Process housekeeping

Dear Mr. Larsen: In your presentations, you dwell on blocking tools and various blocking methods. You mention “housekeeping” like labs are dirty and need a maid to clean them up.We use the transfer or “mandrel-to-mandrel” method in an optical blocker. After the initial process set-up, we proceed with the production. We have not been troubled with housekeeping problems. What issues do you see arising with the method we use and how should we keep control of our process?


Dear….,Thank you for your comments about tooling and your manufacturing process. I am pleased to hear that your process is working well. In my presentations and articles, I attempt to address those practices that I encounter across the industry. There are a wide variety of manufacturing methods both in polishing, blocking, and lathe turning. 

The process that you describe is sophisticated at least in terms of the investment you have made in the machinery. Without seeing your process, the optical blocker aligns the optical center of the base curve with the mechanical center of the front curve mandrel holder. This step eliminates any runout that the base curve lathe may have imparted to the centration of the base curve.I have talked about three elements in the lens holding system: Tools (mandrels), blocker, and lathe. In your process, once the blocker is installed (calibrated), the base curve is blocked true to the shank of the front mandrel very precisely. Assuming that the shank of the mandrel is 12.7 mm and round, the mandrel/blocker part of the system is “taken care of”.

But the condition of the mandrel (12.7mm and round) and the blocker calibration process needs to be validated. Use a micrometer to check to see if the shank is tapered or out-of-round. You now have the base curve precisely aligned with the mandrel and know that the shank of the mandrel is 12.7 mm, and it is round. The next question is: How does the mandrel fit in the lathe collet? Since this is where the dust is, it is where you will need to be carefull about runout. I have seen .01- .03 mm of radial runout in relatively new collets on the best CL lathes in the world.

This is usually remedied by cleaning the collet and the spindle, hence the “housekeeping” reference. If not, replace it making sure that it is a deep collet (12 mm or more). Monitoring these components for precision ensures smooth running process.Even in your case, assuring the cleanliness of the components is critical to achieve the uniform edge capability that you paid for when you purchased the manufacturing system.
Let me know how it goes.