Copyright (C) 1986-2008 by Daniel H. Hudgins, All Rights Reserved.

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This Web site is dedicated to the thousands of "users" of my programs, those who have helped test my programs over the last 22 or so years, and especially those who shared their experiences with me.

You must read this notice: This is a licensed Web site (HTML document and associated files). You must read and agree to be legally bound in contract by the Terms of Use and conditions given in the End User License Agreement ("EULA"), Legal Notices, Instructions, Warnings, Disclaimers, and all other text in "SECTION: 0" of "This Web Site" (HTML document and associated files) before reading or using any of the information, software programs, and or files, contained in, linked to, and or associated with, "This Web Site" (HTML document and associated files). Any use or "Beta Testing" of "This Web Site" constitutes your acknowledgment of your full agreement with the current End User License Agreement ("EULA") and your decision to have this current license supersede all prior and contemporaneous agreements and understandings. Information and files in "This Web Site" (HTML document and associated files) have been placed here so that long time users of "The Author's" programs DANCAD3D.COM (tm) , DANCAM.EXE (tm) , or DANPLOT.EXE (tm) could help proofread the text of the documentation files or screens displayed, and also help test data files, example files, and or any software programs that might be made available from time to time, to aid "The Author" in finding mistakes, bugs, and other errors, omissions, defects, mistakes, and faults. Everything in "This Web Site" (HTML document and associated files) is "Beta Test", "Beta Code", Experimental, Preliminary, requires proofreading, or is being evaluated for possible revision, and is NOT warranted to be free of defect. To help "The Author" report any bugs, foul-ups, defects, or mistakes that you find, see "SECTION: 8" for instructions. "This Web Site" (HTML document and associated files) and all other files and programs by Daniel H. Hudgins are made available "AS IS" without warranty of any kind express, expressed, or implied. All offers and specifications are subject to change or discontinuation without notice of any kind. Please read "SECTION: 8" of "This Web Site" (HTML document and associated files) before trying to contact "The Author."

SECTION: 7.20 is for some "general" discussion about Metalworking, see also the program files in the current distribution of my programs, the other parts of this HTML documentation, and the current On-Line version of this Web site for information more specifically about my programs. Any comparisons of my programs or methods to some others is only given as a vague generality of my opinion and is not intended as a recommendation or reference to any particular products, or methods, always make your own evaluations and comparisons before taking any action.

The illustrations in the sections and sub-sections of SECTION: 7.20 are not intended to be examples of recommended or proper practice, and in some cases may illustrate methods that you yourself would not apply as shown. The variety of illustrations, showing both practical and discouraged practices, has been included to provide illumination of the general metalworking principles discussed in these sections, and other parts of the documentation, in order to help the reader understand some of the many issues relating to the practical matter of producing parts of usable quality by manual, semi-manual, semi-automated, or fully automated machine operation, and how CAD and CAM software, such as my programs that are described in this Web site, might be of assistance to that end.

A couple of the photos in subsections of SECTION: 7.20 where taken using a Sears (tm) Craftsman (tm) Atlas (tm) type lathe, the others were taken while using a ShopTask (tm) model 17-20 type 3-in-1 multi-purpose combination mill, drill, and lathe. When a manual machine tool is retrofit for computer control you need to consider how safety shields should be added, and where the emergency power cutoff switches should be placed.

Be sure to watch all of the video clips linked to in SECTION: 4, in order to see my CAM program DANCAM.EXE (tm) being used to automatically make a part under a form of Computer Numerical Control a.k.a. CNC, and to also see other narrated lessons on how to use my CAD program DANCAD3D.COM (tm) for related tasks.

When making parts, whether by manual or automated means it is frequently necessary to bore large holes to accurate dimensions. When parts are round, boring can be done in the lathe by holding the lathe chuck. Odd shaped parts can be held in a lathe by using a face plate and clamping the part to the face plate off center (while balancing the face plate with weights on the opposite side). An alternative to using a face plate in a lathe is using a boring head in a vertical milling machine. The boring head holds a carbide tipped boring bar and allows the boring bar to be moved to or away from the vertical milling machine's spindle axis to control the radius of the hole being bored.

Since the boring bar is fairly long there is quite a bit of deflection of the tool's cutting tip, and therefore the finish cuts made with a boring head need to be made fairly small, in order to reduce the deflecting forces.

When operating the machine under the control of CAM software such as when using my DANCAM.EXE (tm) holes can be bored by using an end mill moving in a quasi-circular path. Holes of any diameter larger than the end mill can be bored by using the same size end mill just by changing the radius of the quasi-circular path that you draw into the CNC tool path file. The [P]olygon and [A]rc commands in DANCAD3D.COM (tm)'s drawing editor can be used to make quasi-circular tool paths for boring holes automatically with an end mill.

Boring deep holes by using end mills may not be possible though. The boring bars used with the boring head come in fairly long sizes and so may have greater reach than end mills. You might be able to make or setup a special lathe type boring bar in your vertical milling machine that works like a cross between a fly cutter and an end mill to bore deeper holes under computer control in the same manner that an end mill is used under computer control to bore shallower holes.

Here I needed to make a round recess, around an existing hole. The only problem was getting the tool centered around the existing hole. Special gauges are made for this type of work that are held in the spindle and rotated, the part is shifted around until the distance read on the gauge stays the same as its probe slides around the inside of the hole in a circular motion about the hole's center.

Although drills are generally accurate enough for usual types of holes, sometimes you need a hole that is made to more accurate dimensions, and has a better surface finish inside the hole than you can get with a drill.

The boring head can be adjusted by small increments and so can be adjusted after the diameter of the hole is measured to enlarge the hole up to the desired dimension.

One way to get the boring head over the desired position is to use a small short drill to start the hole on the center punch, then remove the drill chuck from the vertical milling machine's spindle and replace it with the boring head. If you do not have the height needed to swap the boring head for the drill chuck you can calibrate the position and move the work-piece to the side, swap the tools, the move the work-piece back into position under the boring head without having to have had to un-clamp the work-piece.

On the side of the boring head is an adjustment that changes the radius of the hole being made. Since there is some backlash in the adjustment lead screw in the boring head if you go too far, i.e. past the desired radius, and need to back-up you should put a few backwards turns on the radius adjustment and then turn the adjustment forward up to the mark you wanted.

On the front of the boring head are some set screws that adjust the tension on the boring head's dovetail, these need to be used to lock radius setting of the boring head before cutting so that the radius does not change while the hole is being bored. The dovetail then needs to be unlocked before you can advance the radius adjustment dial again for the next cut.

When boring all the way through the part you need to raise it off of the machine's table so that the cutter will not damage the machine. Since quite a bit of force is applied to the part while cutting I used three clamps to help hold the part in place. When a part is up on blocks it has a greater tendency to slip around while cutting is going on. It is better to over clamp a part than to risk having it slip and get ruined and have whatever other destruction and injury that might happen when things go haywire and start flying.

There is always some uncertainty about the risk of not clamping a part tightly enough, and damaging the part by clamping it too tightly. Putting brass strips between the part and the clamp can reduce some of the marking an marring of the work-piece that clamping may cause.

Another problem is that the "T" nuts pull up on the lips of the "T" slots and, when you tighten the nuts on the bolts or studs that go through the clamps, you bend the surface of the machine's table or tilting table upward, making the machine table or tilting table no longer flat. Distortion of the machine table from over tightening of the clamps or bolts into the "T" nuts may also effect the needed adjustment of the gib screws on the dove tail, which on an automated machine might not be noticed until the stepper motors stall from too much friction on the dovetail and ruin the part being made.

When you have to hang part of a small part off the table so you can cut all the way through it can be difficult to get a good grip on the part. It such a case it makes more sense to spend extra time to take very light cuts, than to risk having the part twist or slip and be destroyed, with the accompanying mayhem that usually follows a part slipping out of its clamps.

The boring head can be used for making incomplete circles in addition to ordinary holes. If this was being made in a lathe the part could have been mounted off center on a face plate, and the crescent cut by turning in a lathe.

In a machine automated with a CAM program like my DANCAM.EXE (tm) this sort of shape could be made with an end mill by having a series of concentric arcs in the tool path file to rough out the material and then make the finish cuts.

When you do not need to bore all the way through the part is can be clamped without being up on blocks or hanging off the edge of the table. Under computer control you could try to bore down to within a few thousandths of the back side for holes that will need to go through and then use a needle file to remove the thin foil left covering the opening.