Building the James Coombes (with chips)

[Steve WithnellParticipant @stevewithnell34426]

Getting a bit repetitive now – here is the steam chest machining. The steam chest casting is close to dimension and with skill, you could actually file this to size and not use a machine at all.

I reset the backstop then skimmed one side, flipped the steam chest over and skimmed the other. The warning here is that the valve rod is offset in the height of the steam chest, don't make top and bottom equal heights!

Skimming off just enough to clean up the surface will do. I then flipped it over and skimmed the other side. The dimensions are not critical, but if you take too much off the bottom, there will not be space for the valve rod to fit properly with the valve.

Next job is to rotate the chest, the steam chest has to be set up so that the centreline of the gland is on the centreline of the lathe. There will be tears if this isn't all square and Stuart's till will go "Kerching". Skim the gland, centre drill, drill, drill, ream, counterbore. Again, skimming just enough to get to a nice finish on the gland is enough, then I centre drilled (I always centre drill first) and you then need a 3/32 long series drill to drill right through the casting and then into the back off the casing into the little pimple at the back, which supports the valve rod. Then drill 3.1 mm through the gland only, then ream 1/8 inch. Next step is to counterbore the gland with a 1/4 drill.

This is a mod I made to the lathe early on – when I made the Nemmett which has quite a few holes drilled using the tailstock, I got fed up counting handle turns and doing the arithmetic 4 turns + 3 ticks = x. Whilst the mod is really easy, surprisingly it fouls the toolpost when using the tailstock with a centre to support turning longer pieces – I had to take it off to turn the columns as an example. I've seen a variant of this mod with the DRO on top of the tailstock, which should avoid the issue.

Almost done – only the crank web and the crosshead support bars left out of the castings to machine.

[Steve WithnellParticipant @stevewithnell34426]

Just spotted another mod to the tailstock in the last photo. Instead of a locking nut, there is a small handle. This allows the tailstock to be locked in a quarter turn without the need for a spanner. However.

As shipped, and I guess a lot of chinese lathes have the same problem, if you remove the tailstock from the lathe by removing the clamping bolt, you will have a tailstock, a bolt, a nut and a washer. You will also have a lump of cast iron pretending to be the clamping block that locks the tailstock in place. On my lathe and many others, this clamp is so roughly made, the tailstock will not slide smoothly without undoing the nut a couple of turns, which is a pain the in the bum (especially when you continually lose the spanner).

By machining all the working surfaces of the clamping block, parallel & true, which takes a good 10 minutes, the clamping action is transformed. You can then make a handle and have a tailstock which slides up and down quite nicely just by a 1/4 turn on the handle. No spanner required.

The handle unscrews to avoid fouling with some setups.

Steve

[Steve WithnellParticipant @stevewithnell34426]

Here is a trick from Keith Appleton's YT video's – Using Loctite to hold components together for "spotting through":

I've used his trick to hold the steam chest cover to the steam chest. However, I've stuck it to the wrong side!!!

Steve

Edited By Steve Withnell on 21/06/2014 11:53:43

[Steve WithnellParticipant @stevewithnell34426]

Last bit of the castings to go on the lathe before it gets a deep clean to get rid of all that grinding paste I've been making. Some of it can be flushed out, but the felt oiler pads on the saddle will be choked with the stuff. As I wrote at the beginning of this diatribe, some people cover the lathe bed with a cloth to keep this cast iron chips out of the lathe, but I worry about the thing getting caught up in the chuck.

Anyway a last little bit – this is the crank web, I skimmed the back of it in the 4-jaw by holding the crank boss and then flipped it over and again, used the backstop. The boss is turned down to the 3/8 inch thickness, then I lightly centre drilled the boss with a No.1 centre drill. The most important thing about the crank web is the holes. They must be the right distance apart and parallel to each other, so I'm going to drill them both on the mill as one setup. If I do it on the lathe I'll have to change the setup, which won't work out too well.

I left the set up as-is and then machined the small-end down to size – 1/4 inch thick. Doing this solved a problem. When I made the Victoria, I couldn't out if the little web between the bosses should be machined away or left in place. By the time both bosses are machined to size, the web is part- machined away as well. Which gives a clue. The web is not shown on the plan.

This photo is the two bosses turned to size, the little centre mark as a datum, ready to go onto the mill for drilling of the holes for the crankshaft and crankpin.

That's all the turning done as far as the cast components are concerned. The next step is the cross-head guides:

These are a job for files and the Milling machine. Not tackled anything like these before, so should be interesting…

Edited By Steve Withnell on 22/06/2014 10:30:31

[Steve WithnellParticipant @stevewithnell34426]

A quick update.  Now the crankweb is off the lathe,  the small boss doesn't have parallel sides,  the clamping forces must have distorted it,  it's out by a little under 0.1mm across the length of the boss,  but OK across it's width.  I've sorted that by a touch with the file.   The big boss supported by the backstop was fine.

Just looking through the plans again and I have found two more components, the piston and because I'm adding the Stuart governor, a cast iron pulley (hence the other post about mandrels). So not quite done turning the cast iron stuff yet.

Steve

 

Edited By Steve Withnell on 22/06/2014 18:08:50

[lancelotParticipant @lancelot]

Hi Steve, you and me are both about the same stage of build on the coombes …difference is , that mine has sat for a long time with nothing done…will start working on it again after i have got the score running on steam…need to order a lot of pipe and fittings …who is best to get from, i am in northern ireland…

all the best for now

john.

[Neil WyattModerator @neilwyatt]

Hi John,

Cunifer brake pipe from your local motor factor might be the most cost effective source, it's 3/16" diameter, bends easily and can be straightened easily by rolling between two flat surfaces.

Neil.

[lancelotParticipant @lancelot]

Hi Neil, thank you for the tip…i have not been in the shed for a long time thus forgetting to order up lots of necessary fittings, i need to find the size and thread of the fitting connecting pipe to main steam valve on boiler bancock 504 so i can run the score,

cheers , John.

[Steve WithnellParticipant @stevewithnell34426]

Hi John,

One thing to watch for with the Stuart plan's is that fittings are typically 32 TPI threads and the current "standard" for steam models appears to be 40TPI. So unless you want to use all Stuart fittings, double check the threads before cutting…

Steve

[Steve WithnellParticipant @stevewithnell34426]

I was going to work on the cross head guides next, but discovered there are a couple more cast iron components to be turned. One is a pulley for the governor drive and the other is the piston itself.

The pulley is made from a short piece of cast iron bar and I managed to find a very short piece of stock the right diameter. Having sought advice from the team in another thread, here is how I went about it. The pulley has a finished width of 1/4 inch and my piece of stock was just 12mm wide.

I had initially thought to use a tapered mandrel, but Jason suggested there might just be enough length to avoid having to make one. In this picture I've faced the front side and turned the outer diameter to size, then bored a hole for the shaft (there was an existing hole a bit off centre, so I couldn't drill and ream).

Although this is a four jaw chuck, it is a self centering chuck of much higher quality than the three jaw chuck that came as part of the lathe bundle. It's useful for square bar too.

I then decided to use a 60 degree single point threading tool to cut the "V". The "cheeks" of the pulley are only 1/32 inch, so when I turned the pulley over to face off the other side, there was not a lot of material to get hold of. I almost managed to get this done in one, you can see how little there machining is left to do. So then as Bob suggested, I loctited the pulley onto a piece of 7/16 bar and used the independant 4-Jaw to get it clocked to truth. The pulley is the minimum distance from the chuck that would allow me to get the DTI on the shaft. As you can see below. The pulley just needed facing off a little more –

Here is the set up showing the use of the single point tool. This is a form tool and so the machine is run very slowly. I had to run about 50rpm to avoid chatter. Here I'm just taking a light cut to ensure the "V" is square with the pulley on the shaft.

And the finally, the finished article: (well almost – it still needs drilling and tapping for a grub screw)

The loctite I used was "270", which is a "stud locker". I did degrease the shaft and pulley before using the Loctite and found that the bond was perfectly good to allow me to finish the machining after only a couple of hours to cure.

Once the machining was finished, I heated it up over a gas flame expecting it to drop off – which it didn't do. Although the Loctite residue was smoking it was still intent on staying put. I tapped the shaft out in the end, as I didn't want to overheat the pulley.

Steve

[Steve WithnellParticipant @stevewithnell34426]

The last turned cast iron component (unless I missed one) is the piston. As shipped by Stuart, this is just a short length of cast iron bar. The process is pretty classic for piston making. The bar is chucked at about half its length, and a chucking spigot turned.

The piece is then flipped over and mounted by the chucking spigot and all the key machining is done with this set up. This means that the outer diameters and piston rod hole remain concentric, regardless of what the spindle / chuck runout might be.

First two turning operations are to face the piston to length (1/4 inch) and to turn the outer diameter to a gnat's more that the cylinder diameter, this will finished later.

Next I centre drill the piston and followed through with a 5BA (3.3mm) clearance drill.

The plan shows a 1/2 inch recess to accomodate the fixing nut at the end of the piston rod. This could be achieved using a little boring bar, but I used a 12mm (I don't have a 1/2 inch one) milling cutter to produce the recess. The diameter of the recess is not critical, just needs to be big enough to take the nut and a box spanner to tighten it up.

The next operation is to cut the groove for the "O" Ring to seal the piston in the cylinder. I did this using a parting off tool as a form tool and running the lathe very slowly, produced the groove. I made the groove a little deeper than plan, as with the Victoria I could not get the piston + "O" Ring into the cylinder.

With all that done, I cut off the spigot with a hack saw as close to the piston as I could, then mounted the piston in the lathe to face off the last remnants of the spigot. The piston does need to be "square" so the faces of the piston remain parallel, but it does not need to be concentric of course.

So now I have no excuse for not doing a deep clean and getting all that cast iron dust out of the lathe…

Steve

[lancelotParticipant @lancelot]

Hi all, went in to the motor factors and got 25 ft of 3/16 cupronickle pipe and a battery for my Mittytoyo diggy caliper now i need to send for some fittings…again thanks for the tip.

Keep her cuttin lads…

John.

[Steve WithnellParticipant @stevewithnell34426]

Got the lathe cleaned up this morning. The cast iron dust gets everywhere, it was not only on the bed but choking the chuck jaws, the ways on the cross slide and compound. Anyway, once the lathe was cleaned up, I decided to start on the eccentric sheave. In the Stuart kit, a short length of "mild steel" bar is provided. I though turning a chucking spigot would be a good way to set this up.

Then decided have a re-read of the "how to" book on building the James Coombes, it's actually better to start with the eccentric strap and then use that as a gauge for turning the sheave to the right diameters. The Victoria and the James Coombes share the same design, there is groove in the centre of the strap bore, that mates with a ridge in the middle of the sheave.

So now set up with the 4-jaw the first task is to face the eccentric strap sides, down to a thickness of 1/4 inch. Again, I'm using a backstop to keep the strap solid and square in the jaws.

A nice change from the cast iron, now the turning produces fountains of tiny golden chips!

The strap is not a casting, but a brass extrusion. It needs to been sawn into two seperate halves. When I made the straps for the VIctoria, I used a thin slitting saw on the Mill, being careful to remove as little material as possible. In fact, the extrusion assumes the strap will be hacksawed and filed to clean up, removing a significant amount of material.

The consequence of not taking enough material is that the outer edge of the strap is not concentric with the sheave. It makes no functional difference, but doesn't look as good as it should.

Steve

 

Edited By Steve Withnell on 01/07/2014 21:34:24

[Steve WithnellParticipant @stevewithnell34426]

Managed to find my original notes and pictures on making the eccentric strap for the Victoria, for anyone that's interested:

**LINK**

Steve

[Steve WithnellParticipant @stevewithnell34426]

Having faced down the eccentric strap, it seemed sensible to face off the bearing mounts to size too, as the setup is the same – press the workpiece against the backstop –

Then face off both sides to dimension. There are two of these to do, once cleaned up, they can be marked out for boring the holes for the crankshaft. On the Victoria, I bored these holes over size and press-fit a phosphor bronze bearing, because it is harder wearing than plain brass. However, I think it overkill so will stick to plan for this engine. If the engine wears out the brass bearings, well I can fit PB bearings as a mid-life update

Plenty of brass chips too –

Next on the list is to make the glands for the piston rod and the valve rod. These are machined from a brass oval extrusion. The nice thing about having a self centering 4-jaw chuck is that it self centres oval materials too.

This is a spare bit of brass from making the Victoria. Having faced off the outer end, it's just a case of turning it down to produce a 1/4 inch diameter section, 1/4 inch long, then to drill, ream and countersink the opening.

Finally, it needs parting off.

That's the valve rod gland done, the gland for the piston rod is the same process, but with a couple of different diameters to cater for the larger piston rod.

Because all of these operations are done at one setup on the chuck, run out is not a problem, all the machined surfaces being concentric.

Next tasks are to make the steam inlet fitting, these are from the Stuart governor plans and the steam exhaust flange which is a little casting.

I'm finding it quite beneficial to machine the components in groups of like operations, rather than follow each component through to conclusion. The work is faster and I'm not generating any scrap. (So far!). This leaves a lot of drilling and tapping to do.

[Steve WithnellParticipant @stevewithnell34426]

Moving to the Governor plan, the inlet valve arrangement is quite clear.

The components 42 and 49 are machined from a brass extrusion. Finding the vertical centre line is quite straight forward, the horizontal centre line, less so.

The elliptical section is not regular, so to find the centreline, I blacked the sides of the extrusion, then using a square on the wide flat section as a reference, I used the blade of the Sqaure to scrape a line which is then the high point of the section:

That allows the horizontal centre line to be drawn. Next step is to use the 4-Jaw independent chuck to set up the centre of the extrusion. The 4-jaw self-centering chuck can't be used, as the elliptical section is not regular. A round nose tool is used to produce the shaped section.

Having drilled and tapped the inlet, I had planned to part off the flange, but I need a new parting off blade to achieve the depth of cut, so that will have to wait for now. The plan is to drill the mounting holes prior to parting off, so that the alignment with the body of the valve would be good.

Sticking with the brass bits for now, I moved on to component 41 in the diagram above. The material in the kit is a one inch length of brass hexagon, .36 inch across the flats. The machining sequence I used was to turn the straight section first, then to use that to as a chucking spigot. I then turned the end to be threaded, drilled and reamed the through hole and then ran a die down the section to produce the thread. I used a parting off blade to create a groove between the hex portion and the end of the thread.  This sequence is used to ensure the through hole is concentric with the threaded portion.   Any runout is then with the straight section which will not affect the functioning of the valve.

The problem I had was that the die would not cut the full length because of the length of the taper section in the die. Turning the die over, the same taper section. Solution I used was to grind away one side of the die so that the taper was eliminated. Problem solved. The other problem is a mistake of my own making. The thread is specified as 3/16 x 26TPI, which I assumed was cycle thread (BSCY). However, it turns out to be brass thread (BSB). SInce I have the matching BSCY taps, it doesn't matter particularly.

The finished part looks like this:

 

The next brass component is a 3/4 inch pulley that drives the flyballs in the governor.

Steve

Edited By Steve Withnell on 07/07/2014 22:20:58

[julian atkinsParticipant @julianatkins58923]

hi steve,

you are making excellent progress and following your progress with much interest!

i have a set of ME dies with the rear faces ground off to get up to a shoulder.

i dont like the Stuart Turner very old fashioned coarse threads and much prefer ME 40 tpi threads for smaller stuff.

good luck with future progress!

cheers,

julian

[Steve WithnellParticipant @stevewithnell34426]

Thanks Julian – I'll look to use the 40TPI threads in future, the 26TPI do look a bit coarse. I'm still learning what matters and what doesn't – so sometimes I stick to plan because I know no better!

Steve

[Steve WithnellParticipant @stevewithnell34426]

Drifted off plan a bit, the brass pulley is part of the governor, not the engine, but anyway. The process is the same as the cast iron pulley I described earlier, except I had more material to work with. This pulley also has a 3/16 x 40tpi threaded hole through the centre. I've turned a little spigot to hold the blank and once more used a 60 degree single point tool to cut the groove for the drive belt.

Using the tailstock to centre the tap:

Cut off the spigot and face the side and it's done:

I managed to drop it on the floor and apply a couple of scratches, so it will need a polish up before fitting.

The other bit of governor I made a start on, was the little brass casting that holds the drive rod from the governor to the steam inlet valve. A 1/8 hole, drilled and reamed is needed through the top portion.

As a fixture to hold it true in the lathe, I made this:

Which is set up in the lathe like this:

The rest is drilling and running through with a reamer.

Next I'm going back to the engine plan and will finish the machining on the bearing blocks. They are faced to size and now need marking out and machining to plan. I don't intend to fit phosphor bronze bearings as I did for the Victoria.

If you are wondering why I'm using a piece of green cloth as a back drop,  it's because I've run out of green A4 paper!   When I blogged the Victoria I tried using white, pale green and pale blue sheets for the photographs and green seemed to be best background colour.

Steve

Regards

 

Steve

Edited By Steve Withnell on 08/07/2014 21:18:38

[Steve WithnellParticipant @stevewithnell34426]

First task on the bearing blocks is to mark the centre for the bore that will support the crankshaft. I've used a digital height gauge sat on a Sainsbury's granite cutting up board as a base. The cutting up is accurate enough for this, but not for anything requiring close tolerances.

One tip from Master Bodger Stevenson, is to grind back the top jaw of a digital caliper to create an "odd legs" caliper (on the basis these things are as cheap as chips now). I tried my odd legs caliper against the centre line from the height gauge and they agree nicely.

I then set the caliper to half the width and scored a vertical centre line to create the centre spot for the bore. The block is then set up in the 4 Jaw chuck,  utilising the backstop.  First I drilled the bore in stages to 10mm, to create a reference, should anything slip when facing down the bearing block. Once the facing operation was complete, I then bored the hole to size. The external diameter of the bearing that protrudes from the block is not marked on the plan. I chose to machine down to 18mm and the depth of the protrusion to 3mm (as opposed to 1/8th on the plan).

Setting up for boring. This is one instance where I've used a carbide tip tool. I normally use HSS, but this little Glanze boring bar uses small tips which are quite sharp, though not as sharp as I try to keep my HSS tools. Although I have a nice 7/16 reamer, I want the bore to be a little tighter on the crankshaft than the reamer will produce, so I bored to a "custom" fit.

Once the first side is complete, then it's just a case of flipping the bearing block over and clocking to truth.  The backstop helps keep the block square:

Once that side is done, the result looks like this. If you look at the photo, you can see where I've tested the cut for fit before committing to a full boring pass.

Once I've completing the other one, I'll move onto the eccentric strap.

Steve

Edited By Steve Withnell on 10/07/2014 21:56:58

[lancelotParticipant @lancelot]

Hi Steve, this is a shot of the stage i had arrived at on the Coombes …all the bits are now steeping in a bath of Acetone to degrease them prior to spraying a few coats of etching compound on the parts…I have now to paint and reassemble the Coombes and I can try and play catch up…some how I doubt if I will ,you are going like the clappers…

All the best for now,

John.

 

Edited By lancelot on 14/07/2014 21:13:07

[Steve WithnellParticipant @stevewithnell34426]

Hi John, Looks like you are pretty well sorted with your build. I've had to back off this last week as work is very hectic and will continue to be the same for a number of weeks.

I notice in your post, you are using a pretty complex approach to painting the James Coombes. Typically, I just wipe the parts off with meths or isopropanol, depending on what's available, then start a sequence of primer / filler and rubbing down and when I am satisfied with the base finish, then I move on to the colour top coat. All the paint I use is Halfords automotive spray cans. Vauxhall Pine Green worked out to be very good on my Victoria, so will use again for the James Coombes.

The only problem I have with painting, is that any square edges, ie those not rounded off, are difficult to get paint onto and I end up with a very fine line where the edge is through the paint coat. Does the etch process resolve the "edge problem"?

Steve

[JasonBModerator @jasonb]

You really need to knock off the edges, a few strokes with a fine file and then a bit of Emery on a block will be enough to break them and allow the paint to form a film rather than flow away from the high spots.

Etch won't make a lot of difference particularly if its one of the thinner ones where you just need a light single coat to eat into the metal. I only etch Non-ferrous anyway.

J

[lancelotParticipant @lancelot]

Hi folks,usually complaining about shed being too cold …today it is like a blinking sauna …so now checking out the drawings when I put the tools down some years ago (2 I think) it was up to the cylinder and covers, all to the drawing and the latest build book , that drawing is faded by the sun and now illegible the latest drawing supercedes all drawings including the book…first looking at cylinder top cover there seems to be a drawing change …so going up to the den to have a better look at these drawings.

all the best for now,

John.

[lancelotParticipant @lancelot]

Hi all, sorry for seeming to ignore Steves post , my brain was elsewhere… Yes Steve it does seem rather complex, my cleaning process, I will explain… for the last years of working life I spent 22 yrs.. in lear fan R/D…and Shorts bombardier in Learfan to thoroughly degrease parts we used to use stuff M.E.K. now off the floor so if I recall Acetone was the used …Now My reasons for using acetone and etching primer…the chemical draws out all the oil and grime from the casting …cleans the steel and bronze bits… as soon as dry i give them all one light spray of etching primer to stop any rusting (all my Corliss bits done with primer ) also I found it to be a great base for marking out dimensions on, very visible

cheers

John.

[Author]

Posts