rack and pinion

wrote:


Consists mostly of disassembling and removing the burrs, then putting it back together. Not a biggie, and gives an idea of how the machines really work. The only thing I don't disassemble is the spindle, I figure if that's out, it's time to chalk it up as a waste. (Unless, of course, I got it as a freebie from someone that gave up on it.)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

One removes burrs with a file or with a grinder? (I have neither, at the moment).

I'm always glad for an excuse to take something apart, as long as I can put it back together properly.
--
Ignorantly,
Allan Adler < snipped-for-privacy@zurich.csail.mit.edu>
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Instead of the more complicated milling machines you mentioned, you really should consider buying an armstrong mill first. After you've learned to use it, you may find that you have no need for the Homer or the Harbor Freight or any of the other mills.
John Martin
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@aol.com (JMartin957) writes:

Who sells them? What do they normally cost?
I did a Google search for "armstrong mill" and "armstrong milling machine" and found out that Armstrong is a very common name for people and cities and companies in all areas of commerce, but nothing about the milling machine. I then did a dejanews search for articles containing the exact phrase "armstrong mill" that had appeared in rec.crafts.metalworking and found exactly one thread ("Old Armstrong Mill - what to look for?") from 1995, which discussed what seemed to be an antique.
--
Ignorantly,
Allan Adler < snipped-for-privacy@zurich.csail.mit.edu>
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Allan Adler wrote:

Probably a metaphor for using hand tools such as a chisel, drill and files.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

A file was just what I had in mind.
Buying a file, and learning how to use it, should come before any consideration of a milling machine. Even a cheap one.
But that's just my opinion. Others may disagree.
John Martin
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

AKA Nicholson mill. I usually think of an Armstrong mill as a hacksaw... :^) --Glenn Lyford
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Glenn Lyford wrote:

And a Dremel tool is a "portable Bridgeport"
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@aol.com (JMartin957) writes:

Thanks for the clarification and opinion. If you don't mind, I'd like to understand your opinion a little better by asking a few questions. Suppose I decide to design a course entitled "File 101" and teach it to myself. (1) Is there a textbook? Does it come with a set of tests that I can administer to myself to determine whether I should be allowed to move on to the milling machine or whether I should be left back and have to take File 101 over again? (2) Apart from the textbook and tests, I will have to purchase some lab materials for the course, presumably one or more files. Do I need just one file to get what I need out of the course or do I need to get a set of files with various properties and characteristics? (In this connection, also see (9) below). How much should I expect to pay for the lot of them? (3) Presumably, I also need something to use the file(s) on. What might that be? Perhaps an assortment of different pieces of metal in different conditions requiring treatment with the file(s). Where do I get them? (4) I doubt that there is a shop that sells metal with burrs on it to people who need practice removing burrs with a file, so I probably need to learn how to take a piece of metal and modify it in some way so that I can practice filing it. So, let's postulate that the first thing one learns in the course is how to take a perfectly good piece of metal leave it in a condition which requires the use of the file(s) to correct. I find it easy to believe that it takes no special training to ruin a perfectly good piece of metal, but since I am designing a course and need a predictable set of exercises for me to administer to myself, probably the first thing the course should do is explain how to ruin metal in fairly specific ways. (5) Since we are assuming that knowledge of the use of a file is prior to knowledge of fancier tools, the tools that I can use to take perfectly good pieces of metal and turn them into pieces of metal that require improvement using files are probably somewhat limited. What tools would be ok to use along with files? Well, given the other responses to the question of armstrong tools, I would guess we are talking about handtools, including chisel, drill, files, hacksaw. So, the question (2) is naturally widened to include these other tools. I'm under the impression that no one ever thinks they have enough tools, so it is important to define the scope of the course carefully and choose the tools accordingly. (6) Once the knowledge is imparted of how to ruin a piece of metal in order to leave it in a predictable condition requiring a particular technique to correct, it then becomes possible to focus on those particular corrective techniques. That might be considered the proper content of the course. (7) Next, there needs to be a segment of the course, probably after enough experience has been gained with (1)-(6), which deals with cultivating the ability to determine: (a) Whether it is actually possible to correct a given condition. (b) Assuming it is possible, how much effort is involved. (c) Whether that much effort is worth it in a given context. (8) That sounds like a satisfactory course on the file itself, so far as technique is concerned. As far as the matter of competence in the use of files is concerned, that would probably be an adequate preparation for moving on to the milling machine. There might be further sections on applications to design and planning of projects to produce work using a file. (9) I will merely mention the pedagogical issue of whether, in teaching myself File 101, I should cover topics, possibly requiring investment in more tools and materials, that will broaden my general understanding but which I am unlikely to actually need in practice.
Now that I think about it, I vaguely recall that I have in the past read discussions about using only handtools, and that there is actually a school of thought devoted to this high art. I'm not sure whether I read it here or on a woodworking group. I've also seen a TV program on PBS featuring someone who is a virtuoso at this kind of work. I think he has written one or more books, which I may have looked at.
That being the case, I need some further clarification from snipped-for-privacy@aol.com (JMartin957), namely: why is it, exactly, that you feel knowledge of the file is prior to knowledge of the milling machine? Is it because: (A) you think that after a piece of work is turned out on the milling machine, it might need some touching up with a file and one needs to know how to do that without ruining the piece? Or, (B) because you generally prefer handtools and perhaps also regard it as a higher form of craftsmanship than the use of machine tools?
--
Ignorantly,
Allan Adler < snipped-for-privacy@zurich.csail.mit.edu>
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Likely several, look for high school texts in second-hand shops, I picked one up not too long ago and found it both educational and entertaining. The one I found is "Machine Tool Practices", ISBN 0-13-541848-8, I paid $1.98 at Half Price Books in FW, TX. Your results may vary.

In the case of the above, yes.

While one would suffice to start the course, several will be of use long after you own said milling machine. To wit: Medium and coarse flat files (mill or mill bastard), a medium and coarse square, a triangular, a coarse round, a half-round, and a chainsaw file (no particular size, since you're using it for general stuff rather than a saw chain).

New, I have no idea. I buy used, and usually pay a buck each, with this caveat: if you run your thumb over it and it doesn't want to grab, it's dull, and not worth the buck. If you look at it and see a shine from the top of every tooth, it's dull, too. Buy at least one or two new Nicholson (non-cheapistani) files so you have a good idea what a sharp file should work like.

AKA, scrap iron. Plain old mild steel works well for this. In a pinch, you can even buy it at hardware stores in flats, angles and rounds.

Junkyard, side of the road, tagsales, dumpster diving. It's a hobby in and of itself.

The easiest way is to set out to make something, be it useful or decorative, out of said scrap, which will nearly never be of the proper shape for the intended use.
First step is to mark out with a scribe or marker (depending on how accurate your final piece needs to be) the desired end shape.
The next step is to get it close to that shape by applying a coarse brute force method. A hacksaw is typical, though people have been known to resort to torches and bandsaws, or even several of the above. The idea here is to just miss the line you will eventually file to.
All of these processes usually leave a coarse surface more than adequate for cleaning up with a file.

All of these will be of use, but particularly the hacksaw. Buy a good one with a high tension adjustment and several different tooth counts of US made name brand blades. The difference between this and a cheap saw frame holding cheapistani blades is an education in itself.

I'd pay about $20 for a good hacksaw frame, and maybe that much again on several packages of good quality blades.

Indeed, and this is where said tech school text will be of particualr help, but you are also more than welcome to run particular questions past the accumulated wisdom of the group.

I will merely note that while the textbook I mention is nominally about machines tools, they start by teaching you how to file. A review of the google archives searching for the words: apprentice, file, metalworking should turn up a lot of relevant discussion, particularly if you add "Bastow" to the list. A bunch of this may also be on yarchive.net/metal as well.

Unlikely. In fact one of the best ways to learn is to actually set out to make something practical.

AKA, Neanderthals. Less common in metalworking, due to the amount of effort needed to remove large amounts of metal, though they do exist. They tend to work on smaller, high value projects, and will frequently respond to the title of "jeweler".
HTH, and I think your approach to the subject is commendable, I like your thoroughness, and suspect you'll do well with it.
Later, --Glenn Lyford
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Or (C) because the simple act of buying a file and using how to use it might show the people on this newsgroup that you are really interested in working metal and not just reading, writing and asking questions about it?
You obviously like reading, and you obviously like thinking about the consequences of what you are considering. Both of those qualities are commendable. At some point, though, you actually have to do something. Metalworking is a art in which skills have to be built on other skills. To talk about buying a milling machine when you don't own a file and don't know how to use one is like discussing the fine points of marathon running before you have learned to walk. It's asinine.
Buy any of the metalworking books that also discuss hand tool methods. You've already been given some suggestions. Read them, buy some of the basic hand tools and learn to use them, and try making something. Anything. Perhaps then you'll be in a better position to know what type of milling machine will fit your needs.
John Martin
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@aol.com (JMartin957) writes:

I have done some things. I took a crash shop course in a physics department a couple of decades ago in which I learned to use a lathe to make a plumb bob which unscrewed into two parts. I also used the milling machine on my own to take a piece of scrap aluminum (C shaped) and made it into a keyboard with pushbutton switches for a computer I was trying to design at the time.
One of the most valuable lessons I learned from trying to design and build the computer from scratch was how costly it can be to invest money in a project without having thought it through completely. Since then, I'm a lot more careful. Having experienced the difference, I prefer to err on the side of caution.
Continuing with things I've done: as a result of reading Gingery's book on the charcoal foundry, I built a little coffee can foundry, spent months collecting discarded soda cans from the side of the road, consulted with the local fire department about whatever regulations might apply and eventually melted some aluminum. I also built some frames for metal casting in sand. I didn't get further than that because I had to move and all my tools wound up in storage, where they are still located. So, at the moment, I have no tools except those in a little toolbox that the landlord left in the apartment. That has been the situation for a few years and I can't do anything about getting the stuff out of storage. Fortunately, it isn't costing me anything.
Another thing I did was to design and build a blackboard that folds up into a shopping cart that could be used to carry the materials I needed to give lectures. (Never mind that it worked, but not very well, and looked ridiculous.) That was mostly woodworking with a saw and hand drill, which I also used it with an abrasive disk to cut some carriage bolts. I also used a metal brush attachment to the drill to remove some paint and rust from an old EICO oscilloscope. Also, when I was planning to give some public lectures on mathematics at a local Barnes and Noble (see http://www.swiss.csail.mit.edu/~adler/MATHCULT ) and examining an old overhead projector I'd been lugging around for a decade or so, I accidentally broke one of the components, a thermostat that shut off the machine when the temperature got too high. I managed to locate the company that used to make it, get a schematic and parts list for the projector and find a vendor that sold a suitable replacement for the switch. I also realized that it was using asbestos, and found a supplier who provided me with a safer material to replace it. This took a few months. After that, I was able to use it in my lectures.
I've done other things, not very impressive of course, but I would like to emphasize that I discussed most of them on this and other newsgroups, along with my progress on them. So, if you have the impression that I never do anything, you are mistaken.
The simple fact is that, for several reasons, it is a lot harder for me to do things than it is for most of the other readers of this group. If I'm not progressing quickly, I'm not happy about that either, but it is the best I can do under the circumstances. I also know that I succeed occasionally and when I do there is nothing quite like it.

How do you know I don't know how to use one? I have used files. I just don't happen to have any at the moment, since they are all in storage. Oh, I forgot: a few years before taking the crash course in the machine shop at the physics department, I audited a few sessions of a class on metalworking at the Museum of Fine Arts in Boston. I designed a certain sculpture based on the Barromean Rings (you might know them as the Ballantine beer rings, i.e. three rings which can't be separated but such that no two of them are actually linked, i.e., if you cut out any one of the rings, the other two aren't linked), cut out the parts with a hacksaw, and spent a lot of time smoothing them out and trying to adjust their shapes to something I found aesthetically pleasing with a set of little files. I was literally sculpting with the files.
Maybe you are referring to my earlier question about removing burrs from parts of Harbor Freight machines, where I asked whether I should use a file or a grinder, and mentioned that I have neither. That was probably a stupid question, but it was motivated by the following considerations: (a) I don't really know anything about the parts of the imported machine that are going to need modification, neither their nature nor their exact condition nor how much care will be required in modifying them, given the uses to which they will be put. (b) Although I'm aware of using a file to remove burrs, having done it myself, I haven't done it recently and the topic wasn't fresh in my mind. (c) Even so, I've always regarded it as something one does to avoid getting cut by the burrs, not as something one does to protect or improve machinery, and therefore it is at least conceivable that some other method might be recommended when it is not simply a matter of cosmetics and of not getting cut. (d) Finally, from a strictly logical point of view, the fact that one *can* use a file to remove burrs doesn't mean one can't optionally use something else instead. The idea that one might use a grinder occurred to me off the top of my head, partly because I had been wondering whether I ought to get one. If it is a bad idea to use a grinder to fix the internals of Harbor Freight machines, that doesn't indicate that I don't know anything about files: it indicates that I don't know anything about grinders. And in fact, I don't, never having used one, even though I read a little about them in Joe Martin's Tabletop Machining.
--
Ignorantly,
Allan Adler < snipped-for-privacy@zurich.csail.mit.edu>
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Correction: It was a jeweler's saw.
--
Ignorantly,
Allan Adler < snipped-for-privacy@zurich.csail.mit.edu>
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

    I understand that an apprentice was first given one or two files, and two pieces of steel. The task was to make a cube from one piece, and a hole through the other piece to accept that cube in any orientation, with no visible light around the cube as it passed through the hole.
    No, I haven't done that, but I've done a lot of work with files before I ever had access to even a lathe, let alone a milling machine, and I still use them for various things to this day, now that I have lots of powered machine tools ready to hand.
    I agree that you really *do* need to learn to use files and other hand tools to make things -- so you will know how to use them to repair the power tools once you get them -- either older tools which need repair, or cheap Chinese tools which need touch-up before they are depended upon for producing parts.
    In addition to the files, you ideally should get a file card (sort of like a curry comb for critters) to keep the teeth from getting clogged.
    Your long-winded belittling of the suggestion make me wonder about the amount of time I have spent answering your questions here.
    DoN.
--
Email: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Though in a pinch, you can also use a piece of copper or brass, and run it sideways along the angle of the file teeth, which will quickly wear it into a sort of sawtooth shape taylor made to fit the file. Sometimes works better than the file card. An old plumbing fitting or empty rifle shell works well if you mash it flat in a vise first. --Glenn Lyford
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@d-and-d.com (DoN. Nichols) writes:

Neat. There is a book by Ehrenfeucht entitled, "The cube made interesting", which includes 3-d glasses for the anaglyphs in it. One of them is a picture of a cube 31 inches on a side being made to pass through a hole in a cube 30 inches on a side.

I think you are assuming that I wasn't serious. That assumption is incorrect.
I know that I don't know much about metalwork, so I always leave open the possibility, when someone says I need to learn something, that there is a lot more to learn about it than might be apparent to me. So, I just tried to be systematic about finding out what it was and how to learn it, given that I was also going to have to teach it to myself. Now that I've read the replies, I'm satisfied that I do know how to use a file.
Regarding the investment of your time and effort answering my questions, both are greatly appreciated, as is all of the the help I've received on this newsgroup.
--
Sincerely,
Allan Adler < snipped-for-privacy@zurich.csail.mit.edu>
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Alan:
A couple of simple things you can do to "diagnose" the gear mesh. First thoroughly clean both rack and pinion. Do not polish, but be sure they are clean. Then, do a contact pattern check. This is simply applying some sort of compound to the entire rack and repeatedly running the rack end to end several times and reviewing the "pattern" left behind. Obviously, don't use too much or anything that will get into the optics. Any good grease will do. (On a side note the professional gear guys use colored componds similar to jewelere's rougue.)
What you should see ( in a correctly functioning gear mesh) is a uniform pattern on both the rack and pinion through out the entire stroke (all the way round the pinion and full length of the rack). The pattern should be centered on both the rack and pinion and should be as wide as the narrowest member (either the rack or the pinion).
You probably will not see a uniform pattern based on what you wrote. If you see the pattern move back and forth across the gears, then you have a misalignment of the pinion shaft (not 90 degrees to the rack). If you see the pattern move deeper and then shallower in the gears then either the rack is warped, or the pinion is ecentric, or you have excessive wear. Use a dial indicator to determine whether you have an alignment problem and deal with it accordingly if you find one. Alsi check to see if the top of either the pinion teeth or the rack teeth is contacting in the root of the mating gear.
Rack wear is simple to check. Use a caliper and measure the pitch between any two teeth near either end of the rack (just like thread pitch). If two adjacent teeth are too close for you to measure then simply measure between any convenient number ot teeth (say three or four). Then repeat this measurement several times along the length of the rack paying special attention to the teeth in the middle of the rack. Shorter measurements indicate wear.
The pinion can be checked for wear similarly. A helpful trick is to get two short pieces of wire the same diameter (No. 12 copper wire is good enough) and lay one wire in the root of one tooth pair and the other wire in the root of another tooth pair as close to 180 degrees as possible from the first pair. Measure the distance "over the wires". Now repeat this procedure with sucessive tooth root "pairs" all around the pinion You should get the same measurement every time (or real close). Smaller measurements indicate worn teeth.
Hope this helps.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

    [ ... ]

    [ ... ]

    What I would do to examine the rack is to check it on an optical comparator (after a through cleaning, of course). Mount it so you see the rack teeth in profile. Put some clear plastic film under the clips on the display, select the largest magnification you can manage with the optical comparator, and trace the outline of the profile on the plastic film. Now, move to one of the worst teeth, adjust so the bottom of the tooth profile is the same, and trace this one, The area between the two profiles should give you a good idea how badly worn it is.
    To *make* one, the ideal way (with HSM tooling) would be a horizontal milling machine, a proper gear tooth profile mill (for the rack gear -- which is either #8 or #1 -- I forget which end is correct, but when you buy it you can look that up in the catalog. One end of the set is for 135 tooth through rack, and the other end is 12-13 teeth.
    Obviously, you first have to know what the size of the rack teeth are -- both diametrical pitch (or "module" for metric gears, IIRC), and the pressure angle. And if the teeth are cut at an angle instead of straight across the gear (more like "/////////" than "||||||||") you will need to angle the blank, and to calculate a correction factor to your feed using a bit of trig to get the tooth spacing to come out right.
    Note that the angled teeth are a lot smoother in the feed, but you will need better bearings on the pinion, as it will have a side thrust which the straight tooth will not.
    Now -- if you want to avoid the side thrust, but benefit from the smoothness, then a herringbone gear would be ideal -- but more difficult to make. It would look somewhat like this:
    / / / / / / / / / / / / / \ \ \ \ \ \ \ \ \ \ \ \ \

    The typical lube used in the focusing rings of cameras (multi-start threads) is typically a quite thick grease, and has fairly minimal vapor -- unless it is kept in the direct midsummer sun. :-)

    Well -- you have most of what I know about the subject above.
    Good Luck,         DoN.
--
Email: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I looked in my optics books and didn't find "optical comparator", so I did a google search and found some information about it. Based on that, I'm wondering whether an old microfilm reading machine I fished out of a dumpster could be adapted for this purpose. It's housing is made of wood, the optics are in metal and it is intended for strips of microfilm, but I did manage to look at some crystals with it. It's a piece of junk but I've been reluctant to give up on it. The point is moot at the moment since it is in storage where I can't get at it, but I expect that situation to change. Even so, I'll need to acquire more practical knowledge about optics than I have at the moment before tackling it. This would be a lot cheaper than buying a comparator, I think, which would probably cost more than a new scope. But I'm looking forward to trying out this comparator idea for checking out the rack.
--
Ignorantly,
Allan Adler < snipped-for-privacy@zurich.csail.mit.edu>
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

    Your'e unlikely to find them in an optics book -- but a well-equipped machine shop is more likely to have one.

    Those tend to have more magnification, and less depth of field than an optical comparator for machine shop work. Also, the screen tends to be a bit awkward to get to to add a transparent sheet to draw on. The one I have apparently came with optional lenses for 10X, 20X, and 40X, but I only have the 20X lens.
    A proper one has a collimated illuminator, a stage on which the object under test resides (with X and Y motion to move the viewpoint, plus Z for the focus. Usually, there is a way to measure the X and Y motion -- either with big micrometer heads to move the stage, or with dial indicators to measure the motion.
    However, there are minimal ones which are handheld, including a set of reticles to measure various things including small threads, and angles, an eyepiece, and a tube to join them. eBay auction #3855942073 has a set of reticles, but not the eyepiece and tube. I'm not sure, but I think that the price there is a bit high.
    Reliable tools has a nice looking one up for auction #3856418973, but it's heavy (300 pounds), and is certain to go higher, as there are over four days left.
    There is another by Nikon which is still within reason, and it suggests an alternative name "Profile Projector" for the equipment. (Auction #3856039570).
    I don't see any of the lightweight ones like mine -- it *looks* heavy, but is mostly blown plastic shell and a wood base. The size is necessary to get enough optical length for good magnification. Note that it *will* take up a lot of benchtop space.
    Try eBay searches for "optical comparator" (with the quote marks) and one will show up sooner or later. A reasonable price is somewhere in the $200-$300 price range. Unfortunately, this type is not there at the moment. Note that the same comparator shows up in the MSC catalog and in sales flyers for significantly more -- reasonable for a business, but not for a hobbyist. The brand on mine is "Micro-Vu", and the one on the MSC offering is Fowler, IIRC.

    If you want to try to make one, the general design involves:
1)    Illuminator on one side of the stage (or below it with a     transparent stage). (Plan on something like one of the Quartz     Halogen projector lamps in their own parabolic reflectors so you     have adequate brightness for good visibility in a well-lit shop.     Remember that the more the magnification, the less the     brightness remaining.
2)    Moving stage for the device under test.
3)    Lens to focus the image onto the screen.
4)    Angled mirror in the back to bounce the image back and up     towards the screen.
5)    Round ground glass screen with reference lines (cross hairs     plus angle lines and radius lines engraved in the glass, and     filled with black paint.
6)    Ring surrounding the ground glass screen, with a full 360 degree     angle scale on it, and a vernier scale adjacent to it to allow     measuring to fifteen minutes or so.
7)    Spring fingers (similar to those which hold slides on cheap     microscopes. These are used to hold the transparent films,     either for hand drawing to compare worn and unworn teeth, or     printed in a plotter from a computer, or photographically     printed, to compare new parts to their designed profile for     quality-control inspection.
         Good Luck,         DoN.
--
Email: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.