Geared horizontal twin engine

[Brian Rupnow]

I have always thought that the most elegant cross head guides I've ever seen were on the Popcorn engine, as designed a few years ago by Stu Hart of the U.K.  Stu done the original in metric, then I took his drawings and basically redrew them in imperial inch size. I changed very little, and it has always been one of my favourite engines. A week or so has gone by since I finished my version of the Trevithick locomotive engine. I'm setting here this morning on my computer dicking around with the idea of a twin horizontal engine that incorporates the Popcorn cross head guides and operates the cylinder slide valves thru a set of gears similar to what I did on the Trevithick engine.

[crueby]

Thats a neat arrangement, has the benefit of the valve sliders horizontal so they don't tip back off the valve face when off. I remember seeing some early engines with a geared flywheel too to get around the early patents.

[Brian Rupnow]

For the sake of symmetry and balance, I'll put a skinny flywheel on each side. The power take offs and the flywheels are both running on the camshaft.

[Brian Rupnow]

[MJM460]

Hi Brian, great to see another of your creative designs underway.

A thought with those flywheels, a flywheel absorbs and returns energy with each pulse from the pistons.  This will make it crash back and forth over the backlash in the gears and stress the fixing of the gears to each shaft, thus increasing noise and gear wear. 

This would be avoided if the flywheels are on the crankshaft.

Of course, putting them on the top shaft does allow the engine to be set a bit lower, but on a two cylinder engine with cranks at 90 degrees, they probably don’t have to be so big.

Of course, if the engine is not expected to do much work, it probably doesn’t matter much.  Might be interesting to make the flywheels so they could be tried on each shaft, just to see how much difference it really makes.

I do like the concept with steam chests on top where they are easier to see to set the valves, and a shorter overall crankshaft for a more compact engine.

MJM460

[Brian Rupnow]

Other people have used this gear driven design on single acting hit and miss engines, and it doesn't work well on them. The main reason it doesn't work well on hit and miss engines is that there is such great reversal of torque between when the engines hit to drive the crankshaft and then the torque reversal when the engine coasts, depending on the inertia of the flywheels to carry the engine thru a number of miss cycles. This plays Hell with the gear teeth. On a double acting two cylinder engine, you really don't even need much of a flywheel for them to run.

[Brian Rupnow]

This morning I'm making gear blanks from steel. Whenever I buy a length of steel, I always buy it 2" or 3" longer than I actually need. All of the left over pieces are saved for jobs exactly like this. A lot of left over short pieces of shafting end up becoming gears for different projects. I'm not down to "zero scrap", but I try to use up every possible bit of steel that  I buy. The o.d. of the gear, the o.d. of the hubs, and the bore are all put in in this set-up. Then I will flip the part around in the jaws and turn down the remaining bit to the outer diameter of the hub. This gives me a portion of steel to hold in my 3 jaw vice mounted on my rotary table when I cut the teeth into the blank. Then the extra long hub will be shortened to size.

[Brian Rupnow]

That's enough work for today. Both gear blanks are turned to size, and the main crankshaft support is roughed out. I have had a clever idea about cutting teeth in the gear blanks, but I will share that with you tomorrow.

[crueby]

Great progress so far. Looking forward to seeing the RupNow Gear Method!
 

[Brian Rupnow]

This morning I cut the 36 tooth gears. Yesterday, as you seen, the gear blanks were made from two different pieces of steel. I wanted to cut these gear one time only. The gear in the chuck has an extended hub on one side which is held in the chuck jaws. Both gears have been drilled and tapped for set screws and will eventually get keyways cut directly below the set screws.  I inserted a piece of 3/8" cold rolled steel into the gear in the chuck, and that same piece of cold rolled extends thru the second gear, and on out to the tailstock chuck. Set screws are firmly cinched up on both gears, and this lets me cut both gears in one pass. This only works if both gears have the same number of teeth. Now I will trim the hubs on both gears to the finished dimension and add the keyways.

[Brian Rupnow]

In this picture the gears have been cleaned up, and two test holes have been drilled and reamed in a piece of scrap aluminum at the correct center distance. Two scraps of 3/8" cold rolled rod are inserted thru the gears and into these holes. This way I can check that the gears mesh properly. If they are a bit too tight or a bit too loose, then I  can adjust the hole centers in the finished piece to compensate for that.---It makes me absolutely crazy if I just put the holes into the finished piece first and then find out that the gears don't mesh properly. There isn't any good way to fix that!!!

[crueby]

Nice work Brian!

Have you ever taken a look at the clockmakers gear meshing tools? Think they call them depthing tools. Basically like what you made with the scrap block, but with one of the holes mounted on a slide, fancy ones have an adjusting leadscrew to run the slide in and out. Great to test out the gears on, adjust the distance till the gears mesh smoothly. They usually have points on the ends of the shafts, or a set of points that can be inserted into the shaft holes, to use as scribes onto the plates that will hold the gears. I made a set years ago for clock work, and get them out from time to time for other projects.

Mine is like this one, just no where near as fancy or polished as his!
http://www.clickspringprojects.com/pinion-head-depthing-tool.html

[Brian Rupnow]

Chris-I generally have mountains of scrap short pieces of aluminum. I can drill and ream two holes in them in about 5 minutes to give myself a "test block". The bearing stand and gears are finished, and now I think I'll go after the cross-head guides. I happen to have stock of the correct size left over from some other project, and I'm trying to build this engine "on the cheap" which means using as much stock that I can from stuff just setting around here collecting dust.

[Brian Rupnow]

Now, if you squint your eyes real hard, you can see the two cross head guides, turned to correct o.d. and cut to length.--I still have a bit of work to do on them tomorrow---

[Brian Rupnow]

These do end up making a beautiful cross-head guide, but Oh My Goodness there are a lot of machining sequences to get to the finished product from a piece of round cold rolled steel!!!