Hey Higgy, surface grinder ques's for you.

T

tmickley

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Apr 4, 2001
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You're the machinest.
I just started to try using my HF table top surface grinder. It won the battle yesterday. Any pointers on getting a smooth (and even) finish? ...getting a tight tolerance?
Also I'm using one of those $100 single pole mag chucks and find that my pieces will slide around on it and the edges will pull up from heat. Is this normal? Do I need a better/stronger chuck?

What I've figured out so far, tell me if I'm right or wrong on any of this:
I can only take .0025 off at a swipe. This unit is only 1/2 HP.
I can only take .010 to .030 lateral swipes before I start getting a real noticeable cupping.
I have to move the wheel damn slow, much slower than I thought I would have to get a smooth finish.
I have to keep the metal cool enough to touch, I'm spraying it with wd-40 (it was there) and that helps but I'm thinking there must be something better.
I'll just doing small pieces if I want any accuracy (ie folder parts).

I've looked in my machinest books, none have practical operations of a surface grinder. Any help would be appreciated.
 
Hi Tracy,

First thing to realize is that a surface grinder (sg) is not for removing stock as much as it is for flattening the surface of that stock. That said, .002 to.004 is a good window to stay in. Good practice would be to give yourself about .010 to take off one each side and you should be good to go. When I need to surface grind, I'll take the material down to .008-.010 and then removed that last bit on the sg. I hate standing front of the grinder!

Be sure your magnet and your stone is square, and be sure your stone has been trued, and be sure your magnet is true to your table and your stone. This is easily accomplished by simply taking a couple thousandths off of the magnet.Don't worry, this is common practice, and there is a ton of material on top of the magnet to accomplish this. What I do when I am setting up a new magnet is to spray or coat with some dykem and then take off about .002 at a time. Go slow!

We tend to crank these things right along because we lose patience. You have to have patience with an sg. Your feed rate should be super slow. You can almost feel the stone cutting when you do this. You shouldn't need any lubrication, but frankly sometimes you just need it. The bigger units come with coolant capability, but most machinists I know, including myself regard coolant on an sg as unecessary, especially when working with tool steels.

So that leads me to another part of your problem. The steel itself may be getting hardened by your quick passes and the deep cut. Slow it down, and take light passes and you can even do A-2 and ATS-34 and stuff like that. The workpiece should be warm but not hot enough so as you can't even "hot potato" it a little in your hands. Any hotter than that and its too hot.

About your chuck: You may want to invest in a fine-pole chuck off of ebay or someplace. Pricey, but doing small parts requires it. The chucks like yours are for big chunks of stuff. Look around, but be aware that chucks do lose their potency after a while and don't get one that's too old or obviously been around the block a whole bunch. KBC and Enco has some specials this month I think.

A couple more things:
What is the material you are trying to grind?
what is the grit of your stone?
do you have a wheel-truing device for it?

I hope this helps, Tracy. :)
 
Tracy,
imho, the size, grit, and type grinding wheel is the most critical part. With that said, I use a Norton 32AA 46 grit wheel for everything but Ti and Stellite.
Wheels are graded A thru K (or higher), with A being soft and K being real hard. The general rule is soft material, hard wheel; hard material, soft wheel.
On my Chavalier 6x18 machine I can take off up to .004 but I can't index it forward/backward but about .010 per cut.
Heat is causing the bowing.
If you don't have a diamond dresser, get one.
For what we do, a fine pole magnetic chuck is a must have. Something you can do with the chuck you have is to take some thin stock and make a featherboard (like in woodworking) and lay them on each side. That will keep small parts from moving around most of the time.
Double stick carpet tape is a big help holding non magnetic parts down. I use it with pearl, wood, etc.
Just like on a milling machine, think feed and speed.
Good luck.

Forgot to add that Jeff gave some great tips and info. :)
 
Kit Carson said:
Tracy,
imho, the size, grit, and type grinding wheel is the most critical part. With that said, I use a Norton 32AA 46 grit wheel for everything but Ti and Stellite.
Wheels are graded A thru K (or higher), with A being soft and K being real hard. The general rule is soft material, hard wheel; hard material, soft wheel.
Click to expand...

Thanks, Kit. That's a perfect way to look at it. As I was driving home, I was thinking about surface grinders and the inherent process problems people encounter. Definitely having the correct frangible wheel is the best way to stay out of trouble. I'm in the process of getting an old Harig for the shop that I can set up with a 2x72 belt and use it for removing mill scale on my billets. I figure that would be a good place for all my old ceramic belts.
 
Tracy, I don't have any of those problems you described, however I converted mine to use 2 x 72 belts, I'm sure happy with it so far.
 
Tracy, it sounds like you need a good wheel, I also use the one Kit mentioned(he should know if anybody does)
I take .005 down feed and in/out feed around .020 per pass. I take .010 to .015 off a side then flip and take the same off the other side with very little heat and no lube or coolant. It's best to take the same amount off each side, this will help with warpage and if it's damascus this will keep the patern the same on each side. I learned all this the hard way and it was very frustrating. Very good advice from Jeff and Robert also. Keep at it and you will learn to love this machine. I wouldn't be without mine.

Don Hanson
 
Thanks guys. Lot's to chew on there. I guess I was a bit surprised at how slow the whole thing is and wanted to make sure I wasn't way off on this thing. It's NOT like grinding a knife.

I have a good wheel but I suspect it is too hard. It is a 32ar80 - it seemed like a good choice at the time when I was browsing my MSC catalog. I took it off and used the softer wheel that came with it and my cutting got marginally better. I do have a diamond dresser and have used it. Again an improvement, no more thunk-thunk. I see it's going to take some practice and a better mag chuck. My Enco catalog is a couple years old so I've ordered another one. Guess I'll look for a new mag chuck.

Robert, I do have the 2" wheel conversion from Bertie. It just came in. My wife asked what I ordered from South Africa. My standard is answer is 'knife stuff'. She seems Ok with that answer every time. I expect I'll change it over to the 2"x72l but I just haven't had the time to make the arm and tracking wheel yet. Not sure when I will get around to that so I'm stuck using the grinder the 'correct way' until I can cheat and get the 2" conversion kit on it. :D
 
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