If you look at a steer and notice the hump on its back towards its shoulder, that's the Chuck Primal. Notice how the spine curves upwards - that'd be the steer's neck. This primal easily weighs 80# (Pounds).
After inspecting the cut a bit, use the tip of your knife to separate the muscles of the neck from the vertebrates.
Once you've got your game plan designed, start by taking off the first vertebrate. If this picture wasn't of such poor quality, you'd be able to see the contour of the meat alongside the bones.. once you've done a few of these you'll be able to visualize where the meat meets the bones and your knife will walk the thin line, leaving nothing to waste.
Starting at the top of the bone, use the flexibility of your knife to skim down the bone - separating the meat.
You'll have to use quite a lot of force, even with a sharp knife.
Proceeding down the spine, until you get to the neck.
I wouldn't use my best knife for this part - bones wreak havoc on your blade, especially when you're boning out the neck.
Try to follow the bone, to minimize waste (Also, you can always go back and treat the neck bone as a new obstacle. I've pulled 2# of meat off of a hastily separated neck to prove a point).
Now to remove the Chuck from the Should Blade. In butchering, you're not cutting meat - you're separating muscles into smaller primals. Follow the seams.
On your left, you have the chuck - nearly finished. On your right, you have mostly trimmings, although the Flat Iron and Chuck Tender rest inside the shoulder blade. Any wise butcher, and for that matter, any wise department manager will utilize these two cuts for their tenderness - Flat Iron's are a pain in the ass to cut properly but snag a pretty penny. The Chuck Tender yields an extremely lean stew meat.
This is what I'd call the bubble gum. This is always to be removed, for it serves no purpose nigh pissing someone off.
Once you get initial incisions, it should pull out rather effortlessly.
Boneless Chuck - Neck Off. Minimal trimming is needed from here on out. It's time to get your twine!
Tie the roast as straight as you can, the ends are to be removed for trimmings.