Glue with some finish nails to hold it till it sets. Im not sure what you mean by a soffit, when you state you want to attach the purpleheart to the ceiling? Do you want to drop the purple heart down from the ceiling, forming a soffit? Can you give a sketch of what your attempting to build?

Yes, Tom999, you got it exactly. Just a little drop down to attach the tracks for the lighting. . . usually it (track)would be attached to the ceiling itself but since I don't want to disturb the 45 year old lath and plaster ceiling, the connection will be coming out at the top of the wall, which has already been opened and wiring installed instead of the ceiling and that makes the connection go the wrong way, so we decided a little soffit-like run would both look attractive and work with the electrical fittings.

I was going to do what you suggested except I was going to screw instead of nail. So I guess we are in the same basic place. I was afraid that I would need something more stable if the electrician was going to be pushing on it to screw and drill and whatever else they need to do.

Thanks again, Tom, always a pleasure to read your answers.

You can put smaller "blocks" if you want to keet it off the ceiling. These blocks can be screwed on an angle from the sides to the ceiling joists. Then attach the purpleheart "strip" to these blocks. Once the track lights are installed the track will actually help to stiffen the purpleheart board. I would put these blocks perhaps every other joist (32") or so. They can be any lenght so you can "drop" the "soffit" to where you need it. may want to make these out of purpleheart also so that it all matches.
Good luck !

Tom, thanks, took me a while to quite get this to visualize for me, but now that I "get it," COOL! It would look really nice to let the lights drop just a bit from the ceil, and it keeps me from having to resolve the 45 years of "wavy" ceiling against a straight piece of ph. Just drop it 2 inches and let the light glow over the top. . . that will look so cool and I can make blocks, I can even round 'em and make 'em look nicely finished. Oh, the designing juices are flowing, thanks so much! I may need to revisit the light style I chose too. . . oh, so much to rethink, again. Lovin' IT, better now than later.

Then sit back and Enjoy :)

You might want to look at a glue Titebond has for fastening moldings. It's white and thick so it will hold nicely, but a few screws would make it very strong.

By the way, if you haven't tried square drive screws, you'll be pleasantly surprised at how well they work.

Don