i have made tabs on a few occasions.
i found that your working humididty can have some effect.
used a variety of colors best to use ones that are intended for htis purpose. i have used colors that are and are not. those that are not are messier and if using an automated machine that can come into play.
machines do a good job at making a solid tab, doing it by hand takes practice and you need to be careful with dosing/hammer strikes.
microcrystaline cellulose+mag sterate+active+color needs to be evenly mixed for time, if not you have uneven dosing.
after you make a few k by hand you will realize the value of the machine! lol
takes minutes to do what took hrs.