Crack drill distance and long vs short vacuum cycles

[tre]

Wondering how you guys go about determining how far you should drill form a crack for a drill and pop. I go farther for crack that are flexing and shorter for cracks that I don't see flexing much, but I've still run into situations where the crack runs to my drill point when drilling or when he crack doesn't run to the bullseye and I can't flex the crack into it (although I haven't been too aggressive). Also, what do you do when the above situations happen? Sometimes the first one will still work out, but sometimes the spring hammer will make it crack out too far requiring a second drill and pop. The first one I will fill then try again closer.

Also, with the Delta kit, can a longer vacuum cycle work as good as multiple shorter ones? Sometimes I find myself doing a lot of pressure/vacuum cycles near the end of the repair, and I tell myself that it helps, but I'm not confident it always does.

Thanks for your tips/advice.

[Brent Deines]

I drill 1/32"-1/16" past the end of the crack. Typically the crack should "jump" into the bullseye when the mini bullseye is popped using the spring hammer or sometimes even during the drilling process so generally speaking you should not need to apply any pressure against the glass to make the crack run into the bullseye.

If you are having problems with the crack running past the drill hole you are likely not drilling deep enough, especially if it is happening when you are popping a bullseye with the spring hammer. Other things to consider are the type of drill bur you are using. A dull bur or one that requires a lot of pressure as you drill can cause the crack to run and using the wrong size bur or not using the right drilling technique can cause the crack to run when you pop the mini bullseye.

It depends on where the crack is located but in most cases if the tip of the crack extends 1/4" or less past the drill hole or mini-bullseye, it will still hold just fine if properly filled. Much longer than that and I would consider drilling a second hole because as you force resin into the end of the crack it could start to run again.

Using a Delta Kits injector the vacuum cycle should only be as long as there is still air movement within the break. There is no advantage to leaving the injector in the vacuum cycle If there is no more air coming up through the injector.

[tre]

Ah, I had thought it was bad if the crack ran to the drill point before the pop. Thanks for clarifying, and I'll be making sure I'm not using a dull bur from now on.

If there is air still trapped, is there any advantage to alternating between pressure/vacuum a lot vs just leaving it in vacuum?

[Brent Deines]

Alternate back to pressure once there is no more visible air movement. We teach two minute vacuum cycles because that is almost always long enough to get the maximum benefit but if you aren't seeing air movement after 30 seconds you may get more benefit from switching back to pressure. We often find people leave in the vacuum cycle longer than necessary and short the pressure cycle, which is not a very efficient way of removing trapped air using a Delta Kits injector.

[screenman]

Keep in mind if it is a surface crack you will not need vacuum, and if you do use vacuum run a bead of resin along the crack and cover with curing film.

[benswindshieldrepair]

Please tell me if I am wrong: I rarely do crack repair, but when I do, its because the crack is less than 4". So, when I've drilled and popped, it has oftentimes split past the pop point. I put my bridge there and fill what is there. I fill the created bullseye as well as the crack and the small crack beyond the bullseye. I haven't had one fail yet. Is this ok? Seems to me to be... Flame on.

[screenman]

Seems alright by me. Depending on the type of vehicle an crack I might drill up to 3 times. One at the tip, 1 half inch in from that which I fill from and a third as a cleat stop next to any rubber seal that I cannot get behind.

[Brent Deines]

In my experience when this happens the crack typically extends 1/4" or less beyond the hole. While I don't like it when this happens it's not the end of the world. I don't typically drill a second hole either and I haven't had one fail that I am aware of. On the rare occasion the crack jumps several inches I drill a second hole. I don't remember the last time this happened to me but it has happened and I had to assume the crack was particularly prone to run so drilling a second hole made sense.

We had an odd one in our shop today. The technician drilled at the end of the crack but when popping the bullseye the crack changed direction by about 45 degrees and jumped about an inch. A second hole was drilled on this one and everything went fine after that.

If you are using the Delta Kits spring hammer and depth gauge try drilling slightly deeper. The gauge is a a good guide for minimum depth but we have noticed that drilling a little deeper helps keep the crack from jumping past the drill hole.

[benswindshieldrepair]

Thanks for the tip, Brent. Have I told you how much I love this forum and your support? At any rate, also thanks for the mention on the depth of the spring hammer gauge (an awesome invention). I'm always nervous about depth in the few instances that I use the drill.