Building the Potty Grasshopper engine.

[Gas_mantle]

I can fix you up with some BA taps.

That would be great thanks, The Crosskill engine drawings refer to BA threads and the Stuart engine uses BA also so I think I could do with some.

Peter 

[Gas_mantle]

I've now got both cylinder end covers largely completed, they are both similar turned aluminium discs with the top one having as raised boss for the piston rod.

Firstly I tackled the simpler bottom cover and turned to the 52.5mm OD followed by a 2.5mm high raised spigot that will locate in the cylinder.



I struggle a bit with parting off and it hardly seemed worth trying it to preserve the last 8mm of waste stock so opted to mill away the waste from the reverse.



This cheap and cheerful flycutter only cost £14 with a HSS blank included and I'm well impressed with the results it gives - I just guessed how to grind the tool bit but it seems to work fine 



With the bottom cover done, it's onto the top one. I chose to cut the piston rod boss side first as this will give me something to hold onto in the chuck when it comes to doing the reverse. Working at my 150% scaling up the boss is 18mm dia and 10 high it will be later drilled and tapped M12 to take the piston rod gland.

I'll leave the drilling for now as I'd like to drill for the piston rod from the other side first but did add a couple of 45* chamfers.




Parting off I managed to cut about halfway so by my standards I'm calling that a success.



My reasoning for drilling through from the reverse was to ensure the piston rod hole, the cylinder locating spigot and the OD are all concentric to the cylinder centre line so I took time to centre accurately in the 4 jaw.



Just a case now of turning to form a cylinder locating spigot then drilling and ream the 6mm dia piston rod hole. A few chamfers added and very fine skim around the edge completes the part.





I'll drill for the piston rod gland on the mill later now that I'm confident the important parts are concentric

Starting to take shape (the bolts are all exactly the same despite how they look)   



Peter.

[sbwhart]

That's going well Peter 

Stew

[Gas_mantle]

Thanks Stew, I'm having fun building this 

The next part I made was the cylinder base plate, this consists of a circular disc of aluminium 82.5 mm dia and 15mm thick, it's a very simple part but does involve drilling quite a few radial holes and as I never used my rotary table before it took me a lot longer than I expected.

Although not shown in the plan I decided to drill a shallow recess in the bottom cylinder cover and turn a matching raised spigot on the base, I thought this would make it easier to align the 2 components later in the build. I should have cut the recess when I made the cylinder cover but this is an afterthought and it gave me chance to try centreing a circular part on the mill using this DTI holder - it took ages fiddling around with this holder and I need to make something better.





Turning the base with the spigot



With the base turned faced on the bottom it needs radial holes drilling, I did try centreing the rotary table using the DTI holder again but found it far easier to put a MT centre in the table and a wiggler in the mill spindle.



Centering the work piece in the table using the wiggler again



4 holes 90* apart at 18mm radius to secure the cylinder



Then 8 holes 45* apart at 33.25mm radius to secure the whole assembly to the baseplate.



Well, the rotary table seems to work - everything looks properly spaced 



Cylinder assembly taking shape.



Peter.

[b.lindsey]

Still following along Peter. Very nice workmanship so far and I am looking forward to future updates!

Bill

[AOG]

I used to have all kinds of issues centering up on my rotary table when I started using it. Someone here recommended getting a coaxial indicator. It was one of the best tool suggestions I've gotten. At this point I can center up on the table in about a minute. I highly recommend getting one. It will save you a lot of time.

Tony

[Gas_mantle]

Thanks guys 

As for the centering with the DTI,  since I posted a friend has offered to sell me a co ax indicator so hopefully that will help considerably

The articulated arm and DTI method works ok but it takes ages when you are new to using it like I am - it seems to me the arm could have its uses running an edge past the DTI with the spindle fixed but once you try rotational measurements it has its limitations.

Peter

[Jim Nic]

Peter
For centering my rotary table I place the rotab loose on the mill table, fix a length of round bar in the mill chuck then secure it in the chuck on the rotab then clamp the rotab to the mill table.  Takes but a second and is accurate enough for most things I do.    This is not my idea, I have seen it several times on several forums.
Jim

[Gas_mantle]

Cheers, at the moment I don't have a rotary table chuck but I did wonder if it's possible to get an MT2 to a parallel spindle adapter ?

I thought if I could get one preferably in a metric size to fit my collets I could lower the MT2 towards my table and hopefully the taper would centralise it for securing.

I guess would be easy to make one but at the moment I'm not sure I can turn an accurate enough morse taper.

Peter.

[Jim Nic]

Sorry my mistake, I didn't look carefully enough at your picture of the duelling centres and took the lower live centre for a chuck. 
A cheap alternative then is a soft ended MT2 arbour which will fit in to the centre of your rotab and you can then either turn the soft end down to a small enough diameter to fit your chuck or probably easier drill and ream a hole in it and keep a close fitting piece of rod to put in the chuck for use in centering.
Jim

[Gas_mantle]

Hi all,

I had a little break from this engine for a week or 2 after making a mess of the next assembly, I decided to wait till I have a centreing indicator and a height gauge before continuing and also needed to buy some additional materials. It gave me time to work on a little Crosskill casting kit but now I'm a little bit better equipped I'm pleased to say I've got a bit further forward.

As this engine is a Grasshopper it has a frame on top of the cylinder to carry the beam linkages and this seemed the logical way to continue, the first part of this arrangement is a simple steel plate milled to a 39mm square, then make a central hole 24mm dia to sit over the piston rod spigot followed by 4 holes 4mm diameter to secure the plate and cylinder top to the cylinder itself.



Having bored out the central hole on the lathe I decided to drill the securing holes through the cylinder top and the cylinder together a bit of double sided sticky tape worked fine for aligning things square till the first bolt was in.



A snapped centre drill meant I did have to drill one hole from the reverse.



With the mounting plate done it was time to have another go at the upright 'A' frames that I made a mess of last time. In Stewarts plans he gives details of how to make a simple straight edge 'A' frame or a more elaborate one having radiussed detailing, I think the more decorative one significantly improves the look of the engine and decided to have a go at it.

It gave me chance to try out the height gauge :-



I bought this co ax indicator from another forum member and found it made centreing on the rotary table so much easier



I settled on a 5mm slot drill to make the middle holes and cut the radiussed out edges I've never done this before (apart from the messed up first attempt) but it seemed to go reasonably well although the finish was poor - I think it's something I need more practise at and possibly buy a few better quality slot drills.



After what seemed an eternity of handle twiddling and recentreing I finally arrive at these



They aren't perfect by any means but there is still enough material left on them to hand file the outer profiles a little bit better so I'm hoping over the next day or two I'll be able to get them looking a bit neater. 

Peter.

[AOG]

I think that came out well.

Tony

[Gas_mantle]

Thanks Tony

I think with hindsight after I'd plunge cut through with the slot drills I should have changed to better mills to cut the radii and the central holes - the slot drill I used was a part of a cheap and cheerful set I bought to get me started and I think I was expecting too much from it. The finish was poor although I'm happy that things are in line and concentric so I cut very slightly over size in the hope of filing them to a better finish and getting the arcs to blend with each other better.

[Gas_mantle]

Hi,

I've managed to get a bit further by completing the crosshead and the beam.

Firstly the crosshead is a simple 9mm thick piece of steel with a brass bearing insert and a rounded top, I did consider using the rotary table but decided it would far easier to make snug fitting plug to go in the bearing hole and keep taking small cuts and rotating the art after each cut.





After about 8 cuts either side it was virtually a smooth radius and just needed a bit of filing.

It made sense to thread either end of the silver steel piston rod and turn the piston whilst on the rod, the plans show one groove for a ring but as this model is 50% larger I cut 2 grooves that I'll pack with graphite yarn later.



With the crosshead bearing fitted and the threaded spigot turned.



Next on to the main beam, this is made of 2  5mm thick steel flats separated by spacers, having marked out the profile and bolted the 2 halves together its time to mill the edges. I found a scribing block resting on the vice was as good as anything to set the correct angle for the tapers.





I started out filing the radiussed ends with filing buttons but found I could do a better job by eye - after bit of emery to blend in the corners and remove a few machining marks I arrive at this.



With a few temporary bolts holding things together it's starting to take shape 



At the moment I'm just using cheap hardware store type nuts and bolts but would like to buy some better quality ones in metric sizes, does anyone know where I get any in the UK ? Having looked at the usual suppliers I can only find decent quality ones in BA sizes.

Many thanks
Peter

[sbwhart]

Hi Peter going well some nice work 

I get my fixing from http://www.modelfixings.co.uk/

Hope this helps

Stew