Building my own SOHC Rocker Arms

[WConley]

^^^^  Naw, I think you contributed quite a bit Mario.  The discussion resulted in some good improvements to the design.

I'm really looking forward to seeing a real one of these as well!

[Cyclone Joe]

Hello Jay,

Sorry for the delay in getting you a material specification.  Here is a rundown of two easy to purchase & easier to machine materials:

Alloy: 4340
Specification: MIL-S-5000 (also AMS-S-5000) CONDITION F
Min Yield Strength: 130 ksi
Min Ultimate Strength: 150 ksi (equivalent hardness 34 Rockwell C scale)

Alloy: 4130
Specification: AMS-6758 CONDITION F
Min Yield Strength: 100 ksi
Min Ultimate Strength: 125 ksi (equivalent hardness 25 Rockwell C scale)

The machinists I know prefer 4340 over 4130 given the choice because that little bit of extra carbon helps.  How?  The extra carbon causes the material chip, whereas the 4130 wold want to smear more or push.  Also at these hardness levels you shouldn't have too great of difficulty in machining either alloy.

Now, I looked up what the material properties of 4130 in a  hot rolled condition (condition B) would be no greater than 229 HB hardness.  Converted, the material would have a maximum ultimate tensile strength no greater than 111 ksi.  Either option above would be a strength improvement and a more controlled material than getting it in the condition B as the only requirement is that the condition B cannot be stronger than 111 ksi, but says nothing about how weak it could be. 

Maybe the vendor has an internal specification of a hardness range for accepting the material?  Were you able to find out what the hardness was of the material?

Thanks
Joe

[jayb]

Joe, thanks for the information.  Sounds like 4340 is the way to go on this.  I will get in contact with the people you suggested and try to get some if I can't find it locally.  Also, the guy I talked to at T&D didn't know if there was a minimum hardness spec on the 4130 that they use in their SOHC rockers; he just said he orders the steel from a certain source and has had good luck with it.

[Cyclone Joe]

Jay,

If interested, and if you have a T&D rocker, I can have the hardness tested in a low stress location.  If you send it out this week, I'll test it myself on the 9th.  If you cant tell, I'm interested! 

Joe

[jayb]

OK Joe, I'll send one out to you on Monday.  Send me an email with your address; I'm not sure if I still have it.  I'm kind of curious about this myself...

[Barry_R]

I have some wounded T&D cammer rockers if you want to do a destructive inspection.

[jayb]

Previously I'd sent off a T&D SOHC rocker to Joe Burnett for hardness testing.  Joe tested it and returned it to me; it measured 25 on the Rockwell C scale, which Joe says translates to 122K psi for tensile strength.  So it sounds like if I go with 4340 steel for the rocker material, it should be at least as strong as the material used in the T&D rockers.

Mario has also been working on creating the G-code from the drawing, and has sent me the first two operations for the rocker arm.  I set this up in my machine today, and after some screwing around with the code and making my machine work with it, I finally got through the process.  Here's a couple of photos of the rocker arm as it is right now:





I'm not totally happy with the machining on this, for a couple of reasons.  One is that I think the aggressive nature of the toolpaths in Mario's code are moving the zeros around on my machine.  I'm sure they would work fine on a new larger CNC machine, but my machine is old and is a smaller machine, so I generally have to take it easy with the toolpaths to avoid having the table shake and causing accuracy problems.  Also the machining done by the ball mill left stripes on the top surface of one side of the part; again probably a machine issue.  I think I'm going to try re-running another test rocker, but slowing the feeds way down to try to avoid this issue.

In any case, though, progress is being made, and I'm looking forward to continuing the machining on the test rocker arm.  This week I expect to finish machining the rocker shafts, and get them sent out for heat treating.  Then, all that is left is the centerless grinding, and the shafts will be finished.  I still have to work on getting the remaining parts designed and machined (offset bushings for the rocker shafts and spacers for the rocker arms), but those shouldn't take too long.  I'm still hoping to be able to deliver a steel test rocker to Bill sometime in January for the spintron work.

[Mario428]

I had way more trouble generating that code than I ever thought I would, have not done a lot of CAM work like this. The parts we do every day are a lot simpler than this.
But if the toolpaths are too aggressive in alum they will never cut steel without killing tools constantly.
Will have to rethink the process and add more tools with lighter cuts.

[WConley]

To finish 3-D profiled areas out, you can "pencil trace" all of the radii with the proper ball end mill.  This cleans up the corners beautifully.

Yes, 4340 will require some lights cuts to maintain accuracy.  At the very least do a couple of light finishing passes to sneak up on the final dimension.  When I do my final pass, I reduce the stepover to just a few percent of the tool diameter if I'm looking for a good surface finish.  It takes time, but for a part this small it won't be too bad.

[jayb]

I had way more trouble generating that code than I ever thought I would, have not done a lot of CAM work like this. The parts we do every day are a lot simpler than this.
But if the toolpaths are too aggressive in alum they will never cut steel without killing tools constantly.
Will have to rethink the process and add more tools with lighter cuts.

One thing I like about your approach, as compared to the original way I was going to do this, is hanging the part off the end of the bar stock to get most of the machining done.  That makes a lot more sense than my original approach, which relied on the fixture to get the back side of the part machined.  I'm tempted to take another stab at manually programming the part, using this approach.  I know this is a lot of work for you Mario, and I didn't mean to rope you into a big project.  If you continue to have issues getting the code to work let me know, and I'll go back to the manual approach.  It is indeed a complex project...

[Cyclone Joe]

Jay,
I'm not sure who you're getting end-mills from, but the end mills and cutters from Robbjack have produced the best results in my experience.  When I was involved working on a project that needed to have zero cutting mistakes, or any other issues really, we went with Robbjack.  They were helpful in setting proper feeds and speeds with their cutters, plus they have helpful videos.  This may help with your rockers once you start making the steel ones. 

Here is their homepage and a few videos.  Interesting tidbit, if your feeds and speeds are set right with hard steel, you can get away without using coolant!  I had a tool and die maker make a fool out of me.

http://www.robbjack.com/html/tech.html
http://www.youtube.com/watch?v=JATjRSzXgjw&feature=related
http://www.youtube.com/watch?v=FimDQPwCqn0&feature=related

And no, I dont get a kick back 

Joe

[Mario428]

http://www.youtube.com/watch?v=JATjRSzXgjw&feature=related
http://www.youtube.com/watch?v=FimDQPwCqn0&feature=related

Very cool videos and not intending to criticize but it takes a serious machine to do that, especially the one in steel.
I have a lightly used 8 year old machine that would not do that, even with the Fanuc hardware it is just not stiff enough. Unfortunately Jay's machine is a lot less stiff. Never thought the speeds and feeds I used would be a problem.

Got your email on my home computer Jay and will reply this evening.

[Cyclone Joe]

Hi Mario, no criticism taken.  Where I used to work, we used to do this type of tool path machining using well-worn HAAS and mid 1980's Okuma Howa's but for roughing passes only.  Then everything would slow down to a crawl, change cutters and flood with coolant for the final passes.  The last video was more 'for show' than anything since I believe it would be tough to martian any type of accuracy with that much machine movement unless it was a Hermle or a Mori.

Is the machining a result of the tool set up, or tool path selection?

And out of curiosity, what kind of machine does Jay have anyways?

Thanks again
Joe

[jayb]

Joe, I have a Milltronics Partner 1 CNC machine, circa 1991.  5 HP, 26 X 16 X 20 travels, etc.  Bought it used, of course.  I like Milltronics because the company is local to the Minneapolis area, so if I need parts or service it is only a phone call away.

[Mario428]

Hi Mario, no criticism taken.  Where I used to work, we used to do this type of tool path machining using well-worn HAAS and mid 1980's Okuma Howa's but for roughing passes only.  Then everything would slow down to a crawl, change cutters and flood with coolant for the final passes.  The last video was more 'for show' than anything since I believe it would be tough to martian any type of accuracy with that much machine movement unless it was a Hermle or a Mori.

Is the machining a result of the tool set up, or tool path selection?

And out of curiosity, what kind of machine does Jay have anyways?

Thanks again
Joe

Everything comes into play when trying to cut parts. I handcoded all my programs for many years. Did a couple of parts where I had 60+ hours sitting at a computer with a CAD program and a text editor going (2 machines in the DOS days LOL) and I do like that control over the toolpaths. Not enough experience with the CAM software on parts like this so some of the fault lays with the setup in the CAM setup. Some of the fault lies with the CAM software and the decisions it is programmed to make, it assumes a stiff good working machine.
Machine does make a difference, hi feed rates need good servo's with the power not to overshoot and keep the cutter engaged the way it should be

Just had a thought, the code would work fine on my machine I should try it and see how it works.