Cleaning up a tired old carbide grinder

[pontiac428]

as long as you don't grind carbide with it, yes. CBN is excellent for grinding HSS, but won't grind carbide.

For carbide you can use :
Diamond
Silicon Carbide
and I believe ceramic (but not sure)

True for expensive wheels. A true blue US/EU CBN wheel is an expensive accoutrement. Stefan Goetteswinter said in one of his vids that he has a chinese CBN wheel (Shars type) and abuses it heavily with carbide. I thought there was something to it, so I started grinding anything and everything on one of my chinese CBN wheels. A couple of years and some hard floggings later, the wheel is still good and my stuff is easy to keep sharp. Carbide does grind on these wheels, and they take it. Maybe not as efficient as a true (expensive) carbide grinding wheel, but plenty sufficient for my home shop needs.

 

[WobblyHand]

Have a Shars CBN wheel coming. Thought it was worth a try. Should be here Friday.

 

[pontiac428]

Have a Shars CBN wheel coming. Thought it was worth a try. Should be here Friday.

It leaves a mirror finish, but may go slow. Definitely does the job!

For a vitrified wheel (think lathe bits, Co and HSS or anything else), go with Norton white or purple cup wheels. The white is my go-to for most sharpening, because it is precise, cool, and leaves a great finish, but the purple is what I use for grinding/roughing/removal because it is a little quicker and a good deal cooler at the same time.

 

[Watchwatch]

Has anyone built a cup grinder from scratch? I have a kit for the table, but I’m trying to figure out what motor to buy.


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[WobblyHand]

Improved the TIR of the left side aluminum wheel. Examined the bushing under a microscope and stoned the bushing a little more. Then did a better job cleaning up the aluminum disk. Also stoned the nut seating face a little to take off the high spots. Left side TIR now under 0.002". Amazing how much better things go when you get a good night's sleep.

Assembled the grinder. It's together now, but the 3/4" x 16 nuts are not tight yet. Need to use an impact wrench set to 1 (lowest setting) to tighten them. (Another one of Keith Fenner's tips from his grinder refurb videos.)

One thing about the hardware on this, it's not quite standard. Imperial threads but dimensions are close to metric in diameter. Major diameter across the threads were almost 0.020 undersized. Nut external across the flats are 1.010" not 1", nor 1-1/8", closer to 25.5 mm. I understand that the nut diameter across the points has to be less than 1-1/4" or the wheels won't fit. Still it's weird.

 

[WobblyHand]

Staring at the iron tables. Wondering how to make a fixture to hold the diamond point. Seems like the only machined surface that's "trust-able" is the slot. The tables do not have precise edges anywhere else. (By the way, the slot is 12.01 mm, not 1/2". The hex head bolts that originally held the water basins to the grinder had 12 mm heads, but 5/16" - 18 threads.)

To square off the wheel, the slot should be perpendicular to the wheel. So first I need to make a piece that has a tab to go in the slot and and an extension that can touch the backer plate? That way I can position the table slot into being square. Is this sensible? Is there an easier way?

Once square, I need to make a diamond point holder that is guided by the slot, and can adjust the length. From what I understand, the point is set at 15 degrees or so, to minimize tip wear. (Supposed to rotate the tip) Is the angle of the tool bit in the vertical or horizontal axis? What do people use to position the tip? I've seen some screw like assemblies, but no pictures of the internals. The body of this tool is steel (magnetic).

What have people done to adjust the tip position into the stone? I've searched HM for some ideas, but haven't seen enough detail to make one for a carbide grinder. Loads of videos just doing this freehand, on an ordinary bench grinder, but I need some kind of fixture or guide for this.

 

[WobblyHand]

Got some new nuts today. Both left hand and right hand. I will have to cut off 0.012" off the diameter. 1.125" hex across the flats is about 1.26 across the points, might fit through the bore, might not. It's not much of a cut, but at least 1-1/8" is a standard wrench size, unlike 1.010"! Stoned the seating faces. The LH nut had a few burrs. The right hand nut face was very clean and quite flat.

Both grinding wheels came in today. The 80 grit alumina and the 150 grit CBN wheel. The Norton wheel flange was only about an 1/8" thick. My old white wheel had a 1/2" thick aluminum flange. Quite the contrast between old and new. Also the new wheel was 1" thick. My old wheel was over 1.25" thick. The CBN wheel from Shars came in. It's pretty crude. No wonder it was on sale. When I opened the box I was disappointed. The mounting holes (undimensioned in their drawing) were on the large size slightly over 15/32". The heads of the 5/16" socket head cap mounting screws fell into the holes! At first I thought the holes weren't round, since there were so many uncleaned up burrs. Put on some washers and mounted it up. Next go around I will need to see if I can get a nicer wheel. I've never used one of these resin matrix wheels. For 150 grit, the material seems awfully smooth, is that normal? The finish on the aluminum is crude on both sides.

 

[pontiac428]

What have people done to adjust the tip position into the stone? I've searched HM for some ideas, but haven't seen enough detail to make one for a carbide grinder. Loads of videos just doing this freehand, on an ordinary bench grinder, but I need some kind of fixture or guide for this.

You thinking something like this?

 

[WobblyHand]

You thinking something like this?

Sort of, but the picture above the tool is for a bench grinder. The raised edge goes against the bench grinder rest which is very close to the wheel. For my grinder, the reference is the slot in the table. It is machined, whereas the actual edge of the table is a rough casting. I need to make a tool which rides in the 12 mm wide slot in the table. That isn't too hard. I just need to make the fixture a bit larger more like 3-4 inches long to get from the slot (which is the reference edge) to the wheel.

The screw appears to be for advancing the point. What I don't see is how the point is captured, or prevented from rotating. Is this just as simple as a screw pushing out the (loose) point into the wheel? I could make something like this. Would take a piece of 1 x 1.5 6061 and some 1/4" screw and something for the lock nut and turn knob. Think I have some 1/4-28 all thread.

I was envisioning something more complicated which holds the bit in some sort of piston, which is moved by a fine pitch (or differential) screw. I've made differential screws before, might make a 1/4" diameter 24 TPI / 28 TPI screw. That would give about 0.006" positioning per turn. I made a similar screw to position my tail stock on my mini-lathe. I could single point the threads on the rod. I believe one can get 1/4"-24 TPI taps. There's a captured nut, which when spun, that gives some coarse adjustment. The assembly is a housing, a coarse captured nut, a dual threaded rod, and a fine threaded piston. The piston has a recessed set screw to hold the tool. The housing is bored out for the piston (easy) and the captured nut. Can't figure out how to make a curved slot for the nut yet, but I could always just mill a flat slot. Haven't decided if I need a key for the piston or not. Guess I could drill through the housing and install a pin, or a pin held in place by a set screw. I could run a slot down the piston with a slitting saw. To rotate the diamond, I would remove the piston, relax the set screw and rotate the bit relative to the piston.

Of course this concept paragraph is a little over the top, but hey, it seems like it would be fun to make. In some of the literature that I have read, it is recommended that the diamond is only moved inwards a few thousandths at a time for a pass. A differential screw makes this easy 1/4T = 0.0015". For a 1/4-28, 1T = 0.036", so we are talking about moving the knob 1/16T per pass (0.0022").

 

[WobblyHand]

Been thinking about the differential adjuster. Made a drawing. Think it will work. Ordered some stock, since I don't have anything close to the right size. Have bigger pieces, but don't want to use them.

I made a practice piece to hold a 3/8" rod or dial indicator. Thought it might be useful to square the table to the wheel. Block is 1018 steel measuring 1.5 x 1.5 x 1.7. Milled a 12 mm wide key in the bottom to ride in the slot in the table. Drilled a hole through for the rod. Made a slight blunder - a quick measurement showed the dial indicator shaft was 3/8". So I drilled a hole with an 11/32" drill followed by a 25/32" drill followed by an 0.3750" reamer. Well, the dial indicator shaft OD actually measures 0.3772" give or take. So the indicator doesn't fit. An ordinary piece of 3/8" rod does, since the piece I just picked up was 0.373" I hand turned a "V" drill in the hole (0.377), ruining the reamed finish, hoping to open it up a little, but still doesn't quite fit.

Is there a way to use a 3/8" brass or aluminum rod and some grit to open it up the hole in the 1018 just a little? What size grit? I have some 320 (36um) and 600 (14um) paste. The polishing rod is supposed to be softer right? Do I need to prepare the brass rod in any way? I'll use some paper towels to control the grit.

After, I had designed this - and did it, I saw where I could use a slitting saw to make a clamp for the indicator. I had put in set screws. (What was I thinking!) I will cut the slit and put in some SHCS, there's plenty of room for them.