My finish mixer has always been too fast,33 rpm.Fixed other problems so i could use it but the mixer was always going too far around the cup and sometimes falling which necessitated me holding the mixer at the bottom of the cup for four minutes with my finger, not much fun. Finally got a larger stainless bolt,16mm, cut the head and threads off then shaped the end so it fits into the bottom corners of the cup. The mixer weighed in at 95 grms, approx. 3 ounces. Seeing as I was putting finish on a test wrap it was a good time to try it. The mixer now sits right at the bottom during mixing and got almost zero bubbles. The finish set up fine and I only used 0.5 cc's of each part to give it a good test. A heavier mixer can give you a better mix when using a mixer with a speed above the nominal 18 rpm
No problem with the finish on the mettler test or the madeira holographic test and definitely no fish eyes so I now feel more confident using either of those threads. Used three coats of cp and one coat of hi build.
Link to the test photo below.

[www.rodbuilding.org]

ESFNEM Col
Port Kembla, NSW
Australia