I've finally got started on my James Coombes build. Allan will twig what the "with chips" is about…

When I decided to build my first stationary steam engine, I had a very specific configuration in mind. It became very obvious that the Stuart castings and kits like the Victoria are versatile and can be used to build quite wide ranging variants.

My first attempt at a stationary engine was based strongly on the Victoria, but it has some features which are of my design and markedly different.

The James Coombes was configured from some existing Stuart castings and extrusions, then a few extra, like the boxbed, the cylinder caps and crankrod guides were created for the kit.

My Victoria was a long time in the making, mainly because of the time taken to work out the design and build of the bespoke parts. Although the Victoria was built and intended to run on steam, I 've only run it on air, I couldn't face stripping it down to clean out the water and gunk from the steam oil afterwards as it would be on the shelf for very long periods.

So, for the James Coombes, the plan was to build it straight out of the box, but include the governor. The cheap way to make the governor was to use the plan I have for the original governor kit and simply buy the fixings kit, which provides the balls and spring and of course, the fixings.

When I started reviewing the plans, I decided that the four columns that support the cylinder assembly could be improved by using square bar so that the machining would leave square "feet" at each end of a column and to add create the impression of a chapiter at the top of each column.

https://www.dropbox.com/s/guo4vldmcz75rh0/P1030609.JPG

This is the prototype column.

The work is in the early stages, but some photo's to be going on with:

https://www.dropbox.com/sh/zue22yuxsike8wf/AAC8rMwlh2m4e068NRjDTczga

I need to upload some of these to the forum so I can include the images in the post, which I'll do shortly. The Victoria was two years in the build, hopefully I can build the James Coombes to a shorter timescale.

Steve

This is the prototype column, I sketched it out, machined it, had a think about the proportions

and then made four "production" components:

I'm afraid I missed out the lilywork and pomegranates, may be next time

When I built my first engine, the Nemett 15S (the "Lynx" I think it is now called?) I'd make a part, admire it, then throw it on the bench, and move on to the next part. Stupid.

Now they don't get lost or damaged!

When Allan was posting the build of his Victoria, I often pulled his leg about the lack of chips in his photo's (hence the title of the original post). Here is a picture of just some of the material that was produced as a machined the columns. I made A LOTof this in the process.

The serious point to make to folks just starting out, is that this stuff is razor sharp and you do not tug at it with bare fingers. The second point is that I used home ground lefthand and righthand HSS knife tools. The Lefthand tool in particular was suberb at removing material and producing a very nice finish. It did this by producing continuous lengths of this stuff at high speed, which can be dangerous (you really wouldn't want this wrapped around your nose!). One solution I've successfully used with a homemade boring bar is to grind a groove behind the cutting edge, which will break up the swarf and make the cutting operation much safer.

In the photo below, I've swapped my quick change tool post for a standard four way tool post and set up the LH and RH knife tools, which I think is a lot faster for this operation than the QCTP.

Cutting the threads on each of the column was done with a tailstock dieholder:

I did not cut the threads under power, but just spun the chuck by hand. The chuck by the way is a TOS four jaw self centering type. I bought this from one of the usual suspects for about £70, a real bargain, the only time I use the three jaw now is for hex bar.

The mounting studs at the end of each column have a 1/8 inch shoulder, I measured this very simply by using a piece of 1/8 inch silver steel as a gauge:

And the last thought in this post is to remember to protect components from damage when holding them in the chuck. You can just see the use of soft metal sheet (I had a bit of scrap bronze shim in the box) to protect the column from the chuck jaws.

Edited By Steve Withnell on 17/05/2014 20:28:04

It's to do with Allan's thread on his Victoria build. In his photo's, his machines are always immaculate, so from time to time I'd ask him where the chips where. My machines are not immaculate, hence the chips!

Steve

A bit of a dilemma. I set out to build the James Coombe straight off the plan, but made two changes already!

I've started work on the cylinder and it is identical to the Victoria. The steam ports are 1/16 in from the ends of the cylinder. The cylinder end caps for the Victoria have a 1/16 thick boss so when they are fitted to the cylinder, the steam ports are at the very ends of the enclosed cylinder.

On the James Coombes plan, the bottom of the cylinder (the end without the piston rod) is fixed directly to the table plate, so there is a 1/16 gap between the bottom of the enclosed cylinder and the steam port.

In Andrew Wilson's book "Building the James Coombes…" he describes making a spigot 1/16 thick, 1 inch diameter with a 1/4 inch peg on the underside to be a press fit into the table plate, this allows for accurate location of the cylinder before drilling the fixing holes around the cylinder flange. This spigot is a permanent addition an will also serve to eliminate the 1/16 gap between the plate and the steam port. Andrew Wilson doesn't comment on this latter point in the book.

"How" isn't a problem, but will the effort of making the spigot actually make a material difference to the engine when it is running? Also, given how the spigot is fixed, will this cause problems over time? Stuart clearly didn't think it necessary when revising the plans.

Regards

Steve

After completing the box bed, I progressed onto the off-board bearing mount. This component has to have a finished height of 3 inches so that the bearing will end up at the same height as the bearing on the box bed. It's a straight forward job on the lathe, except that the sides are tapered, so it cannot be clamped directly to an angle plate.

In this photo the casting is pressed against a packing piece, but you can see the front edge is not in contact with the angle plate. Using the tailstock to keep pressure on the workpiece during clamping is a neat trick someone on the forum told me about, but can't remember who! It does work.

In this photo, I've shown the packing piece underneath the workpiece. It turns out that the web is actually parallel to the vertical axis, so it can be used as a reference, so this is what is used to clamp against, just needs the packing piece. I've also taped down the packing piece to ensure no unexpected departures from the angle plate.

Finally, the workpiece clamped down against the web

The packing piece has to be clear of the radiused edges of the web. I'm not going to drill the bearing mount until I've completed the bearings themselves, as I will spot through from the bearing into this mount.

Edited By Steve Withnell on 30/05/2014 21:05:53

Next step is to machine the cylinder, I followed the method described by Andrew Wilson in "Building the James Coombes". It's the same method as for the Victoria, it is the same cylinder.

Once the cylinder casting has been cleaned up, then the cylinder is set up in the four jaw chuck using the jaw slots as pseudo V-blocks

The port face is set square by using a set square on the cross slide –

Again using the tailstock to make sure the workpiece is properly seated in the chuck –

Thin card being used all the while to prevent the jaws damaging the softer cast iron. The port face only needs a light skim, to bring it to dimension.

The actual ports are a bit untidy, so these I cleaned up with a needle file, but it's quite difficult to get them to plan.

Next step is to skim the exhaust port, this is done by rotating the cylinder through 90 degrees, the port face itself is now used as a datum. (the port face and the exhaust port should be at 90 degrees).

Here you can see how poor the port face is, from what it needs to be. There is plenty of material to go at to get to a decent finish. The thing to be careful of, is that the tool is used between the flanges, so important to take care not to hit them as the cylinder is whizzing around.

Just a couple of notes on my lathe. I have a centre pop mark on the spindle, in this photo you can also see a matching pop mark on the back of the face plate. Once I'd had the face plate a couple of years I centre popped the back, then took a light skim right across. The intent, if not the reality, is that provided I'm scrupulous about keeping the mating faces clean, the faceplate should run true. I use the same technique with all my chucks too, though not the independent 4-Jaw, to minimise the run-out. Chuck back plates are not expensive for this machine and ir's not hard to machine them in-situ to achieve minimum run-out. Given the runout on my first lathe chuck was 1/16 and I still managed to make a cylinder and piston set, It's not something I obsess about.

Final piece is this –

Two points, my machines are all metric and Stuart kits are imperial, so I use excel to make and laminate conversion charts. The little fixture I made for the Victoria and I pretty chuffed with it to be honest. The plug end is turned to 25.4mm to act as a gauge for boring the cylinder to size, the top flange is a drilling jig, it has a series of 7BA tapping size holes to make drilling the cylinder easier. Last part its that I have turned a recess into the large end which matches the cylinder cap boss, so it can be used as a drilling jig for the cylinder caps. A lot of value from a 30mm length of EN1 ! I'll show this little jig in place when I write up the boring operation.

So boring in action, all sound and fury –

**LINK**

It's a big file, so don't click the link if you are on 9.6K dial up

The spindle speed is around 150rpm I think.

As per the previous post, I made a little plug gauge / drilling jig for these cylinders, here you can see the holes and the recess for the cylinder cap. At this point the gauge is a push fit, there is some resistance to entering the bore. The trick I use to getting to size is simply to "test" a new cut I put on, by just boring a little way (<1mm) and checking with the plug gauge, if it doesn't fit, I take the cut and then repeat. If I've put a bit much on, I can back off the cut a bit and try again. This way, if you do go oversize, there is only a small fraction that is oversize and doesn't spoil the job.The conventional wisdom is to take a number of cuts at the same setting to finish off the bore. I've found that once I've made a number of very light cuts, the effect is the same. The gauge fit the same both ends when I'd finished.

Once the bore is the right size, then I faced off the cylinder with a round nosed tool. At this point the flange face and the bore are at 90 degrees to each other and will be the end we use for the piston rod to enter as the other end is less likely to be as true.

Now the cylinder is turned around with the machined flange against the faceplate, protected with thin card, this should mean the two machined flanges are parallel.

Finally the cylinder can come off the machine – here I've marked the front flange in black marker and also put a little centre pop mark in the top of the casting, so I know which end is which

The machined portface is sat on a piece of card… I'll clean the lathe up, the cast iron makes a real mess and gets everywhere. It also makes an excellent grinding paste when mixed with the way oil, so it really must not be left. I know some folks cover the ways and saddle with a cloth to keep the horror out of the machine, I did try that once, but spent more time worrying about the rag getting caught in the work than I did about getting a good job done. Although I leave a bit of slack in the drive belt, the lathe still has plenty of torque to do damage a low speeds.

Next installment is the drive pulley. Should be a bit more straightforward.

The tools I used for the pulley were ground for the job, so freshly sharp – I wonder if the tool was set too high, so causing the rubbing? There was plenty of dusty stuff!

Next casting to machine is the cylinder end cap, that also provides a platform for the cross head guides, so it's a bit different to the usual.

I've mounted the casting in the 4 Jaw chuck, with a "circular parallel" to keep it as square as possible, I know some people like to use old ball races for supporting thin workpieces.

In this photo, I'm machining the spigot side first:

The approach I took was to take a light facing cut to clean up the casting. The I turned the spigot diameter to a good fit with the cylinder. Once that was done, I reduced the spigot to the 1/16 depth as per plan. Finally I used a "V" tool to get rid of the little fillet that was left in the corner between spigot and plate.

Next job is to drill and ream a hole for the piston rod –

That all progressed with no issue, so next job is to flip the cylinder cap over and machine the other side. To set up the cap, I used the tailstock to press the plate flate against the "circular parallel" and then clocked it true using the reamed hole as the datum:

Again, skimming the plate just enough to clean it up (the plate thickness has no dimension on the plan) then skimming the gland part of the casting to size all that is left is to counterbore the gland to 5/16.

In this picture, you can see I have added a DRO to the tailstock. This arrangement often fouls the toolpost when working between centres or with tailstock support, so it has to be removed.

Finally, the finished (bar the various mounting holes!) part:

Next piece is the steam chest and cover. I'm sticking to plan of getting all the cast iron machining out of the way, so I'll only have one big clean up to do. The I'll finish all the bits requiring the 4-jaw, such as the eccentrics and bearing mounts.