By Chris Jensen, (retired)
We’ve talked about resin and vitrified abrasive flywheel grinding stones quite a bit since they’ve been around forever. CBN flywheel stones are becoming more popular so it’s about time we discuss how to get the best performance out of them.
Let’s start off with some background on CBN abrasives. CBN stands for Cubic Boron Nitride. It is a very hard abrasive. Perhaps the only thing harder than CBN at this time is diamond and there are some diamond flywheel grinding stones on the market now too.
You should consider CBN wheels for a few reasons. First, they hold their balance exceptionally well. They are far less fragile than traditional resin and vitrified wheels. CBN abrasive wheels are best on cast iron flywheel and they give you surface Ra repeatability. Finally, they last longer than resin or vitrified wheels.
There are a few quick guidelines to get the best results from your CBN wheels:
- Always, always, always use clean grinding coolant.
- Do not use the dresser attachment on your machine to dress the CBN wheel. Use a dressing stick specifically designed for CBN. The Goodson part number is DS-CBN. We’ll talk a little more about proper dressing technique in a bit.
- Use plenty of clean coolant when cutting.
- Do not baby the CBN wheel; it must be worked to perform properly.
Now, let’s dig a little deeper into each of these guidelines.
Coolant
We, of course, recommend our Flywheel Grinding Coolant (FG-1101-G or FG-1102-G). This coolant formula contains a synthetic rust inhibitor and provides the lubrication needed to keep the abrasive cutting well. Don’t be afraid to flood the work piece with coolant; it will keep the stone cutting cleaner and cooler which is essential. A good flow of coolant will also clear away the debris you’re creating as you grind. You can also try directing the coolant under the stone which will force the swarf away from the work piece.
To keep your coolant clean, we recommend adding a sludge bag (SB-1) to your flywheel grinder. This will keep any minute particles from recirculating through the coolant and affecting the surface finish. You could also install a Universal Coolant Magnet (UCM-348) to trap metal swarf before it gets into the coolant tank. This magnet can be cut or shaped to fit your machine.
Grinding
For best results, bring the wheel up to speed then hand feed the wheel until it makes contact with the flywheel then feed down .001” to .002” per turn. Maintain a continuous motion – do not wait for the wheel to spark out until the flywheel surface becomes clean. Back off .0008” to .001” and then let the wheel spark out for best finish.
We mentioned before that creating a consistent finish is easier with CBN wheels. This is especially important in high performance work such as top fuel dragsters. Another tip we have for using CBN is to grind flywheels and floaters with coolant and grind discs dry. Yes, it goes against everything we’ve said before, but the top fuel teams that use CBN have proven this method works over and over again.
Dressing
As we said before, don’t use the dresser attachment on your flywheel grinder to dress a CBN wheel. When your wheel starts to load up and make noise, it’s time to dress the abrasive. Hold the dressing stick (DS-CBN) at about a 7º back angle to the face (cutting surface) of the CBN wheel for a few seconds while it is turning. This will unload the abrasive so you can continue to cut flywheels.
That covers all of the common questions we get about CBN wheels, but if you have any other questions or comments, don’t hesitate to contact the Goodson Tech Department at 1-800-533-8010 or drop us an email.