Surface grinding the old fashioned way

Posted on Aug 21, 2020

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Surface grinding the old fashioned way

Whether it's for punching holes, grinding cutting tools, or precision forming tool steel for fixtures, every store has at least one surface grinder. Maybe you have a fully automatic model with all ringtones. Or maybe you are using a manual grinder from the 70s. Either way, it would be impossible to perform many daily store tasks without these much-needed machines.

Although they are familiar, are you sure you want to take full advantage of the grinding advantages of this mechanical workshop partner? This is an introductory knowledge about how to make the most of surface grinding operations.

Let's start with the wheels: there is a dizzying variety of grit, abrasives, bonding mechanisms, and shapes, and some stores may opt for general-purpose rims, rather than seeing which of the many combinations will work best for your application. Here's what you need to know to make surface sanding an efficient and effective process.

 

Wheel steps

A relatively "soft" Grade H wheel is preferred for grinding harder workpieces, while Grade J or K (which are harder) may be more suitable for softer materials. Taking a few minutes to move from one to the other can make a huge difference in how many parts you sit on the bench at the end of the day.

 

Grinding wheel size

When removing large amounts of material, using a grinding wheel of 120 or thicker will complete the job faster than, say, grinding wheel 150. While vitrified alumina grinding wheels are ideal for general-purpose work, shops grinding hardened tool steel and other difficult materials should consider investing in a resin bond ceramic or CBN wheel.

These examples are a simplification since the performance of each wheel depends on many factors, including the type of abrasive, the material being cut, and the amount removed. The idea is to research the options available and not settle for the second-best one during the grinding wheel selection process.

 

Operational success

Once you've got the right disc, cutting fluid, and a rigid setup, here are some extra tips to help you grind effectively:

Always balance the wheel and spindle assembly before use, and if you remove them from the spindle, rebalance them.

●     Dress regularly to keep the wheels sharp.

●     Leave the spindle running after clothing.

●     The speed at which the coolant exits the nozzle should be greater than the speed of rotation of the wheel. The stream should also be laminar (ie flat).

●     Do not let the grinding wheels hit against each other during storage.

●     Keep them dry, handle them carefully and always use the oldest wheels first.

●     Never exceed the recommended wheel speed.

●     Keep cool when sanding: use cutting fluids, oils, and anti-fog

 

Keep in mind that surface grinding is removing small pieces of metal, and the cutting fluid is responsible for lubricating and removing heat from the work zone. Water-soluble or synthetic coolants are great at cooling, but offer less lubricity than regular oil. Still, water-based coolants are arguably the first choice for general purpose applications, and certainly for roughing operations (where heat is a major concern).

For CBN and diamond rims (or in situations where a very fine finish is needed), oil is often recommended. But the oil can get anywhere and it is not pleasant to inhale, so be sure to provide protection from the mist. A fire alarm system is also a good idea and can be a safety requirement in your area.

In any case, the cutting fluids must be kept clean and filtered. Water-soluble fluids should be degreased to remove dirty oil and prevent rancidity (which can be a big problem with machines that are not used regularly).

 

The Importance of Keeping a Firm Grip

Holding the part securely during any machining process seems like an obvious best practice, but if you've ever seen a piece of steel pop out of the left end of a plane grinder, accompanied by flying grinding wheel debris, you'll pay the extra pay attention to your workplace forever.

 

Magnetic holders

Despite the vacuum grips and the double-sided backing tape, the most common (and preferred) way to grip parts while grinding is with the magnetic chuck. There are two main types, electromagnetic and permanent magnet. Chances are your machine shipped with one or the other and you may be stuck with it now, but electromagnets offer more clamping force and adjustment, and it's also easy to demagnetize the chuck and workpiece after machining by reversing the current flow (but they are also more expensive).

Regardless of which one you use, be sure to properly support tall objects by securing them to an angle iron or 1-2-3 block. Also, if you usually grind small objects, look for a thin pole mount or at least wedge them with a thin piece of metal on the side opposite the wheel's rotation (or build a work handle).

 

Maintenance of surface grinding

Everyone is busy and it is easy to overlook machine maintenance in favor of producing parts, especially when the machine is idle for several days. But when you need to hold a tenth of the inspection tooling, you'll want the surface grinder to be as good as the other machines on the shop floor.

Grinding is a true craft with many variables that can take years to master. If you're not getting good results with your submission, don't be afraid to ask experts for advice and guidance.

 

Here are proven routine maintenance methods:

●     Wipe the sander when you are finished using it.

●     Keep the lubricant reservoir filled.

●     If your machine has a hydraulic feed, change the oil according to the manufacturer's recommendations.

●     As mentioned earlier, cutting fluids should be filtered and skimmed, and keep an eye on pH and fluid concentration.

●     Watch for and stay ahead of worn parts, and buildup of rust and crud.

●     Check for chuck flatness with a dial indicator and regrind both it and the table if necessary.

●     If something doesn’t look right (and you have reason to suspect the wheel has been abused), remove it from the arbor and “ring” test it.

●     New wheels should always be ring-tested and inspected for damage. Doing so can prevent a catastrophe.

 

This was just a general overview of one of the most complex machining operations. Grinding is a true craft with many variables that can take years to master. If you're not getting good results with your submission, don't be afraid to ask experts for advice and guidance.

 

More information about CNC Surface Grinder

:: Who needs surface grinders?

:: Surface Grinding Machines in the Automotive Industry

:: How to pick the best Surface Grinding Wheel

:: The Critical Chain Component in Metal Machining: CNC Surface Grinder

 

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