Using insert drills.

Author:Rose, Steve
Position:T&p shop talk

I've heard all the excuses and reasons against insert drills

"That type of drill doesn't work here." "Those drills never cut on size." "We keep welding them up." and "Our holes are too deep."

The fact is, insert drills can be very helpful. There are a few issues to consider that should help in the performance of this drill.

Tool alignment

When using an insert drill on a CNC lathe, make sure the turret is on true centerline. Most turrets have been knocked off center for various reasons. Be sure to use a Blake-type coaxial indicator to check the turret's centerline.

The centerline should be checked for all center cutting tools. The problem is the mysterious crash that knocks the turret way out of line. An off-center turret can have a detrimental effect on the performance of the drill.

If you don't have time or inclination to check the turret's centerline, you can look for sparks from the tool's shank as it rubs onto the part. This is not a good sign.

Coolant supply

Anymore, use of high-pressure coolant is very common. In many cases you just have to make sure the coolant tank is filled. That sounds easy enough, but many machinists have problems keeping coolant in the tank.

In multishift operations, each shift hopes the other has added the coolant. The only solution is to top off the machine as the start of each shift--sounds simple.

The operator must also watch that chips do not feed into the drill's coolant holes. You may have to periodically remove the drill and ensure that the coolant holes are not plugged with chips, restricting the coolant flow.

Depth of cut

It is very important to never exceed the maximum recommended depth when using an insert drill.

Now that we know this rule how can we bend it? Sometimes we have to drill to a reasonable depth beyond that which the drill is technically allowed. Peck drilling with an insert drill is not recommended, but can be used if you need to drill beyond the maximum depth.

In drilling too deep you run the risk of chips getting caught in the flutes and welding the tool to the part. The best way to combat this is with good coolant flow, specifically with rear coolant flow through the tool. Your tool block may need to be modified to achieve this.

When using only standard coolant lines at the front of the drill, it is recommended that you do not exceed a 1:1 depth to...

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