[TheForge] using tools to build tools

[Andrew Vida]

Surface plates are one example of how one may produce extremely precise 
flats with nothing more than 3 plates, a scraper, dye, and some 
patience.  Whitworth was producing plates accurate to 0.000001" (that's 
one millionth of an inch) using nothing but the technique and a scraper.

As for lathes, the main key is CONSISTENCY, not accuracy per sé, when 
bootstrapping to higher levels of precision.  I am still working on my 
book on precision filing, wherein I make clear that a man with some 
skill, decent eyesight, and patience is well capable of holding 0.001" 
precision on non-trivially large surfaces, as well as smaller ones. 
Coupled with a proper knowledge of the linear geometric progression from 
forms such as a prism to that of a cylinder, one is well able to produce 
a bearing of considerable accuracy, and as I mentioned, great consistency.

If you start with a cubic form accurate to 0.001" on the end of a shaft 
to be the lathe's spindle, you may then divide the bearing further into 
an 8-sided affair, which is already approximating a circle.  One more 
iteration to 16 facets is almost close enough to call it good.  At 32 
facets you may call it a crude bearing in terms of its friction, but it 
may be far better than that in terms of its CONSISTENCY.  If you have a 
bearing that is inaccurate, but is also consistently so, i.e. it is 
predictable, then you are in business.  Once you have figured out how 
the bearing fails in its precision, you are armed with the information 
necessary to make corrections, which therefore equips you with the 
ability to produce a more precise bearing.  Once that first step is 
accomplished, you are on your way to bigger and better things.  It is 
the very first step that is most crucial to bootstrapping mechanical 
technologies such as this.

Also bear in mind that that first bearing needs to last only long enough 
to make another set of bearings.

Another thing to consider is lapping.  I can take that 32 sided bearing 
and mount it into an adjustable pillow block affair wherein the male and 
female bearings are lapped into one another.  In the case where great 
care is taken, you might be surprised at how precise such a bearing will 
be.  The phenomenon of surface averaging will work to great effect in 
producing highly precise mating members even where the mechanical set up 
is comparatively crude.  It is the nature of these things to wander 
toward greater geometric precision than less when the motions are 
properly constrained, however crudely.

terry l. ridder wrote:
> hello
> 
> earlier today ( saturday ) i was having a discussion concerning
> inexpensive tools. the subject turned toward the age old questions that
> people have been asking for centuries. how did the first person build a
> lathe, wood turning lathe or metal turning lathe, without all ready
> having a lathe to use. my friends all agreed that the craftsman's talent
> would dictate the accuracy of the tool. they would not agree with me
> that i should be able to use a homebuilt gingery metal lathe and the
> other tools in in the gingery series to build large and more accurate
> tools in a bootstraping manner. they did not see how i could use a metal
> lathe of questionable accuracy to produce a metal turning lathe of known
> accuracy. i hsd no examples to show them since my tools are buried in
> the  garage amongst many layers of materials to remodel the house and
> such. ( the home remodeling was put on hold because of the
> head-on-collision back in 2007. i was hoping on finishing the home
> remodeling this year but it appears that the doctors have other ideas
> for my freetime. )
> 
> i was trying to come up with common examples of using tools of
> questionable accuracy to build tools of high accuracy. for the life of
> me i could not think of any examples.
> 
> would anyone on the list have some exampled that i may give to my
> friends the next time we meet?
>