Porch railing

I didn't explain the 4 way dovetail very well. I took the square spindle blank and stood it on end in a crude jig. with a SawStop saw I cut a 15 degree cut about .7" deep into two adjacent sides. Then I went to our SCM slider that tilts to opposite way and cut the other two using the same jig. That allowed me to reference from the same surface so the resulting remainder was the same even if there were slight variations in the size of the blanks. The blanks were then laid on their sides and the fence was set to control depth. with the blade back to 90 degrees I cut away the 4 small pieces leaving a 4 way male dovetail. The sliding table works well for this type of operation. The bottom of the top rail was then dado cut and just using the saw blade set at 15 degrees the under cut for the female dovetail was cut on a 12/14" table saw with a power feed. A strip of wood was also cut at 15 degrees on the table saw along both edges. This would become the filler parts between the spindles. Stops were set on the Omga miter saw to cut the angles of 15 degrees on both ends of the filler pieces. These would lock the spindles between each other and establish the spacing. A little math was needed to make the 4 different panels come out looking the same in spite of each being a different length. So I had 4 different lengths of fillers. I worked in metric since it is so much easier to do such calculations in. The blanks were put on my hydraulic copy lathe, turned & sanded. A 35mm diameter stub tenon was turned on the bottom. I did several templates and test turnings. Templates were just cut from 1/4" Masonite on the band saw and sanded to final form on the Max oscillating spindle sander. The bottom rail was drilled at 35mm on the drill press. A 3/4" notch was cut into the bottom of the ends of the bottom rail that will fit over a short piece morticed into the existing porch columns. I cut 4 kerfs into the stub tenons on the bandsaw and made a stack of small wedges (200 pc!) to fit them. The top of each spindle was fit into the top rail and a spacer block put in place. After all were installed a very short filler was glued into the ends to lock them in. Then the bottom rail was fit over all the tenons and the wedges glued and driven home.

I had primed all the parts before assembly then spray painted them after. Now I have to remove the old railings and do a bit of patching of nail holes, prime and paint the columns. Then I'll mortice for the bottom stub that will locate the bottom rail and glue it in place. The top rail will have a piece of the spacer material let into it and then slid forward into a matching mortice in the columns. Assuming my measurements are correct this will allow me to set each section on to the bottom support and slide the dovetail piece in. A single SS screw from the bottom will retain that piece. There will be small support blocks under each end, fastened to the columns and in the middle of the long spans. There are a lot of assumptions made about being able to pull all the fits off.
As you can guess by this long winded explanation, it has taken me a lot of time. Crazy old woodworker.

DR Tom, With the system I used there is no need for any "tacking." The dovetail slot in the bottom of the upper rail holds the spindle 4 way dovetail and the filler that fits that slot and has a 15 degree on each end to match the top of the spindle dovetail. That results in all 4 sides of the spindle dovetail being engaged. The entire mess is simply slid in, one after the other until the last piece. That is a very short piece of the DT filler that has been glued into each end to trap all the rest of the parts. The reason the last filler piece is very short is to maximize the remaining slot so that a piece of filler can fit there and be slid into the matching porch column DT notch. That is the only piece requiring any mechanical fastener, a SS screw to keep it in the column.
This was one of those exercises in design that would drive a normal fabricator to drink.
I'm an architect by training but chose instead to develop an architectural millwork shop. My shop will take on projects that most woodworking people (with any brains) would pass on. We do lots of curved work in cabinets, moldings, Corian, plastics and veneers. The Corian & plastics are thermoformed in a 3'x8' oven. We have 3 very skilled CAD people. The shop is equipped with computer controlled tools driven by some very slick software. By the time the parts get to the clamps or the benches they are ready to be assembled with no at-the-bench fitting required. All the pilot holes for the hardware are there so no measuring is required. The primary method of construction is doweling with Confirmat screws used for other (oddball things.) I'm retired now so just do whatever I want. I have full use of the facility but I'm really poor at CAD work. I have a corner of the shop that I do metal machining and I do metal casting out back. Us old guys need to keep finding new challenges or end up couch potatoes. This weekend's project was chemical etching aluminum. Worked quite well. Always push your limits! Until you fail you don't know where they are.