Hello everyone! New to the forum and hardwood refinishing and have been so impressed with the level of knowledge, talent, and community!

Apologies in advance for the length. I am refinishing the original hardwood floors in a home that was constructed in 1966. I believe they are red oak. They did not appear to ever have had any type of refinishing done previously when looking at the edges under the baseboards and were in rough shape.

I've gone over everything with multiple (admittedly far more than necessary - blame it on being a newbie) passes with the American EZ8 Drum Sander. I move from right to left and overlap about half a drum on every pass (~4"). The passes were as follows, all with 36grit:

1. 45 degrees against the grain
2. 135 degrees against the grain
3. 90 degrees completely against the grain (perpendicular)
4. 0 degrees along the grain
5. 0 degrees along the grain (did this pass again as I could still see the cross grain scratches)
6. 0 degrees along the grain

I believe the 6th pass is likely where the chatter marks set in (it was when I first noticed it) with that many passes along the grain.

Question is - will these come out with a 5-15 degree angle on the 60 and 80 grit passes? Or is the only way to get them out with a 36 grit pass again? If I need to do 36, does it make sense to just use the OBS-18 square buff with 36grit? I know people don't recommend them often because they're not good for stripping, but these floors are already bare.

The other issue I have is with edging valleys against the grain. I follow the technique of starting ~12" back, going towards the wall, pull back to me, and then 3/4" to the right, and once I've cleared ~24" I go back across against the wall edge. Despite the dozens of hours of videos I've watched over the last month, I failed to notice (but do now going back and rewatching I see it) that people only use this technique when going WITH the grain. I used this even when going across the grain and as you can see I now have valleys that stick out like a sore thumb.

I believe you're supposed to essentially always have the 'nose' of the edger going along the grain, like a car on a highway. This requires turning the edger 90 degrees when going along the sections to continue along the grain. Would love confirmation if this is correct.

Regardless - looking for feedback on how to fix.

1. My first thought was to go back over with the edger the 'correct' way (assumes the way I listed above is correct...big risk).
2. The other thought was to use the OBS-18 with 36 grit to 'flatten' the areas. I really love this idea for the flexibility that the OBS-18 has with corners and using it to 'buff' all the way up to 100 (will still use the drum sander for 60, 80, and 100 grit if recommended).
3. The last idea was to use the Festool Rotex 150 in orbital mode (essentially much like the edger but sanding spread across the entire pad as opposed to just the 'nose').

I am sincerely grateful for any and all feedback provided here. I know there's a lot of pros out there that probably get a good chuckle out of these amateur mistakes but I dearly appreciate the help.

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First off the object of sanding the flooring is to use as little energy as possible to get results that you want. Working too hard can result if extra work to correct mistakes. Since the floor was pretty even to have a nice looking stain on it, you only needed to remove the top surface after multiple passes. Gradually smoothing out the deepest scratches with the final paper taking the last remnant of the scratch made with the coarse paper. Using the next finer sandpaper and ending with 100 grit will be the best process. Cross grain sanding is never good technique. You may need to use 36 grit straight on to remove these. Then start over with the next finer paper. Sanding at a slight angle can help with getting the floor flat, but may not make the floor completely flat. Be sure to check the wheels for stuff sticking to them to help eliminate a potential problem. A flat plate sander can help. I have never used one, though. After the field has been roughed off again you need to sand the edges incimentally with the same paper as the drum sander with the 100 grit edger final sanding before the 100 grit drum sander. Then you can use a random orbit sander by hand to smooth the line between the two machines. You just need to concentrate on removing practically all of the preceding grit's scratches as you go so there are no valleys anywhere. Once you get as far as you have, you ought to know what little pressure it takes for the machine to do the work without leaving valleys. It takes a light touch with a one horse power machine to smooth the floor without causing more work that needs to be corrected. By the time people are done with the room they have worked on, they know a lot more about how floor work needs to be done. Of course having someone who can help correct mistakes before they become a big problem is very helpful. I don't know where you thought going across grain would be a good idea. Also, going at a 45 degree to the grain is not always necessary unless the floor is cupped or it is the first time to be sanded before the first staining or finishing.

Thank you so much for the feedback here. I've definitely learned a lot of lessons throughout this process. I've always had an immense amount of respect for artisans in their trade and love jumping in and trying to learn the 'nuances' of the trades myself.

With where I'm at in the process currently (entire floor stripped down to 36 grit, some very light chatter marks in the field, and some bigger valleys/dips resulting from going cross grain with the edger), I think my biggest problem is dealing with the edger valleys before moving up to 60 grit. I am looking into potentially buying the Festool Rotex 150, as renting the edger every weekend the last two weekends has me up to $320 in costs already. Would you suggest using something like the Rotex/Rotary sander to get these valleys out, a flat plate sander, or just going back at it with the Edger again the 'correct' way this time?

An edger will smooth the floor faster than a random orbital sander, but you need to be careful with 60 grit. You just need to be careful of how the weight helps the machine grind. The orbital can smooth the surface with a coarser paper over time so that with patience that machine can creep up to a smoother surface. You can tell if you are using the machine correctly since results don't "just happen" like with the strength of the edger. If you can budget a new top of the line random orbit sander and sandpaper discs to use in the future it will be a solution. I would buy 50, 80 and 100 grit discs with it, although 50 is pretty coarse, you can flatten the floor better than spending extra time with 60 and smooth the surface better from drum sander running 36 grit.Then you only need to follow with 80 and 100. If you are going to stain the floor some use 120 grit to blend the big machine to the wall sanding. I use 80 grit hand sanding after a sharp scrapper takes out any circular scratches that show when stain is applied, before the stain had dried.
To help with fine chatter marks using the drum sander, I try to use a firm, but not too much pressure as I back up as fast as I can to stretch out the spots where the paper is fastened so there are less chatter marks. I use a used edger paper to run across the drum with the hundred paper turning, so the very sharp tips of the grit are dulled so the wood will be smoother. Use the random orbit where you change direction in the middle of the room, or use 80 grit hand sanding to blend.