A lot of issues with scales peeling off

[12345678910]

A couple of ideas
yes roughing and flattening.

Acetone.
Unless you come from a lab background, everyone I've ever seen puts a rag on the mouth of an acetone tin, tips up, tips back and wipes away.
Anything on that rag is now in the acetone tin.

Try to think like a lab tech,
(or a good mechanic. Only clean grease from a clean can with clean tools and it never, never goes back into the clean can.)
You only want to take out of a clean bottle, never contaminate the bottle.

Have a clean squirt bottle, only squirt out into the rag, never touch the rag to the bottle. Never let the rag contaminate the bottle.


Clamping
It's tempting to put the squeeze on hard.
You can squeeze out all the glue and warp your materials at the same time.
Those harbour freight clothes-pin type spring clamps apply enough pressure for a well fitted glue up.
I've seen scuffing with abrasive, blasting is best if you clean after.

Corby's
Why not ?
Permanent fasteners - you can't go wrong, until you grind through em and have to start again.

 

[Joshua Fisher]

Also a side note acetone leaves a light film that can break down a glue bond and personally I’d avoid using it for cleaning. Isopropyl alcohol works much better for cleaning before epoxy and to remove any excess glue.

 

[Stacy E. Apelt - Bladesmith]

Correct. Isopropyl alcohol and methanol are the solvents for uncured epoxy. They are also the best for pre-glue cleaning.

 

[fitzo]

Also a side note acetone leaves a light film that can break down a glue bond and personally I’d avoid using it for cleaning. Isopropyl alcohol works much better for cleaning before epoxy and to remove any excess glue.

Wise advice. It should be noted that pure acetone, aka the kind used in a laboratory as "Reagent Grade", leaves no film. The film arises from poor distillation of "recovered" industrial solvents from chemical processes. If the can says, "For Cleaning" on it, know that it has crap dissolved in it that will leave the film Joshua mentioned.
I'll say one more time, when in doubt, pour a little puddle on a piece of clean glass, mirror, etc, and let it evaporate.
The problem with acetone is the good stuff is expensive. I have a pint of Reagent Grade and it cost me $25. I use it to get paint and such off of me. Acetone in itself is less toxic than isopropyl alcohol. I don't want that crap on me that's in the acetone you get from Ace Hardware or a big box. You don't know what it is.
YMMV

PS -wanna see the source of more "film"? Take a paper-towel you use for wiping and soak it in your solvent of choice. Take some of that liquid and do the puddle-on-glass trick. You'll quit wiping those tangs with a towel soaked in solvent, too. Surprising amount of emollients and such added to paper towels and soluble in common shop solvents. All of that interferes with adhesion.