I'm just finishing my CNC. See at http://www.cnczone.com/forums/showthread.php?t=84773 (100% overhaul :D)
And now I'm hit the problem. As my workshop is in attic there are big temperature change. I have Acetal nuts and work great when all is cold. As machine run the temperature rise and in PM time the temperature rise in workshop. At start there is (now) 20 deg/C in the morning and afternoon is aprox 30 deg/C. The nut heat's up aprox 15 deg/C over ambient temperature.
As I search what can be problem for excessive backlash in my machine I find that I doesn't have nut from Delrin but I have nut made from POM-C - the other type of acetal.
So I check property of both and find that my has 9.0 and Delrin 8.5 as thermal expansion coeficient.
As unit say x 10-5 Deg/K
So if I have 30 degre/K swing of temperature My nut 20mm in diameter will expand ?
9.0 x 10-5 x 30 = 0.027
multiplied by diameter 20 x 0.027= 0.54mm?
Is that true that nut wil expand for 0.54mm if temperature increase for 30 deg/K ???