[WilliamD]

I've seen plenty of pictures of surface grinders, and even read about how they work. With how the wheel wears away as it's cutting, how do you maintain a level surface? Also, how does a diamond 'point' true the entire surface of the wheel. I know it's spinning while you do it, but do you just move it slowly? Do you constantly measure the diameter of the wheel to compensate for wear? I understand that the workpiece is on a bed that's moved fairly level and precisely. Or rather you can grind the magnetic chuck true to the wheel. Just some questions I can't really get a handle on.

[Zumba]

Q: With how the wheel wears away as it's cutting, how do you maintain a level surface?
A: The key is to make sure that the stepover (cross slide movement) is only a couple thousandths per pass. On my small 6x18 with a 1/2" wide wheel, my stepover is typically .010"-.020", with a DOC of .002-.005". That way, only the front edge of my wheel is wearing down. The rest of the wheel is "sparking out" cleaning up the last .0001" or so of material that's left over.


Q: how does a diamond 'point' true the entire surface of the wheel?
A: The wheel on my grinder moves at 3450 RPM. I traverse my cross slide fast at a rate of 30IPM. During that 1 second where my diamond point is in contact with the wheel, the wheel spins about 60 full revs. It's a coarse dress but still relatively smooth for a 46 grit wheel.


Q: Do you constantly measure the diameter of the wheel to compensate for wear?
A: Nope. After dressing, I take a couple light passes over a small chunk of steel and measure the thickness with a mic. Then I know my exact wheel height, which will accurately stay the same until my next wheel dress.


Q: Or rather you can grind the magnetic chuck true to the wheel.
A: Yep that's what you do with a new chuck and how you perform basic maintenance on the chuck. Only do it when you actually need to of course.

[WilliamD]

Ahhhh! That makes much more sense. So the wheel would wear at an angle, and the trailing edge wouldn't wear much because it's only removing very little. I would ask about how fast the wheel wears, but I know that's like the "how long is a piece of string" question.

[mog5858]

thanks william i have had the same question just never got arond to asking them and a big thanks to zumba for giving us the low down.

[ironDigit]

thats a nice and clear explanation ZUMBA, thx


but then i cant stand but ask : how do they grind our dearly appreciated leadscrews and ballnuts.

i understand the question the TS was wondering about surface grinding wich is not applicable to leadscrews offcourse.

[Zumba]

I'm no expert on thread grinding, but usually the grinding wheel spans multiple threads. So I'd imagine the same principle applies. The leading edge does all the work while the trailing edges do the cleanup.



As for the shoulder, I don't know. Grinding to a shoulder is problematic with surface grinders as well. I usually say screw it and leave it a bit rough. Don't have the desire to redress just to clean it up.

Good thing ballscrews have no shoulders on the main threads, eh?

[Switcher]

Sorta, like this (1A1 wheel).

.

[ironDigit]

thx men

[keitholivier]

For profile work the wheel may be dressed using a shadowgraph (giant microscope) to the right profile, or it is possible that this even done cnc today. For grinding shoulders one typically uses a cupped wheel so one is using an axial face on the wheel instead of a radial face. This axial face is dressed flat like usual and there are special attachments and microscopes for putting the correct radius on the nose of the tool for grinding corner radii or undercuts. Time consuming and expensive for one offs, but routine for production with multiple machines dedicated to specific tasks sequentially.

I interviewed for a job at SKF to design the tooling for turning bearing races and I was amazed how "primitive" the process was, but it works.... I proposed (back in the 90's) that they could save days of work by doing a solid model instead of the 2D model of the tools that they were using, but apparently the manager who interviewed me thought that was being too smart...

[handlewanker]

Hi all, like all cutting tools, once you have cut the material you need to resharpen your tool to do a finish cut.
Grinding is no different.
However with a grinder you need to maintain a sharp open wheel face otherwise it will get glazed and just rub, which will lead to a rapid heat buildup and burn marks on the job.
Surface grinding is usually reserved for hard ferrous materials namely toolsteel in the hardened state, and only a surface grinder, among other grinding tools, will touch the material in that state.
It's a waste of time surface grinding soft steels, unless you want a decorative shiny finish, as the surface of the material deteriorates rapidly with abrasion, but this is not to say it should not be done.
While a part is being made it is conveniant to surface grind, between operations, to produce a parallel surface, and other times for cleaning up a mating face.
The wheel is usually dressed between each third or fourth down feed of the wheel head, depending on the hardness of the material, as the stone face will by then have blunted, and the cutting just puts more heat into the job, especially if you don't use or have coolant/water, and if you are using one of those small bench type hand cranked surface grinders, then probably you don't have coolant on the job anyway, and are just scratching the material off while the stone struggles to remove it.
I always rapid traverse the diamond across the wheel face to open up the stone during normal cutting, and on the last cut to remove tenths I slowly traverse the stone face with the diamond, and as the stone is now very smooth and incapable of taking much off it leaves a very smooth finish, not glazed as some will point out is a possibility, but a calculated finish method.
You've just got to know your machine, also it saves having to remount a stone of finer grit to do the finish cut.
You can grind right into a corner provided you haven't been hacking into the material before hand, and this is accomplished by the fine dressing of the stone for the finish cut.
Also you can grind the face of a job, with the side of the stone,when you really have to, if you have slightly hollow dressed the wheel face with a hand dressing stick, but this must be carefully done with a steady hand and only about .010" depth is required.
This will produce a face that is dead square to the bottom face, with a corner radius that is only as good as the stone will last.
Normally when the face is required to be ground the corner is cut out prior to grinding, before heat treating and hardnening, usually at the milling stage while the material is still soft.
Here the grinding wheel will grind on it's edge corner and no large amount of material should be removed due to the stone rapidly losing it's corner edge.
Be warned, get tuition before attempting to use a surface grinder if you're new to it, as a stone that bursts in use is like a hand grenade going off 1 foot from your face.
One last thing, you should always grind on a magnetic chuck, to produce parallel work.
Some people will try setting up a vice, for lack of a mag chuck, and wonder why they have such problems, good for non ferrous materials probably, but hardly accurate.
You will also need a demagnetizer if you grind HSS tool bits or any high alloy tool steels in their hardened state, otherwise they just become magnets themselves from the mag chuck, and every bit of ferrous dust and swarf will stick to them.
A simple demagnetizer is a coil of wire with AC current going through it, the job to be placed inside and slowly withdrawn with the current still on.
Ian.

[ZipSnipe]

I agree with most of what Zumba says with the exception of the depth of cut. At the mold shop where I work at we usually go a depth of cut at .0004 and on my own personal projects .0006. The deeper the cut the more ripples(still would look good but not mold quality) you,ll see in the surface where as go light and you,ll see it almost mirror finish.By the way once you use a surface grinder and see the beauty it makes of steel you,ll fall in love with it.

[Oldmanandhistoy]

Hi Zumba and handlewanker,

Just wanted to post a quick thank you for your excellent and informative posts. Its people like you and other posters here that make this website what it is and I appreciate your time and trouble.

John