You just got your process up and running. The parts meet all the gages and specs. (and with no tool breakage!). If a hundred pieces is the whole order, take the rest of the day off. If the order is for 10,000 or 100,000 pieces, you might want to fine tune your process.

This section shows you how to optimize your process for maximum put-through, maximum tool life and up time, or whatever requirements your company's philosophy might dictate:

In the auto industry, the primary concern is maximum productivity within acceptable quality levels. In many cases the tool is expendable so long as it has performed an acceptable number of cycles and has a predictable life– tool after tool.

In the medical instrument industry, the foremost consideration is quality- surface finish, straightness, and concentricity of the hole. Productivity is, of course, important, but in a secondary sense.

In high volume wood machining applications, we’re back to maximum productivity coupled with acceptable quality levels. When drilling wood, a gundrill lasts much longer than when drilling metal, such that the typical hazard becomes one of leaving the drill in for too many cycles. (When the drill gets too dull, it usually doesn’t break– instead, it starts a fire in the exhaust system.)

During your quest for whichever goal you’re aiming for, keep a close eye on what’s happening to the tool during your test runs. Refer back to the Troubleshooting and Tool Wear sections for guidance.

Also, keep a close eye on coolant flow and the type of chip you’re making.If coolant flow becomes erratic you’re getting close to chip packing and coolant stoppage. Most gundrilling machines have a flow sensor which monitors this condition and shuts the machine down before the tool breaks.

This may sound obvious, but I’ll say it anyway: continuously gage the parts being drilled as you’re optimizing. You don’t want to achieve optimum process conditions only to find out later that you made a lot of scrap.


Maximum Productivity/predictable downtime– First, try increasing your feedrate. Keep an eye on the chips that are being generated: too thick a chip may mean too high a feed rate; but if you don’t lose coolant flow, keep looking for any changes in the drill tip condition. If the tip looks OK after several cycles, try increasing the rpm. Do this in small steps of 100 rpm at a time. If everything still looks OK, increase the feed rate up to the point where something ‘bad’ happens, like witness marks on the cutting edges or reduced coolant flow (or, a broken drill.) Then, return to the previous parameters.

You can also try increasing the coolant pressure slightly. Running the pressure too high for a given size may cause the drill tip to wander, causing unpredictable runout (especially in small holes.)

There are also ‘kidney-shaped’ oil holes and double oil holes which allow more coolant flow. Either one may help depending on your situation.

If you want still more speed, you’ll have to alter tool geometry: there are various tool grinds that can in some cases give improved performance. The simplest is the ‘35/35’– additional clearance on the heel of the drill tip that allows more coolant flow to the flute without adversely effecting the basic geometry or strength of the tool.

The next step is one of the so-called ‘high-performance’ grinds which change the tip geometry to a configuration which in some cases gives better performance.

When you get to a point which you feel is optimum, monitor the operation through several drill changes to assure that the parameters are consistently yielding the same tool life results.

Maximum Tool Life/minimum down time– If you’re a small company or your drilling operation is not the controlling cycle time in the process, you’ll probably opt for max tool life.

You can go through most of the steps above, but with a different attitude. In this case you’re looking for all the improvement you can get balanced with maximum or at least reasonable tool life. Your particular method of cost evaluation will tell you when you’ve reached the break-even point.

Maximum Quality– Optimization in a high quality drilling application is similar to the max tool life scenario, but you’ll want to keep a closer eye on the workpiece, since it will probably tell you when to back off.