CBN vs. CBN !?

Just starting to get into ID grinding with CBN wheels, and I need some opinions........

Bonded CBN vs. Electroplated CBN wheels, depending on what rep you talk to they are both "superior" to the other!

I am currently working with a bonded type wheel which is dressable (barely!)
Although the other guy tells me his electroplated wheels which are not dressable (only about .01" CBN material on them) will be better suited to my needs.

Most of my parts are small but multiple internal diameters, with a fairly rigid setup but only a mediochre coolant setup. I have some uneven wearing on the current wheel I am trying which tends to taper my diameters when plunge grinding.....that might just be a crappy wheel....But I would like to hear some opinions from people who have tried both. I will definately try both myself but a few common issues to look out for would certainly be helpful!

A plated wheel is going to look, to the work piece, like a harder wheel than a bonded wheel. Hardness is also relative to the ratio of work speed ( sfpm ) to wheel speed. The higher the wheel speed, relative to work speed, the harder the wheel appears; the higher the work speed, relative, the softer the wheel appears. Wheel speed may be more important than the bonding method.

I would try turning up the wheel speed and reducing the work speed until you get burning of the work, then back off 10% and see how that improves your wheel life.

Coolant is important to wheel life. Especially when we are talking about hard wheels at high speeds. I would try also to improve your coolant feed.

rweil said:

Just starting to get into ID grinding with CBN wheels, and I need some opinions........

Bonded CBN vs. Electroplated CBN wheels, depending on what rep you talk to they are both "superior" to the other!

I am currently working with a bonded type wheel which is dressable (barely!)
Although the other guy tells me his electroplated wheels which are not dressable (only about .01" CBN material on them) will be better suited to my needs.

Click to expand...

The plated wheels have one layer of CBN on them. Nowhere near .010, your rep is full of it. Wear out the grains on top and it is all over.
Since there is only one layer of CBN the way the wheel acts when it is new will be very different than when it is used up 75%. That said it will keep it's form for it's entire life.

Bonded wheels can be dressed but will wear and have to be dressed to keep their form. How often they need a dress will depend on the bond hardness, concentration, stock removal, etc.

If the wheel is straight or the form is simple to dress bonded will be cheaper and much faster. The only time I use plated (and I buy a lot of them), is when I need a complex form in the wheel that I don't want to spend hours dressing in.

Bonded wheels come in a hundred "flavors", plated wheels come in one.
Tell your bonded wheel supplier you want test wheels on the basis that if you do not like it you can return it for another flavor at no charge.

You say "(barely!)" dressable, which makes me wonder, how are you dressing them?
I am going to cry if you say single point diamond.
Resin bond superabrasive wheels have to dressed with a truing or dressing wheel.
This is mostly a function of using the correct grit and hardness dressing wheel.

What you are doing may make a big difference. On small IDs you may as well use plated and throw them out often or rough with a bonded and finish with a plated.
If I have to grind in a 1/4 ID 5C collet to run true in my workhead I'll use a plated mandrel. If I'm grinding a 3" ring I'll use bonded.
Bob

Is there any reason you need to use CBN??

For ID grinding we have had great success with the Norton Targa wheels. Most of what we grind is D-2 or M-2 58-60 rc.

Good advise from Carbide Bob. We don't use CBN for anything under 58 R/C. Over that , it's the only way to fly. Most of our experience is in surface grinding, using a brake controlled truing device. A 16 finish is not a problem. For ID grinding on a cylindrical, or jig grinding, you need high wheel speed. 3/8 or under,we spin 40K on our jig grinder. 3/8 to 3/4 about 15k on our cylindrical. We don't dress our ID CBN quills.

For forms we have used reverse diamond plated blocks from Engis to dress wheels, or we had a CNC surface grinder that we dressed a radius on the corner of the wheel and countoured using the CNC. Redress and use "cutter comp" to compensate for dressing. Similar to pick milling with a ball endmill.

Some people have asked WHY the O.P. is using CBN wheels. He didn't say, and I don't KNOW, but most people would use them in higher volume production. That is where they are SUPPOSED to (and it makes sense) shine. I would think that is why he is using them, BUT you guys are right, you don't know if you don't ask!

Jeff

Agree with Carbide Bob and Jeff. I never new of an electroplated wheel being able to be dressed. We usually only use diamond electroplated wheels for carbide form grinding where profile tolerances are tight. We usually have our electroplated wheel forms turned by the CNC lathe department and sent out for plating in either coarse (.003 thick) or fine (.0015). One can get many uses from these wheels if they are used properly and not pushed to hard. Never had to "dress" an electroplated wheel, but then again I don't use CBN electro's.

And yes, CBN is the only way to grind hardened steel in high production. I'll use for mostly every steel harder than 54 rc. Below that and its an SG60J, providing 8 finishes all day.

Get some different wheels and maybe a new wheel rep.
Good Luck
JJ

Great advise guys. Most of my ID work is between 1" and 3" and rockwell is 58 - 64 with production runs of anywhere from 50 to 500 pieces surface finish 16 or better. CBN so far has greatly reduced my cycle times. and yes, Bob, unfortunately I have been using a single point diamond (please wipe your tears....there is no crying in machining!), but ONLY because this CBN work is on a trial basis so far. I don't want to commit too much $ if we are just going to go back to conventional abrasives. All of my forms are straight, nothing fancy....journals and shoulders. I'm guessing from the response that I should keep working with the bonded wheels for now and perhaps look into a brake controlled dresser? What is the most effective dressing option? I think my biggest problem with dressing is that I can't slow my CBN wheel to less than about 8000 rpm since it is a belt drive spindle. Does that present any issues? Thanks for your patience and input guys.

You run the grinding wheel at full speed when using a brake truing device.
You can also mount the dressing wheel on a gearmotor and let it control the dressing wheels speed.

see this post for some ideas :http://www.practicalmachinist.com/vb/abrasive-machining/brake-controlled-truing-wheels-159296/
Bob

Cbn

Thumbs up for Resin Bond CBN, Agree with others works best on Hardened material.

You run the grinding wheel at full speed when using a brake truing device.