Hi,
scraping is good if you have 0.02mm to 0.05mm or less material to go, any more and its a joke. The process is to mill the surface flat, and if you need that last 0.01mm then scrape.

Epoxy has a Youngs modulus of about 3GPa, and it creeps over time. It is not suitable for mounting anything on a CNC machine.

You will almost inevitably have to machine parts, whether that be a few large parts or more smaller parts is a matter of choice......that they be machined is not. Machining parts to be flat
and square requires very good quality machines run by the best and most careful of machinists......it will never be cheap. Get used to it.

Many hobby builds are designed to try to get around machining and/or thermal stress relief, and almost inevitably end up as a compromise, usually a poor one. Its time to realise that
making an accurate machine WILL require outside help, and that help is not cheap.

My own solution was to cast three identical axis beds in grey iron, 115kg each, then have them precision machined and vibratory stress relieved. This I thought to be the best possible way to
get rigid axes of the highest precision at the least cost. Not that it was cheap. The three axis beds cost $10000NZD ($6000USD) to be cast, relieved and machined. By the time I bolted in the
ground ballscrews, linear rails and fitted a 750W servo to each they cost $16000NZD ($9600USD).

These axis beds were then bolted (and shimmed as required) to a steel frame, made of plasma cut 32mm thick med tensile steel.

My reasoning goes that even if a change the frame, or machine it or whatever, that the axis beds will remain the same. I made them as best I possibly could (afford) and they will last me for twenty
years irrespective of what happens to the frame and other components.

Steel is good and versatile if you can weld. Once its welded you will need to stress relieve. Thermal Stress Relief (TSR) is the gold standard, but not cheap. If you can find someone who has Vibratory Stress Relief (VSR)
equipment that is much cheaper.

I priced TSR recently at $6.70NZD/kg ($4.00USD/kg). It is not cheap but the results are good, and contrary to popular belief amongst hobbyists is a very well known and industrially practiced process.
You just have to get in and play with the big boys!.

Craig