When to move to a new grit.

So i've been sanding my kit recently, I usually sand until i'm not seeing significant amounts of material coming up as I make passes, but there are still noticeable machine marks along the sides of the body that don't seem to come off no matter how much I sand. I made the poor judgement call of gluing the neck and body before sanding so it's difficult to get an orbital sander in those spots, so I do it by hand.

Now that I'm not noticing much sawdust coming up when I sand I'm thinking of moving to the 220 grit, but those machine marks are still bothering me, is this really an issue or will my clear coat fill those small scratches if I leave them and continue sanding with finer paper?

Normally you'd stay at a heavier grit until those machine marks are gone, I'd a similar thing on my Korean ST, i thought they'd get filled in with the clear, but they actually stayed noticeable in spots.
You're best to stay on the lower grits until you're sure you've got them out.
Post up a photo or two to give us an idea of what you're dealing with.

This is probably the clearest image I am able to get at the moment. This is only an issue on the sides, the rest of the body and neck is fine.

https://i.imgur.com/8BFUlcO.jpg

And another.

https://i.imgur.com/H8tzszO.jpg

Yeah, i see what you mean. You may need to step back a couple of grits and give that some more love. When you move up a grit the scratches become more prominent unless you've already worked them out.
If you get up to 400 and you can live with it, then crack on, but otherwise employ the Sand Sand Sand Mantra. Bit of a bugger that you've got the neck in the way but sounds like you are working around it anyway.
Is this an RC?

It's a PRS-1TS, though I'd love to get an RC-4, I love the rickbass shape. I think I will do my best to sand them out, the marks on the horn there could maybe add a bit of character to it since I'm using a dark walnut stain, but those ones inside the cutaway will just look tacky if left I think.

Nice! The inner part of the cutaways is always a problem spot. the best way i found was to get some 20mm or 25mm dowel, wrap some 80 grit around it and sand away. You'll need to be careful of your bindings, so you may need to leave some of the marks as "character" :)

I have those long thin fingers piano players envy, hahaha, so I may not even need to use dowel.
The scratches are coming out with a little (a lot) of elbow grease.

Pictured: one fool who doesn't own an orbital sander 2018 (colourised)
https://i.imgur.com/PIs5gDA.jpg

Ah well, doing it by hand is a form of therapy. At least that what the voices in my head tell me.🤪

Try sanding at 90degrees to how you currently. Sometimes the end grain can be deceptive. You think you sanding with the grain, but are actually sanding across it. If this is the case when you change the sanding direction all of a sudden all those machine marks start to disappear.

I usually sand in a circular motion on the sides, those scratches were just particularly stubborn, i got them all out eventually, but some of them took me about 20 mins of sanding the one spot, suffice to say my arm is a bit difficult to lift at the moment.

hi guys, i was not happy with my original application of stain so i bought an orbital sander to sand it back and start again...i think i have taken a few mm off the thickness of my telecaster body...will this be a problem when i attach the neck and it sits higher from the body?