# 3/16-40?



## shred (Sep 5, 2007)

Poking through some of the plans in Elmers Engines, I notice he uses 3/16-40 threads on packnuts and such.  Is there a reason to use that instead of a 10-32 thread?  A little searching seems to turns up that 3/16-40 is a model pipe thread, but usually not tapered.. though it can be, sometimes.  ???


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## rake60 (Sep 5, 2007)

Personally I use 10-32 threads for the packing nuts.
The threaded length of most of the packing nuts is 3/16" so you get
5.9 threads with the 32 TPI as opposed to 7.5 threads with a 40 TPI.
All it's doing is holding packing in place.  I can't see a benefit in a 
special tap and die for that.

Rick


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## Bogstandard (Sep 5, 2007)

I think you will find that for packing glands a finer thread is used to allow a finer adjustment of the pressure of the gland packing. With a coarser thread you might find it more difficult to strike a balance between just sealed with hardly any friction and not sealed and leaking steam.
In fact sometimes a knurl is put on the adjusting nut so that it can be set by hand rather than a spanner, just to reach the fine tuned stage.
Gland packings on small commercial engines in Europe nowadays are going over to an o-ring seal, these seal ok, but the breakout friction on starting is a lot higher, so the engine surges to a higher speed before it can be backed off to an acceptable tickover.
But in my opinion nothing beats a finely balanced old fashioned stuffing gland for a low friction, no leakage seal.

John


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## Tin Falcon (Sep 6, 2007)

Shred:
    EE plans tend to use odd sized hardware. I am guessing it was more common when the text was written. Some of the later chapters use the 10-32 instead for pack nuts.. One of the reasons to use odd sizes if you are trying to keep fasteners to scale for an authentic look. In practice though one can go up or down a size depending on where in the  model it is.  
I built a see through copy of my PM research verticle oscillator. It uses # 5 fasteners. I substituted #4s . Also that design does not use a pack nut . So a pack nut is not absolutely necessary it just allows for adjustment for wear in the con rod. and gives a little more authentic engine. 
    PM research
http://www.pmresearchinc.com/store/customer/home.php?cat=66
 or Micromark
http://www.micromark.com/

should carry the model thread size of taps and dies if you want to go that route. 
BTW I am in the beginning stages of building a pair  an EE# 47 mill engine with my son I will likely use the 10 -32 for pack nuts. 
Tin


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## shred (Sep 6, 2007)

Yeah, I've been noticing Elmer's like for #3 and #5 size threads-- they go nicely onto the ends of stock imperial-size rods (so it's actually a little curious they're not very popular today).  Anyway, since I prefer to use fasteners I can easily come by without waiting by the mailbox, I've been switching the #5's to #4 and #6 sizes as I see fit-- local stores have a good selection in those sizes.

Maybe someday I'll be working towards replicating scale threads, but until then I'll be happy with what I can get at the hardware store and hobby shop.

Somehow I thought pack nuts weren't normally used on oscillators since there isn't really a pressurized joint to worry about except the main face-- is that correct or did just get lucky on the few I've built?


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## rake60 (Sep 6, 2007)

Packing nuts on oscillators are just for show.

Here's a little tip for you on the 5's
A 5-40 thread is the most common thread used for a scope mount on a 
hunting rifle.  If you have a large gun shop near you they will have the 
5-40 taps and dies in their gunsmith shop.  Talk to them nice and they 
will sell you a set.  

Rick


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## Bogstandard (Sep 7, 2007)

If the oscillator is double acting (power stroke both up and down) it does require a packing joint, or an extended close fitting bearing support for the piston rod. Maybe not too critical in a display model, but when they are built for genuine work powering say a model boat, they are essential to reduce steam leakage and give longevity to the engine, because they serve a dual purpose, stop steam escaping and provide a bearing surface for the side loads imposed by oscillator engines.
Here are a couple of mine that I make for model boat enthusiasts, and as you can see it is fitted with an old fashioned design of packing gland, but very effective. I am just designing one now to be used with both sidewheeler and sternwheeler paddlers.







The vertical one is for standard screw driven models, the horizontal one is for sidewheeler paddle boats.

Here is one of my engines installed in a 50"+ model boat.






These engines will last a lifetime of sailing if correctly lubricated and serviced.

John


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## rake60 (Sep 7, 2007)

I stand corrected on that issue!
I have never built a double acting oscillator myself.

Keep me honest here John.
Bad information is worse than no information at all! 

Rick


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## Bogstandard (Sep 7, 2007)

I wasn't trying to put you down Rick, sorry about that.
It seems that the most popular American small engines are single acting 'wobblers', or oscillators as we call them, and don't call for packing glands, and people make them for fun. It is only the last few months that I have been building engines for fun and entertainment, usually I was (and still am) building for my own use in model boats or from commissions where I am asked to build a specific type, so I always build double acting with stuffing glands so I am more aware than most about what is required.
With regards to what I shall now call my 'fun' engines, I hope to be able to fit one in each month, just for light relief, and build them between the other general purpose machining, which pays for the extras I get for my workshop through either barter or donations. I don't sell any of my engines, I swap them for cash.
I don't know whether to do the Mine engine or the Grasshopper, any suggestions.

John


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## rake60 (Sep 7, 2007)

Put down???  Not at all!
I started this forum in the hopes of drawing people such as
yourself in to learn from.   It WORKED!   :wink: 

I've built both the Grasshopper and the Mine Engine.
My vote would be for you doing the Mine Engine.  
It's a great slow runner, and I know you would be able to make it 
something quite interesting.  

Rick


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## shred (Sep 7, 2007)

I hadn't considered the double-acting wobblers needing pack nuts.  Thanks.  

Also, seeing those reminded me of something.. were full-size wobblers were ever used generally as engines?  I've got one book from around the turn of the century that dismisses them as 'novelties that can be bought in corner shops and not real engines', yet another book from more recently that says "yet there was a day when huge multi cylindered oscillating engines powered steamers"


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## Bogstandard (Sep 7, 2007)

Hi Shred,
Full sized 'wobblers' were definitely used, I remember seeing some pictures in one of my reference books of one installed in a ship from the late 1800's, I think the dimensions were about 8ft bore by 14 ft stroke twin cylinder . A bit big to put on display and run from a compressor, I think the wife would complain at having that in the dining room.

Rick,
I will take your advice, the mine engine it is.
I am displaying what engines I have at a full sized steam rally this weekend, so I have made one of Tin's posters and printed a load of flyers, so you just might have a few more hits on the site from us damned Brits. If you are interested I can take some pics of the stationary engines we used to use in the UK, because I know that is your true following.

John


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