Whenever I glue up a door on my rolling workbench I cross sight the door to make sure there is no twist in it while the glue cures. I shim the door to get it just right. I am now 66yrs old and finding that my eyesight is failing to dial in a perfect cross sight using two four-foot levels at each end of a door. Does anyone have another method ? I have wondered if a laser line would be fine enough to work?
Thank you,
Gary

Use a flat table to begin with. Then you don't have to worry about sighting them in. Maybe make a table top specifically for this purpose that can be stored away until needed. I suggest torsion box construction.

I suppose you could just use a level to make sure all 4 sides are level.

Starting from a flat enough reference surface is my first inclination as well.

Pass doors or cabinet doors?

Passage doors. A rolling workbench is at the mercy of the floor being perfectly flat and coplanar.
Gary

Just means the table/cart has to be built stiff enough to handle it.

All of my shop carts are steel.

You can add levelling feet to your rolling cart that drop down when you are in position to work and retract for rolling. I've seen some expensive heavy duty wheel and pad feet combinations meant for machines and rolling tool chests.
Definitely a light and stiff torsion box would go a long way.

"Start flat, stay flat." is what I learned. I have a 600 lb bench that is rarely moved. The floor is marked where I know the bench is flat. If moved, all I have to do is get it back on the marks and it's flat.
The process of getting the bench flat is detailed in my book "Small Shop Production of Custom Wood Doors".

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Get new glasses

Eye doctor appt on the 27th just in case !
Thank you all for your feedback.
Gary

I used 2x6 3/16 steel and heavy castors for all my shop assembly tables.
They were welded flat, I never trusted a wood torsion box for some reason. I have been known to overbuild things but it never me down. I would screw 1" white melemine to the steel frame and change it once every couple years. Flip it when one side gets too bad but made for easy glue removal.

Pretty resonable if you weld them up yourself.

You could run a tight nylon string from corner to corner and form an X. Look where the strings cross in the middle and that will tell you if you have twist. Get it to where you can see a hair of daylight between the strings and you will be flat.

You could buy a 24" digital level. Zero it at one end then check the relative level at the other.

Okay, take two straight dedicated pieces about 2-1/4” square x 4’ long. Clamp on, across the bench at either end. Using 1/4” shims on top of each end of the two sticks, drive in a Brad or two so the string can be fastened easily. Run the string diagonally, taught, then to the other end of the stick and diagonally to the fourth corner and pull it taught and fasten. Look to where they cross. Lifting the top string should allow the lower string to rise up 1/2 the diameter of the string. This indicates the four points are all in the same plane. Pushing the lower string down will allow the top string to drop half the diameter. And be in the same plane. Check all your points to insure you have what you want.
You can clamp your 4’ sticks to the face of a door if you like, to check for flat. Do not use a level for any part of this process.

Occasionally, I would get a call to “come out and get your warped door”. The last thing I ever wanted to hear. I would gather a few tools, but the first thing I would do is check the door frame. It is not easy to get the string into the corners, so I made pine blocks that would tack into place and put the string where it needed to be.

Nearly every time, the door was flat, and the frame set out of flat. Reset the frame (do not allow it to whammed with a block and five pound hammer!) and pack up your tools. It is also is helpful if you have some corner blocks made up for a door out of the frame.

Your professionalism shows with your quiet use of the corner blocks as you go about your business. Once the strings tell the tale, you need not place blame, rather it is more like “what can we do to get this right…” This keeps us all on the same side, getting it right and on down the road. Call the builder or homeowner, whomever called you, and let them know the problem was discovered and corrected, and all is fine. Thank them for the good work, and move on.

I’ve been using the cross-sighting method for years, but like you, my eyesight isn’t as sharp as it used to be. A laser line sounds like a great idea, as it could provide a more precise and visible reference. Another option might be a digital level with an angle gauge to check for twist more accurately. Some woodworkers also use winding sticks with high-contrast colors to make misalignment easier to spot. I’d love to hear if anyone has tried the laser approach and how well it works!