Grub screws keep coming out of z and x axis

Hi!
I've been experiencing problems with my cnc stepcraft 600 on particular with the grub screws on the z and x axis. As much as I tighten them and make sure they have seated in the hole they pop out while I'm machining a piece. Which means I have to cycle stop and tighten the screws back to place and set the cycle to start again until it completes the cycle. I've even tried disassembling all parts on both axis then reassembling, cleaning and tightening all parts but it continues giving me the same problem with the grub screws. Anyone experienced the same issue and if so have managed to solve it?