Checking for Positive Draft
On occasion tool marks can be so deep that they reduce the draft or the polisher accidentally takes off the draft. The key is to always check for positive draft by putting a six-inch scale on the wall and comparing the angle it makes to the parting line. It takes just a second and that can save a lot of time and trouble.
Make sure that you also check your sidewalls for flatness. Lay the edge of a good scale on your sidewall then look for any light that shines underneath the scale. Wherever light is shining through is where the "bellies" and distortion are, which usually cause drag marks and part sticking.
To remove discoloration from small blocks and inside cavity or core areas the use of any common acid-based product is acceptable. The key is to immediately soak the blocks in hot water, air dry, then coat them in rust preventative. This can be tricky until you get the hang of it.
A second method for removing discoloration from large blocks of steel is the use of any common liquid-brass polish - from a can - on an abrasive "scouring pad," which is then used to rub out the discoloration. This combination cuts the time it takes to remove ugly discoloration from large projects.
Running Rubber Material
A 320-grit stone finish is often the best for molds running rubber material. Diamond polishing may make rubber stick.
Always cool a felt buff with denatured alcohol because alcohol does not "thin out" the impregnation of the diamond in the buff and denatured alcohol prevents the steel from "burning" when the heat from the friction literally burns the steel a brown-blue color - in which case the polisher has to go back to a 320-grit stone to take out the discoloration. When compared to a three-micron finish, felt is like sandpaper, so by impregnating the felt with a glossy coat of diamond the felt never touches the steel, only the impregnated diamond does. Make sure that you always use the flat bottom of the buff and not the sidewall of the buff - as this tends to cut lines into the finished surface - except if you're deliberately patterning a surface with the side of the buff.
Keeping Sharp Edges
The secret to keeping sharp edges is protection. You can do this by keeping the brush and buff rotating in a way that keeps the rotation coming off of the sharp edge and not cutting into the sharp edge. By following this simple rule, rounding off of edges can be reduced. Lapping the edge with wood is the only way to guarantee the sharpness of any edge. Then with a little light buffing the lapped areas will look like the rest of the finish.
Steel or brass plugs should be used in knock-out holes. Wood plugs should never be used because they are not tough enough to prevent the edges from washing away. Most veteran polishers - unless there are special circumstances - don't plug the holes, they usually lap the edges with wood and buff. As long as you are careful about the direction of the buff rotation, all of the sharpness should be kept - plus you have wasted no time with plugging.
Using Shim Stock
One of the most important tools any veteran ever uses is shim stock. For example, when you are forced to grind close to finished surfaces, the apprentice will always try his luck, but the veteran will use a piece of .010 shim stock cut to shape as a shield - which guarantees no tool damage.
Shim stock also may be used as a mirror for checking ribs. Sometimes a job has a rib that runs along the bottom of a core wall, making the back wall of the rib easy to see and the front wall almost impossible to see because the core is in the way. A solution is to take a piece of .003 shim stock and buff it to a high diamond finish by pressing down really hard with a hard buff - three-micron diamond and some denatured alcohol - then you'll have a .003 flexible mirror that easily drops into the rib and turns the hidden front wall into an easily seen back wall.
Fitting Inserts and Parting Lines
CNC machines and all types of dedicated task workers, who have lost comprehension of how a tool works, have made the fitting process a lost skill. The last two thousandths of fitting should be done with a stone, not with a blitzer. Blitzers and grinding marks leave a poor quality finish on the tool and contribute to flashing because they are hardly ever flat. Stoning in the last two thousandths solves both of these problems at once and will prevent a great deal of welding parting lines each year.
Feeling with a Homemade Pick
It's impossible to polish EDM from a rib accurately without a pick to feel the sidewall finish. Even shim stock mirrors can be misleading or unable to see into deep ribs. Feeling with a pick is the only way to check. The easiest way to make a great pick is to take an ordinary paper clip, straighten it out, grind a fine tip on it and bend it to a .020-inch hook. By drilling a hole down the center of a piece of wooden dowel rod you have created a great pick and holder, which costs nothing and lasts forever.
Making Homemade Punches
Quarter-inch diameter, water-hardening rod stock cut into six-inch lengths makes the best homemade punches. Grind whatever shape you prefer on the working end of the punch, then harden it by only heating the working tip with a propane torch until it starts to turn orange. Immediately plunge it into a can of heavyweight oil until it's cool to the touch. Be careful not to harden anything other than the working tip because if you harden the whole punch it could fracture and chip on the end that gets hit by the hammer. These punches are not for heavy-duty pounding. They're for the everyday edge fixing and steel moving toolmakers commonly do.
Nevertheless, these old-time punches have proven themselves to be a lot more durable and tougher than most punches bought from stores today.