Updated bevel gear design

Here is the spreadsheet with the finalised design for my Stuart Victoria build:

http://www.btinternet.com/~steve.withnell/lathe/gears.xls

This now includes the calculation from Franklin Jones for the face width.  Previously,  the calculation was fixed at 1/3 of the cone length.

Steve.

So Just How Did I Produce the Large Wheel?

I did promise I’d describe how to make the large wheel,  since workholding is the challenge here.

 

What I’ve done here is to cut the front face to the precise angle,  bored the central hole at the same setting and the back face of the wheel blank.

 

 

 

 

 

 

 

So here is the little fixture that allows me to hold the blank for cutting the teeth.  It has a second purpose – I used it to drill the holes in the flywheel for mounting the gear,  so it’s also a little drilling jig,  with one set of three holes 2.5mm clearance and a second set of three which are tapped 2.5mm.    The blank has three holes drilled and tapped,  then after the teeth have been cut,  the three holes are opened up to 2.5mm clearance for fixing to the flywheel.  QED.

Return to cutting bevel gears

I had cut two bevel gears so far,  the large wheel mounted on the flywheel and the smaller wheel on the driveshaft.   I had then needed to cut two more,  one to mount on the governor spindle and another for the driveshaft.   I decided to cut the pair connected to the governor end of things from gunmetal,  mainly because I had a suitable piece to hand and because I thought it would add a bit of colour to engine!

These gears are cut using the parallel depth method.  Each tooth requires three cuts,  the first a central (stocking cut) then a second with the blank offset one way then a third with the blank offset in the other.   You can do this in two cuts,  but I think the three cut approach is better,  just taking the two finishing cuts might be more difficult to keep track of.

The gun metal pair are 18 tooth 40DP on a 1:1 ratio.   If you want to cut bevel gears,  this a good practice piece.   My rotary table is 5 degrees per full turn of the handle.   Each tooth is four full turns and the blank roll is one full turn.  No fractions of a turn to keep track off.

This pair cut really nicely and mesh well.   The mesh on the original flywheel end pair was sort of OK’ish so decided to scrap them and make a new pair.  I changed the design to a 2:1 ratio,  which gave me a 36T wheel and an 18T wheel.  The 36T wheel worked out a real charm with a good finish.   I then scrapped the smaller wheel!   Anyway on the second attempt I got the result I was after and the pair now mesh very well.

I was quite concerned about getting the topslide set at the right angle to cut the blanks,  then being able to carry the angle across to the milling machine to set up the rotary table.  My solution was to borrow a sine bar.   I used the faceplate as a datum (I took a light skim with a carbide tool first) then mounted the sine bar.   Here I’m trying to set an included angle of 26.57 degrees!  How close did I get?  Dunno,  but the finished gears mesh well,  so must have been there or thereabouts…

And here is the little assembly.   I’ve started making laminated charts for any reference materials.   I’ve a metric workshop,  so imperial conversion chart very handy.   Done in excel,  I then make them fit an A4 page.   Means I don’t need my specs – sometimes…

This is how I carried the angle from lathe to mill.   Again,  it must have worked well enough as the gears mesh nicely.   When I can find where my copy of Terrapin FTP went,  I’ll upload my updated excel spreadsheet,  which has the final version of the gear designs and a little formula for producing an appropriate face width.

A Few Words –

I’ve been using this blog to record the step by step progress in the build of a unique configuration of the Stuart Victoria.  It’s unique on the basis that the configuration is of my own design as are some of the components.

Copyright to my pictures and my words and the designs of the unique configurations and components do belong to me.

The photographs in this Blog have been taken using a Lumix FZ7 and latterly the Lumix FZ28.   These are “bridge” cameras,  a sort of pretend SLR, in that they have big lenses (the FZ28 is capable of >30x OPTICAL zoom).  Although I bought the FZ28 as an upgrade from the earlier FZ7,  it’s not universally better!  The FZ28 has very good auto flash control.    The photographs are typically taken in Macro mode,  with zoom and flash,  though quite a few pictures were better with only the workshop lighting,  a mixture of tungsten and fluorescent.   Both cameras were good at sorting that out.

The next stage of this development will be to mount the governor and make a couple of bevel gears,  I’ve changed the design latterly so that they will be 1:1 and I’ll publish that design at the time!

Fly Ball Governor – Trial Fit

Finally,  all the components are complete for the governor assembly (not including the bits to mount on the engine!)

First,  finishing off the last piece –

This sits at the top of the governor spindle and is the anchor for the swing arms the balls are connected to.

.All that needs to be done is to cut the 3/32 slot,  which I decided to do using a small 1.5mm slitting saw in the mill.

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I I think it’s pretty obvious whats going on here – the mill was set to    2150 rpm and I took fairly gentle cuts to begin to get feel for feed rate  and depth of cut.  Biggest cut I took was 1mm and that caused no trouble at all.  I should add that at the other side of the vice jaw is a spare piece of material so the vice is clamping square on the workpiece…

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All done – here you can see the calculations to get the slitting saw to the correct positions for making two cuts to get the correct width of slot and properly centred.  I used a micrometer to check the component and saw dimensions before starting.  I also took the second cut at a single pass,  so it was exactly the same depth as the first.

Now,  putting all these bits together and you get:

It’s just a trial fit but it does work.  I have not fitted the nuts to the bolts (the brass plates are threaded) yet.  I might use steel rather than brass,  purely because I think it will look better.  The steel bolts at the top are ‘mine’  and the brass ones  came with the kit.  It works purely by twirling in the fingers,  so it does work.   Final cleaning and polishing should make it look really great.

The drive from the flywheel gears up 2 to 1 to the governor,  so 50rpm at the flywheel will give 100rpm at the governor, hopefully there will be enough energy to drive the steam cutoff.   I’ve been told these small governors don’t work as there is a lack of mass at normal speeds.   I’ll just have to see.

Recap – Stuart Victoria FlyBall Governor

Here is the collection of parts completed for the governor so far…  I have not described the production of the two little brass collars – very straight forward turning operation.  I got the centre hole to size by drilling 4.7mm and then reaming to size to ensure a good sliding fit on the centre spindle.

Fly Ball Governor – Another Bit

The governor is made up of  a number of small parts,  which take care to get right.   Quite a few 10BA holes to drill and tap.

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Starting from a piece of mild steel round bar,  I took a light skim to clean up the material,  then I drilled the centre hole to size.

Next step is to turn down the the front 3/16 inch to 9/16 finished size.

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Then using a 1.5mm parting off tool,  I cut a groove 1/8  inch wide and just less than 4mm deep.

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On inspection,  the slot wasn’t cut cleanly due to deflection from taking multiple cuts with the parting off tool,  so here I’m using a tiny boring bar to clean up the inner faces of the slot

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Finally,  the piece is parted off.  I left the piece a little overlong,  so that I could turn the workpiece around in the chuck and face off with a round nose tool.   I find that deep parting off cuts in mild steel leave a poor finish.  This could be down to poor geometry of the tool or poor technique!   Whatever the cause,  it’s a two minute job to face off to a nice finish.

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Simple task to mill the flats on the workpiece.  Simple maths to calculate the depth of cut from the dimensioned drawings

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Working with these small parts where marking out is especially  difficult,  I been making use of drilling buttons and the mill for co-ordinate drilling.  The buttons are made from the correct diameter of silver steel bar,  drilled and parted off to size.  I then harden them.   This technique makes for accurate placement of holes.

As per previous posts,  I always start a hole with a centre drill to ensure the hole ends up where I planned it to be.

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This  completes the part.   All the operations turned out as planned with the exception of using the parting off tool to cut the slot,  but the little boring bar sorted that.

Build a Fly Ball Governor for the Stuart Victoria

Its been busy recently trying to make time to get time in the workshop to progress the Stuart Victoria.   You may recall from previous posts that I’m using the Stuart Governor castings kit,  maintaining the build of the engine from Stuart parts wherever possible.

I decided that all the plates needed to be identical,  that the holes      needed to be in the right place and I’m not at my best with flat parts  and drill holes.   I decided to make the part as a stack of four plates,  so at least if they were not shaped exactly to plan,  they would be exactly the same.   So I cut four blanks from 1/2 inch wide 22g brass strip and soft soldered both ends whilst firmly held in a toolmakers clamp.  This gave me a solid stack I could machine.

I mounted the stack in the milling vice.  The first hole was located using a filing butting as a drilling jig,  using the edge of the vice jaw as a datum.   Then I calculated the co-ordinates of the second hole and drill that hole as per plan,  (I then followed through with a 10 BA tap loosely held in the drill chuck to keep it square.   My view was that tapping the stack should result in better quality tapped holes than tapping each plate individually.   The tapped holes were certainly good and no problems resulted from tapping the stack.

Once the holes were tapped, I bolted filing buttons top and bottom and the sawed and filed the stack to shape.  I cut the inside first to leave the solder in place,  then the outside,  which removed the solder.

So far,  so good.

As I said earlier,  I’m not at my best with flat parts,  so I decide to machine the 5/16 radius recess.   Clamping the part was tricky,  but by mounting the stack in a toolmakers clamp in the milling vice,  I could remove the small amount of brass to create the recess.

Note I am using a drill chuck and not a milling chuck – not good practice so the material was removed very gently to prevent the drill chuck coming adrift.   It didn’t,  but I would never use a drill chuck for any normal milling operation – it’s a disaster waiting to happen.

Finally,  the stack can be unbolted to reveal the four plates.  Not quite to plan but at least all the same!

Whats in the Box? (That comes from Stuart Models)

One thing I’ve omitted to do in this blog,  is  the contents of the box,  ie what the castings kit looks like.

In order to build the Stuart Victoria to my configuration,  additional items have to be procured from Stuart Models,  these include:

• An additional Steam Chest
• An additional Eccentric strap
• An extra piece of the extrusion to cut the additional steam glands from.
• Gasket material
• More screws, nuts, grubscrews…

More materials are needed,  the Shapely Lady is cut from Phosphor Bronze bar,  which I already had and new studs for the extra depth of the steam chest.  The studs I made from bar stock,  no big deal.    This means that this version of the Stuart Victoria is built 100% from Stuart components where available from Stuart.

In order to construct the flyball governor,  a governor kit is needed:

The Stuart Governor kit can be configured to support the following Stuart engines:

• Victoria
• Twin Victoria
• James Coombe
• No. 9
• Beam Engine
• And probably others too…

The Fly balls are 5/8 inch Phosphor Bronze  so that sets the scaling for the size of engine you might choose to use this kit with.   As a consequence of the layout I’ve adopted for my Victoria,  The Victoria mounting scheme doesn’t work.   However,  the James Coombe mounting does,   so that’s what I’ll be using,  very soon hopefully.

It’s easy to see how Tubal Cain got to the Twin Victoria.   The Stuart Victoria castings are of a high quality and easy to machine (seemingly free of hard spots) and the layout allows the builder lots of flexibility to introduce alternative design ideas.  A great kit in my view and Stuart themselves are  accessible and helpful.

Bearer Blocks, Step by Step (Almost)