Most of us that have mill drills know what a pain not having a way to tighten the spindle can be. Here is my version of a spindle lock or rather than a lock, a way of holding the spindle while you tighten or loosen it.
You still need to use two hands to tighten the spindle, one on the wrench above and one on the spanner wrench below, but it sure beats trying to hold it with straps and whatever else. Some would probably say why not just drill holes in the spindle and use a round spanner wrench but I am one of these weird people that does not like to drill holes where there weren't any in case I want to remove this contraption some day.
1. Hit the scrap pile and found a chunk of stock that would work.
2. Drilled the holes for set screws and milled the slots for the spanner wrench.
3. Put some brass tips on the set screws to keep from scoring the spindle.
4. How the spanner wrench locks onto the lock.
5. Mounted on the mill drill.
