I was talking to a retired EC the other day and he showed me an interesting tool that he'd had made at a machine shop. It was designed to drill the hole through the soffet and roof for a service mast.
I didn't think to take a pic so will try and explain it as best I can.

It was made by pressing a brass bushing into each end of a piece of intermediate conduit. Next they ran a piece of rod that was longer than the conduit through the bushings. They then cut a drill bit extension in 1/2 and welded these onto opposite ends of the rod making one very long bit extension.

To use just mount the conduit to the wall where your conduit will be, attach a drill to one end and a hole saw to the other and drill straight through the soffet and roof. The holes are in perfect alignment.

This probably worked well on tract housing in the days when overhead services were popular.

Great idea. You could probably use a long 3/16 drill instead of the holesaw to make this easier to handle since all you need to locate is the pilot hole. I may make one up to drill the hole I need, just to try the idea. I bet the waste chunk you get out of the holesaw is a good fit in a piece of conduit. Drill out a couple holes in some hardwood or thick plastic for the plugs. Epoxy them in the conduit.

That does sound a bit beefy.... I use a 4'X1/4" bell hanger bit, and just use a level before starting the second hole in the roof - then the hole saws.

I did however hear of a simular set up - but for underground. Thread the bit on the conduit, and the other to the fitting that pumps water in and a large drill. When finished remove the bit, and drain the water out of the conduit and use it.

Mark, if I understand the design right, I think the reason for the big pipe is so you can attach it to the wall with the same supports you will later use for the riser.

Kind of takes all the fun out of aiming, though

"is so you can attach it to the wall with the same supports you will later use for the riser."

And what? Have it spin in the straps?

Mark this rig does not spin the pipe, only the bit spins.

The pipe is simply an alignment jig.

he should've taken a picture

It's funny, but I recently did something kind of similar ... sort of a "poor boys' " version.

A house, converted to apartments, had just been completely remodeled. However, they failed to reconnect the baseboard heaters. I needed to run MC through about 8 ft. of joists thet were enclosed (above the bathroom), from the outside of the building, without tearing the bath apart.

My solution was to use a large "bell bit" (sized for 1/2" EMT) with multiple extensions. To keep the bit running true, I sleeved the bit in a piece of EMT; the back of the drill head rested against the end of the EMT. Drill joist, advance pipe, drill joist, etc. The MC pull was quite easy.

Nice idea John and great service to the customer by not ripping up the ceiling.

we call that tool a roof jack and it works very well, the one that I have is made for 2" rigid. Drill thru the soffit then on thru the roof, the pilot bit keeps the hole saw on track as you hit the pitch of the roof, and both holes can be drilled from below