A Short Treatise on Adjusting Boring Heads

One of my many "hats" is technical support. When a customer calls with a problem or a question, I have a mental list of my own questions depending on that customer’s specific need. One of the areas I touch on is the proper adjustment of the boring head being used. The need to explore this with the customer is one of the reasons people buy our heads. They last so long that the person using it has probably never seen the instruction sheet that accompanied the "new" head. I’ve seen 35-year-old heads come in for repair. The instruction sheet is probably in the original users toolbox in his garage collecting dust while this retired machinist is out playing golf!

Our adjustable boring heads have three main parts. The chrome Dial Screw, chrome Bar Holder and the black Body. The body contains the gib and three socket head set screws to adjust and lock the gib. The 2 outside set screws are for gib adjustment and are preset at the factory. The center screw is the lock screw. In normal operation the machinist would loosen the center "lock" screw, make an adjustment with the Dial Screw and then "lock" the center screw. The 2 outside screws are normally set so that the gib applies enough pressure to keep the Bar Holder from moving when the lock screw is loosened. Please note that even though the Dial Screw threads are class 3 and the web tolerance (the interface between the Bar Holder and the Dial Screw) is held to just .0005" there is an accumulation of tolerance. This would allow the Bar Holder to "chuckle" slightly thereby changing the bore diameter without the users intervention when the lock screw is loosened! To prevent this the factory adjusted pressure on the gib (and thereby the Bar Holder) is just enough to feel some "drag" when turning the Dial Screw. The user can re-adjust this "snugness" by first loosening all three screws, then, while slowly turning the Dial Screw (back & forth is o.k.) adjust first one outside screw until slight drag is felt then adjust the other outside screw until slightly more drag is felt.

Since there is some backlash caused by the accumulation of tolerance, when adjusting to a smaller diameter the user must "back off" the Bar Holder (just like on an engine or turret lathe, remember those?) and then come back to his desired size.

There are times when a user may desire to tighten all three screws after each adjustment. This is doable and will not harm the head. To adjust the head in this scenario the user would first loosen and then re-snug each outside screw to prevent the Bar Holder from moving. Then unlock the center screw, make the desired adjustment and then retighten all three set screws.

If you have any application questions about our product line please don’t hesitate to call and ask for technical help.

Randy Cloud, Engineering