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rmuell01
09-13-2012, 09:29 AM
I picked up a used granite 18x24 surface plate from a local machinery outlet and it's too far gone (It's out by .0035 in a couple of places). Reconditioning an 18x24 would not be cost efficient. Hargrove's will let me exchange it. I remember seeing a number of Cast Iron plates that looked better than the granite so the obvious question is: granite or cast. I live in Michigan, heated garage when I'm out there. Will I be flogging myself in January when it takes a long time for thermal expansion to correct itself, or keep looking for a better granite. I'm sure I will get my money back and or get store credit, which is not a bad thing at Hargrove's.

Rob

lazlo
09-13-2012, 10:37 AM
Pretty much any cast iron straight edge or surface plate will be "out" when you buy it used. You'll need a full-length surface to spot/scrape it in.

A granite surface plate is a lot harder to wear, warp, or otherwise damage. They're also much more common on Craigslist.

If you're just looking for a small plate (18x24) -- have you looked at the Enco surface plates? They're dirt cheap (around $30) and free shipping.

SGW
09-13-2012, 11:45 AM
In "Foundations of Mechanical Accuracy," Wayne Moore (of Moore Special Tools, makers of perhaps the most accurate purely mechanical jig borers ever built) makes the case for cast iron surface plates. Among other advantages (to Moore), cast iron plates can be scraped to true them up when worn. At Moore Special Tool, however, there were surface plates and standards all over the place, and the finest skilled scrapers to use them. In other words, what may have been true for Moore may not be relevant to us in a home shop. Nevertheless, it does illustrate that there is nothing inherently inferior about a cast iron plate.

TheAndroid
09-13-2012, 12:06 PM
Where does one find Dura-Bar or other iron in small quantities for reasonable prices? I'd like to get something small to start learning scraping with.

RLWP
09-13-2012, 12:19 PM
Scrapyards - ancient cylinder blocks and heads for instance

Richard

demerrill
09-13-2012, 05:48 PM
Where does one find Dura-Bar or other iron in small quantities for reasonable prices? I'd like to get something small to start learning scraping with.

http://www.dura-bar.com/distributors/index.cfm

David Merrill

rmuell01
09-13-2012, 08:11 PM
If you're just looking for a small plate (18x24) -- have you looked at the Enco surface plates? They're dirt cheap (around $30) and free shipping.

HMMMM. $110 on sale anyway Lazlo. not sure if free delivery includes trucking. that would be nice.

I've been looking on ebay and cl but it seems everybody wants full price or it's not local for p/u.

oldtiffie
09-13-2012, 10:43 PM
Irrespective of what some may say about imported granite surface plates and their "test sheet", the number who have actually had such a plate tested/graded and not had it pass as a satisfactory Grade would be very small so the chances of getting an unsuitable one are minimal.

J Tiers
09-13-2012, 11:36 PM
I have nothing against a cast iron surface plate...... SO LONG AS YOU HAVE A GRANITE ONE TO CHECK IT AGAINST!

Seriously, who would pay more for USED CI that needs babying, or maybe re-scraping, and wears faster, when the NEW granite ones are still cheap? Cheap as long as you don't need a certificate of traceability, at least.


Irrespective of what some may say about imported granite surface plates and their "test sheet", the number who have actually had such a plate tested/graded and not had it pass as a satisfactory Grade would be very small so the chances of getting an unsuitable one are minimal.

Fact....

It's easier to make a good one than a bad one..... all you have to do is let the process go a bit longer and it gets better (3 flat process).

If some goniff is selling ones that were blanchard ground, well then you might have an issue.

I have two, one with the dubious test sheet, one without. They blue up on each other fine, even with rather thin blue..... They came from widely different sources, at different times, and the bigger one has a visible blemish, although it isn't out-of-plane, it is just a feature of the stone, a difference in the grain locally.

Nick Mueller is a good guy, but the only thing wrong with most of the "chinese tombstones" (his words of disdain) which he likes to make fun of is the lack of traceability.

lazlo
09-14-2012, 09:48 AM
HMMMM. $110 on sale anyway Lazlo. not sure if free delivery includes trucking. that would be nice.

Doh! I must have been thinking of the 12 x 18:

http://www.use-enco.com/CGI/INSRIT?PMAKA=640-0120&PMPXNO=949402&PARTPG=INLMK3