Brain picking: Need some ideas/direction

Could try brazing followed by oil or air quench then tempering? Depending on what kind of steel the dowel is, of course. You'll want oil or air hardening to reduce warpage. You may need to grind it afterwards to get a good finish on it though, and that's extra work...on the plus side they don't need to be ground to begin with.

Tim

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Koz wrote: ...

Maybe try longer pins, eg 4" long pins in 2.5" deep hole.

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Are brazing temps too high? Could try grooved or necked pins wrapped with brazing wire or sheet, pressed in, then locally heated.

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Perhaps modify pins with "hose barb" pattern or a light knurl, and swage rod end after pressing pin in. I think swaging without a pattern on the pins won't help.

Have you considered using knurled/splined dowel pins? See

GmcD

Pardon me; I don't mean to insult your intelligence but have you thought about Locktite or similar stuff. You said there wasn't much tension but implied there was some "torque", presumably meaning lateral force. It seems to me if the dowel pin was fully seated and fitted to the hole according to "instructions", it should work. Locktite is recommended to fix wheels on railroad axels - your load may be less.

Did you try some killer locktite? What about a touch of powdered aluminum with a little water in the hole? Seems that would set 'em pretty good.

John

I would use Loctite 609. Follow the instructions. I've been using it for years in highly stressed situations. Both tension and torque. Only one failure in twenty years or so. That was recently and it must be something I did. Maybe it was past it's shelf life. There are many shaft assemblies on fishing boats where parts I made and assembled for transmitting power from big cat engines to and from hydraulic pumps and motors. ERS

In the old days we would use a Jarno tapered dowel with thread on other end. One solid whack would almost blend the hole and dowel and nothing, not even an elephant, could disloge once set. I still have some Jarno tapered drills for making the holes. Try McMaster Carr, they still might carry them.

Wayne

Can't do it. 400 degrees in oil and can't have any contaminants at all.

Koz

I'll look into this. Maybe press fitting with the right knurl pattern will do the trick. However, I seem to remember the costs for the knurled pins got a little steep. At the very least, it'd be an improvement.

As to Other's comments about Locktite, Aluminum powder, brazing, etc...this is a food grade application and can have NO presence of AL, CU, or glue type items such as locktite. Temp is 400 degrees running in an oil bath, followed by a caustic bath at 200 and an acid neutralization of the caustic.

Koz

I don't think you specified exactly how the assemblies are failing - tension or torque?

Out of the box... Friction welding. Perhaps a fixture on the lathe carriage for the dowel and the CRS rod in the chuck. May be difficult to control the strength of the weld, but that may not be much of an issue in your case.

Or... What about some kind of forming tool? You may be able to grind a groove into the dowels (some simple fixturing on the surface grinder would allow you to quickly place a crosswise slot using a cutoff wheel in multiple pieces in a single setup). Then, a simple die to press the CRS into the slot in the dowel. This would require some care during assembly as the orentation of the dowel would be important.

Now that I think about it, dowels with a slight flat ground into them (and a threaded hole in the end, for a dowel puller) may provide enough room to deform the CRS such that the dowel is able to resist the torque loads. These pins are called "flat-vent pull-out" as per McMaster-Carr.

HTH.

Regards,

Robin

Two ideas come to mind.

Stainless steel roll pin in a cross hole.

A cross hole filled with that plastic that GM puts on the U joints instead of E clips. Lasts forever, takes a lot of torch to blow them out on purpose.

(top posted for your convenience) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net

Sticking with your "no foreign metals, glue, etc." foodservice requirement:

Try a slightly different press fit to see if that solves your stress problem?

If the cracks (on the press-fits) are coming at the bottom of the hole, a hole with rounder bottom corners might not crack? (I don't think you described the failure in enough detail for this to be anything but a WAG). Think finishing the bottom of the hole with a ball-end mill to reduce stress concentration, if that's what's happening. Presumably a drill could be ground to do something like that directly.

Grind divots or a tapered flat on the dowel pin (part that will be inside the CRS) and squish the CRS into them/it with a hydraulic press. If using a tapered flat, be sure that the end of it is radiused to reduce stress concentrations. Hemispherical divots might be better for that reason. This assumes that the CRS need not be perfectly round near the end. I'm guessing that the outer part of the pin needs to be round, so the fully-flatted pins that are available off the shelf probably would not work?

I am curious just where the failures occurred when you used a heavy press in. Would it help if you made the hole for a heavy press fit at the bottom of the hole and a lighter press fit toward the top of the hole.

Or how about grinding a very shallow groove about half a inch from the end of the pin. Medium press fit with the groove inside the crs. Then use a knurling tool with smooth knurls to press the crs into the shallow groove.

Dan

Sorry...phone kept ringing and I was trying not to give so much information as to limit responses..sometimes wild guesses can spark inspiration. I also apologize if any of my responses have seemed abrupt but It's been busy here the last couple of days.

The protruding pin has slight torque on it (impossible to calculate as it's caused by spontaneous miss-alignments) and little tension (50 pounds worst case tension) if things are aligned properly. There is also slight flexing. Every once in a while, the torque on the pin might be higher but not so high that would count as high enough to pull things apart on their own. What seems to be happening is related to the number of cycles. Eventually, either the plug weld breaks off or in the case of the press fits, things just eventually work to loosen the hole in the rod so the pin eventually works itself out. Typical life is about 2 years and in that time, they see about 2 million cycles (quick calculation)

Unfortunately, even a very low failure rate can cause downtime on the order of $ 10 grand an hour. It's clearly worth it to go high tech and expensive to do it right but customers don't want to actually pay for what they would be getting. This puts us in the corner of needing a cheap solution about the equivalent of the plug-weld method on costs while trying to get the results of finish ground induction hardened ends.

I believe that the better way to do it would be a heavy press fit with a knurled pin AND mechanical fastening of some kind. I have to see if the costs would work out though. .

Sooo...basically I was hoping that someone might have a novel solution to send it in a different direction. The 1/2" rod does need to be cheap mild steel and the pin needs one hell of a hard surface to reduce wear and galling without becomming brittle at all.

Thanks to all those who answered

Koz

I am sorry for a stupid question, but why can't you just cross drill it and put in a "cross pin" or even a screw that would hold the axial pin in place. That should not fail much. Should not require a lot of equipment beyond a drill press and a grinder. What am I missing?

Not a stupid question at all. Drilling the soft 1/2" rod is easy..it's drilling into the hardend surface of the dowel pin that will cause problems. You aren't missing anything except trying to get the hardened pin drilled and getting alignment right to cross pin things. Again, it might be a good way to go if I can simplify the drilling part down to idiot-proof in the shop.

Thanks,

Koz

Ignoramus12247 wrote:

If you start a hole with a rigid "center drill", and also a punch, alignment is not an issue. I cross drilled much thinner round things using the center drill.

With the hard dowel, you could do this. Use a grinder to grind a cross groove on it. Then drill the 1/2" rod halfway so that the hole would be above the groove. Tap it and use a headless allen screw to go into the groove and hold the pin.

Again, my experience is much less than yours, but, I think, it will hold up to quite a bit of abuse and also is relatively inexpensive to do and does not require a great deal of precision work.

What about using a shoulder screw and then cutting the head off?

If you are willing to foot the cost, material can be hardened with very little distortion, etc. using controlled environment ovens, special vacuum packs, and so on.

In other words, a threaded part could be made (dimensions adjusted for growth/shrinkage) and heat treated afterwards.

Good luck!