For such a simple task, it’s surprising how many things can go wrong when you drive screws. In the final analysis, the most effective point consisted of 144-degree included angles for the primary point, 80- to 85-degree included secondary point angles, 4- to 5- degree primary lip clearance angle facets, and 20-degree secondary heel clearance facets (20-degree heel clearance facets are automatically ground whenever primary angle facets are 8 degrees or less.
But as lip clearance is gradually increased, the chisel line inclines diagonally to the right towards 1 ‘clock (see Figure 2). Therefore, by paralleling the cutting edge with a protractor, a reading of 110 degrees of the chisel line angle denotes approximately 5 degrees or low clearance; 120 degrees indicates 8 degrees or medium clearance; 130 degrees indicates 11 degrees or high clearance; and 135 degrees indicates extra high clearance.
Be sure to measure the size of your plug to be sure your countersink’s body will make the right-size hole. The key is to make it stable after you turn it upside down to drill the bottom. Countersinks on our site are designed for use in wood or plastics and are not intended for counterboring steel. The hex shank prevents the bit from spinning in the chuck under excessive loads.
CAUTION: When high speed steel drills are sharpened by dry grinding, care should be exercised to prevent overheating. The advantage of a drill press is that you can drill holes exactly straight or at preset angles. Boring Machine Bits – Typically used in automated machinery such as drill banks or CNC machines fitted with tool holders or single size collets.
The drill must be well lubricated during use, and while it is sufficient to apply the oilcan freely to hand or breast drills, this method is not satisfactory with larger power- driven drilling machines. This is easy to achieve by clamping a table-width stop at the back of the table (Photo 3). Position the stop so the jig will align squarely with the front of the machine, and then clamp it down at the edges of the drill press table. If the chisel’s line angle is on a vertical plane pointing to 12 ‘clock (90 degrees in relation to the cutting edges on a horizontal plane), lip clearance would be zero.
But there are a lot of them out there: one piece or a combination of drill bit and countersink, single-fluted or with multiple flutes (or none at all) and a wide range of chamfer angles make for tricky selection. The key to drilling stainless steel is to avoid work hardening by obtaining maximum cutting action in minimum time. About thirty degrees should do it. This should set the main angle of about fifty to sixty degrees. In stainless steel, frictional heat is sufficient to turn such a drill blue, generating temperatures over 1000ºF.
The point angle of a twist drill is the angle made by the cutting lip and the axis of the drill. I retrofitted my Bridgeport with a Bandit control, and Ground thread ball screws and Stepoper motors on X and Y axes only. This defeats the purpose of spot drilling and can result in a less accurate hole. It is wise to place a block of wood or soft metal under the work to prevent the drill from grabbing when it breaks through.
Counterbores on our site are designed for use in wood or plastics and are not intended for counterboring steel. Drill Bits – Normally used with hand held drills or drill presses fitted with standard chucks. Torx-head screws require star-shaped bits that are labeled with a T” followed by a number. Also, it produces over-sized holes and is a primary cause for reduced cutting edge life.