Surface Grinders, general question

Horizontal Surface Grinders make a flat finish on many kinds of material. Lets say 6 inch square by 1/2 inch plate of steel.
Question is, doesn't the diameter of the grinding wheel change ever so slightly from the beginning of the job to completing it? and if so would not the finished surface not be flat and parallel?

Does the surface grinder automatically sense the grinding wheel diameter change due to wear and adjust the height of the wheel to maintain a perfectly flat cut?

In the days of manual grinders, meaning non-CNC, I say no.

The wheel is harder than the surface your grinding. Any variance would be in the millionth's of an inch. Not of any concern to the homeshop machinist.

Bernd

The wheel does wear (although very slightly) even during a small job such as you describe, but keep in mind that precision grinding is generally done in multiple passes, each time lowering the wheel another .0005-.001", so the wear you are worrying about would only accumulate during each pass, and would be negated once the wheel is lowered for the successive pass. To minimize such errors the final pass might only be removing .0002", thus minimizing wear on the wheel. As in boring operations, sometimes an extra pass can and should be made without lowering the wheel until it "sparks out." Dressing the wheel between jobs will also help insure both even grinding across the face of the wheel as well as an optimal surface finish.

Bill

Thanks Guys,
Your explanations cleared that up for me.

The other thing is if you dress the wheel square to the table, then feed across in Y much less than the width of the wheel on each pass, the part of the wheel that gets worn is the leading edge, so unless you wear all the way across the wheel, your Z value remains the same.

Al,
Glad you asked this question. And Bill, Bernd and Shred, thanks for answering. The stone wear aspect of surface grinding has always puzzled me too.
Dennis

I would be willing to bet a person could take one of those milling tables they sell cheap for use on a drill press and add a grinder mandrel with decent bearings to make a small surface grinder. I also never realized how little is taken off a wheel. would be a nice way to get the super finish on steel work. john

I never get tired of learning something new and this trade seems to have an endless supply of items to learn about.

Take yesterday, I was reading through the MSC catalog and read that Dies which are hex shaped are re-threading to be used with a socket or crescent wrench. Round dies are for threading un-cut stock. Round dies also have a adjustable split which I believe is for adjusting the depth of cut.

Thanks for asking this question. I too wondered how they compensated for wear.

I had the opportunity to get my hands on very inexpensive a 6x10 surface grinder. (I think that was the size)

But I was in the middle of losing my house and much of my possessions...

Question is, doesn't the diameter of the grinding wheel change ever so slightly from the beginning of the job to completing it?

Click to expand...

Yes it will. In fact abrasive wheels are designed to beak down with use. this allows for sharp abrasive to be exposed and the wheel stays sharp. IIRC Harder material requires a softer wheel so it stays sharp and does not glase over.
A point of fact though all tools wear slightly with use that is why manual machinists take a couple of rouging cuts then measure before taking finishing cuts. And that is why CNC machines have tool wear compensation tables.
A surface grinder is a finishing tool . Grinding is meant to remove tooling marts from say fly cutting. It also allows for as you said a flat surface and precise thickness. It is only designed to take off say the last .005 inches from a surface.

With any tool you almost never just go by dial input. Touch off the tool either with a piece of paper in between the tool and work or take a light trail cut.With a surface grinder gently lower the wheel to the work until you get a light spark . measure the material. take a cut or two that you calculated. measure again cut again. It is called sneaking up on the dimension.
This method can be used for all machine tools lathe, shaper, mill,surface grinder.
If you have not already done so download and read a copy of TC 9-524 Army machine tools.
Tin

As Shred pointed out the wheel wears at its edge.

As you start you will notice the "step" from prior to current ground surface is pronounced and sharp.
As the wheel wears this step becomes a slope - assuming you grind both back and forward then once the width of the "slope" approaches half the wheel width - it is time to redress the wheel.

Sometimes the width of the slope will induce chatter requiring dressing sooner.

Typically I dress before any grinding op. and it generally gets the job done.

As Tel pointed out this is generally a finishing op. However sometimes you need to perform a "ploughing" on hardened steel - then carry on regardless until close to finished size, then dress the wheel and finish.

Ken

Interesting discusion, while most surface grinding is done as a finishing process, as in grinding to achieve a dimension that you cannot get with a milling machine, I often will square my stock on the mill leaving a small amount for grinding. I like to start with a square piece of material. After milling I will surface grind 2 parallel surfaces to size then clamp the stock to a precision angle plate to get the third surface perpendicular to the first 2. One of the first surfaces needs to be clamped to the angle plate at this step. Next place the part on the surface grind table with the 3rd surface down against the chuck. Now I grind the 4th surface, which is parallel the the 3rd to size. Now I have 4 sides of a cube to size and they are parallel and perpendicular to each other. There are 2 more sides to be finished at this time. I place the angle plate on the magnetic chuck and place the part next to the angle plate and turn the magnet on. Now I clamp the part to the angle plate with a clamp or two. The surfaces against the chuck and the angle plate should be one of the finished sides. Turn the magnet off and remove the angle plate and part assembly from the chuck. The surface of the part and the angle plate should be flush at this point. Rotate the angle plate 90 degrees and turn the magnetic chuck on. By doing this, when I grind the 5th surface it should be square to the surface I used as a reference when clamping. The 6th surface can be ground to size now by placing the part on the chuck and turning the magnet on and then grinding to size. Now I should have all 6 sufaces parallel and perpendicular to each other. I know, it seems like a lot of work just to square up a piece of stock but I have found that starting with a piece of stock that is squared up this way leads to a much better finished product. As a caveat, the stock will only be as square as your angle plate and your clamping abilities. When performing the next operations on the mill or lathe, I can indicate any surface and know that my part is in the vise or chuck true. Apprentices in our shop would make our own angle plates and grind them from a journeymans angle plate of known accuracy. The angle plate was then checked in our metrology dept. with a cylindrical square. Our goal was less than .0001 in 6 inches accuacy. The surface grinder is a very useful tool and can make a job much more accurate. I would be lost without mine. Dave

The idea of using a X/Y table to put together a homebuilt SG. While simple in concept, for all but the smallest parts would be very difficult in use. The X feed on a small X/Y table is .100 feed per turn, so 2" is 20 turns, on an SG 4-5 turns is 10-15". A small magnetic clamp weights 75+ pounds and is a foot long. This will quickly overload most of the small tables. No grit protection for the screws and ways, your X hand in line with a grinding wheel, and so on.

Small manual SGs would be cheaper to buy complete than built out of a new XY table and used mag clamp. They have a small footprint my 5 x10 is 18 x 24 on the floor the table is 30" so allowance for that, and the handwheels stick out the front about 10". Look for the type that sit on a cabinet, and can be lifted off. If the SG is one piece they get heavy. I'll guess the grinder is about 600lbs and the cabinet about 150. I purchased from a machinery dealer $300 with clamp and extra wheels, expect all grinders to be 3phase.

Just my opinion of course.

Surface grinders are handy things to have around the shop. Not 100% necessary for hobby work, but under-appreciated. You can do some wacky setups that would blow apart on the mill. You can trim down hardened steel parts, regrind vise jaws and bases, cut stock and so on. Bit trickier to do Al and brass though. Bogs also had some useful postings on the subject a while back.

Further to Dave G's comments - I have worked with a lot of precision toolmakers over the years and many of them start by "blocking up" as per Dave's method (I ran a toolroom for 15 years).
The logic being if you don't start out perfect, everything you do from there will go downhill.
Having said that it would drive me nuts when the same degree of precision was applied to a relatively crude fixture as opposed to say an injection mould.
Can't argue with the principal however.

Ken

i build plastic injection molds for 35+yrs before doing what i now do, and it becomes second nature. get it square and the rest becomes easier, even with fixtures,you never know when the engineer will change his mind and you will next need to make it a swiss watch. just try and get it as sq. as you can even in the mill and it will make all you set-ups easier,just like using a four jaw chuck the more you use it the faster and easier it becomes. jonesie

Surface grinding shouldn't be considered a finishing operation only. Using the correct wheel and method, a surprising amount of material can be removed in a hurry.

We routinely would plunge grind several hundred-thousandths off punches and other tools. Grinding is the easiest method for some parts, especially when hardened to 60-62 RC.

Grinding is another manufacturing process that takes a little time to get used to.

Kevin