UNITAC Inc- Drilling Methods


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Drilling Methods

The following are deep hole drilling methods that may be carried out using the STS or DTS.

Solid Drilling

Only one operation is necessary to obtain the required hole diameter. Often no subsequent machining is needed because of the high quality surface finish, straightness and hole tolerance.

Counterboring

This process is used to open up a pre-bored hole to obtain a more exact diameter. In some instances where machine power is limited, a hole can be drilled with a smaller diameter drill head and counterbored to the required diameter.

Reaming Reaming is carried out to obtain a precise hole tolerance. Under normal cutting conditions an H6-H8 tolerance can be kept. The depth of cut per side is smaller than when counterboring since the main purpose of reaming is to achieve good hole quality.
	Chip Forward Reaming Heads with ID threads Heller® style are easily adapted without modification to a gun drilling machine, and in combination with a coolant adapter, also, to lathes, milling machines and machining center. These heads can be used only for through-hole reaming. Coolant is pumped through the boring bar to which the head is attached - then through the head between guide pads and over the cutting edge. Chips are expelled forward through the existing hole.	Chip Back Reaming Heads with ID thread Heller® style are used in the STS only, for both blind and through-hole reaming. Coolant is pumped over the boring bar and tool. Chips are expelled through the center of the boring bar and out through the spindle. In reaming through holes, the exit end of the part must be sealed.
	Chip Forward Reaming Heads with a four start thread are designed for use in double tube deep hole drilling systems. They can be used for through hole reaming only.	Chip Back Reaming Heads with a four start thread are also designed for use in double tube deep hole drilling systems - but can be used for both blind and through-hole reaming.

Both chip forward and chip back reaming heads have a single lipped carbide cutting edge with a precision ground chip breaker and two carbide guide pads that are extra long for added directional control and better burnishing performance. The tools are stocked in the maximum diameter of each size range and finish ground to order, ensuring excellent chip formation, surface finish and size control.
Depending on the production setup, Unitac reamers can be used either to follow an existing bore, or to straighten a non-concentric bore. Standard carbide cutting speeds are used, with a typical feed rate of 0.635 mm per revolution for diameters as low as 10.16 mm. On some materials, surface finishes below 20 micro rms can be obtained. Hole tolerances of + or - 0.0127mm or closer can be held, depending on setup and finish diameter required. All reamers come with a quick-change thread and with sufficient carbide on the cutting edge for several regrinds.
Standard lead angles on Unitac reaming heads are 20° lead and 45° lead heads. A guide bushing is recommended with the use of both 20° lead and 45° lead heads. In some cases, however, a guide busing may not be requisite with a 20° lead head.