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

No part of "This Web Site" (HTML document), including associated files, may be: distributed, sublicensed, transmitted, copied, archived, mirrored, modified, bundled, embedded, sold, given away, rented, loaned, or shared in any form without express written permission in a formal Vendor agreement contract dated and signed in ink obtained directly from Daniel H. Hudgins by registered postal mail. All agreements for permission to distribute expire after a period no greater than one year from the date of the signing of the agreement by Daniel H. Hudgins. See the current "EULA" for information regarding limited copying and storage for the purpose of "Beta Testing" "This Web Site."

To view or use the current version of this Web page you may need to reload or refresh the display of this page by your browser. Just clicking on the browser's [Reload] or [Refresh] icon may not be enough to insure that all of the page's most current contents have been cached and displayed. Some browsers may have additional commands to help display the page's most current contents such as: holding down the [Shift] key and clicking on the [Reload] icon, holding down the [Control] key and clicking on the [Refresh] icon, holding down the [Control] and [Shift] keys and clicking on the [Refresh] icon, pressing the [Control] and [F5] keys, pressing [Control] and the [R] key, or some other combination of keys or clicks. Check to see which commands your HTML browser uses to load the most current page contents into its cache and then to display them onto the screen.

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 make holes in the center of round parts so that the wall thickness of the part is machined to accurate dimensions. In a lathe a boring bar can be used to enlarge a hole drilled into the part.

A boring bar can be used in three ways in a lathe, for internal turning i.e. the same as external turning except the point of the tool points from the lathe's spindle axis rather than to it, for internal threading, and for facing the bottom of holes.

Lathe boring can be programed for automated production by using CAD and CAM programs like my DANCAD3D.COM (tm) and DANCAM.EXE (tm). Lathe tool path files for boring are two dimensional drawings. If you need to program internal threading a third axis needs to be programed, i.e. the spindle axis so that the motion of the tool is synchronized to the rotation of the part. Automation of the spindle axis probably requires using a servo motor rather than a stepper motor. If the lathe spindle is set to have 36000 steps per revolution and the CAM program puts out 106000 steps per second, then the top speed for the lathe spindle would be about 176 RPM, which should be more than fast enough for threading.

Boring of this sort can also be done by using a CAM program and an end mill in a vertical milling machine, but centering the part accurately in the milling machine might require a fixture or chuck that has been calibrated to the location of the vertical milling machine's spindle.

The lathe boring bar has two positions for the tool bit, straight across the boring bar for internal threading and turning, and at 45 degrees so the tip of the tool bit can extend past the end of the boring bar in order to make facing cuts at the bottom of the hole.

When the tool bit is sharpened for use in the boring bar quite a bit of extra clearance is required since when turning inside the part the surface of the part below the cutting point is coming toward the tool bit, whereas in normal external turning the part is moving away from the tool bit below the point of contact and only a little, or sometimes no, clearance needs to be ground off of the tool below the cutting edge. The bits I use most of the time are ground to look a little like a cats claw or talon turned upside-down, i.e. curved back from their point to fit within the radius of the hole being bored.

Since opening a hole with the boring bar is not easy or possible in many cases, you need to start with a hole large enough for the boring bar to get into it, then enlarge that starting hole with the boring bar.

The first step in making a hole in a part in a lathe is to use a center drill to make a prick for the drill to catch on. If there is no prick then the drill will probably wander off center and snap off.

Since it is probably not easy or possible to center punch accurately with a center punch and hammer, a center drill can be used to drill a prick like you would when you need to support the work with a live center or dead center. The center drill is short and stiff, and so probably has less tendency to wander off of center and snap in half.

Once you have made the prick you can switch from a center drill to a regular drill of small size. After making a small hole you can use successively larger drills until you have an opening large enough to accommodate the boring bar and its tool bit.

A somewhat larger hole is required when the tool bit is mounted in the 45 degree end of the boring bar, than when the tool bit is mounted in the 90 degree end of the boring bar. So the size of the boring bar used depends on how small the final bored hole size will need to be.

Once a hole large enough for the boring bar and its tool bit has been drilled you can open up the hole by turning from the inside, i.e. internal turning. When the tool is mounted in the usual way with the point going toward the machine operator it can be hard to see what is going on inside the work-piece. If the tool bit in the boring bar is turned around so the tool bit now points to the back of the lathe, and the spindle motor is run backwards, it may be possible to see better what is going on inside while cutting.

When you get near to the final dimension it is good to take several cuts without feeding the tool into the work-piece since the boring bar flexes and may cut the hole diameter undersize on the first few passes over the work-piece.

Here you see the tool bit set in the 45 degree position so that the tip of the tool bit is past the end of the boring bar. Depending on how the tool was sharpened you may want to have the cutting done as the tool withdraws from the hole rather then when it is pushing into the hole.

Here the boring bar is extended so that cutting can be done deeper into the work-piece. It is not too clear in the photo, but near the rim of the cylinder the thickness was left at about 0.150 inch so it could be drilled and tapped, then down about and inch and an eighth from the end the cylinder wall thickness was reduced to about 0.075 inch for the center portion.

The cutting was only done a little over half way down the inside of the cylinder since the boring bar was not long enough to go all the way, and the internal holding chuck jaws where used to hold the part, which prevented the boring bar from going all the way down even if it could, since it would hit the chuck's jaws.

This part started with a piece of tubing that was machined to a thinner wall thickness, so a starting hole did not need to be drilled before the boring could commence.

In this photo you can see better that the boring is only going down to a point above the four jaw lathe chick's jaws. After this end was finished the part was flipped around to do the other end in the same way. To have the cuts meet in the center, the part had to be aligned by using the dial gauge (see the photo in the section on using the dial gauge). Since the part was thin, care needed to be taken in adjusting the four chuck's jaws since too much pressure would distort the part, and it would not run true to the previous cuts.

The boring bar holder fits into the lathe's tool post and is compressed by the bolts in the tool post. Notice that one side of the boring bar holder is cut out allowing it to be compressed. Since the boring bar is round, and the hole for the boring bar in the boring bar holder is round, the boring bar can be rotated in order to adjust the angle of contact for the tool bit on the internal surface of the work-piece. It is important to check that the tool bit is only contacting the work-piece at its tip, and not rubbing along its face below the cutting tip. The clearance angles change as the hole is opened up while boring since the radius of the hole in the work-piece changes, and so you may need to rotate the boring bar to adjust the cutting angles once the hole starts getting larger.

The boring bar should not be extended more than is needed for the depth of the hole being bored, in order to keep flexing to the minimum. The boring bar holder allows the boring bar to be slid in an out to adjust the portion that is extended from the tool post in the lathe.

Because the boring bar holds the tool bit lower than the regular turning tools used on this tool post, I had to put some tool bits under the top of the tool post to act as spacers to raise the boring bar holder by about the radius of the boring bar. I could not put brass strips under the boring bar holder to raise it within the tool channel in the tool post since the boring bar holder barely fit without anything under it.