Don’t even need to approximate. Hold a scrap or your rail cut to rough length on the top of the skirt board and against the post and wall. Mark the angles using the wall and post as the straight edges. If everything’s plumb, you’ll cut both at the same angle.

yeah, i built one similar to that so i could wheel it out whenever i needed power tool access. the 2000W inverter is able to start all the tools i own, and has a built-in charger function. https://www.reddit.com/r/SolarDIY/comments/10r7up0/diy_battery_backup_cart/

If you have a (pretty standard) carpenter's square, there are degree measurements on it. If you place the square against the railing, then hand a weighted string from the pivot location (all the angles will pint to it), it will tell you the angle of the railing.

Match that value on your miter box.

I've got one of those 12" angle finders for cutting trim - I've done stuff like this with it, like measure at each end for the height of the rail, and run a string or tack up a straight scrap of wood. Find the angle for each end. For something short like this, I might first cut from plywood or a 2x4 to make a template, cut a little fat and shave it bit by bit on the chop saw til it's a perfect fit, then transfer to your actual lumber. Many ways to skin a cat, I'm not a pro but I really enjoy designing and installing trim; windows and doors are more my thing though.

The easiest way for you to approximate this would be to get a piece of scrap cut at 37degrees on one end and rest it on the cap wall and slide it up next to the post or wall and then make a scribe.

Almost all stair cases fall in the 36-39 degree range.

Cut your rail long and sneak it in. You’ll have to make adjustment cuts on the post and wall. It’s not uncommon for to have to cut a 37 at the post and a 38 with a 1 degree adjustment at the wall because of how out of plumb/square the framing is.

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I understand it wouldn't power it for long, but I never use it all day or I'd bring the bigger gas generator with me. Maybe what I was really asking was if one battery can handle the surge of a table saw (3k or 4k surge watts) or use 2 batteries to spread the load out. I'll keep in mind the cheap charge controller.

There are a few ways you can go about it:

If you have a scrap piece of wood, you can cut it at an angle that you know is too wide and make small adjustments until it fits well in that lower corner.

You can make a few measurements to find the sides of the triangle that would form from conecting the top stair corner to the pillar and use that to calculate the lower corner angle.

You can use a speed square to get a fairly good approximation.

You can hold the handrail next to the gap at the appropriate heights and mark it with a pencil against the walls and like up the blade with the pencil marks.

However you approach it, don't worry too much about getting it perfectly flush with the walls. It is very likely that they are not flat (highly improbable that they are flat), and even a millimeter difference in position will visible change how it sits.

https://youtu.be/RtnnEnUJPu0

Speed square has a "pivot" edge you can use that will show you the degree of cut you need to make.

In theory a 12v 100ah battery can supply 10amps for one hour when inverted to 120v. There is, however, some overhead for the inversion and I believe you can't run the battery down to 0%, so it's somewhat less than that hour. If the saw is 15 amps, I would guess it could power it for 30-35 minutes. I would get a cheap charge controller to manage the charging aspect. You can usually put in anywhere from 12 to 24 volts and the controller can convert to what the battery needs and stop when full. These can be $15 on Amazon, and despite what many say, work pretty well.

Trigonometry

Yea but I can’t figure out the angle on my saw to have it flush with the wall

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I had a really difficult time with a piece of maple because it has a very tight grain structure, which makes it difficult to penetrate with stain. If this is maple and not pine, it could be part of your problem.

Not even remotely close to pine. It's 'rubberwood', 'acacia' or whatever catch-all term they use for generic import hardwood.

The key issue is surface prep and finishing method. First, your sanding isn't even. Whether you haven't gotten the original finish off, or we're seeing bits from your previous attempts, you can clearly see how the surface varies across the top and especially the side profile. Going this dark with stain alone is extremely demanding in terms of surface prep. There are also fundamental limits to how much stain different woods will accept.

Shellac will help with evenness, but not with darkness. The opposite, in fact. But that's not a bad thing.

What you need here, if you insist on a dark finish with wood that doesn't want to go dark, is to do what the factory did: tint. They don't stain, they use tinted finish (toner) to get the color in the finish itself, not the wood. Then the wood doesn't matter, it doesn't matter that they used a grab-bag of scrap hardwood that never matches, you just tint it to hell.

Problem with this, and a fundamental problem people have refinishing commercial furniture, is that it's not easy to use toner. You can't apply it by hand without getting some streakiness. It has to be sprayed. What you can do, however, is find rattle-can toner. See if there's a Mohawk dealer near your, or consider ordering some. A couple cans should do a top like that.

Watch some pros if you need to understand more about how colorwork is done: John's Furniture Repair and Tom Johnson Antique Restoration

You're the second person to mention oak, so I suspect that's correct. I like your idea of wipe-on polyurethane! I can handle scuff sanding, I just need a break from the power sander for awhile 😅. Thank you for your advice!

I did for my final sanding. I went over the top with 400 grit to make it smooth. Should I have kept it at 200?

Thank you very much for those excellent tips!

I'm glad that you don't think it looks blotchy! I am probably being a bit too overzealous with wiping. When I tried this stain previously, I took the opposite approach and it ended up looking tacky. I need to keep working on finding that happy medium. Thank you for your advice!

Great question, I'm truly not certain about this. I tried looking it up once I sanded it down, and the color/texture reminded me of pine, but I'm no expert whatsoever, so it may very well be oak.

>he braces are fine. I’d probably add a short one on the side to tie back to the middle
>
>Feel free to pm me for any other questions

Thanks so much! This is why I posted my question! :) I got a while before I'll be building it, so when I get to a second draft, I'll take you up on the p.m. Thanks again.

It looks to me like you still have some of the old finish in the wood. Whatever it is just sanding may not get it all out if it's deep in the grain. What does it look like underneath? You may have to try some type of stripper first.

The stain you have looks like a good start. I would suggest a tinted top coat to even out the colour. Minwax Polyshades is a product that I have used with excellent results even on woods that are difficult to stain evenly. Good luck.

It's not pine. It's "plantation hardwood", aka rubberwood trees that no longer produce enough latex to keep them alive and so they're harvested for lumber.

I would try a dye stain if the gel isn’t getting you the results you’d like. General Finishes Espresso will get you the results, but you’ll likely need to use a bit of the extender if you’re not spraying the finish. If you opt to hand apply and not use the extender, be prepared to almost immediately start wiping off the stain since it will dry rapidly on the wood. Also, ship the conditioner. While helping prevent blotch, it stops some of the stain from absorbing into the pores.