My good friend, Dave Colmbs of Washington Calibration wrote an excellent article about surface plates. In fact, he wrote such a good such a good article that it will be published this summer in Home Shop Machinist. Dave laps in and certifies surface plates in the Rocky Mountain region and can be reached at (719)685-5747. Due to the fact that Home Shop Machinist will be publishing this article, we have agreed not to run it on our site until after that issue has been released. So I have a few little tricks that I have stashed up my sleeve that may help you out. One is on surface plates and a few on grinding.

Checking Flatness: When checking flatness of a part on a surface plate, it is best to do this with the part supported on 3 points. You can buy jackscrews that are made specifically for this, but these tools have some limitations. Number one, they are relatively expensive. Number two, the base diameter of these tools is usually fairly small compared to the overall height of the tool making them somewhat unstable. Take a look at the photos below and you will see a simple little set up that is cheap, easy to make and provides a nice solid foundation for checking flatness while leaving easy access to the adjusting screws. Chad Henneck came up with this idea, passed it on to me and I love it. All you have to do is find some socket head cap screws that fit your 1-2-3 blocks and machine the sockets out to accept a decent size ball bearing. We used tungsten carbide bullets in these parts but ball bearings work just as well (I have the screws installed toward the outside of the 1-2-3 blocks for demonstration purposes, they actually work better installed in the center of the blocks).

If you have never checked flatness using 3 points, it is pretty simple, all you have to do is spread out your 1-2-3 jackscrews on the surface plate and place your part on top of the 1-2-3 screw jacks, then zero your indicator directly above one of the ball bearings, now move your indicator over the next ball bearing and zero out the indicator, only this time use the socket head cap screw for adjustment. Then move on to the third ball bearing and zero your indicator over that ball bearing, again using the socket head cap screw for adjustment. Re-check all three points fine tuning with the cap screws until you read zero directly above all three ball bearings. Now you are ready to check flatness, simply move your surface gage around on your surface plate with the contact tip of your indicator on the part being checked, making note of flatness as you move around the part.

Grinding Larger Parts: The problem with grinding large parts in a squaring set-up is that the magnetic chuck wants to pull the part to be squared down to the chuck, not allowing our angle plate to hold the part square. I have taken some photos of a simple set-up that works well if your mag chuck is in tip top shape. The photo below shows an angle plate set-up to be ground square with another angle plate as a holding fixture. I have supported the angle plate that needs to be ground with two identical ball bearings (see photo).

This method keeps the part being surface ground parallel to the chuck in the Y axis and also keeps the part from being pulled down to the mag chuck. When you have a double angle plate set-up and are grinding the end of long thin parts, you can use one ball bearing for support. This will also give you a repeatable Z height. As a side note, take a look at how I have relieved one side of the grinding wheel. This wheel is 2" wide and was giving me problems with chatter. When I dressed down half of the wheel, the chatter problems went away (excellent results). Another surface grinding tip: I have never tried this one but it makes sense. If you are experiencing heat build-up problems with your grinding wheel, try dressing down the center of the wheel so that you have two cutting surfaces. This will allow coolant to flow thru the relieved portion of the wheel while leaving two thin cutting surfaces working on the part which also reduces pressure between the grinding wheel and the part. And another thing! The next time you build a dressing block to hold a diamond for truing your wheels, try putting the hole in the block that holds the dressing stick at about a 5º angle. This will allow you to rotate your diamond when it becomes blunt, exposing a fresh cutting sharp cutting edge on your diamond.