Finding door cut off for new threshold

Bob,

I would completely remove the old threshold leaving the door hanging normally. Then I would put the end of the new threshold on the floor and against the door on the hinge side and mark is with an awl. Then I would repeat that procedure on the lock side of the door making certain that sufficient pressure is applied to the threshold gasket so the door will seal tightly. Then you can use those two marks to make a straight cut line for your cutoff.

Another couple of points is to use a clamped straight edge for the cut and make sure you score the cut line to avoid tear out if any part of the cut is across the grain. Even a fine blade will tear out on veneer.

Unless your straight edge has a surface for the saw to ride on, tape the entire surface to avoid scratches. The metal bases on circular saws are notorious for scratch delicate surfaces.

A couple more thoughts; if the door swings out you can make the cut at a small angle for a tighter fit. It's usually not a great idea for doors that swing in. And, you can also purchase a slide on weatherstrip for the bottom of the door. I did that when I installed a new front door on my home and it works great.

Bob - I don't know how much this will help, but with the right tools, the difference in floor level can be measured. I did it here in my old 140 year old house in several rooms and had great luck. I even used this method for a landscaping project.

Tools needed are one of the new digital leveling systems with a light beam. You also need a drill press with a depth stop.

I found a good flat piece of hardwood (plywood, MDF or hardboard will do fine) and drilled identical holes using the depth stop on my drill press. I then cut up a couple of dowels and put marks on them at equal lengths from the bottom, stuck them into my blocks (pre-drilled holes were the dowel size). To test my system, I placed them on my level workbench and set up my laser level. When I got the line dead center with the lazer beam, I knew I had my measuring stick. To test it, I shuffled the blocks and found them to still be on the mark.

I placed one block on the low point of the floor and set up the level so the beam was on my mark. I then moved the other blocks around and measured the distance between the marks on the dowels and the beam. I now know how much my floors have sagged in the past 140 years.