The Steamboating Forum

All very fine but in practice, if you try to torque the thin nut down to specifications first, which you must do (how else do you measure the torque?) that thin nut will strip out. The whole purpose of tightening down the nut is to stretch the stud and clamp the joint. Not to keep the nut from backing off.

I would like to see someone get a socket on a thin nut and then lean on it with a torque wrench anyway. The next sound would be bad language and barked knuckles!

The reasoning in that article is wrong. The person who wrote it has not worked on machinery. The jam nut works not because there is stretch in the stud between the two nuts. There is just no way that a thin nut or even a thick nut will stretch the stud in such a short distance. It works because of the distortion of the threads in the thin nut. You can feel it in the wrench as you snug it down. Two thick nuts wouldn't work nearly as well.

There were about a zillion flat head Ford V8 engines built between 1932 thru 1948 and every last one of them had the jam nut on top. And, in that design case, they took the concept to its logical conclusion and stamped the thin nut out of sheet metal.

The use of solid jam nuts died out as soon as proper designs came along. The stresses on small steam engines are so low that you can get away with a lot. When the stresses began to climb with the advent of I.C. engines, the use of short studs that could not stretch went away. With a long enough stud so that it is stretched to a significant fraction of its yield limit, the need for locking devices of any sort went away. You can take a modern car engine to bits and not find a single locking device. And at over 100 h.p. per liter (litre) of swept volume for some of them they are under a lot of stress!

We do it for looks and because some of the studs in our old designs are so short that the difference between taking the slack out and too much torque (ping!) is so narrow. In many modern designs the torque is not given as such but specified by instructing that the slack be taken up and then the nut turned an additional angular amount, sometimes given in a certain number of flats on the nut. This is true of the small engine in my sailboat (Japanese). The idea is to stretch the stud a certain amount.

I think that you should do what pleases your eye and not worry too much about it. And when we meet at steam gatherings we will have something to squabble over. If it works loose you will have something to do to impress the bystanders. I find that fiddling with my oil can works well for that. Once in a while I put a drop of oil in a center hole in the end of a shift just to see if the gawkers are watching and know anything. They never are and don't. Ah, well.

Quote: "have to have a closer look at the bolts the next time"

Mike, yeah just about all threads are rolled now, even threaded rod, acme screws, ballscrews etc. For the latter it is two horizontal circular dies, and the threaded rod rotates between them and the lead of the thread advances it through the machine. Any time I'm running a die over a piece of stock, I think about how easily and perfect those machines do it.

-Ron

I don't know if this was necessary but like a criminal in a Dirty Harry movie "I gotsta know". so I turned a plug to fit the standard with a small hole in the center and set it up with a plumb bob. Now the plans call for the holes in the standard to be drilled 1/2 ". The bolt/stud size to fasten it is 3/8, I'm assuming to allow a bit of movement to align it. My holes were drilled 3/8" and reamed to .377 to allow a .375 spotfacing pilot to slip in the hole with a bit of clearance. When bolted to the base the standard only moves a few thousandths in ant direction. when checked with the plumb bob I am off center about .020. I even retested with the standard rotated front to back . I do not think this .020 is of any concern but what do I know. does anyone see that this will be an issue.

Frank

The offset of 0.020 is not a problem, it could be 10x that amount without problems, as long as the conn rod had clearance over the entire rotation 360 degrees. However having the crosshead (and cylinder) bores set at exactly 90 degrees to the crank centerline is the important requirement. This is real important with standard journal bearings that do not have self aligning features.

If you are using spherical bearings on both ends of the conn rod, then the 90 degrees is also not critical. Not many people do that, however we are building a big wood framed walking beam engine, and spherical bearings is the only way I know of to get OK bearings with the frame constantly changing dimensions.

As Fred states, it's a non-issue in that axis. It's a large issue in the axis aligning with center line of the crankshaft, which would cause binding of the crossheads. I meant to suggest this and forgot, but it is better to locate those standards after the crankshaft is built. Not a deal breaker of course, but it makes it easier to build the crankshaft and locate the big ends on the throws. Allow things to float on square and then secure. On assembly of mine, I tried different orientations and used the most free running of cylinder placements. Then marked the standards and base with centerpunch marks for reassembly after paint.

-Ron

I haven't been to active on the M the last week or so, I've been rather busy with work. I did pick up some castings for steam sirens though. I'll have to get some bar stock ordered up and get a few sirens built so they are ready to go. Whoop WHHooopp Whooooooop!

I decided to work on the M a bit today. I thought I could do some simple ( ha ha ) lathe work. I am working on the bottom heads.



And this is where I am at this point. Chucked up on what will be the 1 1/2 x 18 thread.
My limited machinist skills is telling me to go ahead and turn the 3 1/8 dia and drill and bore the 33/64 .515 all the way through then flip the head and chuck up on the 3 1/8 dia, and ,check the 33/64 hole for runout, and if its out more than .001 or 002, chuck it up in a 4 jaw and zero the bore. Any one have a thought or two?


Thanks in advance Frank

Difficult to be sure Frank, as from here I cant 'feel' it. I'm not keen on gripping such a small stub for initial 'de-skinning'. As always it's about getting that first true surface to work from, and a good tight grip is essential for that. I think I might turn it around (perhaps in the 4-jaw, for centring) and start on the stub (not necessarily to size), to get a better grip. Gripping rough cast surfaces can be 'ify'.

Mike Rometer wrote:Difficult to be sure Frank, as from here I cant 'feel' it. I'm not keen on gripping such a small stub for initial 'de-skinning'. As always it's about getting that first true surface to work from, and a good tight grip is essential for that. I think I might turn it around (perhaps in the 4-jaw, for centring) and start on the stub (not necessarily to size), to get a better grip. Gripping rough cast surfaces can be 'ify'.

I did turn it around and rough in the small area(to be threaded) as it had taper in it from the foundry pattern. I did remove all the skin with a brazed in tool then switched to my carbide insert tool.

It went pretty well, two things I could have done differently 1- the dia that fits inside the crosshead liner it fits snug now, but I wasn't thinking, it hasn't been honed yet, so it may be a thousandth or so loose . (I'm not real concerned) 2- And I'm not real concerned about this either, the plans call for the packing gland nut to be tapped, I don't have nor am I buying a 1 1/2 x 18 taper tap and bottoming tap to thread the nut. I threaded the bottom head using the dimensions in the machinist handbook as to Maj. and Min dimensions and will do the same for the nut until it fits. They may not interchange but then again why would they have to.



A lot of turning to get from raw to finished!!!

I agree about the thread. There's nothing wrong with a one (two) off in this type of case, there are plenty of precedents, and it's YOUR engine. Keep it up, good work.