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General Mach Discussion / CNC porting cylinder heads - options?

« on: June 30, 2008, 09:25:18 AM »

Here is a tidbit for those that always wanted to CNC port cylinder heads but did not know how to probe the ports for a reference.

If you start out with a probe tip the same shape as the cutter tool you will use (WE use a 3/8" ball tipped tool on a long taper shank) then you can take the polar array and probe a slice section of the port one step at a time.

For example position the head in a fixture you would use to hold it during machining. Pick a center point location that allows you to get as far down the port as possible. Next start the array running and allow it to step down a certain amount each cycle. When you have reached the bottom you will have series of slices that can be used to create a cutting program to replicate what you have probed.

Next rotate the head in the fixture to setup the other end of the port and repeat the process.

As long as you use the same shape tip as the cutter then the probe shape will translate directly to the cut shape accurately.  You can then cut it like you probed it.

Just A Thought (;-) TP

First post. Let me know if I'm in wrong place 
Got some complete beginner questions regarding the possibilities of CNC head porting. The above post was the only mention I could find regarding cylinder heads....

I'm carrying out a CNC retrofit to my Bridgeport vertical mill and have been looking for a method that might allow me to achieve at least a basic level of CNC porting and digitizing ports. Ideally full 5 axis is the way to go but trying to build a dual rotary table (A & C) looks like it'd be a nightmare with respect to backlash (adding servos or stepper motors to a couple of rotary tables). I'm not aiming for mass production level, more a case of saving my semi arthritic wrist from countless hours of grief manipulating an air-powered die grinder  This is more a hobby project than mega buck investment.

Not sure I've interpreted the post above correctly but am I right in thinking the probing is done on a 3 axis machine to the point where the head must be rotated to allow better port access? If the exact rotation co-ordinates are noted, CNC porting of the head can then be carried out in various stages on a 3 axis machine, as long as each batch of probing/cutting is carried out at the same exact position?  It would obviously be more time consuming than using a dedicated 5 axis machining centre (such as the Centroid) but for me, time is more readily available than cash 

I'm a total newbie when it comes to digitizing....  say for instance I wanted to digitize an existing, painstakingly developed, hand shaped port, can the Mach3 automatically send the probe on a journey around the port, recording the co-ordinates as it goes, therefore saving an awful lot of time having to manipulate the probe's position manually? Does some kind of preliminary plot have to be entered to tel the probe how close together the contact points should be? Will it do this in XY&Z?

Can those co-ordinates then be imported into a separate CAD program (eg Rhino) for further manipulation/smoothing before directing the mill to carry out the work?

If anyone can point me towards any tech articles/books etc that might help, please do. I've found very little info with regard to CNC porting of cylinder heads, apart from the very high end, dedicated machining centres by the likes of Rottler and Centroid etc. I'm sure much of what I'm trying to achieve has similarities with work carried out by many people on this forum, even if theirs isn't automotive in nature.