What's new
What's new

Why would you want a cast iron surface plate?

LOL, cause it was FREE!!!

Had a big pile of junk donated to the museum a few years back. In the pile was a 12x18" or so Taft-Pierce cast iron surface plate (probably 90-100yrs old). Main advantage is that they are lighter than solid granite of similar dimensions and the magnetic quality can be a plus.

The smaller ones like at work have threaded holes in the sides so handles can be attached. The plate can be taken to the work for testing if the work is too big to carry to the plate.
 
“Why would you want a cast iron surface plate?”

Because they are so much better than the plastic ones. ;) (Sorry)

But seriously. What is it you use now to do your lay-out and inspection?

I don’t know how any one can live with out one. From scribing lines off a height gauge to running you parts under a D.T.I, to blueing things for flatness. I couldn’t live with out mine. Most important thing in the shop other than the machines.

Regards Phil.
 
Cast iron vs granite.. that is the question. Have used only granite for the past 30 years, any special reason to use cast iron (except for magnetics)? I guess for bluing there would be some advantage because of the flaked out areas. Otherwise there would be too much stiction. Any other reason to go with cast ?

TMD
 
G’day Doc.

Sorry I should have read that in myself.

In your line of work. Go the Granite. Thermal stability I figure is its best asset. Either obviously can be produced to great levels of tolerance.

Granite. =

Thermal stability. Nil corrosion, Low stiction Easy maintenance.

Cast = Heritage maybe. But you gave up die filers.
Durability. I take this to mean you can beat up on a cast plate with out chipping. Still results in a beat up plate.

It was once stated that cast plates were easier to resurface, once they got damaged / worn. That might have been the case when every one had a “Forrest” some where close by. Not sure it’s the case now days. I note many of the granite manufacturers, offer re-surfacing.

Regards Phil.
 
Many of the cast iron ones have holes in the ends.

Handles or pegs can be installed to lift and invert the plate in order to either spot another one (the three in rotation) or else spot a surface on a machine too large to put on the plate.

-Matt
 
If a person were doing a lot of scraping-in of flat surfaces, a scraped-finish cast iron plate is the best surface to do a "blue check" against. At the powerplant, we have tilting pad type thrust bearings in our big hydro usints. These bearings have babbitted thrust shoes which are about 40" long ont he longest dimension and weigh about 1500 lbs apiece. After rebabbitting, the babbitt is machined on a good tight Bullard to a flatness within a half thousandth either way. The shoes are then scraped in to final flatness and for parallel with the support
buttons" on the opposite ("bottom") of each thrust shoe. Flatness has to be within a few tenths over the run of the shoe, while at the same time, we need a scraped pattern for minimizing stick-slip firction of "suction" between the babbitted bearing surfaces and the steel thrust runner that rides ont he shoes. I had bought a Starrett granite inspection grade surface plate about 4' x 4', ordered with tapped inserts for lifting eyes. We had been bluing the plate with the lightest haze of Prussian blue and checking the babbitted shoes against it. We found there was a good deal of "suction" and began to wonder about the type of blue contact we were seeing on the shoes. A few years after getting the granite surface plate for checking the shoe cotnact, we had occasion to send a set of shoes out for rebabbitting. The vendor was the patentee and OEM of the tilting pad type thrust bearings. They were let several of spend a few days in their shop to witnees the rebabbitting, machining, and scraping. One thing that surprised us was they did NOT have any granite surface plates in used to check blue contact on shoes being scraped in. Instead, they had cast iron surface plates with a finely "flaked out" finish. These plates were checked regularly against a master. We asked why cast iron was preferred and were told that it was for reasons of having an infinite number of contact points rather than a single flat surface. The other answer was that granite surface plagtes in this type of service tend to wear or "saddle". A Cast Iron plate can be checked and rescraped, while granite plates would have to be sent out to be ground and possibly some sort of lapping process done to get final flatness. We had developed out own method which was to pick up the thrust shoes being scraped with a bridge crane, invert them and rub the shoe on our granite surface plate. This thrust bearing maker used a smaller cast iron surface plate, blued in the same manner we do, but suspended from their bridge or jib cranes. The brought the plate to the work- which is how lathe beds and similar work are checked when being scraped in. They advised us we were not getting a really good representation of contact by using a granite plate, claiming the "broken up" surface of a scraped iron plate gave a better representation of surface contact. I thought it over and we kicked it around ont he ride back to our powerplant and we agreed. We are going over to cast iron plates for scraping-in, and will use the 48" x 48" granite plate for layout and setup work or for shcking the cast iron plates against.

Joe Michaels
 
I use both a cast iron and a granite. It just depends on the situation. The cast iron I keep right on the bench and use it for mainly grneral layout work while the granite is saved for the more persnicity jobs. The cast iron plate is not scraped only ground yet the last time the certification people were in to check out plates I had them check the cast iron one and it was .0005" for the whole surface (12x18)
 
I've often thought I should get a granite surface plate, and have my epitaph sandblasted in the back, so when I "go to my reward", they can haul the plate out of the shop and mark my grave with it. Or is that just the Scotsman in me trying to save a few pennies? :D
 
Sure you can use plate glass as a reference
surface. But it has to be supported on a
granite surface plate to be really flat....



Jim
 
I've often thought I should get a granite surface plate, and have my epitaph sandblasted in the back, so when I "go to my reward", they can haul the plate out of the shop and mark my grave with it. Or is that just the Scotsman in me trying to save a few pennies? :D



that's funny. I was wondering if I was the only guy that was thinking my surface plate would make a good grave marker. or I was thinking maybe have the side of it engraved and donate it to a school that promised to teach flatness in shop class.
 
anyone have a thot on the usefulness of plate glass for a hobbyist? i have heard such being used as a surface plate.... thanks, don e.

Take a look at glass some time.

It's not particularly flat. (unless ground to be.

Plate glass is "floated" on a bed of liquid tin. All while being continuously pulled , rolled and poured.

Plus it cracks, chips and scratches.

But.. glass can be better than nothing.
 
They used to make real surface plates from glass. It's discussed in the Connely book.

Yes, but it was not "plate glass". I have an assortment of optical flats. Up to 200 mm diameter. None of them were produced from plate glass.

Floated plate is so full of stress as to be worthless for any purpose that also includes the word "flat".

Next we will be talking about "annealed plate", a true oxy-MORON!
 
I like a finely scraped cast iron surface plate better for a scraping master than the equivalent grade granite master. One seems to be able to spread the blue on it thinner, whether be canode or dykem. One can judges the thickness against a reflective surface, so it is easier to judge evenness. As others said it has less stiction. Given a good scraper hand one can fix it against a master.

There are drawbacks as well. They will rust if not treated properly. If a part dropped on them, it will raise a burr. Because it is not truly a flat surface, very small parts need to be put on a carrier to measure. They are much easier to scratch than granite, scraping chips on a part can damage the plate. Because the surface is slick it is a lot easier to smear the blue on it than granite, you need a better roller to keep the blue even. They are more expensive than comparable grade granite surface plates.

I would still love to have a large one. I have a 24"x12" and a 14"x9" or so CI plate...the 24"x12" needs to be scraped, the other i scraped at the Tuckahoe class. I am glad i have them.


dee
;-D
 








 
Back
Top