Question:
We are desperate for an accurate blocker. We have had several but so far, none have given us the accuracy. We have had good reports on your blocker.We use DAC lathes and brass blocks with “O” Morse tapers. Our polishers have this taper. Will we need to replace all our blocks?
Answer:
When I come to a lab, I start with the lathes. Assuming that you use 12.7 mm (1/2'') collets, I use both a 12.7 mm gage pin and our blocking tools in the lathe collet and check the runout. If I can't get better that .005 mm runout, then I clean the collet or replace it. Interestingly, often I find that our blocking tools run truer than the gage pin in older collets because the irregularities in the collet sink into the plastic tool. I can send you some tools.Once the collet is validated, I block a few buttons and put them in the lathe collet to see if they have the same runout. If not, I look to see where the variation is coming from. This variation can be from the tools or the blocker. Remember that both the side and face of the button have to be running true.
In moving to a static blocking machine, I look for consistent prism and axis. Properly working static blockers give consistent results. So, if I repeatedly get .02 mm prism (.04 mm runout) at 80 degrees, I can adjust the blocker to minimize the prism. If I get random results, the problem is in the blocking tools. You can take a loupe and look at the 12.7 mm shanks of your brass tools. I suspect that they will not be smooth and will probably have a raised rim at the bottom which will measure 12.72 + -. If this is the case, they will not be held in a collet properly.In regards to you polishers, you mentioned that they are fitted with 0 MT's. Two features of our blocking tools are that they are straight 12.7 mm precision ground diameter and solid Delrin. We have found that having an internal taper makes them not stiff enough. Other benefits are that being solid and straight, you can put the dial indicator on the tool (in the lathe collet) to check runout and then the button. Plus, they are inexpensive ($3.00.)Many labs are blocking the raw blank, cutting the base curve, polishing it, and measuring C.T. They then transfer block to the front block without using the blank as a locating surface. While this adds a few steps, you are depending on the collet and blocking tool precision only. This method does not strain the blank as when it is held in the lathe collet. Also, you only need one type of lathe collet.The main thing to validate regardless what style of blocking tool you use is that they are repeating.
Please let me know more about your polishing machines, specifically the spindle design. I can look into providing female adapters or new spindles.
In summary, a thorough look at all of the lens holding parts of the lab will probably bring to light areas which could be improved. Once this is taken care of, maintenance will be pretty much house keeping. House keeping is very important and may require a culture shift. Going through this process every morning to validate that the lathe collets are running true and then blocking a blank to catch prism problems before they get to final inspection will improve throughput.
I'm looking forward to your information and results if you can go through this validation process. That will give me a starting point to make recommendations.
