Drivetrain and Spline cutting

We have turned one eye to the business of the drive train and prop-shaft for Befur.

I have concluded that I am putting a CV joint in the drive train, to allow the engine to be mounted horizontally, and also going to use a toothed belt drive from the engine to the prop-shaft, so allow me to install the engine off-centre, and improve internal layout.

The “Drivetrain”

The sequence of elements in the drive train are:

Engine crank, toothed (cam) belt drive to 1.25″ “jackshaft” supported in 2 plumbers blocks,  CV joint (ex Ford Sierra XR4!), with attached shock absorber, thrust bearing, stern gland/stuffing box prop-shaft (with 2 cutlass bearings (it’s 7 feet long!)) and Prop (21.5″d x 23″ pitch)

You can see the approx layout below (although one of the two jackshaft support bearings is yet to arrive, and a dual v-belt pulley is substituting for the final (smaller) toothed-belt pulley (oh, and yes the engine is not in place yet 🙂 !! )

The Drivetrain plan

Making a half-shaft

As part of this process we will need to make a “jackshaft” to take the place of the original half-shaft fitted in the Sierra. This involved cutting a 25-spline shaft. Having never done this before I decided to have a trial run.

The idea is to hold the shaft in a dividing head (rotary table) on the milling machine and then use an end-mill (actually a slot-drill in this case) to cut “slots” (each pair of slots leaving a spline in between).

So firstly we turned the trial bar to the O/D of the splines (as measured from the CV joint) – Of course as there are and odd number of splines we can’t actually measure the diameter, but some “mark-1 eyeball interpolation” provides an answer that works

Then (after some head scratching) realised I needed to arrange the cutting edge of the mill 50% of the radius of the bar forward of the centre line of the shaft; this means that the vertical and horizontal faces of the cut we make will each be at an angle of 45-degrees to a normal drawn at the point of the cut (easier to see than describe!)

Then we just need to index the shaft round 14.4-degrees for each slot, and keep feeding in until we get a fit (e.g. when the bottom of the slots equals the ID of the splined hole in the CV). I actually wound up “climb milling” to get better visibility, but the solidity of the Ramboudi mill meant that this was no problem at all!

The pic and video below explains all;

CV on trial "half shaft"

CV on trial “half shaft”

A video:

Other bits

I also managed to find a stern gland on ebay. Fortunately it arrived slightly smaller than advertised, so I could re-cut the shaft hole, so it’s as good as new 🙂  …. and then found an untouched cutlass bearing casting at the SBA Auction, so machined this to take an ex-ebay cutlass bearing – all in all I saved several hundred pounds when compared to purchasing these items from new – pics below:

2 thoughts on “Drivetrain and Spline cutting

  1. Peter Bourke

    Hullo Malcolm
    Had to smile to myself when I read that you cut the splines by coming down half a radius.
    I remember as an apprentice[ 50years ago] being bawled out by my foreman for cutting a spline by inclining the millhead 45 degrees.To refresh your memory I too am building an A.A.Leak 3&5×3. Bogged down at the moment thru lack of money. Trying to sell our 35 yacht -which we have owned for over a decade- to finance the show.
    Just obtained a Beaverpal vertical mill. Already have a chinese lathe 14″ swing 42′” b/c .
    The engine is going into” Wyuna,” a 26ft Maurice Griffith “Eventide” which I bought for $2,000 many years ago. I intend changing the rig from conventional Bermuda to a more traditional and practical gaff rigged main. I want the boom and gaff when not under sail to lay forward of the funnel The booms goose neck will be attached to the tabernacle and the mast will pivot above the lowered sail.
    I notice with interest that you are employing a Hastler rig. Great idea, but curious to know how you get on when dropping the mast etc?
    Now my main reason for contacting you is regarding Befur propellor size, Most of the information I have gleaned is that the pitch is at least 150% of diameter. Was it a deliberate decision to use 21×23 prop? Reassuring to read that you are using a 1 1/4″shaft.
    Wyuna currently has a 1″ shaft which I know I would be stupid not to increase its diameter but have been reluctant to do so. Your article has finally convinced me to do so
    A bit further down the track I am obviously looking at boilers and like yourself favour a Yarrow type .
    I am a member of the Steamboat Association. of Australia but our members in Adelaide are scattered few and wide.
    Without sounding too patronising I can,t thank you enough for your excellent blog and I
    use sy- befur as my first point of reference and mentor.
    Happy as a kangaroo with two pouches [had to do the Aussie bit]
    Kindest regards, Peter

    1. sybefur Post author

      Hi Peter, thank you for your nice comments, its good to meet another Leak Builder.

      Your Questions:
      On the Mast: My plan is only to drop the mast when trailering the boat – better minds than mine tell me that the raised mast will help minimise rolling when steaming or at anchor. When sailing and steaming it seems unlikely that the sail will be “over” the funnel/exhaust at any time, and if I am steaming with sails furled the junk rig allows you to “reef up” so raising the “boom” out of harms way – however I am planning on dark brown sails to mask the accumulated muck 🙂

      On the prop: The 23″ pitch was as a result of computations provided by John King (SBA guru and Yarrow boiler designer). I think that the pitch is principally determined by the available HP and intended engine speed. We are planning to run the Leak quite fast (~600-700rpm max) to extract the maximum power (for skiing and ramming!).

      On the propshaft: I can’t actually remember why I opted for 1.25″ (probably my belt and braces approach to engineering) and the fact the propshaft is 84″ from CV joint to prop – this also resulted in me adding the second cutlass bearing in the middle of the stern tube.

      Also Simon Maltby’s Steamboat forum is a great source of advice and information


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