusted to slightly less than the thickness of your glass. That's really critical when cutting thicker pieces of glass. If the screw is all the way down (like most people have it, but shouldn't), then you apply too much pressure to the score and will have more trouble getting a good break.

It's also helpful to let you know to "always screw up" when using the running pliers.

Brad or anyone.

I understand the use of the screw, but not the benefit.
Since the glass is not flexible, neither the glass nor the pliers know the position of the screw when the break is made. Once pressure is applied to the pliers, the glass has to fully break for the screw to come into play.
Thus my question, what good does the screw do.

let me add one thing here. The thickest glass I break is 6 mil, so thicker glass may behave differently.

Barry Kaiser wrote: Once pressure is applied to the pliers, the glass has to fully break for the screw to come into play.

This isn't true. The screw stops the jaws of the pliers from coming together, which controls the amount of pressure applied to the glass. So if the screw stops the jaws from coming together part of the way through the break, as opposed to all the way through, the amount of pressure applied is different and that affects the quality of the break.

The thicker the piece, the more critical it becomes. But even in 3mm glass, it's a factor. 3mm with the jaws all the way together will not break as easily as 3mm with a small space between the jaws.

So, how do you set the screw to the correct depth? It would seem to be a very narrow range between too tight and too loose since there is so little flex involved in breaking the score. It would also appear necessary to adjust it each time you break a new piece of glass, especially BE since the thickness of each sheet is different.

Personally I never use the screw. I apply pressure until I see or hear the score start to break and then release the pliers. It might be necessary to apply the pliers at the other end of the score line if the break hasn't completed.

Jim

The Hobbyist wrote:So, how do you set the screw to the correct depth?

Set the jaws to the thickness of the glass. Then turn the screw 1/4 turn to tighten just a little bit. You don't need to do it for every single sheet of glass, just for 3mm or 6mm when you change thicknesses.

If you're more experienced and can rely on your own ability to recognize when you need to ease up on the runners to relieve the pressure then I suppose you can get by without the screw, but not everyone's as experienced as you are, Jim.

Looks like I have been doing it wrong for 20 years! What I thought I was told was to put the jaws on your glass then tighten the screw, then back off a quarter turn. I suppose it makes more sense to advance it a quarter turn but this has worked for me for all these years and therefore conclude that it is not an exact science. I have told many students to do it the way I do and I can only hope it is working as well for them.

Michele-MD wrote:Looks like I have been doing it wrong for 20 years! What I thought I was told was to put the jaws on your glass then tighten the screw, then back off a quarter turn. I suppose it makes more sense to advance it a quarter turn but this has worked for me for all these years and therefore conclude that it is not an exact science. I have told many students to do it the way I do and I can only hope it is working as well for them.

I'm confused. If you tighten the screw so that the jaws of the running pliers are the same distance as the thickness of your glass, then back off a quarter turn so that the jaws are further apart than the thickness of the glass, then the pliers won't close on the glass at all. Am I misunderstanding?

I've never used the screw in 40 years and I've cut all sorts of glass. I just take the screw out and throw it into the trash.

Brad, yep, that is what I have always done. I just assumed that when I actually press to cut that the give in the plastic covers was such that the right amount of pressure was applied. That being said, I am now going to advance the screw!

cleaner cuts are made with a properly adjusted pair. Zero flaring at the start of the cut.

Kevin Midgley wrote:cleaner cuts are made with a properly adjusted pair. Zero flaring at the start of the cut.

Why?

The glass doesn't know where the screw is at the beginning of the run until the pliers stop pressing. And by that time the run has already started.

When you throw away the screw, just go ahead and discard the breaking pliers and buy Silberschnitt Running Pliers. They are pricey, but very easy to use and they swivel so you can slowly run a long cut not only from the end but along the length. The pliers are aluminum and the contact parts are high quality hard rubber, not dipped plastic, and are easily replaced.

Do keep the old screw pliers and use them to tap long runs (a trick I learned a long time ago).

This is for Barry.
When you have cut as many miles of glass as I have and are concerned with clean cuts and zero flaring you will adjust the screw.
The bonus is less stress on you hand.
However since you know what you are doing don't bother.

Kevin,
Everyone is answering that they have cut miles of glass with the screw. I have cut miles without. That is not the point

My question is why the screw actually makes a difference.

I do not know why, but I can tell you that (in my case ) it makes a great deal of difference
The other Jim

I am hoping this is just a fun topic for everyone. I am not trying to be argumentative. Just trying to have a fun and informative discussion.
I am wondering, in the name of science< why the screw is necessary.
Even if you have successfully used it for years, i wonder why.

The amount of pressure does not change until the stop is hit. Thus, the glass should break when the pliers are applied.

Does anyone want to present a theory as to why it is necessary?

Come on guys. There is a lot of glass knowledge here.

Barry Kaiser wrote:The amount of pressure does not change until the stop is hit. Thus, the glass should break when the pliers are applied.

The glass does start to break when the jaws clamp around the glass, but it doesn't break optimally.

If you have no screw, then the jaws come into contact with the glass and continue to move closer together until they come all the way together. This excessive pressure can make the glass more likely to flare at the starting point.

If, on the other hand, the screw is set properly, so that the gap is just slightly less than the thickness of the glass, the jaws stop applying pressure once the score starts to run. As a result, flares are not as likely and the score will be cleaner.

Bottom line, you can break glass with or without the screw set properly, but you will get better breaks with the screw set the right way.

Throughout this discussion are you using breaking pliers with the customary plastic cushions on the jaw faces? It seems to me that if you are then they have a greater effect on the break than the screw. Uneven pressure is the cause of the flare and that pressure comes from the cushions as they touch the glass. In my experience those cushions are not made to very high tolerances and very likely are thicker or thinner on one side of the score than the other. Therefore they apply uneven pressure regardless of the screw position. Also, the pads wear down, usually unnoticed, which also contributes to uneven pressure.

Or are you using the pliers without pads? That's a different matter.

Jim (still) "The Hobbyist"