Slice a granite surface plate, make scraping straightedges?
 

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

Slice a granite surface plate, make scraping straightedges?
 

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!

Slice a granite surface plate, make scraping straightedges?
 

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.

Slice a granite surface plate, make scraping straightedges?
 

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

Slice a granite surface plate, make scraping straightedges?
 

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

Slice a granite surface plate, make scraping straightedges?
 

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

Slice a granite surface plate, make scraping straightedges?
 

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.

Slice a granite surface plate, make scraping straightedges?
 

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