New Surface Plate

[Bob Korves]

It did not come with a cert. It has some small scratches and small dings.

Is the plate ground or scraped?

 

[foxmusfast]

It was scraped. It is a Busch brand plate.

 

[Aaron_W]

I know these have a legitimate use, but every time I see or hear them talked about I think of this.

 

[EmilioG]

Do temp fluctuations adversely affect cast iron surface plates more so than granite?

 

[Bob Korves]

Do temp fluctuations adversely affect cast iron surface plates more so than granite?

Good question, Emilio. I have never seen the answer or any discussion on the question. Regardless, they are generally used for different purposes, depending, so the question may be moot. Both move with temperature and with loading, and cast iron often moves with time. Granite surface plates wear less and are much quicker and easier to calibrate than cast iron plates, unless the iron ones are ground. Smaller cast iron plates are often used for machine repair and calibration by taking the CI plate to the machine. Granite plates usually have the work taken to them. The advantage of CI plates is that they are much easier to calibrate yourself, if you have the scraping skills and an accurate master plate, usually granite. CI plates are also used for less than high precision work in shops not in need of it, for layout and less critical measuring and testing work. The CI plate can be used on rougher work, and then re-calibrated as needed in the shop, without sending it out, but again also requiring a good master plate. As purchased, ground CI plates are typically less accurate than scraped ones, and require regrinding to return them to original calibration. More than you asked for, and no real answer, but perhaps that helps...

 

[Ulma Doctor]

Do temp fluctuations adversely affect cast iron surface plates more so than granite?

simple answer, yes
the relative thin sections of CI will expand and contract at faster rates than a solid chunk of granite

 

[projectnut]

As a side note most shops that use surface plates for precision measuring are climate and temperature controlled. By in large the temperature is controlled at 68*F + or - 4* humidity is usually controlled between 35% and 45%. At least these were the parameters where I worked. They are also the parameters I use for my shop.

 

[ddickey]

There is a guy in Iowa selling two cast iron plates both 18" x 24" for an offer. I know one is a J.C. Busch Co. .75" thick. Think I might have to pass it up.

 

[RobertHaas]

CI is also magnetic which is a benefit doing precise mock ups.

Local prototyping shop uses several different fixtures on their 48" x 120" certified CI surface plate. The owner paid more for that plate then his Haas 5 axis machine.

 

[projectnut]

There is a guy in Iowa selling two cast iron plates both 18" x 24" for an offer. I know one is a J.C. Busch Co. .75" thick. Think I might have to pass it up.

The precision surface of the Busch plate is only 3/4" thick, but the complete plate is 6" thick and weighs 180 lbs. Here's a link to their catalog describing surface plates:
https://www.buschprecision.com/Busch-Precision/PDFs/Marketing-Materials/BuschCatalogWeb.pdf

Busch is an excellent brand. The machined version of the plate is within .00025", while the hand scraped version is within .00020". If the prices are reasonable and you need a plate I would go for it.