You mean additional bracing will add 35kg to the 65kg? It will become a bit heavy for steppers then. Problem starts that it's ok for steppers at 1:2, but steppers are not like servos to spin reliably at 3000rpm or even 1000. So i think then it could be better to use bigger motors/ that will need bigger and much higher voltage drives /


Then just brace with 1 plate on the 80mm side from bottom of the gantry beam. That should be enough. You keep the weight right, also the rails themselves when bolted on are very strong. As bend from forward backward movement could be the biggest eventual problem and that will prevent it . You could always bolt sth at the back later if needed.

Or just don't brace at all, i like a bit OTT so you may not listen to me. When build my first machine and my current one, at the end i decided to make everything strong as i think it must be and then think how i will move it.

Have you thought for servos? I assure you i will never go back to steppers again. I could point you to servos that will not break the bank, still untested though by me. Direct from manufacturer. I think they must work well. Around 600$ 4 x AC servos with drives, you have to add transformer and make PSU for 100$ more.

Steppers will be half the price though and work fine more or less up to normal 5-8k mm/min feeds depending on screws and other details. Servos 1:1 could move up to 30k mm/min, which is ultra nice. BUt at the end i moved my machine today for first time with 16k mm/min, so all depends on what your final purpose is.

So to simplify, or stick with your initial plan, or build as you like and go with servos.