[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.
:cheers:


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]

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.
:cheers:


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;
[ame="http://www.youtube.com/watch?v=sxpzWw3o49o"]YouTube- 5-Axis CNC Porting[/ame]

[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]

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

[Skin]

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

Oh gosh here we go ;o) I spent years trying to get my head round this. it comes down to (for bikers) your Yamaha / Honda split in philosophy... One would polish the inside of their exhausts, encouragine the flow of exhaust gasses, the other would leave them coarse. The belief being that like on the side of a river, there are lots of little pockets which create little whirlpools (eddies) the whirlpools act ironicly firstly as insulators (gas convection to gas is very poor) and secondly in the belief that you cannot get a better slippery surface than a fluid against fluid...

For what it's worth

James (aka Skin)

[carbidecraters]

You would be money ahead by buying an older Fadal 6030 and outfitting it with a couple of rotary tables. We use a 6030 with a fadal vh275 for the B and a fadal vh65 for the A for porting. The centroid and rottler machines are not worth the money they get for them. You can do a lot better and achieve much better results from a robust machine that was build for 10K rpm like the Fadal. There are quite a few that use Fadals for head porting because they are cheap and hold .0002". There are those that even want to sell you a renishaw cyclone and a cheap rotating fixture with encoders on it for big bucks. Do it right and look around ALOT before buying anything.

[mattpatt]

I've ported a fair few two strokes in my time, and on one of the cylinders I do quite often I'm making some programs to do it on my FADAL 3016.

Now it's only a 3 axis, so I can't get in everywhere I need to, but it does do the majority of the tedious work for me. Then all I have to do is get in there with my die grinder and tickle it up a bit.

I'm now looking at building a program to do the exhaust port, as there's usually a fair chunk of material to remove, and getting the exhaust port right on a stroker can be the difference between a snail and a whippet.

Because of the shape of the port I'll have to do it it two operations, but I don't see this as too big a task. The only real issue is mapping the standard port, and the modified port I already cut into solidworks. I don't have a digitizing system, so I've cut up a few cylinders and measured them up by getting 3 planes as datums and then marking out points on the port walls.

From this I can build a 3D map of the port and surface model it. With this done I can cut it on the CNC machine.

Oh if only there were a few more hours in the day!!!

Regards,

Matt.

[D.L]

Why not pour a few silicone molds of the ports and laser scan? Or slice them like a loaf of bread and scan the slice for a vector spline trace to build your surface model?
But, you have to come up with the killer port shape to begin with.
And once you've hand ported a 2 stroke single and flow tested a good shape, you've negated the need for cnc porting.
But it would but good to have all the good port shapes as cad files.

[mattpatt]

D.L

One issue is that the standard cylinder has a pretty rough and ready casting, and whoever sets the mold does it on a Friday afternoon, as very often the port is not centered.

I've cut maybe 100 of these cylinders, and I have some good designs for the ports depending on spec. The lowest spec just needs a bit of a tickle to true up and increase area just a tad, and the 'race' spec needs a good deal of material taken out.

Making a silicone rubber mold and laser scanning is the obvious way to go. I did this originally on a couple of two stroke cylinder and also a four stroke head, but the quote for laser scanning was so ridiculous I'd need to do 1000 heads to get my money back! To put you in the picture, I'm in Thailand where technology is available, but at a high price.

Slicing the silicone plug is a good call. Thought about it, but haven't done it yet. However, the accuracy of the model will only be as accurate as my slicing

Anyway, the first off cylinder exhaust port is cut and I'm quite pleased. Just need to pull the surfaces of the model a little here and there, but apart from that it's good to go, and saves me around 3 hours grinding time.

As soon as we have a loose 30k kicking around we'll get a laser scanner, but until then......

Thanks for your input,

Regards,

Matt.

[D.L]

Hi Matt, I know it's another can of worms to porting, carting and home cnc.
But, there are guys on cnc zone using home made laser scanners.
I have fooled about with home scanning and vector tracing, and my personal opinion is it all sucks!!!
Building a proper cad model geometry with splines and filleted corners is the only way to fly. Organic mesh shapes and wobbly vector splines are a nightmare, to say the least.
You could get a point cloud from a digitizing probe like a brown and sharp, there are also home made digitizers on cnczone using mach3 software.
(another can of worms)
My best answer is, pour the molds / slice at 2mm segments / scan at high res / trace the JPG image with good 2d cad (microstation).
If you use spline / fillet construction with matching attribute on all slices eg; 3 splines and 2 fillets you will get a mickey mouse 3d surface model.
A lot nicer than a polygon mesh!

[mattpatt]

I'm still a little worried about not getting the silicone plug sliced perfectly, which would make the rest of it all a bit pointless. Having said that, my first attempt wasn't perfect so I'm willing to try again. How would you slice it?

Another thought was slicing the cylinder down a mill or two at a time and scanning that. Once I have this scanned jpg I can throw it on a plane and sketch geometry, or convert it to a DXF and use that, but as you rightly say, sketching myself and keeping the right (same) number of splines etc would be the right way to go.

I have a couple of stock cylinders, and modified cylinders that have either seen good action or a bit of a mishap, so chopping then up isn't a problem.

[dynosor]

I'm still a little worried about not getting the silicone plug sliced perfectly, which would make the rest of it all a bit pointless. Having said that, my first attempt wasn't perfect so I'm willing to try again. How would you slice it?

Cast plaster of paris around the silicon plug in a square section carboard box with a footprint stable enough to be placed on a mill table.

After it has set, mill the cast down a millimeter at a time. Use a scanner to capture the profile of the section and capture X/Y co-ordinates from the picture using Photoshop - I have done exactly this with small flimsy rubber parts that needed to have sectional measurements taken by potting them in expoxy to stabilize them. In this instance, I pulled the rubber part out and just measured the edge of the cavity after polishing on wet abrasive paper.

You need to create feducial features that you can use for co-ordinate references - I suggest you cast two pencil into the box at diagonal corners and use the to align the cast on the scanner or the scanned image in Photoshop.