Flex-Hones® are a great addition to every machinist’s bag of tricks. They’re essential for getting the best finish on cylinders, guides, etc. When we say best finish, we don’t mean smoothest. Flex-Hones® are intended to create a consistent cross hatch on the bore surface so that oil has something to cling to. Without this cross hatch, the oil will simply flow away without doing its job.
Let’s talk a little bit about Flex-Hones®. You may know them as ball hones or dingleberry hones, grape hones … gotta love creative machinists!
By definition, the flex-hone® is a resilient, flexible, honing tool with a soft cutting action. So what does that mean? It means that flex-hones® adjust to the cylinder surface. That’s why they’re used after the cylinder has been sized with rigid honing stones.
There are 3 factors in choosing a flex-hone – Abrasive, Grit and Size.
Flex-Hones® are available in several abrasives – silicon-carbide, aluminum oxide, alumina zirconia and diamond are most common in engine building/machining. Each of these abrasives has a purpose.
Silicon-Carbide is generally used on aluminum and cast iron but can also be used on brass and non-metallic materials. Silicon-Carbide is the most common abrasive in automotive work.
Aluminum-Oxide is used on hard materials such as hardened steel, hardened aluminum and other hardened metals. One of the most common applications for aluminum-oxide flex-hones® in engine building is Nicasil (nikasil) cylinders.
Aluminum-Zirconia is used on brake rotor flex-hones® among other things. This abrasive incorporates man-made zirconia with aluminum to create a rugged abrasive that is ideal for ferrous and non-ferrous metals.
Last, but not least, is Diamond. This abrasive is great for heat treated steel, high nickel stainless steel, chromed or plated material, MMX aluminum alloys and more.
You already know about grit. The higher the number, the finer the grit, the less material is actually removed. Flex-Hones® are available in the typical range of grits, from 20 to 800. The most commonly used grits for engine building work run from 120 to 400.
Every Flex-Hone® is color coded for fast identification of the hone’s grit. You’ll find this color-coding on the tip. Refer to the list below to determine what grit you have.
120 Silver (no color)
240 Navy Blue
800 Light Blue
Whatever size cylinder you’re working on, odds are there’s a Flex-Hone® that will fit the bill. They start at 4mm (5/32”) and run all the way up to 24-1/2”. (NOTE: Goodson doesn’t carry every single size, but if you need a size other than what is stocked, let us know and we’ll order it in for you).
Flex-Hones are made oversize so you need to choose the size based on the size of your cylinder. If your cylinder is a non-standard size select the next largest size. For example, for a cylinder that has been machined to 3-3/8”, choose a 3-1/2” hone. The “flex” that’s build into the Flex-Hone® will adjust to the size difference.
As always, if you have any questions about Flex-Hones®, feel free to contact the Goodson Techxperts™ at 1-800-533-8010 or check out these articles in the Technical Library.