Bal-tec™ Home Stick Lapping
Lapping is the most accurate material removal process. It can also produce the highest quality surface finishes. There is a secret process widely used by old-time gage makers to remove very small amounts of material from a cylindrical surface while maintaining or even improving the geometry. This technique is referred to as “stick lapping”.
During this process the cylinder to be lapped is rotated slowly between centers or held in a rotating chuck. A surface speed somewhere between 200 and 400 surface feet per minute (which is quite slow) is the proper speed for this process. A 3/8” inch diameter cylinder should be rotated about 70 R.P.M. (revolutions per minute).
The very flat, abrasive-covered surface of the stick lap is simply stroked against the rotating surface of the cylinder to be lapped. The lap is lifted up and stroked again and again until the cylinder reaches the desired size and shape. Each stroke will remove a few microinches, depending on the size and nature of the abrasive grit being used and the pressure applied.
A typical diamond grit could run from below one micron on the fine end, up to fifteen micron at the coarse end. One of the beauties of this process is that the diameter of the cylinder can be contoured by selectively stroking the stick lap more frequently in one area of the cylinder than in the others. This process can be used to produce an extremely straight cylinder or it can be used to selectively reduce the diameter toward one end or the other.
For press fitting bearing on a shaft it is very desirable to have the leading end of the shaft slightly smaller than the back end. When pressing a dowel pin into its mating hole, it is very desirable to start the pin standing up in the hole. You do this by selectively stroking on one end of the dowel pin while it is rotating. When the stick lapping tool is brought into contact with the rotating cylinder the cushy nature of the operator’s fleshy hands will bring the stick lap into perfect contact with the rotating surface of the cylinder, literally within micro-inches.
The standard “stick laps” are made of lapping grade cast iron. The smallest version is our part number 34-10-CI it is three-eighths of an inch in thickness, three-quarters of an inch wide, and ten inches long. The largest version is our part number 15-10-CI it is one-and-one-half inch wide, three-quarters of an inch thick, and ten inches long.
One of the most valuable features of this tool is the ability to mount very thin Mylar tape that is coated with diamond abrasive to do this. over the stick lap and use it this way. The surface of the stick lap is coated with a low viscosity liquid and the film rolled down. This procedure can produce a surface finish of micro inches or even sub-micro inches.
A very effective tool for use with the stick lap is a diamond-charging roller. This tool can be used to embed abrasive-grains deep into the surface of the cast iron lapping tool. The bonded-in abrasive will increase the stock removal by the stick lap and it will armor plate the tool to reduce wear. See Diamond-Charging Roller Part# DR2 or this website.
Price is $135 for the large version and $125 for the smaller.