Need to find a quality tool which can hold the drill motor itself in order to make sure a VERY STRAIGHT hole is being drilled thru a post?

I have 6" x 6" vertical posts that supports 6" x 8" horizontal beams where by 5" x 5" x 3/8" thick angle iron is used to support the 6" x 8" beam to the 6" x 6" post. Some of these 6" x 6" post have the 6" x 8" beams on both sides of it and... show more I have 6" x 6" vertical posts that supports 6" x 8" horizontal beams where by 5" x 5" x 3/8" thick angle iron is used to support the 6" x 8" beam to the 6" x 6" post. Some of these 6" x 6" post have the 6" x 8" beams on both sides of it and so will be using 1/2" x 7 1/2" long grade 5 bolts to run through both pieces of angle iron that are on opposite sides of the post, and so I need some sort of QUALITY-MADE jig, bracket, guide etc tool that can hold the drill motor itself (which has a spade bit) and allow me to drill a very straight hole through the 6" x 6" post that the 2 pieces of angle iron will be bolted to. Sure, I will be drilling the holes in the angle iron a little over-sized to compensate for a little bit of error but I still need something that will hold my drill motor straight since I have arthritis and not able to hold a drill as steady as I once did. Sorry but lag screws/bolts are out of the question ok
Update: Please keep in mind that at the least an approx 6 1/2 - 7" long spade bit will be needed to drill completely through the 6" x 6" vertical posts therefore the jig, guide, bracket, etc will have to provide the ability to hold the body of the drill motor while at the same time still having an approx... show more Please keep in mind that at the least an approx 6 1/2 - 7" long spade bit will be needed to drill completely through the 6" x 6" vertical posts therefore the jig, guide, bracket, etc will have to provide the ability to hold the body of the drill motor while at the same time still having an approx 6-8" gap from the post in order to provide the space necessary for the long spade bit which will be inserted in to the drill motor
Update 2: Also keep in mind these posts are already in the ground and also there are drill presses (more stationary) that sit on your garage floor and their are PORTABLE drill presses which can be carried in one hand, and so don't just reply with "use a drill press" unless you're actually going to be... show more Also keep in mind these posts are already in the ground and also there are drill presses (more stationary) that sit on your garage floor and their are PORTABLE drill presses which can be carried in one hand, and so don't just reply with "use a drill press" unless you're actually going to be specific as to what drill press you are referring to, provide the make and model, and you personally have used this in order to verify that the drill press is quality made and will properly do the job.
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