Sunday, 27 March 2016

You have to be a bit eccentric...

During the week commencing 21/03 there was quite a bit of activity on CR828. Work continued on the boiler to get it ready for the hydraulic test requested by the Boiler Inspector. All we need now is the pair of large blanks required to blank off the safety valve mountings and we'll be good to go.

The crankaxle has had a lot of attention. Colin Boyd measured up the crankpins for ovality and parallelism. We knew from the previous overhaul that the RH pin is slightly tapered (for reasons unknown) and Colin confirmed that this is still the case. Now that we have the sizes Nathan will be able to machine the big end bearings to size and then we can get them scraped in to the required fit.

For the first time in more than half a century the eccentric sheaves have been removed from the crank axle. This is not a job for the fainthearted but Alan French made up an excellent special tool that allows the square headed clamping screws to be accessed deep inside the eccentric castings. The castings are a beautiful piece of 19th Century workmanship but they are heavy....very heavy..! Once the sheaves were removed it was a matter of cleaning them up and then reassembling them so they can be checked for wear. Three out of the four were found to be surprisingly unworn but the RH forward eccentric is the exception and shows about 0.037" of ovality. So that we give the newly white-metalled eccentric straps the best start in life all of the eccentric sheaves will be mounted on a mandrel in the big lathe and skimmed back to full circularity. There is therefore a lot of lathe work coming up in the next couple of weeks...

Removing the gauge glasses in preparation for the boiler hydraulic test. The regulator handle will need a lot of polishing before 828 goes back into service.....

View looking into the smokebox during replacement of the five washout plugs. JF MacIntosh designed the Dunalastair boiler to generate large volumes of steam (828 has a Dunalastair I boiler and Dunalastair II cylinders and motion) and the number of boiler tubes testifies to this...not much room for water...!

A grubby hand inserts the rearmost fusible plug into the roof of the firebox.....the firebox has two fusible plugs, the purpose of which is to alert the footplate crew to very low water level in the boiler. The plugs are hollow and lined with lead. At normal water levels the lead is kept relatively cool. If the water level gets too low the lead quickly overheats, melts and is blown out of the body of the plug. This is followed by a jet of steam and water blowing out into the firebox. This immediately alerts the crew who should take appropriate action to try and increase the water level as quickly as possible. At the subsequent official enquiry the Driver and Fireman will have a lot of explaining to do.....!!!

Removing the gauge glass fittings requires some special tools......!

Bothe gauge glasses removed and blank flanges fitted for the hydraulic test
Concentrating hard - Colin Boyd is using a large micrometer to record very accurate measurements on the RH Crankpin. JF MacIntosh sized the bearing surfaces very generously on his locomotives. The crankpins on 828 are 8 inches in diameter. It was features like this that made the MacIntosh locomotives perform so satisfactorily and achieve such long lives.

The Caledonian Railway in MacIntosh's days preferred to build their locos with inside cylinders. This gave greater stability and reduced wear and tear on the track (outside cylinder locos have a tendency to sway from side to side under the power impulses from the pistons). The price for this was the requirement for a very complex crank axle. The Caley used a variety of types of crank axle but by 1899 when 828 was built they used fully built up steel axles. Because these were very costly and time consuming to manufacture they were bought-in from outside contractors. Here, on one of 828's RH crankwebs we see the identification number that allowed the Caley (or LMS) to trace the manufacturing records of this particular axle. Note also the highly polished surface of the journal for the axlebox bearing.

Crank axle with the RH Eccentric Sheaves removed. The LH Eccentrics are still in place. The leftmost of the two is the eccentric that gives forward motion; the other one gives backward motion. 

The crankaxle with both sets of eccentric sheaves removed. As a "fully built" axle it consists of nine individual parts pressed and dowelled together. Manufacturing a replacement would be horrifyingly expensive today....!

One half of the LH eccentric sheaves being cleaned in the Shed's parts cleaner - a very useful piece of equipment indeed.
Both sets of eccentric sheaves on the bench at the north end of the shed. It takes three people to lift them when they are assembled. Nathan Lightowler is measuring the diameter at 90 degree intervals so that we can check for wear.

Saturday, 19 March 2016

Reaming, Reaming, Reaming.....

This week's work on CR 828 has been mainly about reaming bolt holes and trying to avoid as many steel skelfs as possible... Nathan Lightowler has also been very busy machining fitted bolts for the RH Driving Hornblock. He's also progressed the machining of the new steel casting for the LH Driving Hornblock. We had a bit of a disappointment when it became clear that despite Nathan's very best efforts the Shed milling machine just doesn't have the capacity to handle the new horn block. So rather than struggle on and perhaps get an unsatisfactory result we took the decision to send the casting out to a suitable third party machine shop. The silver lining to this particular cloud is that it frees Nathan to tackle the machining of the big end bearings and the eccentric straps. We plan to crack on with this during week commencing Monday 21st March. Once the machining is complete there will be a lot of hand fitting to get the components bedded properly to their respective crank pins and eccentric sheaves.

A welcome sight..! The RH Driving Hornblock now fully bolted to the frames. The new bolts were made a slight interference fit and then driven into the holes using a seven pound long handled hammer. Hopefully it will be a long time until they are next removed...!

With the RH Hornblock refitted it was time to make a start on truing-up the holes in the LH Driving Horn where we had to make a weld repair to a crack that ran through several bolt holes. The Welder did a great job in trying to preserve the holes during the repair and it was possible to ease them back into a circular section with some filing and then the trusty reamer. There will be no need to anything more here until the horn block casting is lifted into position.

All the holes in the leading edge of the horn are now reamed circular and to the same size...

This object is the horn clip that bolts onto the underside of the RH Driving horn. It has two main functions. 1) It ties the open ends of the horn block together to give the structural rigidity necessary to resist the powerful thrusts of 828's 18 1/2" pistons. 2) It transmits the weight of the locomotive to the suspension springs on the crankaxle. In total the crankaxle carries about 18 tons of the loco's weight so the horn clips on either side of the loco carry about 9 tons each. The circular holes in the clip are for the spring hanger pins that connect to the axlebox. In this view we are looking at the top surface of the clip. The square holes at each end are for the studs that carry the large nuts that clamp the clip to the hornblock. 

This view shows the side and the bottom of the clip. The seatings for the springs are the two large circular recesses. The clip weighs about 35kg and is made of cast steel. It looks a strange colour because it had just been removed from the Shed sandblaster. We decided that it would be a good idea to get two new clips made and these will be produced in the next week or so by Blantyre Castings who manufactured the new horn block a few weeks ago.  

The weather in Strathspey was very sunny and warm during the week and here is our old friend enjoying a view of the Spring sunshine......hopefully it won't be too long till she'll be back out enjoying it....

Sunday, 13 March 2016

Let's get these bolts fitted...

Quite a lot of progress with 828 in the last few days. Most of the attention has been on the RH Driving Hornblock where we need to true up the bolt holes in the frame and the horn block casting. One disadvantage of inside cylinder locos is that the piston thrusts are transmitted through the axleboxes and the hornblocks. On a loco like 828 each piston thrust may be as much as 12 tons so the bolts need to be a tight fit. Because the bolt holes have been progressively opened out at different times in the long life of the loco it's important that we remove as little metal as possible when truing up the holes. This meant that it's better to do it with an expandable (adjustable) reamer driven by hand. It is excellent exercise....then having reamed the holes truly circular and parallel we need to make up bolts that are a very precise fit in the holes. The bolts need to be slightly bigger than the holes and driven into place using a heavy hammer. In our case the bolts, properly known as fitted bolts, are manufactured in the shed machine shop by Mr Nathan Lightowler who can turn them up from hexagonal bar stock in a very short time - and every one is a perfect fit...!

John Greig has carried on white-metalling the remaining eccentric straps and these are now all ready for machining in the lathe and then hand-fitting them to their respective eccentrics. The eccentrics themselves will need to be dressed and polished to ensure there are no rough surfaces to tear the white metal.

Starting to ream out the bolt holes with an expandable reamer and a big tap wrench...

eight holes reamed circular and parallel ready for the fitted bolts.

Nathan Lightowler machining the first of the fitted bolts......only 43 to go after this one, Nathan...!

The first fitted bolt alongside my calibrated lunchtime orange...
The first eight bolts driven home.....

The hammer that drove the bolts home.....they are a tight fit...!

View of the bolts from inside the frames...

Crankaxle moved down to the machine shop awaiting fitting of the big end bearings and the eccentric straps - all newly white-metalled by John Greig
General view from the new mezzanine floor...828 crankaxle, 5025 bogie and main springs plus No.17 "Braeriach" just crying out to be converted into the 0-6-2T that Eric Cooper had always intended....!!!!!