jigs and fixtures

A jig is guided BY THE CUTTING TOOL (not, the jig guides the cutting tool). A jig is not really ever clamped to the machine (in my _very_ limited experience), it moves over the drill press table freely and must be used by an operator.

You typically only find jigs as drilling or similar types. Basically, the jig will locate the work in relation to the drill bushings, support the work as needed, and clamp the work. The cutting tool will typically enter through a bushing ("drill bushing") which is typically pressed into the jig's body. The holes into which the bushings are pressed are precisely located in relation to the jigs datums (sometimes the holes are bored using a "jig borer"). A jig may be seen as a template.

You can also ream, bore, tap, counter sink, counter bore, etc. with a jig.

The fixture, however, is much more diverse. Fixtures only locate, support and clamp (like a jig) the work, but the cutting tool never touches the fixture, at least directly (unlike a jig). Fixtures are clamped to the machine (if being used in conjunction with a machine).

A vice is a fixture, a very versatile one at that. However, tool and die makers, machinists, designers and engineers create specialized fixtures for only certain parts or groups of parts. Fixtures can be used in milling, turning, gauging, etc. You will typically only see specialized fixtures in mass production although in some cases, a one-off part may be so oddly shaped that on must create a special fixture just to machine one part (not very common).

Fixtures typically include reference surfaces to set the machine off of. Horizontal (not CNC) milling fixtures, for instance, may have a *gage* which is a piece of ground steel to set the cutter off of (normally some type of shim stock or gage stock is used between the *gage* and the milling cutter such that the operator can *feel* the fit between the two). In this case, the gage would set the cutter on the Y-Z plane as the X axis does not have a datum.

My explanations are lacking and probably hard to understand. You can read this text: Jig and Fixture Design, 4th Edition. Hoffman, Edward G.. Delmar Publishers,

1996.

Any half decent shop guide should give you a good idea as to how these things work. I don't mean shop guides for home machinists, but rather for aspiring machinists, tool and die makers, mould makers, etc. The text should include the phrase, "machine technology" ;-) Your local vocational college's library should have a half decent selection

HTH.

Regards,

Robin

**************************************************************************** * * * ****************************************************************************

You might want to keep an eye out for "Jigs and Fixtures" by Colvin & Haas and published by McGraw-Hill Book Company. The copy I have is copyrighted

1943, but also bears dates going back to 1913. You should be able to find a copy for $10 or so. **************************************************************************** * * * ****************************************************************************

On 22 Oct 2003 18:24:42 -0400, Allan Adler pixelated:

Hmmm...

I found "Jig and Fixture Design" by Edward G. Hoffman at Hamilton Books last year, sight unseen. It turns out that it's an all metalwork book vs. a woodworking jig book. It appears to be a textbook since he talks about students. He has written 17 books about tools and manufacturing engineering. 334 pages, paperback, 8x10", 1991.

Want to trade for Martin's book? I can't find a copy of that locally. ;)

- Metaphors Be With You -

Web Application Programming

I've finished reading Edward G. Hoffman's book, Jig and Fixture Design,

3d ed, and enjoyed it. I didn't do any of the exercises, and may need to work through it again sometime more carefully, but I feel better informed than I did before I read it.

I've also finished reading Gingery's book on the metal lathe. I think I learned a lot from it, and will continue to do so. I've ordered the remaining books in the series on building your own metal working shop from scrap metal and am looking forward to reading them. Meanwhile, I've started reading and thinking about the book on the Li'l Bertha electric shop furnace.

Ignorantly, Allan Adler snipped-for-privacy@zurich.ai.mit.edu

****************************************************************************

• *

• Disclaimer: I am a guest and *not* a member of the MIT Artificial *

• Intelligence Lab. My actions and comments do not reflect *

• in any way on MIT. Moreover, I am nowhere near the Boston *

• metropolitan area. *

• *

****************************************************************************

What aspects of metalworking are you most interested in, Allan? Those are both interesting books, but they're aimed in very different directions. Is there something in particular you're looking for?

Ed Huntress

Some of the most interesting reading...... Then get some of the HSM hardbounds. I like the"Shop Wisdom of Philip Duclos"'

Paul in AJ AZ