Building the Potty Grasshopper engine.

[crueby]

The parts so far are looking excellent - very nice finish on everything. That is a pleasing design - love the arced bracket above the cylinder.

[sbwhart]

That's looking well Peter:-

I've used quite a few of those RDG flywheels and there good value for money, I was going to use one for my build but at the size of my model they just wouldn't have looked right that's why I used a smaller laser cut wheel.

I'd be interested to see how she performs with steam, that would be a first for my models.

Cheers
Stew

[Gas_mantle]

Thanks Stewart, I had intended on making a short video of it running once completed. I've found someone who is prepared to make me a boiler so I'm hoping to have one just after Christmas and will make a video of it running on steam (assuming it runs).

I'm hoping that as it's 50% larger the heavier wheel will allow for slow running. Even in it's present state it is surprisingly heavy - the 1/2" thick steel baseplate is maybe a bit of overkill but will at least give it good stability.

Peter.

[Gas_mantle]

Hi all,

I've now managed to complete the crankshaft and main bearings they are simple components with little to show but for the benefit of other beginners thinking of building this engine I've taken a few photos.

The bearing blocks are a matching pair of arched plates with a brass inserts they are made from 20mm thick steel - the marking out of the centre ring is poor but it's only a guide for boring out.



I'd probably have been able to bore out the centre holes faster and with a better finish on the lathe but as I've just bought a 50mm boring head I thought I'd give it a go and chose to do both bearings together. The boring head coped ok but I was a little disappointed with the finish, as these holes will just carry loctited brass inserts the finish should do for this job - hopefully next time I use the head I'll have a bit more idea what I'm doing 





Next job was to mill the sides to size, after taking ages to do the first side I used a bit of common sense and chain drilled the remaining 3 close to size.



With a couple of small oil holes drilled in the tops I then made a close fitting steel plug as a guide for roughing out the arched top in the vice.



A bit of filing and polishing plus brass inserts completed the bearings so it's on to the crankweb - this is a simple steel block milled to 12x18mm with 2 x 9mm holes.



The 9mm crank pin served as a guide for radiussing the ends.



Bit more filing should soon profile and clean up the resulting part



With the parts profiled, the bearing brasses added and the crank loctited I finish up with this little trio



I'll pin the crankweb later once I'm satisfied it runs true and also make a couple of oil cups for the bearing tops.

Peter.

[kvom]

For running on steam you'd need to be aware of thermal expansion of both the bore and the piston, and that can depend on the steam pressure.  You can use the coefficients of expansion of these materials to do rough calculations, but a close fit will almost certainly get too tight.  The rule of thumb for steam locomotives is to build them half worn out.  If you use Viton or PTFE as piston rings they might well compensate.

[Gas_mantle]

Thanks Kvom,

I'm hoping to get the engine running on steam (albeit only occasionally) but I've had mixed results in trying to fit 'O' rings in the past so was initially going to try with rings made from graphite yarn.

The piston is brass in an aluminium cylinder - I guess that isn't ideal but I don't intend the engine to ever work under load and it will only be run occasionally for short periods.

Peter.

[kvom]

Aluminum conducts heat very readily, so it will get hot quickly regardless of load or speed.  But the only way to find out if it will run is to try it.  Given steam's expandability it will run at a lower pressure (and lower temp) than with air if it runs at all.

Nice work on the build.

[Gas_mantle]

Hi all,

I've managed to cross another part of the list by completing the bracket carrying the valve linkage, in the plans it calls for a piece of square steel tube and the soldering of a pair of cylindrical bosses. Since I have scaled my build up by 50% the tube I needed was a peculiar size and proving difficult to buy, secondly I don't yet have and soldering equipment so I set about trying to fabricate using a piece of scrap aluminium I had laid about.

The part will attach to the valve chest with 4 M3 bolts so the first job was to use the chest as a drill guide then roughly mark out the profile to be machined. The top hole will ultimately carry a 4mm rod with a pair of cranks



Next job was to mill roughly to size and cut 2 parallel sloping faces





I forgot to take a photo but I next milled out a central channel and a 'U' shaped cut out for the back to arrive at this



A bit of turning on the lathe to make 2 aluminium bosses for the pivot rod - unable to solder, a dab of Loctite was used to get a secure bond



Some light milling to even out the central gap then use the bosses as a guide to rough out the rounded profile on the top



A bit of a round about way of doing things but after some filing and emery it's looking like the one in the plan



Once in place on the cylinder assembly it's starting to take shape 





With a bit of luck I'll get the cylinder and crank bearings bolted to the baseplate next so I can start on the pivoted upright beam.

Peter

[Gas_mantle]

Hi all,

I've managed to get a bit further so it's time for an update for those still following along 

The flywheel at 10" dia was to large to turn on my 8x16 hobby lathe but another forum member living locally offered to help me about by turning it on his larger Harrison lathe. It's a 6 spoked casting fron RDG tools in the UK and at just over £20 it seemed a bargain nicely fitting the style of engine I'm building.

Here it can be seen in the Harrison



Although the casting did have a few small hollows it turned out well and I'd like to thank Phil for his help. I've made a start on cleaning up the spokes but there is still quite a bit more to so I'll do it in stages while building the rest of the engine



The next part to tackle was the pivoted support beam, in Stewarts design some of the parts have the option of a simple design or a more decorative 'ringed' style. I've already made the 'A' frame in the decorative style so it made sense to keep up the theme. Basically it involves sandwiching 7 rings between 2 parallel uprights and the soldering everything together, at the moment I don't have any soldering gear so I set about fabricating a version from steel then securing it with pins and Loctite 638.

Firstly the 7 rings were turned and parallel flats milled on 2 sides.



Using a wiggler to accurately things position I set about drilling 3mm holes in the flats and thread them onto a silver steel rod



Once happy that all 7 rings fit nicely I milled the sides flat.



This gives a rough idea what I'm aiming for.



With the sides cut to length I drilled the pivot holes and made a post to allow me to round off the ends in the mill



I wasn't too sure about the best way of drilling and pinning the sides to the rings to get good alignment but decided that after Loctiting the rings to the centre rod I drill all the holes on the side beams but only the centre ring.



With centre ring pinned and the whole assembly held in line with end bolts it was time to drill into the rings.



With everything pinned in place the component is suprisingly strong so its time to mill out and file away the waste from the central rod



The end result still needs a bit more filing and tidying up but it's largely complete





With the flywheel and beam in place it's starting to look like and engine 





Peter.

[vcutajar]

Still following along Peter and learning new things as you go along with your build.

Vince

[Gas_mantle]

Thanks Vince, as a newbie to engineering this is a good learning exercise.

I've made a start this morning on the swing beam pivot base and hopefully will get it all bolted down to the base in the next couple of days, that then only leaves the eccentric assembly and the link arms to the 'A' frame and I should be in a position to start testing it 

Peter.

[sbwhart]

That's coming along well Peter those RDG fly wheels are good value I've used them in the past the blow holes can be easily filled.

Cheers
Stew

[Gas_mantle]

Thanks Stew, I also was quite impressed by the wheel casting, for £20 the have got to be a bargain.

There's a good chance I'll have a boiler in the next few weeks so I'm hoping to give it a try on steam :-)

Peter.

[b.lindsey]

I am still following along too Peter. Beautiful work as always. That will be a fine addition to your engine collection.

Bill

[Gas_mantle]

Hi

The next few components were mainly just brackets etc so I didn't take many photos although I did take a few while making the decorative handles on the valve linkage assembly



Not quite there but getting close


The horizontally placed one has a better profile but as a first attempt I was reasonably happy with the results


Alongside the link rods that will connect the beam and 'A' frame.


Here is the work so far with a guest appearance from a 3" dia vertical boiler I bought secondhand - I'll see how the whole set up performs and possibly permanently link them up as a self contained unit.


Showing how the link rods sit and the handle that will take its feed from the eccentric and operate the spool valve via a pair of cranks.




It's partially bolted to the baseplate here and I'm pleased to say it seems to line up nicely and moves without and binding etc, so fingers crossed I'll have a runner soon :-)



All that remains now is to make the eccentric and do a bit of milling to the baseplate and it should be pretty much finished :-)

Peter.