Chris's Build of Steering Engine

[crueby]

That is a spectacular machine, maintained to perfection. Wow.

[crueby]

I took the engine base to my carving station and dug out a ball end stone tip, and used that to smooth off the tiny little steps left by making the radiused trays under the crankshaft. Then set up the little sandblasting airbrush and went over all the milled surfaces to remove the toolmarks left by the end mills. This will give a nice smooth surface for the paint later on:

The next major parts I was going to make were the vertical walls, but a major function of the walls is to hold the gear shafts. Before I do that, I am going to make the gears, so that if need be I can tweak the positions of the shaft holes in the walls slightly. So, time to spend a little time in the gear calculating app (I use Gearotic Motion) figuring out the gears before cutting them. The pictures and plans from Michael showed the desired diameter and number of teeth for all the gears, but thats at full size. For the model, I have gear cutters that will be close to, but not exactly, the tooth sizes. I need to decide on what module size cutter to use, and whether I need to add or subtract a tooth from the count to make it work out the right size... Then go dig out some stock and start shaping!
 

[cnr6400]

 

[crueby]

Thanks CNR!  Great to have you and your elves in the front row!

Spent some time this morning with the gear calculator, calipers, acme rod, etc, and think I have things mathed out. Looks like I can keep the designed hole positions in the vertical walls if I make the following combination:

• Rear spur gears, Module 1.75, 58 teeth and 10 teeth, original was 55/10.
• Front worm/spur gear, Acme rod with .625" OD, 5 TPI, spur gear 2.762" OD and 30 teeth. Rough cut with M1.75 #8 cutter, then hob with acme rod

That wil leave the center distances within just a few thou of the design, which is close enough to work as is. To be sure, I will make the gears and test mesh them and see, don't want to have to make the walls twice. The walls have one side relieved out leaving a gusset grid, so plugging and re-drilling the wall holes will not work, they have to be right first time, and they are going to be made from some large brass stock which is too expensive to goof up.

So, next step, start cutting gears!   

Oh, and there IS one other gear set in the engine, the one that controls the valve movement from the upper gear shaft. I have some smaller acme rod and matching acme nuts sitting on the shelf from previous projects that will work out for those parts.

[Michael S.]

A perfect base plate for the machine.
When painting brass I first use a zinc based primer. and then comes the color that lasts better.

Michael

[Michael S.]

Your way is the right Chris.
The gears specify the bores of the shafts and if you want to make them yourself, mistakes can be avoided. It is a complex machine where everything has to be right.

Michael

[Mcgyver]

Another great project - thanks for posting it.  At the rate you crank out amazing projects, I guessing it'll be running by next weekend

[Kim]

The base looks great, Chris!   

Looking forward to following the progress on the gears!

Kim

[crueby]

A perfect base plate for the machine.
When painting brass I first use a zinc based primer. and then comes the color that lasts better.

Michael

Thanks - just checked, and the paint brand I am using has one, I'll give it a try! The brass is tough to get a good adhesion on, sounds like this will help.

[crueby]

Another great project - thanks for posting it.  At the rate you crank out amazing projects, I guessing it'll be running by next weekend

Tough deadline - I better hurry!   

Next weekend is the big fall event up at the logging museum in Maine. For anyone in that part of the world, well worth the trip up just north of Bangor, at least three Lombards will be trundling around the grounds, one steam and two gas powered. There might be a third gas one there if Paul gets it moved there in time. The steam one is the one I measured for my model several years ago.

[crueby]

A while back I had worked out how to make a worm/spur gear set using a length of Acme threaded rod - much cheaper than buying a commercially made set, unless you get really lucky and find one the right size in some other bit of machine that can be salvaged from. Some of you helped me figure out how to do this, pointing me at other threads on gear hobbing and some videos online where it was demonstrated - most useful help!!


For this model, I need a worm gear slightly over 5/8" with ideally a 4 TPI pitch. I was able to find a 5/8"x5 tpi threaded rod, which is close enough. An Acme thread is not quite the same as normally used on a worm gear, but it is pretty close and will work fine for lower speed applications like this one. A piece of the threaded rod is modified to make the cutter, the Hob, used to make the matching spur gear. If you have a lathe capable of cutting this type and size of thread (mine wont), you can make the threaded rod rather than buying it.


So, first step was to cut a length off the longer threaded rod that I had bought, and turn down one end round to aid in chucking it. When I did the first tests, the threads didn't grip that well and tended to slip while cutting the spur gear.

Then over to the mill to cut four flutes into the rod with a 1/8" diameter end mill. The cuts were done in several passes, working my way down to just below the bottom of the thread. The cutter was lined up so that the cut edge was on the centerline of the rod, making sure to get the direction of rotation of the mill taken into account, leaving the centerline edge as the cutting edge.

Put the rod into a small smooth-jawed vise (actually the little Martin Models mini vise built from their castings a couple years ago) to file some relief on the tops of the teeth behind the cutting edge. The top surfaces of the teeth were marked with a felt tip pen so I could tell where I had filed off some metal.

Taking care not to file into the cutting edge of the teeth, filed back the rest of the teeth to give the leading edge some room to cut. This was done on all four sections around the rod.

Here is the hob, ready to use. It is sitting next to the smaller one I made as a test a while back, along with the test gear made with it.

Now, to make sure that my calculations were correct and the cutter is working, I want to make a test gear. The final gear will need to be nearly 3" diameter and .586" thick (the sides of the gear get tapered in on both sides to match the original, that is why it is so thick). I have a slab of brass large enough for that, but don't want to risk it on un-proven methods. So, since I do have about 1 foot and a half of 2-1/4" diameter brass round bar bought cheap as a 'drop', I'll make a test gear from that.

To hold the gear for cutting, I need to be able to do the roughing out as a normal gear cutting operation, the use the hob with the gear able to rotate freely. When making the original test gear, I made up a little arbor that will work for this one too. All it needed was a new center spacer. Here is a picture of the arbor plus the test blank, which was faced to thickness and drilled/reamed for the 3/8" shaft it will ride on. The spacer on the arbor was turned to 3/8" diameter, a sliding fit in the gear blank hole, and a few thou longer than the thickness of the blank. The end cap on the arbor is flush on one side, and countersunk on the other. With the flush side towards the blank, the blank can spin ferely but not move side to side. With the countsunk side in, the blank is securely held for cutting the initial teeth.


So, next time I'll start roughing out the blank, and describe the rest of the process in detail (both for anyone wanting to do this themselves, and as a reminder to myself how to do this on a future project! ).

[horst.b.0]

Reminds me of Harald‘s video: <a href="https://www.youtube.com/watch?v=ce8-WFwaI70" target="_blank">http://www.youtube.com/watch?v=ce8-WFwaI70</a>

[Roger B]

Some fine metal sculpting as ever   

I'm following the worm with interest   

[Michael S.]

Hi Chris, I recently got workshop elves too!
He thinks he can make the steering machine out of Lego pieces. 😉
I hope they don't become a nuisance in the workshop.........

Michael

[crueby]

Excellent - better keep him fed and distracted, or he'll start stealing small shiny parts off your workbench!