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To date I've only made classicals (10) with a Spanish neck (after Cumpiano and Natelson style), but I want to switch over to a bolt on so I can make a few steel strings. When making classicals, I've used a stacked heel and simply sloted the stack to accept the sides. Can I use a stacked block inside the guitar for a bolt on, or is a one piece block the way to go? Reason I'm asking is I'm thinking about building the neck with a stacked heel as I typically do and then just cutting off the end on my table saw and using that as my inside block. I'm looking forward to working on a guitar with the neck separate from the box for a good part of the process, but I've never had to deal with adjusting the neck angle (I'm building the Robbie O'Brien neck jig now) or routing for a truss rod. Any advice or suggested preferences appreciated. Thanks!

Glued stack is fine as long as the joint won't have to face heat for removal. Using the cut off for the inside block will have the wrong grain orientation for bolts.

I switched from the traditional Spanish heal to a bolt on about 15 years ago and do it exactly in that manor. In fact I basically build the guitar using the same exact method only the neck system is a bolt on, everything else is done the same. WHen I build a steel string I make the neck block and heal separate but there is no reason why you cannot do it the way you describe.

What David said. Are you planning on putting a truss rod in a classical? IMHO the additional weight of a truss rod in a classical neck does not feel right as in oddly heavy.

One of the many benefits of bolt on is that before you glue the tongue down you can string the guitar up and ensure that you end up with the right neck angle and bridge height.

Good luck!

Having a stacked configuration for the head block is adding a lot of unnecessary joints in a place that you never want to have a separation, and for what benefit? I make my head blocks from baltic birch plywood which I know will never crack.

Well, I can't see how the bolts would care about grain orientation.

However, if you used the cutoffs in the same orientation as the neck itself, that would end up with the sides being glued to endgrain, which I don't think is a good idea.

I think gluing sides to end grain is problematic and bolting parallel to the block grain is asking for a split if there is any kind of mortice.

If you use a solera to set your neck angle you could still do so with a separate neck and block by bolting them together before gluing on the back. One thing to remember is the neck is tipped back on a steel string rather than forward as it is on a classical. I add a spacer to raise the neck off the solera when I use it for steel strings. A lot of steel strings are "flat" where the neck connects to the body so fitting a neck block is relatively simple.
Stacked heels are relatively common and accepted on classicals. On steel strings one piece necks are more common. I build mine with a block glued on the neck shaft and carve the heel from that. I also use a separate piece for the peghead, joined with the modified bridle joint Martin used to use. It's a compromise that doesn't look too bad and still saves a little wood.

Thanks for all the replies. My thinking is that I will use a mortise and tenon bolt on joint. Really hadn't thought through the end-grain on the head block. I have been using baltic plywood for the the tail block on my last several builds, and could see going that way on the head block as well, just wonder if I would have problems routing a mortise in plywood; otherwise, I'll probably go with a solid mahogany block. In response to DannyV's question, I've never used a truss rod on a classical, but could see myself instally one, if I were to build one using a bolt on joint (no plans to do so right now). Thanks again guys.

" just wonder if I would have problems routing a mortise in plywood;"

Cut the tenon on the neck, line that area with Saran wrap and glue up the neck block around it with a few layers of baltic birch plywood. The plastic wrap will keep things from sticking and allow you to "form" the mortise around the tenon . You can then fit your sides in a fashion similar to your usual Spanish construction.
A router or table saw can also be used to cut the mortise, but if you are gluing up the block anyway....