PDA

View Full Version : Flat Ground Stock Specs?



Paul Alciatore
03-12-2009, 01:48 AM
I have purchased flat ground stock several times now. The first times I wanted some spacers for use around the shop: cheap parallels for milling, etc. I got some Starrett brand and cut it to various lengths. I discovered that nominal dimensions are not held and square flat ground stock was not square: it could be off by two or three thousanths from one side to the other. I carefully marked all square pieces with file notches on one side so I could keep them matched. OK, I can live with that.

Today I got delivery of a 24" length of 1/5" X 1" piece of "Precision Flat Ground Stock", again the Starrett brand in their factory wrapper. A quick check showed that the 0.500" dimension varied from 0.500" to 0.503" in various places along the length and at one point I found a 0.002" difference from one side to the other. The 1" dimension showed similar variances, especially at one end where it lost about 0.002" in under six inches.

Is this normal for flat ground stock? What should I expect? Is there a better brand?

topct
03-12-2009, 08:37 AM
A quick look at one list I have for precision ground shows from + .001 to . 005 for a tolerance. Its made to be able to finish grind to your final spec. Most metal is made oversize as to stated dimension.

Carld
03-12-2009, 10:46 AM
The flat ground stock is not precision ground. You have to finish grind it to size. It's not always flat and may have a slight warp.

Bruce Griffing
03-12-2009, 12:07 PM
I think the problem is that the nominal precision is in thickness only. If you are concerned with width - I think you are SOL.

Paul Alciatore
03-13-2009, 02:09 AM
Well I looked up the specs on the Starrett web site. Would you believe Thickness +/-0.001" and Width +0.000/0.005".

"Precision" ground stock??? Heck I can do better on the mill without half trying. Even at that, the one I got is out of spec. I will attempt to have it replaced.