The Nitty Gritty of Abrasive Safety

By David P. Monyhan (retired)

Conventional abrasives have taken a back seat to PCD and CBN cutters in the automotive world. Since most common engines being rebuilt these days are made from multi-alloy components, they are more easily machined with PCD or CBN. But PCD and CBN can’t do everything, so abrasives are still needed in today’s high end machine shops.

The diesel market still depends heavily on abrasives due to the hardness of the iron and steel components used in diesel power plants.  Abrasives are widely used for surface finishing, porting and polishing, cylinder honing, crankshaft grinding and polishing, flywheel grinding and more.

Before getting into specific applications, there are some things you should keep in mind regarding all abrasives. I call these the Abrasives ABCs.

1. Match the abrasive to the material you are working on. Some, or should I say most, companies ask that you select one abrasive that is supposed to be the “Grand Puba” of abrasive material to grind anything and everything. Let me tell you that is not the case. If you’re working on a hard material, you want a softer abrasive. Be sure to match your abrasive to the material. For example, if you’re machining nickel-chrome valve seats, you’ll want an abrasive designed to cut nickel-chrome.
2. Make sure you have a sharp and pointed dressing diamond or star dresser.
3. Make sure you have clean grinding coolant for applications that require it. Old, dirty coolant will make the stone work harder and won’t flush the debris away as efficiently.

Okay, let’s take a look at some specific applications.

Valve Grinding

This is where a traditional type of abrasive is required.  A valve should be ground. To grind a valve properly you need to match the abrasive to the type of material you are grinding. Valves have changed a lot over the years and the materials used are very different from what was ground back in the day. Today stainless steel, titanium, Inconel and stellite are used in addition to the standard iron and steel.

By incorporating the Abrasive ABCs into your grinding procedure, you have the best chance to grind the material to the finish required for the application without stone load. Keep in mind some valves have a special coating that prevents you from grinding at all. Pay close attention if you see any cautions and or notes from the manufacturer to insure you don’t grind away the coating.

Seat Grinding:

Here again, valve seats have evolved and, of course, machine manufacturers have also evolved. Many shops have migrated to using multi-angle carbide cutters that cut multiple angles simultaneously. However, in my travels around this great country I still see a lot of seat grinding going on. Valve seats come in a variety of materials - nickel chrome, Stellite, cast iron, copper beryllium, and powdered metal. You simply cannot expect one grinding spec to accommodate all of these varying materials.

Surface Grinding:

Here is where abrasives are still being used. I stated earlier that a lot of shops have acquired the newer cutting machines that use CBN and PCD. Some of you have converted your existing grinding machines to also use the CBN or PCD. But as good as CBN and PCD are there are applications that just need to be ground. Diesel cylinder heads with exposed valve seats or pre-cups. Aluminum cylinder heads with exposed valve seats or pre-cups.

Surface grinding machines are designed to run either multiple segments that form the whole grinding wheel that are individually held in place with wedges or single piece wheels mounted directly to the drive spindle of the motor. If you use segments, you have a pretty good selection to choose from. Segments generally come in three different specs.

1. Silicon-carbide abrasive for cast iron and aluminum
2. Aluminum oxide abrasive for steel and hardened metals
3. Aluminum oxide and silicon-carbide combination abrasive for aluminum, cast iron, and hardened iron and steel.

Always be sure to replace your segments in a group. If your machine uses 10 segments, you should replace all 10 of them at the same time. This helps with machine balance and concentricity. 

Surfacing Belts:

This is still a very popular method for a quick clean up on the surface or even a final surface for some applications - especially exhaust manifolds. The beauty of a belt surface is there is little to no set up. However, you still have to match the abrasives and also grit to the material you are grinding. Make sure the belt you use has a waterproof, poly back so it won’t tear or fray during the surfacing operation. Some types of belts require a lot of down pressure and others don’t. Silicon-carbide 40 grit is generally used for cast iron. Silicon-Carbide 80 grit is for aluminum. Zirconia-Alumina 40 grit is for cast iron and steel but needs a lot of down pressure. Most machines running this belt have an air or hydraulic hold down system incorporated into its design. Aluminum oxide 40 grit is standard on most machines and works with little down pressure. As always, remember the Abrasives ABCs.

Porting and Polishing:

I know you can buy CNC ported cylinder heads but you would be very surprised just how many shops still do it by hand. These little cartridge rolls or tootsie rolls, as they are called, need to be the highest quality you can find. They are not all the same.  The good ones are fully glued to prevent them from un-rolling during use.

Some key things to remember when porting and polishing are:

1. Use a porting a polishing fluid to improve the finish and prolong the cartridge roll.
2. Never use squashed or reformed cartridge rolls as they may become shrapnel when spun.
3. Never use a bent mandrel as this will cause vibration and reduce your ability to control the abrasive while in use.
4. Always wear safety glasses when doing this type of work.

Cylinder Honing

Hundreds, maybe even thousands of articles have been written about cylinder honing by people smarter than me. I’ll leave the details to the experts from Sunnen, but I will highlight the things we all need to know.

Honing stones are designed for specific materials, size ranges and types of honing such as manual versus machine honing. Grits range from around 70 to 600 for most automotive applications. Bore ranges are down to about 1.250”and up to 9.00”.

Keep in mind certain honing stones are designed for specific types of honing. Hones with felt wipers are designed for dry honing only and are generally used with hand-held drills for very light stock removal. Traditional vitrified stone sets with aluminum wipers are used in both hand-held and machine drills and must be used with a good quality honing oil. Never used tranny fluid or a concoction of “marvel mystery oil and solvent” or any other down-home recipe as it will attack most bonding agents that hold the grain together causing premature failure of the honing stones. Always match the honing stone to the material you are honing.

If honing stones are used properly, they will wear consistently. Good quality honing oil will keep stones free cutting and prevent loading up. New stones will sometimes need to have the corners radiused to conform to the round cylinder bore. In the event your stones do become loaded up, you can dress them with a diamond file or even use a stone against a stone to assist in unloading the built-up material.

In extreme cases of taper, the stones will actually be worn at severe angles. When this happens, you will need to use a truing sleeve to get them trued up. In automotive honing we need to be aware of cast iron, hard sleeves, short cylinders and, of course, blind holes. We need to insure we have the correct stones for different types of cylinders before we start the honing process. Remember the harder the component the softer the stone.

Cam grinding wheels:

Cams are finished ground after they go through the manufacturing process. Camshafts are made in both steel and cast iron and some are harder than others, even when made from the same material. Most cam wheels are in the 100 grit range and are available in diameters from 18” to 20” and widths are 3/4” up to about a 1-1/2”. Premium wheels are used for materials above the 55 Rockwell spec. They are made from a green silicon-carbide and have a grit of around 70. Cam wheels require a lot of clean coolant and must have a very sharp diamond for periodic dressing to prevent loading and therefore burning of the lobe during the grinding process.

Crank grinding wheels:

 

 

 

 

 

 

 

 

 

These big rascals are the biggest grinding wheels or abrasives used in the Engine Rebuilding business. They range from 18” in diameter to 40” inches in diameter. They come in widths from ¾” to 3-1/2” in width.  As with every other abrasive, one wheel cannot be expected to do everything be it automotive or diesel. You must match the wheel to the material you are grinding. If you are grinding automotive and the journal is less than 35 Rockwell a traditional medium grade wheel will do the job. If you are grinding harder diesel or performance crankshafts (over 35 Rockwell) then you need a wheel designed specifically for these types of applications. Grinding wheels will load up so they need a constant flow of clean, high-quality coolant and lots of it. A very sharp diamond is an important player in maintaining the proper dress to grind.

Crankshaft Polishing:

Polishing belts are just what the name says: they are for polishing……PERIOD!

I have seen too many shops attempt to correct a poorly ground crankshaft with polishing belts. If the crank is ground correctly the polishing belt will do its job and improve the finish as well as remove minute imperfections in the journal surface. Polishing belts are available in widths from as narrow as ¾” up to 2”. Grits are from 240 to 800.  I like to see the use of polishing rouge in the mix to improve the finish to a nice luster.

Here are some of the key things to remember about crankshaft polishing belts:

1. Scalloped edge belts are for polishing the radii on the crankshaft.
2. Match the width of the belt to the journal width.
3. Use polishing rouge for maximum shine.
4. Chamfer oil holes prior to polishing.
5. Polishing belts are more prone to moisture-damage than wheels. Store belts in a clean, dry area at room temperature. I heard of one shop that keeps them in the refrigerator and says it protect the belts from the humidity.

Flywheel Grinding:

There is lots to talk about when it comes to flywheel grinding.

General purpose stones do a pretty good job on most cast iron flywheels. Not all flywheels are made of cast iron.  They are also made from cast steel, billet steel and aluminum with steel wear inserts.

Flywheels are becoming popular again due to stick-shift cars getting better gas mileage. Big, over-the-road trucks all have clutches. That means flywheel grinding. If you are grinding flywheels and don’t know where to start or which wheel is best for the application, use the middle wheel and go up or down the scale from there. If your supplier only offers one type of wheel to grind them all, find a different supplier. Remember soft stones for hard flywheels and hard stones for soft flywheels.

1. Always maintain clean fresh coolant
2. Always inspect your dresser, especially if it is a star dresser. The star dresser must rotate.
3. Diamond dressers need even closer inspection as the diamond can sometimes be knocked off and the operator will unknowingly grenade a flywheel stone during dressing.
4. Always wear eye protection.

Grinding wheels and abrasive belts are a part of everyday business in the machine shop. How we handle and store them is the challenge for all of us. Heat, cold and heavy humidity can wreak havoc on any grinding wheel and especially on abrasive belts. I have a few final thoughts about abrasives for you:

1. Blotters are not just a place for the company’s logo. Never mount a grinding wheel without a blotter...period.
2. Do not over tighten. Tighten just enough to hold the wheel firmly.
3. Ring test wheels prior to mounting by knuckle knocking the wheel and listening closely. It should ring like a bell and not like a clunk.
4. Inspect wheel dressers periodically.
5. Ensure wheel safety guards are in place at all times.
6. Never exceed maximum RPM of wheel.
7. Visually inspect each wheel before use. If in doubt throw it out. Nobody wants to be a pirate every Halloween.

Treat your grinding wheels and all of your abrasives with care and they will perform the job you need to do when you need to do it.

You may have noticed that I skipped over Flex-Hones and Ultra-Finish Plateau Hones. While these are abrasives commonly used in engine building, they are a separate abrasive family that I’ll address at another time.

See ya in the shop,