Boring head

This article shows the making of a boring head  that is similar to commercial designs.  The arbor has an  MT3   taper  to fit my mill's  spindle, and a Jacob's taper is used to mate the arbor and boring head. Shown below, two of the boring heads have been black oxide finished.

<< You can get the drawing at Here>>

1. (Taper arbour)

Setup to machining for purchased MT3/JT6 arbor.

The Jacob's section has been machined flat. 
2.  The tang has been removed and the flat section from the Jacob's taper is held in the chuck for drilling and tapping  the 12 mm draw-bar thread. 
3. (Taper arbour)

Arbor secured  in lathe spindle with draw-bar, ready for machining to 12mm diameter. 

4. Micrometer shaft threaded -- diameter 10 mm, pitch 0.5 mm.  Material is free-cutting steel.

5. Machining micrometer shaft.

6. Engraving micrometer scale lines with 0.1 mm slitting saw, depth of 0.1 mm.  

See Article Number 48 for making a small slitting saw arbor.
See Article Number 15 for the design of the Simple Index Stand.

7. Slitting saws and arbor.  The best thickness for a scale line is in the order of 0.2 mm.

8. Punching numbers on the face of the micrometer using a punch mark holder.  

See Article Number 14 for making a Punch Mark Holder.

9. Engraved lines have been filled with a marker pen to improve contrast.

Note that the micrometer dial has 25 divisions and the micrometer thread has a 0.5 mm pitch.  Thus, a complete turn of the dial moves the boring head 0.5 mm, and adjusting the dial one increment moves the boring head 0.5/25 = 0.02 mm.

An Allen head set-screw is fixed in the center of the micrometer head with Loctite, medium strength.  An Allen key can then be used to adjust the boring head.

10.  Making a custom-sized, metric tap, 10 mm x 0.5 mm for the internal thread of the micrometer.

Material is carbon steel. (0.45% carbon steel)

11. Cutting flutes while special tap is held in Simple Index Stand.

After cutting flutes the relief angles are ground or filed.

12. The special tap, machined, heat treated, and ready for use.
13. (Body)
The body is made from 55mm round free-cutting steel.

14. Body centered in chuck using the setup shown.  

Bore a 17.2 mm hole for the micrometer dial head, followed by finishing the rest of the hole to 9.5 mm.

Thread the 9.5 mm hole with the custom tap.  (See #12.)

14.5 A temporary sleeve guides the custom tap.

The sleeve has a 17.2 mm OD and  9.5 mm ID.

15. Taking care to align vise to milling table, as next steps require precise parallel cuts.
16. (Body)

Slotting  prior to cutting  dovetail.

Depth of cut is 8 mm using a 12 mm roughing end mill.

17.  Completed dovetails, to be followed by honing with an oil stone.

18. Cutting away unnecessary parts of the sub-head, leaving allowance for finish milling.

19. Sub-head  surfaced with fly-cutter, using slow feed to produce a fine finish.

20. Drill sub-head holes and ream to 12 mm for a exactly size of boring bar shanks.

21. (Sub Body)
Preparing  sub-head for dovetails  using roughing end mill. 

22. (Sub Body)
Dovetails finished.

23. Setup for beveling gib  plate.  Material is mild steel, 3 mm thick.

24. Lightly machine  outer surface, followed by sanding off machining marks on a belt sander.

Note that the sub-head and head are tightened in an aligned position, and that the head and arbor are joined by the Jacob's taper.

25. Boring bar parts.

26. Use left and right screws to adjust gib tightness. Use center screw for locking.

Completed !!