BPG_Austin

justaguy, I'm not intending to rain on the parade, but aren't cranks lathed vs the 5th axis? Where I work its REALLY hard to mill a cylinder to less than .0005" tolerences. (from 2 sides of course). I *think* this type of work will need a lathe, but I'm not an expert by any means. We've got 26 fadals at our shop. They aren't known for precision machining but do hold to half a thousandths. I'm interested to learn the machining process if they don't have to be lathed!

svp928

BPG, I think Justaguy's machine IS a lathe, per se- it has a milling spindle mounted on a rotating coupling to allow 5-axis milling to be performed while the part is clamped between the front and rear chucks. It probably also has a lathe turret, or 2, and can do conventional turning work as well. The milling head allows "turn-milling" to cut the rod journals. A lot of shops have these machines now, and many crank shops are getting them because its so much faster to do small lots. It IS a lot of programming, if you don't have software for it- and no, Bobcad will not handle 5-axis well.

If its a Mazak Integrex, you can buy software from them that they developed about 10yrs ago to cut cranks. We currently use Mastercam for 5x stuff, but if I had my choice, it would be Hypermill. For a mill-turn like this, Esprit is a good choice...

This only roughs out the crank-Eventually, it has to go in a crank grinder for finishing.

Steve

IcemanG17

Sean
Super cool.....

danglerb

Once you have any crank modeled, shouldn't it be fairly easy to modify pretty much any way you want?

What would the raw steel billet cost for a crank, or a cam?

IcemanG17

It probably takes a couple "tries" to work out the kinks....which adds to the cost....but I wonder how much the blank steel billet weighs to start with? My guess is 200+lbs....since the finished crank is around 55lbs....

tveltman

Billet for a flat plane crank will be lighter than a cross-plane, since you are only removing most of the material on one set of faces rather than two...

EDIT: Unless it starts out round, then it won't matter...

BPG_Austin

Really interesting, thanks Steve. Justaguy, it would be really cool to see a picture of the crank being milled on the 5th. Amazing technology.

LT Texan

flat crank, 944 heads and cams....shakes like hell?

Rick Carter

With currently available rods and pistons how much can it be stroked and maintain a decent rod to stroke ratio?
Interesting link.

gargoyle28

Hey everybody, this is Greg, Sean's draftsman. I'll try to incorporate any ideas you guys have that would be beneficial. This is new territory for me but I am very willing to learn about all it takes to make a great crank, or any engine component really (I'm on the lookout for ideas for stuff we can make for my "racecar", it's a Honda tho)

The single plane crank I drew there was really just using the single plan throws/counterweights (not sure of the proper terminology) from the dual plane crank. Of course I can change anything in any way that is needed. I'll be doing some research on my own as well.

puyi

Aston Vantage GT2 use 4L7 flat crank . I think that 6L2 vette engine are flat crank equiped.

the pros, much simpler exhaust system, peak HP, reliability. the cons vibration

The race car which use it, usually experience destruction of parts around the engine like starter, oil pump etc....but the motor it self is reliable !

Puyi

gargoyle28

since his car is a dedicated racecar maybe it is plausible to use a single plane crank

danglerb

I doubt it. The benefits are all in an rpm range beyond what anybody deems reliable in a 928 block. Despite all of the dry sump, scrapers, etc. nobody I know of is running a 928 routinely above 7k rpm.

OTOH a standard configuration crank stroked just the right amount and with the proper journal sizes to match a non custom rod and piston might be pretty popular.

Working out the details to cnc port stock heads, might be the most popular option. Maybe starting with one of the 944 heads.

justaguy

Guys
6.5" O.D blank would weight around 300lbs at $ 1.00/lb thats about $300. Thats the cheap part.
Before we get too technical I am looking at this project as a training exersize for my guys to become familiar with the 5-axis machining center.

The whole thing is in the what can we make for fun category. If we end up with a usable crank I would consider it a bonus.

I would build a dual plane stroker before I would consider a single plane.

We have the model now so feel free to make your suggestions changes are easy and cheap in the virtual world
Sean

svp928

Sean, where do you buy 4340 VAR for $1.00/lb ? Not raggin on ya, but its more like $4-5.00 around here...
LAst 300m I bought was $9.00/lb with ultrasonic inspection.

What model of machine is it? We have a Mazak and a Hermle, so I may be able to answer some questions for you...