Re-Conditioning Granite Surface Plate
The actual process of reconditioning my surface plates, although being the ultimate goal in my project, was nearly disappointing in it's simplicity. The preparation was arduous, the final inspection was greatly satisfying, but the actual process of reconditioning - Aahh.
The process used is "Dry Lapping" which requires us to embed diamond powder into our Cast Iron lap using a hardened steel roller and then run this lap over the granite surface until tolerances are achieved. The key here is "until tolerances are achieved" which is where experience, shall I say craftmanship, is required to become efficient in this effort. On my large 36"x24" plate I looked at the pre-inspection Moody Method data shown below and created a plan, a guess at best, of what grit to use, where to concentrate my lapping, and how many passes to make.
The actual process of reconditioning my surface plates, although being the ultimate goal in my project, was nearly disappointing in it's simplicity. The preparation was arduous, the final inspection was greatly satisfying, but the actual process of reconditioning - Aahh.
The process used is "Dry Lapping" which requires us to embed diamond powder into our Cast Iron lap using a hardened steel roller and then run this lap over the granite surface until tolerances are achieved. The key here is "until tolerances are achieved" which is where experience, shall I say craftmanship, is required to become efficient in this effort. On my large 36"x24" plate I looked at the pre-inspection Moody Method data shown below and created a plan, a guess at best, of what grit to use, where to concentrate my lapping, and how many passes to make.
Now the first time I did this I have no idea what the results would be and the only good way to obtain feedback was to re-perform the very time consuming task of inspection by the Moody Method with the Autocollimator. Below you can see
Needless to say I was able to refine this inspection process very well and each time I went through the process I searched auctions and ebay for a Mahr Differential Level which would replace the Autocollimator process while improving the cycle time. Unfortunately I never found a price point on this instrument which I could justify.