What kind of heating system do you have. Forced air will draw the airborne dust in and then relocate it into the rest of the house if the filtering system is not up to par. You can seal off the room you're working in with a visqueen flap if there are no doors.
There are tricks in cutting crown to length by using a precut measuring stick and then allowing for that length in the measurement. This allows very accurate measurements for a one time only cut, to save all the back and forth cutting and fitting.
C-man posted this tip I believe here before.Or WillyT or chief woodworker or LeoG....somebody will fess up
Maybe this was it:
Join Date: Jul 2007
Location: So. Florida
Here is a tip for cutting crown, if ya-all promise not to spread it around.
To get lengths right, like between two 90 degree outside corners, cut two sample pieces. Cut a 45 on the left one and a 45 on the right one. As they sit on the wall cut them both off at 90 degrees, 10" long. I picked 10" because it's an even number, and I'm a simple guy.
Now, when you go to get a wall measurement, set the two pieces up so the miter closes up, and make a fine pencil mark on the straight end. From that mark to wherever the crown goes you can get a wall measurement from that corner by adding 10". If you do that on the other corner, you will have the dimension between marks that you can add 20" to.
You can cut the actual crown a bit heavy to fine tune the mitered fit.