Tools and Surface Plate Questions

While we are on the subject, thinking of the cast iron surface plates.
Once they are scraped flat, properly supported and stored, will they retain their flatness or will it need to be rescraped down the road?
I can see why you would want all the stress worked out of the iron.
Thinking of the cast iron plate Rex just finished, it would be a shame to have to repeat the process.
 
While we are on the subject, thinking of the cast iron surface plates.
Once they are scraped flat, properly supported and stored, will they retain their flatness or will it need to be rescraped down the road?
I can see why you would want all the stress worked out of the iron.
Thinking of the cast iron plate Rex just finished, it would be a shame to have to repeat the process.
Hand scraped surface plates which are done by hobby machinists are usually ongoing works in progress, improving them as personal scraping skills improve. You have the plate heat treated to remove stresses, and then ring the thing well before starting to scrape it. It will probably move some more over time and need an occasional refresh of the scraping to deal with wear and any residual stresses being let out over time. Not having a solid and stiff mounting to properly support the plate will tend to make it move around as well. Bottom line, it will need to be tested at intervals, against a KNOWN accurate granite surface plate or by professional certification techs. I have 2 nice cast iron surface plates, one 8x16" the other 14x18", both works in progress. I have the smaller one fly cut to remove imperfections, and the larger one is a nice hand scraped Brown & Sharpe that has light surface corrosion from decades of proper storage. I need to put together some sort of crane in my shop to move the cast iron plates back and forth from the scraping bench to the granite plate to mark them up for each scraping pass. They are too heavy for moving them back and forth by hand and poor back for the number of times it takes to get them properly scraped in.
 
Could you purchase three used granite surface plates and use the three plate method to level them?
 
Could you purchase three used granite surface plates and use the three plate method to level them?
If you work at it for a LONG time and have the correct knowledge, skills, and patience -- and you stick to it -- you can get it to grade A or AA accuracy, maybe even better, but how will you know when you get there? The three plate method requires strict care in how the stones are properly rubbed together and then carefully tested for improving results, and that is not easy when "lapping" very heavy chunks of granite. It can certainly be proved to be possible, and perhaps actually has been, not just hyped, but it is in no way a quick, cheap, and easy way of acquiring a accurate surface plate -- it is the exact opposite of that.
 
I bet my plate weighs about 1000 pounds, the forklift sure grunted when I lifted it up. Tim
 
Cast iron plates have one distinct advantage; being ferrous, they accept magnets and wonderful surface for assembly or mock-up work.
 
Back
Top