Author Topic: Sweet Pea build  (Read 9736 times)

Offline Barneydog

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Sweet Pea build
« on: January 15, 2021, 12:19:55 PM »
Hi All,
I have now moved on to my next loco build and have decided to post the build here for you. Several years ago I bought a part-built Sweet Pea consisting of fully built frames, horn castings, axlebox cast iron block, part machined wheels, a bag of assorted bits, the build book by Jack Buckler and a full set of plans.

It has sat on the back burner for all this time but it is now ready to build. I have collected a large amount of the metal required to more or less complete the build.


The frames were un painted but have been stored completely wrapped in kitchen clingfilm. Now they are out I have sprayed them with grey etching primer to avoid them rusting during the build. They are very well built from 5mm bright mild steel plate. They are perfectly square and not twisted atall. You will notice this is the 0-4-2 version. I have several changes I want to make to this model including either a change from Hackworth to walchaerts valve gear or a mod on the hackworth to improve it, change of regulator to a ballvalve system, a rosebud grate or possibly gas firing to name but a few. More of these as and when they are decided.
I have started on the horn machining but will post that later.

Cheers

Julian

Offline Barneydog

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Re: Sweet Pea build
« Reply #1 on: January 15, 2021, 12:59:05 PM »
Hi Guys,
Yesterday I started the machining of the hornplates. They come as four bronze castings. Unusually they are generous enough on their size to not have to worry too much. As you can see from the photo they are an offset tee shape. The narrow side of the tee sits in the horn opening with the top of the tee facing the axle box and the leg of the tee bolted to the back of the frame. I intend following the build process of the book as much as possible as this is a proven build order. Th casting is clamped into the mill vice upside down on some packing to give a little clearance from the vice jaws.

On all the casting I am keeping the narrow side of the tee against the fixed jaw of the vice. This will ensure that they are all the same. The measurements given in the book and on the plans do not need to be deadly accurate but it is important that they are the same for every casting. If they are not it will put the wheels out of alignment. The leg of the tee needs to be 3/16". The sides of it change slightly as the frames are made from 5mm steel which is slightly thicker than the 3/16" alternative. Looking at it logically the only critical measurements are the narrow side of the leg and the top of the tee. The narrow side sets how far the wheels sit from the frames and the top of the tee holds the axle boxes. They are machined as one before being split into four so the faces need to be identical.

All top faces were machined but I left the narrow side slightly bigger than the required .244" for later squaring and adjustment.

Once all four were done they were each machined the other way up. The top of the tee needs to be 3/4" wide. The tee sat on a couple of spacers to hold it clear of the top of the jaws. The sides were machined on all four.

Next each tee sat flat on the top of the vice jaws and had the top fly cut so they were all the same thickness. Digital readouts helped with this. I machined the thinnest until it was correct then zeroed my readout. The other three were machined until each read zero on the readout.

All four were machined again on the narrow side of the leg to bring them all to a uniform size and to ensure the face of the leg is square with the top of the tee.

Here are all four completed just needing a quick clean on the edges with a file. Next job is to cut to length and fit them

Cheers

Julian

Offline sco

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Re: Sweet Pea build
« Reply #2 on: January 15, 2021, 02:04:43 PM »
 :popcorn:

The old man has been building a Sweet Pea for 20 years or more - I reckon he is at about the same stage  ;D

Simon.
Ars longa, vita brevis.

Offline Barneydog

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Re: Sweet Pea build
« Reply #3 on: January 15, 2021, 05:50:59 PM »
Hi Simon,

Perhaps you need to give him a hand.
I want this built as quickly as I can. My last one was a Simplex which has taken me about three or four years. Too long but a steep learning curve.

Cheers

Julian

Offline Barneydog

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Re: Sweet Pea build
« Reply #4 on: January 15, 2021, 06:38:09 PM »
Hi Guys,

Spent the afternoon outside today finishing the horns.

Marked and cut the four castings in half. There is a little spare length but nou much. Eaqch one needs to finish at 2 7/16" which only gives about 4mm spare. You will have to excuse my use of imperial and metric measurements. I work all the time in metric and only use imperial when it suits me. Mostly when reading plans. Often I will convert to metric.
Anyway moving on. I used the lathe to clean the cut ends of the castings and to finish to length.

I cleaned one end on each then marked them for length. Blue marker pen then a scratch with calipers set to 2 7/16". Shortened to the scratch mark in the lathe. I kept each pair from each casting together.

I marked them all 5/16" from the bottom for milling away to fit horn supports later. The top edge of the narrow side was filed away to a curve to match the curved corner of the openings in the frame.

In the mill and mill away the bottom edge.

They are now handed and will only fit on one side of the cutouts in the frames to I kept them tagged together when not working on them.

I made a rough axlebox from a bit of ali just to position the horns while fitting them.


Clamped onto frames, squared and drilled. The holes on the frame were 3.6mm for 4ba bolts but I used M4 stainless button heads with stainless nylok nuts behind. Drilled through 4mm whie clamps were on.

All four done and the bar of cast iron for the axle boxes sitting in front.

Next will be the horn support bars which will be made from Stainless. I plan to use alot of stainless to avoid problems with rust and excessive amounts of dripping oil.

Cheers

Julian

Offline Firebird

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Re: Sweet Pea build
« Reply #5 on: January 15, 2021, 09:03:09 PM »
Hi

Looks like you made a good start. :ThumbsUp:

Will be a beast of a loco

Cheers

Rich




Offline propforward

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Re: Sweet Pea build
« Reply #6 on: January 15, 2021, 10:41:37 PM »
Lovely. That's going to be a fascinating build, and I shall be following along.
Stuart

Offline joe d

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Re: Sweet Pea build
« Reply #7 on: January 15, 2021, 11:08:32 PM »
Looking good already, I'll be following along.  A locomotive is on my one-of-these-days list.

Joe

Offline Barneydog

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Re: Sweet Pea build
« Reply #8 on: January 16, 2021, 05:36:14 PM »
Thanks Rich, Stuart and Joe. All praise gladly accepted

Well this afternoon my wife said "You could go outside for an hour if you want".  Guess what?  I'm gone!

Needed to build the hornkeeps next. They go across the bottom of the horns to add support and help stop the horns spreading with the load.

Four bits of 5/16" square cut to the length of the bottom of the horns.

All machined to length in the lathe and drilled on the ends 4mm. Middle hole is drilled and tapped M5 for a bolt to go in later to stop the axles dropping too far when the loco is lifted. Each one has been engraved on the inner face to indicate the position and front direction. This is because they are each used to drill the bolt holes in the bottom of the horns.

All four bolted on with M4 stainless bolts and stainless nylok nuts.


Checked after and realised its not stainless bar its mild steel. Now they are made they can be painted or nickel plated later. They will have to come off to fit the axle boxes anyway.
Took just over an hour so a good job done today. Axle boxes next hopefully tomorrow or monday.

Cheers

Julian


Offline FKreider

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Re: Sweet Pea build
« Reply #9 on: January 17, 2021, 03:37:45 AM »
Looks great!
-Frank K.

Offline Barneydog

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Re: Sweet Pea build
« Reply #10 on: January 17, 2021, 08:35:55 AM »
Thanks Frank

Unfortunately square stainless is not available here so the choice is waste and machine round down to square or use another metal. I will have to get the nickel plating kit out.

Cheers

Julian

Offline Barneydog

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Re: Sweet Pea build
« Reply #11 on: January 18, 2021, 06:08:46 PM »
Hi Guys,

The next job is the axle boxes. These are machined from cast iron.

This lump of cast came with the loco. Its enough for all four boxes.

The design above calls for solid axle boxes. The trouble with this is that once the wheels are glued onto the axles the boxes can only be removed by first removing the wheels. The design is solid as these are easier to machine. Because I am modifying the Hackworth motion I need to redesign the boxes on the rear axle so I decided it would be easier to make them into split boxes.
First job was to square and size the block of cast ready for machining. I have a CNC mill so used this as there would be a large amount of handle turning on the manual mill. The CNC system acts as a power drive in all directions in manual mode.

All four faces were cleaned up, squared and sized. I took it down to 45mm by about 26mm.
I marked one of the larger faces that will stay against the fixed jaw on the vice. This face will also be the outer face on the completed axle boxes.
First move is to mill the channels on the sides so they fit the horn blocks. I milled along the middle of the first side and took several cuts to go 4mm deep. Once this was done I left the depth alone and using the other two axis's widened the channel until it was 18.5mm wide and the lip on the front against the fixed jaw was 3mm wide.

This needs to be the same on both front lips so the boxes sit level in the horns and all stick out the same distance from the frames. I then turned the block over in the vice keeping the same face against the fixed jaw. I repeated the previous operations to machine the channel on this side to match the first side. The only difference was when the depth neared 4mm I measured the land between the channels until it matched the openings on the horn blocks. This was 36.5mm.

With both sides identical it was time to cut them up. Had I been using solid axle boxes this would have been three cuts but because I am making split boxes each box needs to be cut in half. To allow for a little more cleaning up of the cuts I had to make them slightly shorter.

One at a time I sliced of 20mm lengths in my bandsaw. I have adjusted the blade so it gives an almost 90 degree cut. It is within a half degree so good enough. As I sliced them I labelled the sections so the cuts match each other. They will now stay in these pairs throughout machining for accuracy.

Along one edge of the face that was against the fixed jaw I have scribed a line along the length of the bar to give a common edge for all the boxes. This will be the front edge of every box and will be the common edge for many measurements from now on.

Here are all four boxes ready for drilling which will be the first job next time.

I had planned to install needle roller bearings in the axle boxes but they were a bit too wide to fit comfortably in the boxes and like solid boxes could not easily be removed from the axles if necessary. They would also have increased the size of the axle from 17mm to 20mm diameter. In the boxes for the rear axle I need to add four M5 tapped holes to the inside faces so this would have been virtually impossible with the 26mm diameter of the bearings. This is an easy compromise as a steel axle running in a cast iron box should wear very well.

Cheers

Julian

Offline Firebird

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Re: Sweet Pea build
« Reply #12 on: January 18, 2021, 06:25:42 PM »
Hi

Nice work Julian  :ThumbsUp:

Why mod to valve gear??

Cheers

Rich

Offline scc

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Re: Sweet Pea build
« Reply #13 on: January 18, 2021, 09:17:13 PM »
 :popcorn: :popcorn: :ThumbsUp:

Offline Barneydog

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Re: Sweet Pea build
« Reply #14 on: January 18, 2021, 10:42:41 PM »
scc Thanks

Rich,
As we have discussed many times I want to change the Hackworth valve gear motion to make it work better.

For everyone else's benefit I will outline here why it is needed. As designed the main slider mechanism sits on a shaft supported by a tube and brackets attached to the main frames directly above the rear axle. There is a rod linking the axle to this slider but as the axle goes up and down on its suspension it alters the valve openings and makes the running very rough. The designer understood this problem and in the build book replaces the rear springs with blocks of rubber. This removes almost all the movement so keeps the valve events more accurate. A consequence of this is that the only viable suspension is on the front axle. Myself and Rich have discussed several times mounting the support bracket on the axle boxes so they go up and down with the suspension and keep the valve events correct. I have to make new brackets and alter the axle boxes to mount them on. I got the design from the Sweet Pea facebook group.I will give full details in the next few days as I make the bits and will give credit where it is due then. It means the suspension can go back to fully sprung and so work properly.

Cheers

Julian