use CNC fly cutter to machine heads and manifold intakes
15 February 2017
15 February 2017,

Skimming heads is the bread and butter of many machine shops.  The CNC flycutter is the preferred tool for the job.

use CNC fly cutter to machine heads and manifold intakes

Why Skim Heads with a CNC Flycutter

If the deck surface on the head or block isn’t smooth or flat, it needs to be refinished. A head may become uneven after welds or other repairs have been made.  You may want to mill it to increase the compression ratio. If the manifold surfaces on a head are corroded or eroded cleaning you can clean it up with a flycutter.  Maybe you have an aftermarket intake manifold and the angle isn’t perfect.  A CNC flycutter is just the trick to get it right.  And get it right you must.  Mistakes are costly because once metal is removed it is gone.

Get ‘Er Done Right

First things first.  If an aluminum head is warped, fix that before you skim it.  It will reduce the amount of metal you need to skim. Then check for flatness.  The flatness specs will depend on the application (for performance engines the flatter you get it the better the performance) and the engine.

Before you make your first pass, make sure you’ve got the block squared up. The surface of the head must be absolutely parallel to your cutter.  Once you’ve got it aligned perfect make sure it is rigid.  There is no tolerance for movement in this procedure.


Before you start, look up the recommended specifications for the engine and the head gasket.  In order for the gasket to properly seal the finish must be as recommended.  The Ra (roughness average) in microinches varies depending on the metal (aluminum or cast iron) and the type of gasket.  So check the gasket manufacturer’s recommendation before you start and check your work with a profilometer when you are done.

Of course, it goes without saying (but we will say it anyway) make sure your feeds and speeds are correct and you use plenty of fluid.   Now you are ready to skim.

Get the Right CNC Flycutter

Sierra American CNC flycutters

Sierra American CNC Flycutters

Make sure you are using the right flycutter for the job.  Sierra American Multi-Systems are perfectly balanced for higher RPMs and longer life.  They are sold individually in 1 ½”, 2”, and 2 ½” diameter sizes as well in multi-size sets.

The ¼-20 alloy set screws let you skim with stability.

Every CNC flycutter made by Sierra American is made right here in the USA and backed by a full 5-year warranty.

If you aren’t skimming with Sierra American, you aren’t skimming with the best.  Be sure to ask for Sierra American by name.


P.S.  Just a word about gasket removal.  Don’t use the wrong tool to scrape off the gasket before you machine the head.  You can gouge the surface and make the machining job much harder.  Use a chemical gasket remover and a gasket scraper.  Don’t chisel at the gasket, put scraper at an angle that has it almost parallel.  Instead of causing damage, the scraper will slip in under the gasket without further damaging the surface of the head.





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