Cast iron versus granite surface plate

[4GSR]

Back in the days years ago, your cast iron plates are generally used for taking impressions when your scraping and fitting. That way, you don't put wear and tear into your granite plate. Your granite plate is used to check the cast iron plate and straight edges, and make adjustments to them. At least, in some shops, that's how it was done.

Now days, granite plates are more readily available than cast iron surface plates are. In fact, I haven't seen a new CI plate for sale for many years now.

 

[Fredz1]

Sure do like my 12X12 shiny black bathroom tile. Mounted my dial indicator off about 4" and ran it around the surface, could not see the needle move.
Sure is accurate enough for any of my .....-punching layouts.
If/when I break it, very low cost replacement.
When I'm done with it, it stands out of the way, with the refrence books on the book shelf.
Just my 1 1/2 cents worth.

 

[benmychree]

An advantage for cast iron plates is their lighter weight, when used as a reference surface for scraping where the plate has to go to the job rather than the job on the plate. All the other reasons posted are also of note, especially the magnetic base use on the plate; as far as scratching, one needs to take care to clean the plate and the work piece of the debris that does the scratching (in any case). For me, I'll take cast iron as a first choice, and this applies to all forms of scraping masters, such as straightedges. Another thing, aimed at scraping use, is that granite plates, so far as I have ever seen, lack the handles used to lift and manipulate the plate.

 

[Bill C.]

What are the advantages / disadvantages of a cast iron versus a granite surface plate? Someone nearby has a cast iron surface plate for sale. I've considered getting a granite plate but never actually got around to it. I never really heard of a cast iron surface plate before.

All the inspection and layout plates I have used were granite. They are heavy and are not moved once set up. Cast Iron by it nature can scratch and likely needs a oil coating to protect it from rust. Doesn't hurt to use a cloth or plastic cover on both of them.

 

[silence dogood]

If the CI is in good shape, good price, no shipping costs, then what is the problem? I just buy it. Mark

 

[Andre]

Also, cast iron does not transfer blue as good as granite. Okay, but not great.

 

[Bill Gruby]

Also, cast iron does not transfer blue as good as granite. Okay, but not great.

Why would you want to blue up a granite inspection plate? Granite plates are not lapping plates. What you are lapping could damage them beyond repair.

"Billy G"

 

[Andre]

Why would you want to blue up a granite inspection plate? Granite plates are not lapping plates. What you are lapping could damage them beyond repair.

"Billy G"

Not talking about lapping.... just saying that granite holds and releases blue better than CI. Prussian blue doesn't hurt them from what I've read, and you have to blue them up anyway to scrape your CI plate in every once in awhile. It might stain the plate though.

 

[Bill Gruby]

Not talking about lapping.... just saying that granite holds and releases blue better than CI. Prussian blue doesn't hurt them from what I've read, and you have to blue them up anyway to scrape your CI plate in every once in awhile. It might stain the plate though.

I will ask the same question another way.

"Why do you wish to blue a granite plate in the first place?"

"Billy G"

 

[4GSR]

Also, cast iron does not transfer blue as good as granite. Okay, but not great.

That's a first for me. I've never had a problem using Prussian Blue on any CI plate I've dealt with.

Now, on the subject of Prussian blue, there is a difference between Dyken and Permatex brand of Prussian blue. The Permatex brand will not lay very good, where the Dyken will do fine. Since I changed over to the Canole Blue, I'll never go back to Dyken brand.

(excuse my spelling here)