5"g Simplex steam loco build (hopefully)

[Builder01]

Hi Bazmak,

Yes, in order to cut left hand threads, traditionally you cut from the head stock to the tail stock. So, the chuck turns in the normal direction, but the tool moves from left to right, away from the chuck. As you say, you have to reverse the direction of the lead screw.

The pins in the nut for the Super, are 3/16" in diameter, 1/8" long. The reach rod fork can be "sprung" such that it will not come off the pins. It does not need to be any fancier than that. I believe I pressed the pins into the nut block, along with a drop of Loctite. The nut should be made of bronze, not brass. Bronze will wear much better.

Attached is a photo of some of the small boring bars I have. They are made from solid HSS tool blank. These take a bit of time to make. The one in the front, with the red layout dye, is the one I cut the internal thread for the nut. The round piece of brass is my "proof" or test nut, to see if I could make the nut. You can just see into the nut that the thread is left handed, you can also see where the two entry points are for the thread.

To cut the thread for the nut, you start with the tool inside the nut and cut on the way out, toward the tail stock. A diual indicator is handy to know where your reference points are. You do not want any distractions while cutting the nut. As you get towards the end, you can only test the screw in the nut after a pass is made on each thread. So, a single pass, involves two cuts, then test fit the screw. By making the screw first, you will get the idea.

I made the screw first. I measured the thread using the three wire method, as obviously, I did not have a test nut! The pitch diameter for the double lead thread, is the same as a single lead. There are thread pitch diameter calculators on the web and will also suggest what diameter wires to use. I used to do it the old fashioned way, but the online calculator is so much easier. If you get to this point, I can post the numbers if you are interested.

As for posting my own thread, I probably will not. Don't have enough time, although I do have a few friends on a mailing list that I occasionally send updates on my locomotive build. If you have questions about your build, I will be happy to post a few photos or comments as time permits.

David

 

[bazmak]

Finished the reversing arm and screw assembly to a slightly
improved finish.Davids quality has made me feel guilty.The assembly
works well will improve the finish when everything else is connected up
A dozen small carbide slot/end mills arrived from China so will
now drop back to finish the cylinders which will then allow pinning the
piston rods etc and lots of pins to make and a few more levers etc

 

[Buchanan]

I am really enjoying this build, it is taking shape fast and looks real good. When making nuts for difficult threads, I have cut the male thread an inch or two longer, or cut a second identical male thread and made a tap out of the extra length. To get the tap hard enough, I just case harden the tap portion and it works really well. To make the tap, turn a slow taper on the end of the thread and flute it with a ball nose end mill. Don't worry too much about small burs in the threads as they snap off when the tap starts cutting and also give a little clearance. I also file a little relief on the tapered portion after fluting. These taps work well in brass or bronze and not to badly in mild steel and cast iron. They are good for a quite a few holes. Buchanan

 

[bazmak]

Thank you for your comments Buchanan,if the thread is 1/4"
then i could use silver steel for the tap,its something i have never done
so it would be an interesting exercise.Priority at the moment is to hopefully get this loco running on air,it would be a major achievement.I have gone as far in 3mths as i did in 3 years on Heilan Lassie.I am not rushing but have more available hours and i have made/bought a lot of tooling i never had before
Heilan Lassie was a 3 cylinder in 3 1/2"g and i made the cylinders and valve
with just the Myford lathe and a vertical slide so i am looking forward to finishing the cylinders etc with mill and DRO. Start tomorrow

 

[bazmak]

All this talk about screw cutting 2 start LH threads has peaked my interest
David (builder 01) you made ,ground down a piece of hss and cut the nut
i admire your skill
After your comment Buchanan i realized you were the builder of THAT CLOCK
which i have followed with awe
It got me thinking about making a tap from silversteel or a cutter for making the nut.In the near future i may try both ways.One thought i had was to turn
down a piece of 1/4" silver steel and single point cut 2 or 3 threads the dia could then be reuced to the half line like a D bit and the various clearances milled
before hardening. 2 threads could then be cut at once with a no of passes ??
Any comments would be welcome. Meanwhile i am going out to the shed
with fingers crossed to finish the cylinders Regards barry

 

[Builder01]

Hi Bazmak,

Thank you for the kind words.

If you are gong to make a tap, why not make it like a regular form of tap. Why would a D bit be better for cutting internal threads? A D bit seems to work well as a straight reamer, but, a tap? Maybe I have misunderstood you.

David

 

[bazmak]

Instead of having to grind an accurate single point tool
then screw cutting a 2 start thread,why not single point a 2 start thread
before grinding as a D bit etc prior to hardening.In theory you would be 2 point cutting and the thread form would be more accurate the a hand ground single
point tool.I used the same principle to make 3 tooth gear hob which i used to cut gears well

 

[bazmak]

A good hard days work.Machined all the ports with a solid carbide 4mm slot cutter.Driiled and tapped and connected up the exhaust passage. The steam passages are called for as 9/64 x 1/2" by chain drilling and needle file
Not easy i set up at the correct angle and drilled 4 holes 3mm dia.Drill tried to run and rather than risk breaking it i decided to mill.My new 4mm cutters
had 4mm shanks and were long enough to go full depth of 25mm.However took my time and great care and finished one 3 more to go.By positioning the
slot just right produced a nice curved inlet to the cylinder and with clearance to
be machined on the end covers it should work well.Steam passages are better
slightly oversize for inlet and exhaust or so i have been led to believe

 

[Builder01]

Hi Bazmak,

For your "two point" cutter, you won't know until you try. It will probably work. Although. you will be removing twice as much material at a time versus a singe point cutter. Hopefully, in bronze, it won't be a problem.

Progress on the steam ports and cylinder face looks great!

David

 

[Buchanan]

Here are a few photos of home made taps. The smaller, around 1/4 inch and down I use silver steel. Any thing larger I use mild steel and case harden.
Fluting is not very critical at all. When using silver steel, temper a little more than you would for a cutter. Almost starting to go light purple, rather than pale straw, otherwise it will be rather brittle. You can get a bit of an idea of the color in the photos. With case hardening (torch and case hardening powder. 4 or 5 minuets) there is no tempering to worry about and you have a tough core. That split tap was made adjustable with a brass wedge
because it came out undersized. Possible with case hardening. The only problem with case hardening is that if you want to sharpen the tap you have to re case harden. With the lead screw on the lathe, my Dad left the tap attached to the end of the lead screw so that when the nut wears out again he knows where the tap is. The new nut is a cylinder that is soft soldered into the old nut body for easy replacement. you can see that it is longer than the original. I am enjoying this build, keep it up.

 

[bazmak]

I have never seen a slit tap before,i assumed it worked ok
As for hardening i had in mind to just harden and not temper
but i suppose for cutting brass/bronze the temper would be good
for small light cutters i did nit think brittle would be a disadvantage ?
Tell me how you find time to show an interest in anything else except
that marvelous timepiece.I have always assumed that really small threads
for clocks are not cut but formed.Do you use small commercial BA or
is there other threads ?

 

[Buchanan]

The split tap worked fine. Knock in the wedge till it cut the thread big enough.
Small taps just break to easily when glass hard. I have far to many interest for my own good and there is never enough time. I use metric threads for the clock, a set of swiss taps ad dies from 1.2 mm down to 0.3. i use down to 0.5 mm quite often. Smaller than that, you have to hold your breath for too long when you use them to get any enjoyment out of the job! http://cdn.homemodelenginemachinist.com/images/smilies/confused.gif

Cutting small threads is a mix of cutting and deforming.
The taps have no flutes, just a flat on each side, there is some swaf. Hole size is fairly important.
The tap in the photo was made by a friend and it has 3 flats and is basically triangular, it cuts very well.

 

[Builder01]

That tap makes the 1/4"-20 double lead thread look giant! Nice work!

David

 

[bazmak]

What tap,i can only see the match.First few days of my apprentice ship
a common tale was that the USA had made a S/S tube the dia of a human
hair(about 5 thou) and sent it over as a sample of their precision.As the story went the Brits sent it back tapped and fitted with a screw

 

[Builder01]

Good one Bazmak!

David

 

[bazmak]

Just had a pleasant few hrs in the shed and finished the cylinders steam passages etc.I am now ready to start building every thing back up so please DAVID keep an eye on me and let me know when i am doing something incorrectly,as i am now in uncharted territory.Never got to this stage in the past
Although with Heilan Lassie i did part build the boiler and finished the smokebox etc a lot was cosmetic for my own satifaction.I never got far with coupling/conn rods,linkages etc and have no idea of timing etc.At the same time im getting familiar with what order to assemble etc and what can be left as sub assemblies.Knowing what order to put things back saves a lot of wasted effort.My plan of attack is to fit just the driving wheels











for min resistance while
i make and fit all the linkages etc to the front side only.Reversing gear etc
Any parts yet to be made i make and fit as i go,so i can find and rectify and problem areas

 

[Builder01]

Lookin' good Bazmak! I will follow closely, I'm sure you will be fine. Once you have the motion plate and guide bars attached to the the rear cylinde cover, it is possible to remove the cylinder and motion plate as one assembly. You only have to remove the big pin in the crosshead, the connection to the lifting arm and radius rod and the connection to the return crank at the bottom of the expansion link. Then you only need to remove the screws that hold the motion plate to the frame and the screws that hold the cylinder to the frame.

David

 

[bazmak]

Thanks Dave thats very helpful.Looking hot outside,im taking the wife for
a sunday lunch

 

[Builder01]

Also forgot to mention, you have to remove the steam line to the chest and the exhaust! (small detail!). By the way, on the Super, the main steam in and exhaust are flanged and bolted to the cylinders. I think the drawings for the Simplex show them as screwed. I don't know if it is too late for you to consider this or not.

David

 

[bazmak]

Thanks Dave,i havent thought of that aspect yet,but i have drilled and tapped the cylinders 1/4"bsp. (only suitable tap and die set i had). May be able to incorporate std comm. compression fittings ? or screw a flged conn to the cylinders to bring the flged conn inboard of the frames. Near future thoughts
I have made a no of silver steel pins and made a couple more lever arms
as i start to assemble the near side.Realised i had made 2 reversing arms when i only need one. Made a temp/adjusting eccentric rod to conn everything up
and getting everything turning over.Some pins i may remake
/redesign where the metric nyloc nuts look a little bulky. Waiting for the arrival of some taper pins so i can finalise some conns and hopefully some advice
from Dave the builder 01 on sequence of ops. Weather is warming up so i am slowing down