Author Topic: My Little Donkey  (Read 4459 times)

Offline Laurentic

  • Full Member
  • ****
  • Posts: 310
  • Nr Yeovil, Somerset, England
Re: My Little Donkey
« Reply #15 on: November 03, 2022, 10:37:01 AM »
Loved the way you fabricated that 'casting' Jason, I admit I had to read it a couple of times to see excatly what you had done and how it was made up, but having done that I was even more impressed.

Nice and unusual looking model, ususual meaning different, good one, liked it!

Chris

Offline Jasonb

  • Full Member
  • *****
  • Posts: 9467
  • Surrey, UK
Re: My Little Donkey
« Reply #16 on: November 03, 2022, 01:25:51 PM »
Thanks, I do seem to be attracted to the models that are a bit different from the usual subjects.

Jo, although CNC cutting from the solid would be an option that is now available to me I think I would more likely go for a fabricated construction for those parts. Possibly cutting at least the more curved pieces on the CNC or maybe sending out for laser cutting. But I doubt it will see the light of day, however there are two Stuart subjects drawn up and I recently got the materials to revisit one of Anthony's engines that never ran so watch this space.

Offline Jasonb

  • Full Member
  • *****
  • Posts: 9467
  • Surrey, UK
Re: My Little Donkey
« Reply #17 on: November 04, 2022, 08:33:11 PM »
I came across this little gem today, would make a good companion for the donkey. Pity there is no illustration of the pump but I expect it to be very similar to the Bassett-Lowke one if not the same.

Offline Jasonb

  • Full Member
  • *****
  • Posts: 9467
  • Surrey, UK
Re: My Little Donkey
« Reply #18 on: November 05, 2022, 06:54:00 PM »
Those that have Been paying attention will no doubt have noticed that the hole in the cylinder mounting flange for the piston rod is quite large and that there is no short spigot to locate the bore of the cylinder. The reasons for this are 1. it would be tricky to counterbore and thread a larger hole than the 3mm piston rod required to take the gland from the underside. 2. forming the spigot to locate th ecylinder would also be tricky though could be done by mounting the frame on the rotary table or using a boring & facing head if I had one.

To overcome these two issues I turned up a separate piece from Cast Iron bar and loctited it into place, this section of the drawing should show how it works.



The crankshaft is made up from a length of 5mm PGMS with the over thick crank disc loctited into place and a silver steel crank pin retained with a CSK screw. Here you can see the turned and reamed crank disc has been screwed to a scrap block, its ctr location found and then offset to drill and CSK the hole for the pin retaining screw. After that it was loctited to the shaft and once set the shaft was held in a collet and the disc faced to the required thickness which ensures the face is perpendicular to the shafts axis.



A quick circle drawn onto the 3D model of the cylinder showed that it could be carved out of  apiece of 40mm dia CI bar so a piece was sawn off and then faced both ends leaving it a little over length. I then milled down 3 sides, one to form the port face and the other two to make it easier to hold in the 4-jaw before ctr drilling to mark the location of the bore. Withe the block back in the 4-jaw and the ctr drilled hole set to run true the cylinder could be bored and the end faced off true to the bore while bringing the cylinder to final length.



Moving back to the mill with the port face upwards in the vice the ctr was found and the inlet and exhaust port holes drilled as well as drilling and tapping for the valve chest studs.



It was then a case of standing the cylinder on either end to drill the steam passage down to the port and mill a slot to connect that drilling to the end of the bore. The cover stud holes were also drilled and tapped M2 on their PCD at the same set up. Vice stop in use here to save having to re find the bores ctr when it is turned up the other way.



I could have used the CHC to profile the cylinder with it stood vertically be decided on the manual method of firstly reducing the width either side to that required to match the valve chest using full height passes the swarf was coming of in nice long ribbons.



The last bit of machining on the cylinder was done with it mounted on a mandrel and held in the spin indexer to make a series of cuts to form the "rounded" part of the cylinder. After machining these were just blended into one another by filing.






Online Jo

  • Administrator
  • Full Member
  • *****
  • Posts: 15294
  • Hampshire, england.
Re: My Little Donkey
« Reply #19 on: November 06, 2022, 10:40:42 AM »
Love the use of 5C collets in a Spin indexer to enable the outside profile of the cylinder to be machined round.

Jo
Enjoyment is more important than achievement.

Offline Jasonb

  • Full Member
  • *****
  • Posts: 9467
  • Surrey, UK
Re: My Little Donkey
« Reply #20 on: November 06, 2022, 01:18:52 PM »
Bet you wish you had kept it now :LittleDevil:

It's quicker and easier than using a bit of bar across the vice jaws method as you don't have to keep stopping the spindle to move to the next position and easy to get all the facets the same which makes for easy filing. You can also offset either side of the ctr line when milling upto the edge where the valve chest edge is.


One of these various "little" engines would be a nice winter project for you as it could all be done with sexy and his new friend so you can do it in the warm and if you need a break after 20mins you can just leave it and come back in a while.

Offline vtsteam

  • Full Member
  • ****
  • Posts: 753
Re: My Little Donkey
« Reply #21 on: November 06, 2022, 03:12:44 PM »
Beautiful model again!
Jason do the drilled steam ports look like a right angle inside the cylinder metal, or do they rise obliquely from the cylinder end to the steam chest?
Steve

Offline Jasonb

  • Full Member
  • *****
  • Posts: 9467
  • Surrey, UK
Re: My Little Donkey
« Reply #22 on: November 06, 2022, 03:46:03 PM »
On these smaller engines I tend do drill them parallel to the bore, it's not as though I'm after every last bit of performance where the slightly smoother flow of angled drillings would perhaps offer a tiny percentage advantage. They do end in a 118deg drilled hole not the flat bottomed one drawn, 2mm dia in this case


Offline vtsteam

  • Full Member
  • ****
  • Posts: 753
Re: My Little Donkey
« Reply #23 on: November 06, 2022, 05:46:40 PM »
Thanks! That looks a lot easier for a small engine.
Steve

Offline Jasonb

  • Full Member
  • *****
  • Posts: 9467
  • Surrey, UK
Re: My Little Donkey
« Reply #24 on: November 19, 2022, 06:49:26 PM »
Two blocks of cast iron were milled up to the overall sizes needed for the valve chest & cover and a couple of ctr drill holes added to aid clocking them in the 4-jaw.



First the valve chest was turned to form the spigot for the gland, final cuts were done with a 1mm radius tool to leave a small fillet where the spigot meets the chest.



The same methods were used on the chest cover to form the boss where in inlet pipe screws in, this was tapped M4 x 0.5 metric fine. I've taken to using my old Unimat 3 four jaw chuck on a 1/2" parallel arbor for smaller items as that can be slipped into the 5C chuck and saves having to change to the larger 4-jaw.



Then back into the mill vice to drill the stud clearance holes and mill out the cavity in the chest which was roughed out with a couple of drill holes then a few laps around the edge with a 4mm dia cutter to form the rectangular cavity.



Progress so far





The valve was machined on the end of some 8mm square brass bar, first the cavity



Then the slots for the nut and rod



Offline vtsteam

  • Full Member
  • ****
  • Posts: 753
Re: My Little Donkey
« Reply #25 on: November 20, 2022, 02:36:16 PM »
That looks great, Jason!
Steve

Offline Jasonb

  • Full Member
  • *****
  • Posts: 9467
  • Surrey, UK
Re: My Little Donkey
« Reply #26 on: December 05, 2022, 08:26:36 PM »
Thought I better finish off the details of the last few bits.

The eccentric strap was made from two pieces of 4mm thick brass, I milled steps in the sides and drilled and tapped so they could be held together with M2 fixings while the main hole was started with a drill and then completed with the boring head.



Due to the compact design which the scotch yoke allows there is no room for an eccentric rod so the end of the strap was formed and drilled to fit directly into the fork of the valve rod. Final shaping was done by filing



A groove was turned around some 16mm steel bar and sized to suit the strap, this bar was then offset in the 4-jaw and drilled and reamed to fit the crankshaft. At the same setting the boss was turned and after parting off the boss was drilled & tapped for a M3 grub screw.



I started the cross head by turning the two smaller diameter lengths either side of the larger diameter central section then moved over to the spin indexer to add an 8mm counterbore and 5mm through hole.



After silver soldering in a piece 8mm diameter brass that had the end reduced to 5mm into those holes it was back into the lathe to drill and ream 6mm for the slipper. With that done it was back to the indexer to tap the larger boss M5 x 0.5 for the pump ram and the smaller one was tapped M3 x 0.5 for the valve rod. The last job before parting off from the parent bar was to mill as slot to clear the crank pin.



The pump body was constructed in much the same way - Turn the outside, add some locating pockets, solder in some stubs and then finally machine.



The last bit of machining I have a photo of is the cross head slipper that was turned to a sliding fit in the yoke's 6mm bore and then cross drilled and reamed for the 4mm crank pin.



With all the bits roughly assembled I set the eccentric by eye  and gave it a try, after increasing the pressure a bit it was running but not as smoothly as I would have likes but good enough to strip down and then sort out the bugs on final assembly. I actually found one of them as I took it apart, on setting the eccentric I had got it a bit tight to the bearing and this was causing some drag. These are all the bits.



I put it back together carefully checking for smooth rotation as each piece was added and found that the end of the crank pin was just touching the outer edge of the hole in the yoke which was putting sideways load onto the piston rod and pump plunger. With a little machined off the offending pin all went together well and on trying it on air again I could now run at less than 5psi and get down to a nice slow tick over.

<a href="https://www.youtube.com/watch?v=T871NGafEAo" target="_blank">http://www.youtube.com/watch?v=T871NGafEAo</a>

« Last Edit: December 05, 2022, 08:34:27 PM by Jasonb »

Offline steamer

  • Global Moderator
  • Full Member
  • *****
  • Posts: 12697
  • Central Massachusetts, USA
Re: My Little Donkey
« Reply #27 on: December 05, 2022, 08:57:31 PM »
What a sweet little pump!     It would be at home on a steam launch at twice size.

Nice!

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Twizseven

  • Full Member
  • ****
  • Posts: 773
Re: My Little Donkey
« Reply #28 on: December 05, 2022, 09:40:18 PM »
Jason,

You certainly achieve some amazing results with your fabrication skills.

Colin

Offline Admiral_dk

  • Full Member
  • *****
  • Posts: 3752
  • Søften - Denmark
Re: My Little Donkey
« Reply #29 on: December 05, 2022, 10:13:02 PM »
Great looking, running + pumping  :ThumbsUp:   :ThumbsUp:

What is not to like  :cheers:

Per

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal