Elmers Grasshopper Engine

[kiwi2]

Hi all,
I've managed to finish Elmer's Grasshopper engine. I'm always surprised by how much work goes into these models.
I used rubber O rings to seal the valve and piston shafts. The seem to seal without creating much drag as long as they are well lubricated. They are OK with compressed air but I'm not sure how they would go with steam. I can run the engine on a bit less than 3psi air pressure so I guess the construction is OK.
I think I'll give Elmer's Mill engine #33 a go next.
I didn't much enjoy making and fitting the steam chest on the grasshopper. It's a really fiddly mechanism to make and get adjusted correctly. I think I may try modifying the design of the mill engine so as to use a spool type of valve rather than the steam chest design favoured by Elmer. I think this will mean a much greater valve movement. Does anyone have any thoughts on the relative merits of spool valves as opposed to steam chest type valves?
Regards,
Alan C.

 

[Arcane]

Kiwi2.... a fine engine. I LIKE IT!!

 

[Herbiev]

Great looking engine. I love it.

 

[danstir]

Very nice engine, congratulations!!!

 

[Sshire]

Alan
Very nicely done. When I built mine, the first of Elmer's for me, I wasn't thrilled about making the valve. If you're going to make more of Mr. Verburg's designs, you'll notice that valve used a lot. I can make them, pretty much, without thinking now. It's simple and it works. That said, I'm the last guy to stick to the plans. Always looking for a more interesting approach, so try a different valve or porting or size or shape. That's the fun of this for me.

 

[PeterB]

It looks great Thm:

 

[rebush]

Kudos to Kiwi2 for a excellent engine. Thanks for posting pictures. Roger

 

[kiwi2]

Thanks for the comments Stan. I take your point about Elmer's engines commonly using the steam chest design. I'm in two minds about trying to use a spool type valve or making 3 or 4 steam chests. Or at least 3-4 of the shuttles which are the fiddliest things to make - particularly machining out the little recess on the bottom. If I do stick with the steam chest, I'll solder the bottom plate to the body so they don't move in relation to each other when I'm trying to get the final adjustment right. A couple of locating pegs between the valve body and the cylinder may be useful as well. The steam chest design has been around a long time. I have an old book called Model Steam Engines which has a drawing in it which is pretty well the same as Emer's. There's no date on the book, but an ad on the back advertises "The Model Engineer" magazine for 4d an issue.
Hi Herbie,
Your picture looks like Elmer's mill engine #33. If it is, I like your modification to have everything sitting on a flat base rather than the stepped arrangement shown in Elmer's original drawings. Can you post some pictures showing the details?

Regards,
Alan C.

 

[Inky Engines]

Alan

Congratulations on a very nice looking Elmer's Grasshopper - I'd love to see it running - as you say there is not much wrong with the build if it runs on 3 psi - my aim with these Elmer engines is 'breath power', but its only occasionally achieved. I haven't tried O rings to seal piston and valve rods, but on these engines I've failed to achieve any significant improvement from any type of packing (PTFE, graphite yarn, etc), over and above a good fitting packing nut alone - any improvement in the seal is lost in increased friction.

Elmer's #33 Mill Engine is a good choice, but also take a look at #41 Factory Engine - I followed the idea of another contributor and built the two together!

Kind regards

Geoff at Inky Engines

 

[Sshire]

Alan
Here are some build photos of the grasshopper steam chest and valve.

http://s1126.photobucket.com/user/sshire/slideshow/Steam Chest

 

[kiwi2]

Thanks for the pictures Stan. The part which gave me most trouble during fabrication was machining the recess under the shuttle. The smallest end mill I have is 1/8" which is far too big. I ended up using a spherical dentists burr to rough it out and a 1/16" cylindrical burr to tidy up the edges and the bottom of the recess. (My Father was a dental mechanic so I have a good selection of burrs).
Do slot mills come in 1/16" diameter? I presume you have to be real careful not to break them.
I used a slitting saw to cut the slots in the top of the shuttle.

Regards,
Alan C.

 

[Inky Engines]

Alan

1.5mm (or 1/16") Slot Drills are readily available (in the UK at least), surprisingly robust, and certainly well worth their small cost if you intend to build more of Elmer's engines. I use mine not only for the valves but also for Elmer's many fork slots - although a slitting saw could of course be used for the latter.

Kind regards

Geoff at Inky Engines

 

[Sshire]

As Geoff said, 1/16" slot drills (called center cutting end mills in the US) are readily available. You do have to be very careful about lateral pressure on the tool. I use high RPM, plenty of cutting fluid and very slow feeds.
I broke a few early on, but after slowing my feed, I've been OK. That said, I have 4 in in the shop.

 

[thayer]

I actually did all the detail work on my valves with a 1/16 end mill. You can see them taking shape starting on post #45 of the build thread for my Elmer's #33. I haven't touched it in a while, but now that model airplane season is over in my shop for a while, I will make some more progress soon.
http://www.homemodelenginemachinist.com/f31/elmers-33-novice-makes-chips-19478/

Thayer

 

[kiwi2]

Thanks Thayer. Your build looks impressive. The supports for the crosshead guides are outstanding.
1.5mm end mills are very expensive in New Zealand so I've ordered some from CTC tools. While I'm waiting for them to arrive, I'm experimenting with making a shuttle valve cylinder. I may look at doing both types to compare them.
Regards,
Alan