Piston Bowls

[Fingers]

The trick with 3D on a 3 axis machine is to get the CAM to output G18's and G19's and then use circular interpolation for the path in the XZ or YZ plane. THAT will give you the best surface with the least wiggle since all the arc segments are tangent to each other.

But what you have givven me will work fine.

Thanks

:thumb:

 

[dmaxlover]

The trick with 3D on a 3 axis machine is to get the CAM to output G18's and G19's and then use circular interpolation for the path in the XZ or YZ plane. THAT will give you the best surface with the least wiggle since all the arc segments are tangent to each other.

But what you have givven me will work fine.

Thanks

:thumb:

I may be wrong, but I believe the post needed to spit out arcs while 3D surfacing requires a S post. The post that Wolf used is a M post. M posts are must cheaper and easier to make, and most of the world can get away with them. Now on there 5 axis machines, a S post is required, especially if there doing full 5 axis machining.

If the machine gets real jittery, just turn down the feedrate. I have that problem on our machines when doing high speed surfacing, and the control can't keep up.

 

[Fingers]

Ran a couple samples. Look good. Hope to have pictures to post tomorrow. I am waiting on a kit to measure the chamber size on the samples before I commit to cutting pistons. If all goes well, I might be able to get the rotating assembly off to get balanced Monday, next week.

 

[WolfLMM]

did you have to do some editing?

 

[x MadMAX DIESEL]

If all goes well with testing and you decide to sell these publicly, what would be the cost? I know its early to say, but ballpark?

 

[Fingers]

I am not really in it to sell them. More of a project for myself. I am more than happy to help whomever though.

Blanks are ~$200 each, machining on top of that. Say $50 value added? Heck WolfLLY or another machine jocky might want to get into the piston carving way. I am sure they would be faster than me.
:thumb:

 

[Fingers]

did you have to do some editing?

Always.

I will show yours compared to mine tomorrow. You have a lot tighter pattern than me, but it takes a while to carve.

For grins, I carved out an electrode for the EDM to finish the bowl. (why? Because I can) Reflash aside, I like the look of the EDM. If I would do this on all of them, I would tweek the electrode a bit to enhance the finished product.

I will let others decide which looks best.

 

[jheyob]

For grins, I carved out an electrode for the EDM to finish the bowl. (why? Because I can) Reflash aside, I like the look of the EDM. If I would do this on all of them, I would tweek the electrode a bit to enhance the finished product.

So you roughed the bowl in with a mill then made a huge electrode the shape of the bowl and plunged it for a finish?

 

[Fingers]

Pictures!

First, Thanks to WolfLLY for the NC file.

I tried to label each attempt.

Wolf's SurfCam bowl was with a 1/2" ball mill and took ~30 min to cut. (cranked up the original spindle and feed rate to 150% of original) Spindle was humming at ~6000 RPM and Feeds ~60 IPM. The MasterCam Bowl was with a 3/4" ball mill and took about 12 min. (Spindle at ~5500 and feeds ~40 IPM) The main time difference is the Mastercam roughing passes were much more aggressive.

The Electrode was the same for both EDM passes. I roughed it out with a MasterCam generated NC file and then massaged the tooling marks out of it by hand. But alas, the darn thing was flawed from the get go because of poor tooling selection on my part. (Copper is sticky and the ball mill was less than sharp) So there are a few pitting marks that I didn't get rubbed out.

The one bowl was done all by EDM and took forever. Not how I would do it, but I was curious. The last .010" I used a finer setting to try and get the finish to come back and still complete some time this week. The high EDM setting pitted the electrode slightly, and that finish transfered to the bowl.

The second EDM bowl was hogged out with a 3/4 ball mill in about 4 min with about .010" stock retained. EDM time was about 1/2 hour +/- and used the same finish setting as the First attempt. There are like 50 setting finer than that, but the finer, the longer it takes.

I did not have good enough flushing for the electrode.

Each attempt has flaws, but all in different places.

 

[madmatt]

Dang!

 

[Bobcat]

I know i don't know what i am talking about but could the bowl be done with a raised center like what you squeeze a lemon or whatever on? I assume this would raise compression though but it looks like it would strenghten it plus would give more surface area for cooling. I know a totatly dumb question...

 

[WolfLMM]

I will cut pistons for anyone, long as it is ok with fingers.

 

[jheyob]

I would get a few graphite electrodes shaped and see if you can get a better result with using 2 or so of them to do the finish burn.

 

[mainer]

? for you with the edm... is the edm going to affect the properties of the metal enough to worry about??


at work we are doing some prototype blackhawk heli engine shafts and were going to edm the splines on the ID of the shaft but they wouldnt approve it because it affects the properties of the material. it looks nice and smooth but it is burning the metal out....

just curious your input on this

 

[WolfLMM]

It does affect the properties, but only a few microns thick.


Older edms are worse about this, than the new edms available today.

 

[JoshH]

The ECM sure looks nice.

 

[Fingers]

I know i don't know what i am talking about but could the bowl be done with a raised center like what you squeeze a lemon or whatever on? I assume this would raise compression though but it looks like it would strenghten it plus would give more surface area for cooling. I know a totatly dumb question...

Putting a "tip" in the middle?

That adds nothing significant to the strength. The middle of this bowl is ~1/4" from the injector. That is half as far as the stock bowls.

I have seen it on a lot of other pistons though.

 

[Fingers]

? for you with the edm... is the edm going to affect the properties of the metal enough to worry about??


at work we are doing some prototype blackhawk heli engine shafts and were going to edm the splines on the ID of the shaft but they wouldnt approve it because it affects the properties of the material. it looks nice and smooth but it is burning the metal out....

just curious your input on this

The impact of the reflash layer depends on the material. In some materials, like that shaft. The reflash can have micro-cracks which could be the starting point for a failure.

ID spines in a blind hole on a one off piece are a pain in the butt without EDM.

 

[Trippin]

Great job Fingers and WolfLLY!

I just found and read this thread. After our last conversation, I'm glad to see Surfcam was able to generate some paths for you. I had no idea you had posted the geometry or I would have genrated some code for you as well.

Looks like the post could use a little tweaking to get rid of the faceting in the finish product or perhaps play around with setting #85 in your Haas control if it is a pre 2000 version OS.

Looks like you're about done, let me know if you want me to generate some different code.

Guy

 

[Benito]

Finger bowls? Scorpion bowls??