CNC head porting.. Diy???

[Zriuz]

hey I'm not sure if this might be the right forum but you guys all toy around with small displacement.

I'm not a machinist i'm an electronic engineer but real good in autodesk inventor. I'm on the market for a knee mill that i could cnc retrofit (i guess i'll be baying a bridgeport mill) so i could toy around with. Now here is the deal:

I race 125cc shifter karts and one of the things i'll like to do with the machine i buy is add 2 more axis to port cylinders and head (I got many left overs from previews builds that i could use to digitize the ports). Before i buy a machine i wonder if there is space for such a task on a bridgeport like mill. the specs on the mill say that it has a 12" travel on the Y axis, but i seen some pretty big parts being stuffed on some of them. (not sure if there are different bigger models)

If there is a will there is a way, so i'll like to see some positive replys. Remember I'm buying and retrofitting a machine for my garage, and building the 2 other axis. maybe i can pull the job off with only 4 axis, not sure tho

Thanks in advance.

[RICHARD ZASTROW]

Don't forget the programming requirements. IMHO you'll need 5 axis. That means you'll probably need a 5 AXI$$$$$$$ CAM system as well.

Dick Z

[camarogod98]

Ive got a sweet 4 axis bridgeport that i just put up forsale in the classified section. It would be very easy to add a 5th axis drive to it to power your trunnion on tilting table. machine has 16" of Y travel and has a fresh centroid retrofit on it.

[AirChunk]

Wow , this is something I have thought of but never attemptd . I have been hand porting those cylinder for for 23 years now , but have only been doing cnc stuff for about 2 years . I was thinking of buying one of the rhino machines for the cylinder porting ---- but never quite got enough dough up for it . So I bought an entry level smithy cnc1240 to cut my teeth on.

But now with the big 4 stroke influence cnc porting looks way more attractive.

The most critical and probably hardest part to cnc on a 2 stroke is the roof port heights and angles .

[RICHARD ZASTROW]

Sorry, I thought Zriuz was referring to 4-cycle heads. Like Airchunk, I hand finished 2-stroke ports for years.

Consider using an air powered die grinder with a 90 degree head. Mount a fixture on a rotary table to hold cylinder vertically.

Depending on tool and cylinder dimensions, you can use the z-axis for height location, x & y for depth into ports, x-z interpolation and y-z interpolation for port radii and tool form taper/ radius for port angles and transfer port angles & blending.

That only requires 3 axis. The 4th (rotary) axis could be included to index from port to port and maybe interpolate as well.

It's been done before with modified dental tools.

Dick Z

[HellPhish]

porting cylinder heads by hand is pretty much divining. CNC'ing them without overall knowledge of their physics is voodoo. more flow does not = more power. to come up with a progra that works and work well will take a few cylinder head sacrifices as the specs will have to be just right to do what you want.

the likes of AFR, TEA, Trickflow, Edelbrock, etc, all go through many incarnations of programs to figure out what works best and even .01" too much or too little material can mean the difference between a damn powerful engine, or a dog. if you would like to port out the head, start by hand and start small. clean up the runners but do not oversize them too much, do some bowl blending but dont increase the size too much, etc, and work your way up.

you CAN do it but you have to take your time with it and learn what works. competitive teams wont be wnting to share what works. the basics are that you want the air/fuel to atomize as much as possible, you want no puddling, no mirror surface (do NOT polish). the air entering the chamber should be fairly non-turbulent going in BUT you want "swirl"" as it enters the cylinder. this means you should very very carefully make the backside of the port as gental a turn as you can so the air isnt slamming into a wall and creating turbulence on the topside of the valve. the short side radius should also be worked to direct the air into the cylinder. the valve area is usually where you will find the most gains.

on the exhaust side, theres less chance of making it fubar. the general rule there is that 65% of intake flow on avg.

do not worry yourself about peak flows and and such, what you want is usable power and is something you should work at incrementally. small changes and few changes at a time so you can see problems and advantages as they arise.

hope this helped, good luck.



edit, aww crud... disregard.. i should get through the whole thread next time

[RICHARD ZASTROW]

Ref. HellPhish #6: In order to reduce surface "sticktion", We used to polish the intake surfaces and then glass bead blast them.

Dick Z

[Skin]

Originally Posted by HellPhish porting cylinder heads by hand is pretty much divining. CNC'ing them without overall knowledge of their physics is voodoo. more flow does not = more power. to come up with a progra that works and work well will take a few cylinder head sacrifices as the specs will have to be just right to do what you want. the likes of AFR, TEA, Trickflow, Edelbrock, etc, all go through many incarnations of programs to figure out what works best and even .01" too much or too little material can mean the difference between a damn powerful engine, or a dog. if you would like to port out the head, start by hand and start small. clean up the runners but do not oversize them too much, do some bowl blending but dont increase the size too much, etc, and work your way up. you CAN do it but you have to take your time with it and learn what works. competitive teams wont be wnting to share what works. the basics are that you want the air/fuel to atomize as much as possible, you want no puddling, no mirror surface (do NOT polish). the air entering the chamber should be fairly non-turbulent going in BUT you want "swirl"" as it enters the cylinder. this means you should very very carefully make the backside of the port as gental a turn as you can so the air isnt slamming into a wall and creating turbulence on the topside of the valve. the short side radius should also be worked to direct the air into the cylinder. the valve area is usually where you will find the most gains. on the exhaust side, theres less chance of making it fubar. the general rule there is that 65% of intake flow on avg. do not worry yourself about peak flows and and such, what you want is usable power and is something you should work at incrementally. small changes and few changes at a time so you can see problems and advantages as they arise. hope this helped, good luck. edit, aww crud... disregard.. i should get through the whole thread next time

Wasn't he saying he was goign to take an existing porting profile, one which was successful and digitise it, and use that as a standard template?

I catually think this is a good idea, been contemplating this for a while now, we have a Bridgeport, and all that would be needed would be a 4th axis, and software to write the programs, we use SolidCAM, sits nicely in with SolidWorks, and intuitively helips you to write what would otherwise be incomprehensib... impossible programs

Best of luck mate, and let us know how they go. I know you're an Autodesk seat, but if there is anythin i can do to help I would really like to help.

James

[rab]

I've done some porting on wooden flutes - I don't know if it's at all similar to what you need but you may get some ideas, here's the video;

YouTube- 5-Axis CNC Porting

YouTube- 5-Axis CNC Porting

[BobWarfield]

Rab's setup and software would certainly do it, but like some have said, it isn't clear it needs 5 axes to do those little ports. They don't look like the have the nasty deep elbow and valve clearance issues a lot of automotive heads do. Even a lot of those could be done on a 3D with patience and multiple setups.

Mapping a proven ported design with a 3D probe would definitely be the first thing I'd do. I bet a damaged head with ports intact would be cheap to come by--if you don't break something, you're not going fast enough.

After that, you could mod it to do better if you wanted, or just turn out more like that.

In order to do these things on less than 5-axis, it's also worth getting a thorough understanding of how to program undercuts.

Cheers,

BW

[HellPhish]

Originally Posted by Skin Wasn't he saying he was goign to take an existing porting profile, one which was successful and digitise it, and use that as a standard template? I catually think this is a good idea, been contemplating this for a while now, we have a Bridgeport, and all that would be needed would be a 4th axis, and software to write the programs, we use SolidCAM, sits nicely in with SolidWorks, and intuitively helips you to write what would otherwise be incomprehensib... impossible programs Best of luck mate, and let us know how they go. I know you're an Autodesk seat, but if there is anythin i can do to help I would really like to help. James

the issue is companies without a race program do a "best overall" type cnc program for their heads. two teams could have the same engine setups but their power and porting could be quite different.

thats another reason why i like the start slow approach. it lets you have a very specific program.

Ref. HellPhish #6: In order to reduce surface "sticktion", We used to polish the intake surfaces and then glass bead blast them. Dick Z

now, a lot of what i see companies doing is leaving the CNC tooling marks and advising not trying to "finish" the head with polishing. though... wouldnt bead blasting actually help on a stock cast port?

[RICHARD ZASTROW]

HellPhish: I believe stock ports may be too "lumpy". What I tried for was straight or smoothly curved surfaces. Then the surfaces were polished to remove slight irregularities. The polished surfaces were then bead blasted to reduce the surface tension or "sticktion" of air/gases flowing by.

Somebody wrote a paper on this subject. I think it had something to do with laminar flow within a tube. (that's a mouthful) LOL

There are "lumps" that may or may not improve flow. They are more like "deflectors" that channel flow where you don't want it, like around valve stems.

Dick Z