Shares of 3D Systems (DDD) and Stratasys (SSYS), the 2 top publicly traded 3D printer makers, rose after a sell-off Mon. 3D Systems slid almost 14% and Stratasys fell 10%. Although it's unclear why, speculation centered on comments on Seeking Alpha and Motley Fool that shares have risen too far too fast and might be due for correction. 3D Systems has been No. 1 on the IBD 50 list of top stocks since Oct. 29. 3D Systems shares rose 4.2% Tue. Stratasys rose 1%. ProtoLabs (PRLB) rose 1.1%.