H11 handling / Machining

I have a job coming up (I think) where I'll be making some #10-32 mini rod bolts out of h11.

Any tips?? What's the deal with coolant and this stuff...I've read you have to be careful touching the bolts. But is that during manufacturing or only after heat treat?

My plan is to machine, then have the threads rolled. Already spoke to thread rollers. Then heat treat to 260ksi, and cadmium plate.
I've read it's pretty stable during heat treat, so I don't think they'll move too much (esp with this part's geometry. It's .988 OAL, .790 under the head)

The turning is easy, I have some pilot drilling and a 5/32" hex to broach in the rear. Was going to use polygon solutions rotary broach and their coated bits. Hex is only .100 deep so I was told by polygon to make sure I tell them that and they'll stub the bit for me.

I was planning roughly 100 bolts per drill / broach bit but I really have no idea. I'd rather figure low and be pleasantly surprised

Thanks guys!

Machine is a Mori SL-1a

Nothing..really? I figured some of you guys had experience with this stuff! Don't let me down :p

I have machined literally many Tons of H13 TOOL STEEL. H11 seems to be commonly used for hot work forging dies. I don't know why you would use this for a relatively low temp connecting rod As for as touching them causing problems,, this sounds like someone blowing smoke.. Edwin Dirnbeck

This is quoted from an ARP fastener publication:

Cyclic fatigue failure originated by hydrogen embrittlement

L-19, H-11, 300M, Aeromet 100 and other similar high strength “quench and temper” steel alloys are particularly susceptible to “hydrogen embrittlement.” Extreme care must be exercised when handling these materials, and kept well oiled at all times to prevent hydrogen gas and moisture from accumulating and attacking the metal. This type of failure is easily mistaken with Stress Corrosion.


Cyclic fatigue cracks propagated from a rust pit (stress corrosion)

Again, L-19, H-11, 300M and Aeromet 100, are particularly susceptible to stress corrosion, while 8740 and ARP2000 alloys are less susceptible to stress corrosion. These materials must be kept well oiled at all times and never exposed to moisture including sweat. Inconel 718, ARP 3.5 and Custom age 625+ are immune to both hydrogen embrittlement and stress corrosion.

Of course, this is talking about connecting rod fasteners.

--David

I know I've read all that.

I researched the stuff for the last two weeks but I haven't found much on machining it. Of course there's the little snippets here and there .... but no real world machine experience!

That's why I asked on here.

And I was also worried about handling the bolts, introducing moisture and then finding out that they failed due to stress cracking later on. Not stress cracking due to vibration or fatigue, but due to material handling.

Basically I need the 260 Ksi after heat treat and am trying to avoid blowing through broach bits and drill bits by going with MP 35 or ( what this company originally requested) MP159.

H11 can get me the 260, and still be relatively easy to machine.

I have done enough research and figured out the way to make the MP159 rod bolts but they're going to be crazy expensive.
I was trying to provide this company with a cost effective solution

Fry Steel caries MP159 in smaller diameters, for instance .270 and .3325 centerless ground. You can find out what they charge for it.

Mind giving us a little more info on what you're trying to do? Sometimes the engineers do need a little talking to about what's pragmatic to design and build. Either more fasteners or upsizing a little sometimes is the smart way to go.

If these are fasteners for miniature connecting rods remember that clamp loads can be reduced by plastic deformation of the rod material, so excessively strong fasteners are sometimes wasted. The thread rolling and any "waist" in the fasteners will have to be done just right too. Extra pieces should be made for destructive testing and to find the yield point for maximum clamping values.

(Pragmatic Machinist would be a nice sub-group for PM).

A stupid question - is there a reason not to farm this out to ARP or SPS? They're the guys with the expertise to do this for minimal (sorta) cost and maximum chances of success (definitely).

That's who I got the quote from (Fry). 2.76 or so per bolt material cost.
My local place tried to rape me at $6/ea per bolt (2 of those .3225 rods were $1500....I was like wtf!!)

I'm a mechanical engineer. This place that was asking me to quote has no clue what they need. The print was horrendous, and it specified AMS 5842 MP159....that was telling me that someone with zero design experience simply picked a steel they *thought* they needed for the application.


After a little brain picking with the "engineer" I found out he simply was going by UTS. And wanted 260 Ksi.

GS Aerospace produced the bolts for them in the past..and honestly the threads looked like sh***ttttt. But I do not think that's the reason they stopped dealing with them.

After speaking with Kyle at Superior Thread Rolling he said that this is crazy to use MP159 in this low heat application. He told me that the only place he sees these fasteners used is at the base of rocket motors.

I already suggested stepping up to a larger diameter bolt for more clamping force, but they stated there wasn't room (enough meat) on the connecting rod.

They did send me a rod...and piston. The piston does look rather large for the size of the rod, and that is certainly what is causing the failure of these tiny rod bolts at high RPM. Obviously there is little force on the bolts when the piston is traveling down, but all the mass isn't helping the bolt situation in the other direction.

I do not think quantity is high enough for ARP or SPS to produce these. I already spoke to SPS about a possible off-the-shelf solution..they do not stock anything.

So...back to the H11. I've gotten enough information between heat treating, thread rolling, machining etc but I still wanted some real world hands on experience from you guys

Who's actually machined it lol

Evan, glad to hear someone with some sense is handling this. I've not worked with H11, so can't help you there, but do have a decent collection of aero fasteners, mostly in A286. I would still contact ARP for a quote. They will do small lots, not sure of the time frame though. Probably more responsive than SPS. They would be helpful for material selection too, there still may be a better choice than H11 for the bolts.

My concern is that high-end bolt manufacture isn't trivial, especially when looking for best UTS. It may require specific ordering of heat treating and cold working, including thread rolling and shank strain hardening after "regular" H/T.

Seem odd to have a large piston, small connecting rod situation, especially since going larger on the rod big end doesn't introduce forces like those on the reciprocating end. Is the crankcase too small, so they can't increase the rod clamp section? And if they're using Al rods, then my comment on failure of the base material in compression is in play. They'll need decent bearing surfaces and load path the the head (and nut?).

Then there's getting consistent clamping loads, which can't be just a torque value. Are they measuring stretch?

And this might be a good application for a 10-36 thread, rather than 10-32. Since these are specials, not a big deal to increase the pitch one step and gain a little more margin on cross section. If they're using in-rod female threads, 10-36 taps are not hard to get. Getting custom nuts is more of a pain, but given what you've mentioned so far I don't know if they're using them.

If the rods are aluminum, they'll want to control the minor diameter carefully and go for a closer fit to the screw.

Unified Screw Threads, Standard Series

I'm limited on how much design change I can force them to implement. I hinted at a new rod design and they kind of brushed it off.

I really don't care what they do with the bolts after they purchase them from me...I was just trying to be helpful and provide them with different options for their current "problem".

The engineer I spoke to at the purchasing company did mention ARP by name...so I'm making an assumption here, but I'd assume they already tried contacting ARP to produce these rod bolts. If not, I have no clue why.

The rods are not aluminum. I'm not sure of the alloy, however.

The issue is this...they are using a standard rod and a grade 8 bolt in their regular motors, and have a race motor based on this same design. The race motor was self destructing at high RPM using the grade 8, but stayed together revving higher using the supposed "MP159" bolt from GS Aerospace.

I sent the sample bolts out that the company provide. I'm having the alloy tested by an Engineer friend who has access to a fancy metal analyzing gun. I should know soon if they're really MP159.

I'm skeptical because on a sheet of hand-written notes that was provided to me, it said the threads were rolled after heat treat.

When I spoke to Kyle at Superior, he said it's possible, but it would blow through dies like a mofo...and that cost would just get relayed to the customer.

So something isn't adding up here....

(Although that could be the reason the threads looked so bad...let me post a pic of them under the scope. One min)

Higher-end bolts are thread rolled after heat treat, and yes, it does damage the dies sooner so the cost goes up. If the manufacturer wasn't replacing or refurbing the dies often enough the tread quality would suffer. Small issues at the OD would be manageable, but roughness at the root (the peaks of the dies) would be bad.

Any additional pictures you can post? Are these RC racing engines, or something else?

Milland said:

Higher-end bolts are thread rolled after heat treat, and yes, it does damage the dies sooner so the cost goes up. If the manufacturer wasn't replacing or refurbing the dies often enough the tread quality would suffer. Small issues at the OD would be manageable, but roughness at the root (the peaks of the dies) would be bad.

Any additional pictures you can post? Are these RC racing engines, or something else?

Click to expand...

yupp i got that info from Kyle. He was the one who said technically its possible, but above Rc 50 the dies will last around 300 pcs, vs 10k pcs if it was softer and rolled pre HT.

It's a mini 2 stroke motor. much much bigger than RC. again this is all due to rod design...not my fault, I'm just trying to come up with a solution for them lol

Top fuel uses L19 (ARP's name for H11) all the time in rod bolts, head studs etc.

I was simply looking for the most cost effective solution to this company's problem. I am still going to quote the MP159 but I was just trying to provide options. The MP159 bolts will likely be around $50 each...and that's crazy for a tiny 10-32 bolt.

EDM sinking the Hex (to avoid roatary broaching) was $16 each in the low quantity, rolling was around $4.56 each, Material $2.76, Heat treat will be a lot charge...and that's before I even touch it.

I will give ARP a call and shoot them the print and see what they say for producing it complete.

ohh and I have big hands so that piston doesn't look that big...but it is. 2.525" dia

I don't know too much connecting rod bolts, but if you just need 260 ksi, why not 4340 (or 300M if you want some margin for softening at temperature)? Connecting rod temperatures (on a 4-stroke at least) aren't that high.

Evan LaCava said:

I will give ARP a call and shoot them the print and see what they say for producing it complete.

Click to expand...

Sounds good, please let us know what they quote. If it's more than you'd expect I would just go with the "it'll work" aspect over what trying to piece it together from other vendors will get you. And a broken engine is a lot more expensive than a "costly" bolt.

Top fuel replaces hardware very frequently, so they lower the risk of catastrophic failure due to stress or atmospheric corrosion. I'll bet the customers for these engines don't want to do that, so you'll be better off with a premium material that can be reused without worry about handling. So I hope a better choice than H11/L19 can be found. Ditto the 300M, still a risk unless handled right.

Has the company told you how they measure tension on the bolts? They can't measure stretch, and the next best way, ultrasonic, isn't going to be used in the field. If it's just torque then I'll bet there's so much load scatter that failure isn't a "weak bolt" issue.