Elmer's Grasshopper - Double size and stylized

[bananarchy]

Howdy folks. Now that I've spent a good deal of time on these boards admiring everone else's handywork, it's finally time to start making some chips of my own. I've been doing various things in machine shops for a number of years, but this is my first foray into model engines. Elmer's #37 caught my eye, as I've always liked beam engines and grasshopper beams are particularly fascinating to watch. Never having been one to leave well enough alone, and having access to CNC capabilities, the original design has been substantially modified. The first iteration was simply a 2x scale up of the original design, followed by aesthetic modifications and a seriously overgrown flywheel (11.75" diameter). Here are a few shots of the solidworks model -

One of the main ideas behind the big flywheel, aside from looking neat, is to ensure smooth, very low speed operation. To that end, ball bearings are going to be used in all the rotating bits and nylon bushings for the pin joints to reduce friction. Also, using the weight and CG numbers from the model, the counterweight was significantly enlarged in order to offset the weight of the beam and give what should be reasonably good balance, again to ensure smooth running at low RPM.

This last week, I finally got the chance to make the major CNC components all in one run, aside from the flywheel, for which I'm still waiting on material. First, fixture/bolt holes were drilled in a 6x13x0.5 plate for the column, leg, column fork, and beam.

Next, a fixture plate was drilled, tapped, skimmed, and not photographed. The workpiece was bolted down, starting with the leg...

and cut at 7500rpm, 40ipm.

Then the column

and the beam

and the fork and bearings

The fork, bearings and leg all have extra material and fixture holes which will be machined off in subsequent operations. The setup allowed all the parts to be machined using the same machine zero, which worked well. The only issue I encountered was the screws not quite being equal to the task of holding the fork down during machining, and it moved around a bit, but the damage is only cosmetic and it should be salvageable. Next up - cleaning up and doing remaining operations on the parts I have so far, then starting in on the base plate.

-Neil

 

[vederstein]

WOW! this might be the largest Elmer Engine built!

 

[crueby]

Should be a great looking engine when done - keep the pictures coming!

 

[Lawijt]

Wow , what a great work.

 

[bananarchy]

Thanks for the kind words. I made some small modifications and figured out the rendering software, so here are a couple more pictures of the cad model. I added the center cap to the flywheel and redid the eccentric strap. I changed the brass toppers on the arm and column too, but I'm still not quite happy with those. I have some shop time lined up this weekend, so hopefully I will have the base and some other things done soon.

 

[Chiptosser]

Wow!! nice. I wish that I could learn to do cad like that.

Thanks.

 

[bananarchy]

Got some more work done over the weekend finishing up the parts shown above. The hold down lugs were milled off of the leg, and then the pivot pin holes were located and drilled.

Next, the bearings were bored, skimmed, drilled and tapped.

Boring bar to get everything good and straight, leaving .020 or so for a .750 reamer

then reamed to final size

After both bearings were reamed, they were stacked together with a .750 pin in the bores before the bottoms were skimmed, in order to ensure proper alignment.

then set up for drilling and tapping for the mounting screws

Next, finishing ops were done on the fork

which was then test fitted to the column

Crank bearings and crankshaft were test fitted. The crankshaft is .500 ground 303 stainless, and the crank bearings, which are a tight slip fit in the blocks at the moment, will be held in place with retaining compound on final assembly.

Also, a lovely brass globe valve to use to throttle the engine was acquired, courtesy of steamfittings.co.uk.

which was added to the model, along with some modifications to the parallel motion links

Next up will be the base plate, and then the flat brass components (links, eccentric strap arm, valve crank ends, valve cover and valve plate) will be CNCed in one batch as with the aluminum parts.

-Neil

 

[bananarchy]

Update time! I've managed to complete the base plate and several of the brass components since last time.

First, a few modifications were made to the design, including fancying up the piston and conrod forks and changing to a hexagonal bolt pattern and shape for the lower cylinder head. Here are some updated shots -

First off, the base plate was faced, drilled and tapped, and the leg pocket was cut in the same setup.

Then on to the the flat brass components, which were all cut from .125" bar - the parallel links and valve train components.


Two links

one eccentric strap arm

and two valve crank arms

Next, it was time for some lathe work making the rod forks and the connecting rod

1" brass stock for a fork

Two of these were done with the same profile, but they will get somewhat different treatment later. On to the connecting rod, out of 3/4" material.

These parts were my first experience using computer generated code rather than hand writing it on a lathe, and I'm very pleased with the results. The software (HSMWorks) is wonderfully integrated into Solidworks and very easy to use.

The con rod and forks then get a number of mill operations, most of which are yet to be done.

I also made the pin and spacers which connect the links to the beam, which was a simple turning job.

As it stands now - I've had some issues getting the aluminum to polish properly, and I think I'm going to stick to a brushed/sanded finish on the aluminum parts, but the brass shines up nicely.

Next up, once the forks and con rod are completed, will be playing with some stainless and making the crank disk and crank shaft. Stay tuned.

 

[bananarchy]

Now for the crank disc! I haven't done much with stainless prior to this, but I selected some 303 for ease of machining, used some nice fresh tools and couldn't be happier with the results. I started off with a 3x3x0.5 piece of material

which was drilled with a #3 for the 1/4-28 crank pin hole and then with a Z drill in two spots, one of which was reamed .435 for a press fit onto the crank shaft. Bit of an odd size, yes, but there was a brand new carbide tipped reamer laying around, and I'm going to be turning the crankshaft to fit, and shooting for .0007-.001 of press.

The second large drill hole was used as an entry point for the 1/4" end mill that was used to cut the pocket, in order to avoid having to plunge in the material.

Next, a fixture plate was cut with a spud to locate on the pocket and allow cutting of the profile

The profile was done with a 1/2" carbide cutter, running at 200sfpm

Followed by a decent size chamfer on the outer edge, which was repeated on the opposite side after the part was flipped over

Very happy with how the finish turned out -

Next up will be finishing up the forks, and probably a crank shaft and pin before long


-Neil

 

[bananarchy]

Update time! I've been doing lots of machining and not much sharing lately, so it's time to remedy that. Picking up where we left off, once the forks were finished up, it was on to the cylinder heads.

For the lower head, the original design was modified to use a 6 bolt pattern to mount it to the base, rather than 4. A piece of aluminum was skimmed down to 1/4", then drilled for the #10 and #6 screws to attach it to the base and cylinder respectively.

Next, the upper head was a fairly straightforward turning job

followed by some drilling and threading

Next, the steam chest components were all cut at once, since they utilize a common bolt pattern and thus can use the same fixture (steam chest, valve cover and valve plate).

Workpieces -

Steam chest (1/2" thick aluminum)

I decided to fancy up the valve cover a bit, Stuart models style, using a 1/16" carbide cutter

The completed valve plate, cleaned up

The steam chest was then drilled and tapped for the valve rod and tapped 1/4-40 (first time I've ever seen that thread) for a 1/8 compression fitting

Next, finally, the cylinder! The bore and one end were done first -

Then into the rotary table

The valve surface was milled, then the sides, the belly roughed, and then finish cut. The fact that end mills aren't flat on the bottom prevents one from getting a perfectly flat surface, but multiple passes at different offsets smoothed it out fairly well, and it will be covered by the lagging anyway.

The port cutting and tapping for the steam chest, along with the exhaust port, were done in the same setup.

Then back into the lathe in some soft jaws to finish up the remaining end

The piston was then turned from high temperature Teflon round, since I figured this would be fairly low friction and obviate the need for rings.

This was threaded onto the piston rod (3/16" 303 stainless precision shafting) to turn the final diameter (not shown).

Trial assembly -

The connecting rod was finished up, with a bearing bore and flutes applied with a 1/2" ball mill. A previously scrapped fork serves as good fixturing for the other end.

The crankshaft was a simple turning job, 1/2" ground shaft with a turned down diameter for a press fit with the crank disk. I left extra length on this diameter that was a couple thou under, to make sure everything lined up well on assembly. I aimed for the neighborhood of .0007" of interference.

The assembly was then put back in the lathe to remove the extra shaft nose and take a light facing pass on the crank disk, to get everything nice and even.

Not super thrilled with the finish, but I was nervous about running too many rpm. Should clean up OK though.

There are a few more valve train parts to go, including the eccentric and eccentric sheave, which should happen next week. Then the flywheel, and we should have a runner.

 

[bananarchy]

So I've been remiss and neglected the thread, and finished the project in the meantime, so here is a whole raft of updates!

Next up, the valve, done out of teflon. This made use of a very long and scrawny 1/8" HSS two flute I found laying around, which would have been completely awful on anything metallic but cut the teflon like butter.

Next, the eccentric strap. The only thing I had that was big enough was a very dodgy piece of what turned out to be naval brass, I think. Definitely a good bit harder than 360 brass, and nice to machine.

With a couple other simple bits done, it was finally time for the flywheel. 6061 Aluminum, one board-foot (12x12x1")

Clamped in place, with reamed dowel pin holes into the fixture for relocating the second op.

Faced and roughed - the 1/2" end mill was run at 7000rpm and 60-70 inches per minute. Machine time, if you were running production on this part, was on the order of 45 minutes per side.

Finished first op, with ball nose and corner rounder work

Same story for the second side, but with the addition of drilling and reaming the crankshaft hole (.500) and drilling for the flywheel center cap screws (#2-56)

All other machining was done with thin webs connecting the spokes to maintain as much stiffness as possible, then the webs were removed. To my significant relief, everything lined up quite nicely.

After moving some clamps, the outside was profiled out

And, of course, test fit immediately

The hub cap was a fairly simple turning job

And a tapered keyway to accept a gib key was cut in the crankshaft. Not having any sine bars, the shaft was placed flat in the vise and I approximated the taper with a 1/2 thou stepdown, which seemed to work fine.

The last cosmetic addition was lagging for the cylinder. Since I didn't trust myself to make something decent looking out of sheet metal, and I like the look of fluting, this was done from 2" brass round bar, which was turned to match the cylinder flange diameter and then drilled and bored to clear the belly of the cylinder.

A spud was turned and then drilled and threaded to fit in the center bore of the rotary table, which was mounted in the mill.

A 3/8" ball nose was then used to cut the flutes

The part was then transferred to the vise to cut the slot for the valve chest

The cylinder was drilled and tapped for a set screw to secure the lagging

About .002 of clearance was left in the slot and length dimensions, and the fitment ended up quite nice

Next up, a base, some plumbing, and it's done

 

[bananarchy]

I got my hands on some 8/4 african mahogany, which was glued up a bit oversize, then thrown in the mill

Roughing and finishing passes were done with a 1" ball nose

I got a tiny bit of tearout on one top corner but the rest of it was fine after I changed the lead-in in the code. I used a 0.040 step down for the finishing pass, and after sanding this up, I would cut that in half or less if I were to do it again. A relief was then cut for the flywheel

Pockets and holes were also added for a braided stainless supply line going in and 1/8 copper pipe coming out, with turned brass bulkheads for each.

A 1/4" aluminum plate was screwed into a relief on the top of the base, and 10-32 socket heads attach this plate to the base plate of the engine. Before final assembly, I called in a favor from a friend with access to a laser cutter and ran two sets of gaskets.

There is always more polishing/finishing work to do, and I'm still toying with the idea of some kind of brass finials on the top of the leg and column, and there is a tad of axial runout in the flywheel that I need to chase away, but it's close enough for some pretty pictures.

And a bit of video:

[ame]https://www.youtube.com/watch?v=iaqZlQOq7x4[/ame]

Overall I'm very happy with the operation. Following a bit of tinkering, the running is basically silent, and on very little pressure. A moderately big aquarium pump is used for air supply, and I don't actually know how much pressure it puts out, but it's not a lot.

Next up may well be a Stuart No 1.

Thanks for reading.

-Neil

 

[chucketn]

Very nice work, Neil!

Chuck

 

[bouch]

And a bit of video:

https://www.youtube.com/watch?v=iaqZlQOq7x4

Overall I'm very happy with the operation. Following a bit of tinkering, the running is basically silent, and on very little pressure. A moderately big aquarium pump is used for air supply, and I don't actually know how much pressure it puts out, but it's not a lot.

Next up may well be a Stuart No 1.

Thanks for reading.

-Neil

Looks great! Very nice job on it.

I've built a Stuart No 1. I suspect you'll enjoy building that engine, when its done its well worth the effort involved.

 

[ShopShoe]

Great Job bananarchy!

I like all the stylized touches you added and the nicely done wooden base. As has been said before, Elmer's designs can be seen as starting points for all kinds of individual interpretations and enhancements.

I do really like this one.

Thanks for posting,

--ShopShoe