The Bolton No 5 Vertical Open Column Steam Engine

[MJM460]

After yesterday’s concentration on those small threaded parts, I took Gary’s suggestion and opted for something that I didn’t need a magnifying glass to see the result. I must admit that more normally, I go for satisfaction of a big complete, but easy component first. So today’s effort is the flywheel.

Preliminary fondling revealed that the casting was generously dimensioned, included a boss on one side for chucking purposes and the main section was quite even, making setting up in the 4-jaw relatively easy.  The raw cast boss was not very suitable for the dial gauge but I managed to grip the main OD so there was enough clear to run the tip of the dial gauge.  Because the casting is still not totally smooth, I used a spirit level on the jaws to get a repeatable position before reading the gauge, and was pleased to get a good result.  The process was to grip the OD, centring on the OD as well as possible, turn the chucking boss to a size that matched one of my collets and completing the recess and inside of the rim before transferring to the collet for turning the outside diameter and the recess on the other side.

While it was in the collet for the OD, I made a start for the bore with my largest centre drill and then drilled 5 mm diameter.  The end of the centre drill is 3/16” so just a little under 5 mm.  I hoped this would give a good start to the drill.  I followed the 5 mm drill with a 6 mm end mill, using it as a drill.  I am told this makes a hole very true and round.  Then I went for the 6.2 drill before reaming.  Of course that reminded me sharply that my drill set with 0.1 mm steps only goes up to 5.9 mm.  I feel that 6 mm is too small for a 1/4” reamer (6.35 mm), so what to do?  I decided to use the 1/4” drill, and sure enough, after the preparation, it drilled a little small, and way too tight for the shaft.  Whew!  Ran the reamer through and obtained a beautiful fit.  And the rim should run true, as I have not shifted the set up used for the OD.

The OD ended up as 38 mm compared with the design 35.  As it is valuable extra moment of inertia, I see no reason to just turn it down.  Of course, if I planned to install the engine in a boat, the smaller diameter might be an advantage, but my intent is that it will be a stationary engine.

I left enough of a hub to tap for a set screw instead of tapping from the OD as designed.  I managed to extend the parting tool blade enough to part off between the collet and the back of the flywheel.   It worked just fine, though should not have bothered, as I decided tapping the hole for the set screw was not going to be very easy, so put it back in the 4-jaw, centred very carefully (easy with finish machined surfaces for the dial gauge to ride on), and tapered the hub before drilling the hole.  I could easily have parted off as well.  I held the flywheel in the vice, supported on an angle block at the correct angle for the taper on the hub.  This kept the tap holder clear of the rim of the flywheel.

Well, that’s another component off the list.  I had better tackle the bearings next.

Thanks for looking in.

MJM460

[gary.a.ayres]

Neat job! You deserved the treat of working on a more substantial part after the pins yesterday.   

 

[MJM460]

Some tricky parts today.  The bearing castings arrived with two faces machined so I had the bottom face and one side properly at right angles.

I laid each in turn on parallels with the base against the fixed jaw of the vice and a hard plastic strip against the moving jaw to spread the load a little.  Then I could face the opposite side parallel to the first.  And promptly forgot to take a photo.  They seem to be awfully small to try and clamp down.

I clamped an angle plate on the mill table with a tooling block and some packing to drill the holes for the mounting bolts and the bearing cap screws.  At each location, I did a little spot face with and end mill, drilled right through 2.0 mm, tapping size for M2.5, and drilled down to about the required parting line height 2.5.  Then I intended to tap the lower part of the holes, but of course the tap was not long enough.  That will have to wait until I can set up only the lower half of the bearings. 

I used my Laminex “surface plate” to mark the height of the split line.  The plan was to use the slitting saw but I could not work out how to grip the casting well enough and still reach through with the saw blade, so I clamped it all down on the bench with a wood scrap as a saw guide and cut through with the hacksaw.  Made sure the cut was in the available waste section, and repeated for the second bearing.  The cut faces were better than I sometimes achieve, so I was quite pleased with that step.  I then clamped the two base sections onto the mill table to machine both bearings at one setting to get the heights equal.  The available scrap to allow splitting the bearings and machining the faces was over 2 mm, and my saw cuts did not use as much of that as I expected, but I left the top half a bit over dimension as it gave me more meat to tap a hole for an oil cup.

I tend to find everything moves if I try to hold things together by hand to mark the vertical centreline.  My method seems a bit over the top, but ensured an accurate straight vertical line to locate the bore.  Then set up over the slots in the table to allow the drill and reamer to go far enough through, centre drilled, drilled 5 mm, 6 mm end mill, 1/4” drill, and reamer for each bearing in turn.  I had to test with the shaft and was pleased to find the bearings sat flat, and the shaft turned nicely without jamming.

I then made a tight mandrel and mounted the first bearing on it to face the bearing sides.  It seemed to work well for the first cut so I continued through all four sides.

The cast surfaces look a little squew wiff, but the two bearings sit flat on the base, the shaft turns freely even when holding the bearings down firmly and the faces are square to the shaft.  So they function as required.  Adds a little character though.  The last few photos will be in the next post shortly.

I need something easier to follow those, perhaps the crank disk tomorrow.

Thanks for looking in,

MJM460

[MJM460]

A few more photos of machining the main bearings.

Still have to install those oil cups

MJM460

[Johnmcc69]

 
 Very nice work MJM!
 Looks to be a nice little engine!
 
 John

[steam guy willy]

Hi MJM,  Just caught up with this post and good to see a new engine under construction.  looks like a nice set of castings... do bronze castings require the same ageing as the cast iron ones seem to benefit from?  the crank part 11 looks quite thin and will the engine turn in the direction to keep the part screwed on ?

Willy

[gary.a.ayres]

2mm wiggle room notwithstanding, it was brave of you to split the bearings with a hacksaw!

 

[deltatango]

It's great to see so much progress, and good outcomes.

Some of your low-profile clamps look like Harold Hall designs and very useful.

David

[MJM460]

Hi Johnmcc, thanks for commenting.  I am glad that you like the engine.  I am trying to make it look a bit more finished than my usual own designs.

Hi Willy, glad to have you looking in.  Regarding the ageing, I am not a metallurgist, and am not sure what the ageing actually does in cast iron.  Sometimes I wonder if it is that coat of rust, and that I am just not in the “in” group to understand the joke.  But there may be much more to it.  Perhaps someone will chime in and set me straight. 

With bronze I am also not sure.  These castings are not new, though I don’t really know how long ago they were bought.  Perhaps the merest trace of patina, a slight grey colour perhaps.  But some alloys are known to age harden, a process where the atoms reorganise themselves  structure slightly over time, and the result is a harder alloy over time.  I think perhaps more common in aluminium alloys, I don’t know if this happens in bronze.  Others have complained about bronze castings being a bit soft, and even the instruction booklet points this out, but this has not shown itself so far.  Perhaps it hardens over time, pr perhaps I just haven’t squeezed it hard enough yet.  I just don’t know.

Hi Gary, I don’t have a power hacksaw, or the space to store it, so I just use the hand powered version.  I carefully clamp a piece of timber to stop the saw blade skidding onto the good part.  The part was too small for two protector pieces so I went carefully in the middle of the available area, and held an ice cream stick against the blade to stop the blade skidding towards the clamp.  And obviously clamping the part down firmly is vital.  I thought I had included a picture, but now I look again, I put in another twice and forgot the important one.  So it is attached today.  I make sure I have sharp good quality blades available and cut quite big sections when necessary.  You can see in the pictures, it went particularly well this time.

Hi Delta tango, Thanks for looking in.  Well spotted on those clamps.  I made them some time ago and am slowly getting familiar with how and when to use them.  They work well, as so many ideas on his excellent site.

Today the crank disk.  A simple casting with a chucking boss on one side.  Seems regular and clear and has plenty of metal to make the part.  I managed to make it a little larger in diameter than the design.  Also I really feel that 3 mm is too thin for a crank disk that is threaded onto the shaft, and has the pin screwed in.  Carefully juggling of all the dimensions of the base plate as well as the affected dimensions on the cylinder and steam chest, showed that I could accomodate 5 mm in the assembly, and the casting was enough, so I made it 5 mm thick.  Definitely looks more the part.

The face opposite the boss was pretty flat so some parallels behind it helped me get it square in the 4-jaw chuck, and somehow I managed to get the dial indicator between the jaws to get it centred.  I pulled the parallels out before spinning up the lathe.  I turned the boss to a collet size and faced that side.  Then I turned the disk around and held the chucking boss in a collet to face the other side.

I drilled and tapped for the shaft, then once I was happy with the thread, I put the shaft in the tail stock drill chuck, a drop of locative on the thread and screwed the shaft firmly home.  Left it in the chuck overnight to cure.

Of course, when I tried to take a progress photo, the camera battery was flat.  So it is now on charge, and a photo of the crank disk tomorrow. 

And attached is the missing photo of my set up for splitting the bearing blocks with a hacksaw.

Thanks for looking in.

MJM460

[MJM460]

Today, back in the shop as promised to finish that crank disk.

But first I decided to make some estimates as to whether cutting away the excess each side of the crank arm part of the disk, would make s significant contribution to balance.

As discussed in other threads, the problem with balancing a single cylinder reciprocating engine is that you have a rotating force due the the big end and crank, and a reciprocating force due to the piston, piston rod, crosshead little end and part of the con rod.  These cannot all be balanced by a single rotating force. 

The big end mass can be balanced by a mass the other side of the centre of the crank, so that is the aim with those cut outs we often see in crank disks.  As the weights to be balanced are all the same material, I only need to compare the volume of the fairly simple shape I would remove from the disk with the volume of the big end once machined to final dimensions. 

The big end is a simple rectangular shape.  The bearing is not split, but just drilled.  The crank pin is inserted through the hole and screwed into the disk.  The calculation came out quite close, the big end dimensions plus allowance for about a third of the conrod vamp out at 800 mm^3, while the sections I can remove from the crank disk gave 720 mm^3.  Just as well I managed to squeeze a 5 mm disk out of the casting into the base. 

Of course it is not just a matter of volume(mass), the distance from the axis of rotation also matters.  The big end is effectively slightly outside the crank pin, while the sections I remove from the disk are mostly much closer to the axis, so not as effective for balancing.  So basically it would be better if I could add a bit to the opposite side of the disk, but the base dimensions just do not allow it.

Still it looked like the cut out should help so I decided to do it.

I supported the disk on the rotary table with a wooden packer drilled for the shaft, which extended down through the centre of the table.  Using the table like this also had the advantage of allowing me to concentrate on clamping down the disk, and then rotate the table to get the reference lines square on the mill.  I drilled to holes to form the corners of the cut outs, then hacksawed out a good part of the waste, but being careful to cut well clear on the waste side, and returned to the table set up to mill to the lines.

One of the saw cuts drifted a bit, but the material to remain was safely protected by my wooden block clamped in place, so just an extra pass or two with the mill.  I still have troubles with shadows with these tight setups on small components and I didn’t quite get to the line on one side of the crank.  It’s not easy to see, and will be mostly obscured by the bearings and big end, but I think I will set it up again tomorrow and try and take another mm of that side of the crank.

Not much to show in the way of swarf or dramatic progress, but lots of time fiddling with the setup to get alignment of the cuts right, and keep the clamps clear of the chuck, so lots of learning.  The result is not perfect, but nothing to stop the engine working, and I am happy with how it looks.  Consider it extra features to add interest.  With a bit of luck that final trim won’t take too long tomorrow, and I will be able to move on to the eccentric.

Thanks for looking in,

MJM460

[gary.a.ayres]

Progressing nicely. I'm sure your thoroughness in assessing the balance issues will pay off.

[MJM460]

Hi Gary, thanks again for the encouragement.  It’s always welcome.  That calculation is certainly not a very accurate approach to the balance calculation, but it did demonstrate to me the relative magnitude of the relative mass of the big end and the amount I could remove from the crank disk.  When I get the piston and crosshead done I must remember to weigh them, so I can calculate the reciprocating forces at a reasonable running speed, to compare with the rotating force due to the big end.  Of course you can’t balance a reciprocating force with a single rotating force, but it will be interesting to get a feel for the relative magnitudes.  When I have the conrod machined, I may be able to try a simple static balance to see if the calculation is in the right ball park, remembering that the ball park for Australian rules is very big by the standards of other codes.  (This was a finals weekend)

First I set up that crank disk again on the rotary table and trimmed a bit more off the side of the crank as mentioned yesterday.  It came out quite well.  I realised that it would have been easier to insert the crank pin so I had a solid reference point for the callipers, instead of measuring to my layout lines.

I then managed to trim a bit off the crank outboard of the pin, a tiny amount, but in principle a  valuable contribution to the balance calculations, due to its distance from the axis.  I am feeling quite pleased with the result. 

Then I had a look at the eccentric casting.  Again a generous size with no obvious defects.  It had an concentric boss on one side of the main cylindrical part, and an eccentric boss the other side.  The guide book instructions made my head spin with the sequence of centering, turning one boss, turning the eccentric with its flanges and a boss for the set screw, offsetting in the 4-jaw and so on.  I just followed the steps one at a time, but in my concentration, forgot to take progress photos.  But at least I can show the finished eccentric.  I used the parting tool to machine that section between the flanges and experienced a little chatter one one side, just visible in the photo.  I hope it will polish out with a little wet and dry, or a little file.  Perhaps it will even hold a little oil and be useful, I dont know.  If all else fails I can try another from bronze rod.  I think that would have been easier if anything, but the casting was supplied so I had a go.

But completing the eccentric is a major milestone.  It means that all the crank end components can be assembled for a family shot.  I have not yet drilled the bearing hold down bolt locations or the column feet locations, as I want to retain as much flexibility as possible until I can check how everything lines up with the cylinder and valve rod.  I have the feeling that I might have to juggle small offsets in the eccentric strap and locate the columns carefully to make it all line up.  But two family shots, so you can also see how that crank disk turned out.

I think the next step is to work on the cylinder, a much more complex job, so I suspect progress will be slower in the days ahead.

Thank you to all for looking in.

MJM460

[Ramon Wilson]

Hi MJM, just checking in to see how things are - looks like you are making some real good progress 

'When I wer a meer strip o a lad' ageing cast parts for a while was usually done to allow the stresses to relieve from being freshly cast. The shipyard I started out on certainly had a lot of examples lying around slowly developing their 'special orange coating'. There were lots of old  ideas (myths?) for helping the process along too - peeing on them was one - burying them for six months another  Whether that actually worked I have no idea but those who did the machining certainly thought so. I certainly did the latter, more in hope than judgement, to the mill table I had cast for my Linley mill but as far as peeing on it was concerned - no I didn't  I can say it machined beautifully without any movement but it was a big lump (to me)

Keep up the great work and good luck with the cylinder

regards - Ramon

[gary.a.ayres]

Starting to look like an engine now - or at least a bit of one. You have beaten me to the turny-wheels stage even though I started ages ago.   

My approach is at the opposite end of the spectrum from yours. My first test of the balance of weights will be the first time I run the engine and see whether or not it shakes itself to bits ...

Good progress on your build - following along...

 

[steam guy willy]

 Hi MJM,  Looking good and progressing well  ,  Will you be balancing the crankshaft complete with the eccentric  on a pair of knife edge parallels ? of course this would have to be done when the eccentric is in the correct place !! I think that if micro adjustment is needed to achieve this, holes could be drilled and filled with lead and a brasss screw added to conceal this operation ? to reduce weight on the crank pin  if required a hole could be drilled from the threaded side ?   This may be taking things a bit too far ...and I don't do this on my beam engines as the are quite slow running ....Just some thoughts and questions that always come up in the middle of the night !!

Willy