I'm trying to assemble the tools for scraping the saddle ways of a 1970s
Bridgeport series I vertical milling machine back from the typical
swayback wear pattern into flatness. One of the requisite tools is a
straightedge for testing flatness. I've seen the cast iron type made by
Challenge Machinery, which cost $100s even used. And I've followed
Michael Morgan's efforts to supply similar cast iron designs at various
stages of finish.

But I wonder, could not a granite surface plate be sliced up into
straightedges? I note that Starrett sells straightedges made of granite
instead of cast iron:

http://www.starrett.com/pages/437_straight_edges.cfm
(e.g., 2" x 4" x 24" black granite for $426)

Given that a new 12" x 18" B-grade import surface plate sells for about
$30, and could be sliced up into about 3 18-inch straightedges, ya gotta
wonder, eh? Machine some handles and epoxy them on?

As to the actual slicing, I have a wet diamond tile saw that I have used
on granite, so this is not a problem, and at $30/each for the slab one
could even afford to spoil a few tries. This diamond saw can cut
bevels, which has me thinking you could cut a custom tool shape to fit
inside dovetails. Or, granite kitchen countertops are the rage now, so
there must be shops nearby that could slice up a surface plate into
pieces. Or the local tombstone shop must have a cutting ability (isn't
that how granite surface plates were themselves invented, by a tombstone
maker during WWII when metal was scarce?).

Richard J Kinch
Palm Beach County, Florida USA
http://www.truetex.com/machinery.htm

You can always make 3 flats for a very low cost.
Remember that the only surface that 3 pieces can be perfectly mated to each
of the 3 is a flat surface. Thus you merely need to make the 3 edges or
surfaces you need to mate with each other and you end up having 3 of them -
sell off two and you will actually make a profit!

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works every time it is tried!

Bob May writes:

You can always make 3 flats for a very low cost.

Yes, but my impression is that the 3-piece process for originating flats is
simple but extremely laborious. Besides, I already have a surface plate
and would use that to scrape a steel straightedge if they're going to cost
$100s to buy. But if a granite straightedge could instead be simply cut
from a $30 granite surface plate, it wouldn't be worth the effort to
originate any of the surfaces.

The local waterjet abrasive shop has cut some granite plates with their
machine. Works great.
Dan


--
Please note new addresses...

http://home.comcast.net/~cassarole
"Richard J Kinch" wrote in message
. ..
I'm trying to assemble the tools for scraping the saddle ways of a 1970s
Bridgeport series I vertical milling machine back from the typical
swayback wear pattern into flatness. One of the requisite tools is a
straightedge for testing flatness. I've seen the cast iron type made by
Challenge Machinery, which cost $100s even used. And I've followed
Michael Morgan's efforts to supply similar cast iron designs at various
stages of finish.

But I wonder, could not a granite surface plate be sliced up into
straightedges? I note that Starrett sells straightedges made of granite
instead of cast iron:

http://www.starrett.com/pages/437_straight_edges.cfm
(e.g., 2" x 4" x 24" black granite for $426)

Given that a new 12" x 18" B-grade import surface plate sells for about
$30, and could be sliced up into about 3 18-inch straightedges, ya gotta
wonder, eh? Machine some handles and epoxy them on?

As to the actual slicing, I have a wet diamond tile saw that I have used
on granite, so this is not a problem, and at $30/each for the slab one
could even afford to spoil a few tries. This diamond saw can cut
bevels, which has me thinking you could cut a custom tool shape to fit
inside dovetails. Or, granite kitchen countertops are the rage now, so
there must be shops nearby that could slice up a surface plate into
pieces. Or the local tombstone shop must have a cutting ability (isn't
that how granite surface plates were themselves invented, by a tombstone
maker during WWII when metal was scarce?).

Richard J Kinch
Palm Beach County, Florida USA
http://www.truetex.com/machinery.htm

But I wonder, could not a granite surface plate be sliced up into
straightedges?

Sure can. I did this a few years ago when I reconditioned a bridgeport clone.
Worked for me.

Gary Repesh

Richard J Kinch wrote:
I'm trying to assemble the tools for scraping the saddle ways of a 1970s
Bridgeport series I vertical milling machine back from the typical
swayback wear pattern into flatness. One of the requisite tools is a
straightedge for testing flatness. I've seen the cast iron type made by
Challenge Machinery, which cost $100s even used. And I've followed
Michael Morgan's efforts to supply similar cast iron designs at various
stages of finish.

But I wonder, could not a granite surface plate be sliced up into
straightedges? I note that Starrett sells straightedges made of granite
instead of cast iron:

The problem with this is that a granite straightedge just slabbed off a
large surface plate will be VERY heavy. You probably want a 36" long
straightedge. A 24 x 36" granite surface plate will usually be 4"
thick, and weigh about 15.625 Lbs per inch of width, calculating off my
surface plate. So, a 3" wide straightedge would be about 50 Lbs. I find
Michael Morgan's cast iron 25" straightedge to be heavier than I'd like.
Comparing it to photos of Starrett iron straightedges and their descriptions,
Michael's is at least 50% heavier than a Starrett the same size.
The granite job would be 3 times heavier than mine! Imagine curling
a 50 Lb weight bar for 8 hours straight! You'd be in the hospital!
I DO have a 2" wide granite straightegde salvaged from an air-bearing
slideway, and it is WAY too heavy for any spotting/scraping use. It even
has a series of holes bored in it to lighten it.

http://www.starrett.com/pages/437_straight_edges.cfm
(e.g., 2" x 4" x 24" black granite for $426)

Given that a new 12" x 18" B-grade import surface plate sells for about
$30, and could be sliced up into about 3 18-inch straightedges, ya gotta
wonder, eh? Machine some handles and epoxy them on?

What use would an 18" straightedge be on a Bridgeport? The worst wear
is usually on the bottom of the table, and that is going to be at least
32" long. As all hand scraping books advise, you need a straightedge
as long as what you are scraping, and then some. it is INCREDIBLY
hard to get something bigger than your straightedge flat across its
full length. I know! I have done it, and it was a total bear. I needed
some very exotic tools that few people have access to, such as a
"Talyvel" ultra-precision level.

Jon

Jon Elson writes:

What use would an 18" straightedge be on a Bridgeport?

I was only wanting to work on the knee-to-saddle ways (25 inches long, the
table and column seem OK). At 2 inches wide, and trimmed to a truss
profile, a 24-inch long slice of granite should be well under 20 lbs.

I suppose for a 42-inch table, the stone would be over 100 lbs, and one
would be considering some kind of tool-balancer suspension.

On Thu, 26 Feb 2004 11:20:01 -0600, Richard J Kinch
wrote:

Jon Elson writes:

What use would an 18" straightedge be on a Bridgeport?

I was only wanting to work on the knee-to-saddle ways (25 inches long, the
table and column seem OK). At 2 inches wide, and trimmed to a truss
profile, a 24-inch long slice of granite should be well under 20 lbs.

I suppose for a 42-inch table, the stone would be over 100 lbs, and one
would be considering some kind of tool-balancer suspension.

I would be interested to learn if the granite is sufficiently stress free to
get away with it without needing to lap the slice.


Mark Rand
RTFM