Wet Grinder with CBN Wheel - Best Practices?

[007Rob]

Hi Everyone,

We just picked up a new (used) J&S CNC wetgrinder and it came with a big 'ol vitrified CBN wheel installed. This was a nice surprise, we grind a lot of K360 material which can be fairly challenging so we're hoping this helps make it a bit easier. None of us here have any real experience grinding with CBN so I'm just looking for some advice to make sure we are on the right track.




My first question would be, as far as using this wheel for grinding tool steel are there any precautions we should be aware of? Assuming it should be fine to run it similar to an Aluminum Oxide wheel on a wet grinder, light downsteps and bigger cross feed passes?

I can see a part number written on the wheel, and I can find a company called "SMA Abrasives" but I can't find any other info when I try to google the part numbers on the wheel. As least the surface speed is listed which is nice. Does anyone have any idea what grit this wheel would be?

Seems like the machine was used with coolant, is it ok to grind dry?

The other questions I have are related to dressing this wheel. Haven't checked yet, but since the wheel is already installed I'm assuming it is running true to the spindle currently.

Looking through all the past threads regarding CBN wheels, it seems like the best option for dressing this would be a brake controlled or motorized dresser with a silicon carbide wheel installed. With a 2nd less desirable option being to use a piece of molybdenum or norbide as a dresser and then using a dressing stick to free up the bond. Thinking we might try making a simple motorized dresser ourselves, any other good options we should be aware of?

Is the step of using a dressing stick to open up the bond also recommended when using a brake/motorized dresser?

Thanks in advance for any help, I'm sure I will have more questions as we get this thing setup and start using it.

 

[michiganbuck]

A grit diamond is like a single-point dressing diamond but it is a matrix of diamonds in a bond..much like a diamond wheel. Then use a white stick to push the wheel bond lower than the CBN grits. Norbide will shape a wheel form but is not for wheel dressing/truing. CBNs and a little noisy but do grind very well. you still need to consider the grit size for surface finish, heat, and pressure on the part. Most CBN act harder than AO wheels so a little more care in fixture-held and blocked-in parts.
Brake dressers are also good for CBN wheels.
(X) Single points and cluster diamonds are not for CBN wheels.

CBN wheel should be indicated on the OD when mounting, to run.001 0r better. A brand-new wheel tight on the mount may run this close but if not loosen the flange nut and make it so.
A single flange nut should be made as tight as an average guy can make it with a proper wheel wrench and then a little tighter

 

[CarbideBob]

You will need a dresser/truing device.
Motorized dresser the best and easiest. Right behind this is a brake device.
Down the ladder is this style (https://www.mcmaster.com/6166A11/) but they work like shit.
I would not even bother trying a cluster diamond or moly stick on a CBN wheel.
Highly doubt you could run this wheel dry.
Bob

 

[007Rob]

A grit diamond is like a single-point dressing diamond but it is a matrix of diamonds in a bond..much like a diamond wheel. Then use a white stick to push the wheel bond lower than the CBN grits. Norbide will shape a wheel form but is not for wheel dressing/truing. CBNs and a little noisy but do grind very well. you still need to consider the grit size for surface finish, heat, and pressure on the part. Most CBN act harder than AO wheels so a little more care in fixture-held and blocked-in parts.
Brake dressers are also good for CBN wheels.
(X) Single points and cluster diamonds are not for CBN wheels.

CBN wheel should be indicated on the OD when mounting, to run.001 0r better. A bead new wheel tight on the mount may run this close but if not loosen the flange nut and make it so.
A single flange nut should be made as tight as an average guy can make it with a proper wheel wrench and then a little tighter

Thanks Buck, great info. Hopefully we can figure out what grit this wheel is, it sure looks very fine hopefully it's suitable for what we want to use it for. If not, oh well

You will need a dresser/truing device.
Motorized dresser the best and easiest. Right behind this is a brake device.
Down the ladder is this style (https://www.mcmaster.com/6166A11/) but they work like shit.
I would not even bother trying a cluster diamond or moly stick on a CBN wheel.
Highly doubt you could run this wheel dry.
Bob

Thanks Bob. I found your post from way back where you showed the motorized dresser you built, we may try something similar if we can't find a good deal on a brake truing device.

 

[007Rob]

I have found a chart on this site: https://www.eaglesuperabrasives.com/cbn-wheels/grit-size/

It seems to indicate "B126" would fall around a 120/140 grit range which they consider suitable for "medium grinding" so that's promising

 

[eKretz]

The wheel grit is in microns, so a B126 contains ~126 micron abrasive particles. This equates to about 130 "grit" in the common parlance. Should be a decent general purpose wheel. A little on the coarse side for softer material (which you shouldn't really be using it on anyway) but should do fine on harder stuff.

And I'm with Bob on the dressing. A wheel dressed with a good motorized or brake dresser cuts WAY more freely than one dressed with a moly stick.

 

[EmGo]

Just one little thing to add ... if you are used to aluminum oxide wheels and got a little careless around them, no biggy, in fact can touch up the fingers so you don't run the girlfriend's nylons; don't treat cbn that way. It'll rip you right open, and doesn't heal well either.

In fact I'm looking at a scar from 1974 right now ...

 

[michiganbuck]

Here found a video of using a grit dresser, They are made like a diamond wheel with having diamonds in a bond (they are not cluster diamonds). They are handy because they can be set at a height relative to the part height, and can be easily positioned to face and back wheel dress.
Whereas brake dressers may be obligated to be most easily used at the dresser height.
Running a multiple-parts job I like to have my dresser set at height and on the chuck. Actually, I use my dresser height as a gauge with the part finish spot/size .0005 or .001 below the dress height, I just finish the first part then bring my dresser to just touch the wheel, usually this .005 or .001 to finish part size height. With this I use my hand wheel number like a precision measuring device, so no need to micrometer the part. I may have my indicator standing on my mini plate check steel, for a quick occasional swipe to monitor the diamond wear on a long-run job.
Needless cranking hand wheels to dress, and measuring can be a huge time waster.
OT: and spotters can be huge time savers
Video:

 

[CarbideBob]

Here found a video of using a grit dresser,

Seems I am very wrong.
Ignore my above posts and I apologize to all toes stepped on.
I should not talk but like being here.

 

[michiganbuck]

Seems I am very wrong.
Ignore my above posts and I apologize to all toes stepped on.
I should not talk but like being here.

Bob,
Nobody said you were wrong about anything. At least I did not.
if it is the grit dressing..that is just another option of how to do it.
Motorized and non-motorized break dressers work well.
Likey the angle wheel would work..although I have never tried one.
Buck

 

[007Rob]

Excellent info all around, really appreciate the tips. Excited to get this machine going I will for sure provide some updates once we make some progress.

Keep stepping on toes Bob most of us here are wearing steel-toes anyway

 

[michiganbuck]

Bob,
We only have a hand full of grinders hands willing to share their experience so your input is very important.
Buck

 

[eKretz]

I don't think Buck meant to offend you Bob. He's just adding to the available options. Not a man here who doesn't think you're a valuable contributor, especially in this forum section.

And I sure didn't feel like that wheel in the video dressed with the molded grit dresser sounded like it cut very freely. Not sure that does much better than a moly stick, which while usable after trying to open up the bond, just doesn't cut the mustard compared to a powered or even good brake dresser. I figured that out not too awful long ago myself when Bob recommended it a few years ago in a thread here. Tried it and the wheel cut much freer.

 

[michiganbuck]

I think Steve Barton is one of six or so top guys making grinding videos, He tries to mention all the fine points of the subject of each video. In one video he shows dressing a diamond wheel with grinding steel, I have done this and also dressing with grinding on a piece of brass to suck out, and wear the high places.
More than one way to skin a cat, The power brake wheeled brake is likely the best(as Carbide Bob mentioned) for dressing/trueing a diamond or CBN wheel, and the friction brake next best, likely the NewMan/Desmond* angle wheel or the Grit dresser next best, then grinding a soft material like steel or brass is the next best(IMHO). Some may consider grinding steel or brass is the hack method but in grinding you gotta do what you gotta do, certainly, if you don't have the money for the very best or the time to wait for new equipment.
I have seen steve do things I would not do and likely he would find trivial fault with my methods but out of respect for a fellow we would not call each out on small differences.
I apologize to Bob if he was offended but still don't see that my posting Steve's video was calling out a fellow grinder hand or suggesting that he, Bob was in any way wrong...
and don't want him to stop posting on grinding subjects.

NewMan* dresser/desmond..I have never tried that dresser.

Oh, and what we did for plate-mounted wheels just grinding with the high place can be done with surface grinder wheels, working on the high place... taking small down feed, and crossing both ways.

 

[jccaclimber]

Thanks Buck, great info. Hopefully we can figure out what grit this wheel is, it sure looks very fine hopefully it's suitable for what we want to use it for. If not, oh well



Thanks Bob. I found your post from way back where you showed the motorized dresser you built, we may try something similar if we can't find a good deal on a brake truing device.

Can you link that thread? My search skills apparently aren't up to capability today. Not having a brake dresser I rigged a bench grinder as a powered dresser once, but it would be good to learn a bit more about the right way to do this.

 

[michiganbuck]

Here is one outfit you might call. I don't like their photo of such a long stick-out if their grit dresser.

If you have a segment of a broken diamond wheel you can vise hold it and use it for a CBN wheel dresser....but the CBN wheel pushes pretty hard on the dresser, more than a single-point diamond dressing an AO wheel, so be sure to hold it well. ..and set it to the left so it does not climb into the wheel. and the same with any dresser type.
480-966-9311

Truing and Dressing Diamond and CBN Wheels

Truing and dressing diamond and cbn wheels

www.bgsusa.com

SMA wheels

Account Suspended

 

[CarbideBob]

Can you link that thread? My search skills apparently aren't up to capability today. Not having a brake dresser I rigged a bench grinder as a powered dresser once, but it would be good to learn a bit more about the right way to do this.

Maybe this one down aways??
https://www.practicalmachinist.com/forum/threads/brake-controlled-truing-wheels.159296/
The only note I would change is that is best (faster) to run the motorized opposite the wheel rotation.
Be careful of direction if it tries to unscrew the nut on the dressing stone. You will know when this goes wrong.
I dress, true, reshape a lot of diamond and CBN wheels.
Shop vac or better.. this process makes clouds of dust that get everywhere in the building.
One can do it wet but oh-my. This is so very sensitive to the stone grit/grade used to a specific wheel.

No offense was taken.
I just do not want be seen as steeping on Buck's toes as he is a true wiz with serious chips in his shoes on this tool grinding stuff.
I do mostly flat work, he knows rounds which are so much more complicated.
Bob

 

[michiganbuck]

Thanks for the compliment Bob, You are spot-on with your posts.
We used CBNs of every type/shape for CNC cutter sharpening and making because they would hold the there shape for a very long time. I did not use them for general surface grinding but did try them on surface grinding a super hard CPM steel which they did not do well enough to beat the AO wheel I used for that part.
OO7 rob do let us know what kind of work you try the CBN wheel on and how you like it. * I suggest keeping it on its mount ..and getting another mount for changing AO and the like/easy dressable wheels.

Mostly OD use and face use diamond and CBN wheels are put on tight and left on the same wheel mount for life. Plate mounteds are shimmed behind to get <.001, and OD wheels are indicated <.001 / this is so at the end of wheel life you only waste <.001 of wheel.
Tool sharpening cup wheels with only a 1/16 or 1/8 diamond thickness corner edge can be mount changed because they self-dress quickly.

 

[CarbideBob]

Here is the thing/problem with CBN and diamond bonded wheels.
They come in so many flavors of grits, bond types, hardness and structure.
All these need to be matched to an application. One wheel spec can be poop and another be like magic with small changes.
Figuring out the right one is trial and error and at $300 each this is expensive.
If you are spending 10K per month on wheels they all will come knocking on the door and fly in "experts". Those days for me are long gone.
All my wheels are custom made to specs I have found to work for this or that.
Sometimes a wheel works, you order a second and it is shit. Interesting is that I have this problem more with the biggest places.
The OP has one wheel optimized for who knows what. If if does not work well do not let that turn you off to CBN.
Sticks are used to open a wheel. My ideal wheel never ever needs a stick.
Hand sticking also kills wheel corner radius. I would move bonds, pressing time, concentrations to not have this.

Can you stick a 1A1 and keep it straight? Not me.
Then there are all kinds sticks to be used. This is the same mess. I have eight different ones, six different dressing dressing stones and every one does something the other will not do.
Some grinders run only in oil, some in water...very different wheels.
Carbide grades used are a minefield of chaos, grinding wheels of this nature are the same.

How do you make a "porosity" wheel in this ilk. These wheels have very open holes. Seems the ":secret" is that you toss coffee grinds in the mix.

More to the OP ... That is a very, very nice grinder and I hope it makes you good money.

BTW, CBN wheels will grind carbide but not as well or fast as diamond but miles better than a green wheel.
Bob

 

[007Rob]

Can you link that thread? My search skills apparently aren't up to capability today. Not having a brake dresser I rigged a bench grinder as a powered dresser once, but it would be good to learn a bit more about the right way to do this.

It was indeed the thread that CarbideBob linked above in post #17. Some really great info in here guys, much appreciated