Trireme Olympias by Richard Braithwaite

[Richard Braithwaite]

First stage of oar production.

The jig bolts onto the milling table of my Unimat and allows for different tapers to be milled by fitting a spaced under the bolted on top piece.  4 setups required per oar shaft to taper each side (so the jig has to last for 4 x 170= 680 setups and clampings - hence protective strips of wood under clamps!).

Each oar shaft takes about 1 hour to machine to a square taper (including marking up) with the milling cutter making 5 x 0.2mm cuts per side. The cutter could certainly manage deeper cuts on this soft wood but 0.2 mm seems the most I can safely do without too much vibration and sideways deflection of the oar shaft (particularly the last few cuts when it is at its most slender).

A wedge is fitted underneath the tapered part of the shaft for alternate sides to prevent vertical deflection. (wedge machined to the same taper - using the same jig.)

 

The image below shows the setup after each of the 4 sides have been machined. The supporting taper can be seen fitted under the shaft on the images on the right (2nd and 4th setup)

Edited Friday at 05:47 PM by Richard Braithwaite

[BANYAN]

Interesting but very effective approach to cutting the tapers Richard.  Appears this approach may be easier than setting up a shape follower (duplicator) arrangement.

 

cheers

 

Pat

[Richard Braithwaite]

12 hours ago, BANYAN said:

Interesting but very effective approach to cutting the tapers Richard.  Appears this approach may be easier than setting up a shape follower (duplicator) arrangement.

 

cheers

 

Pat

Interesting. What does a shape follower look like?

Edited Saturday at 11:53 AM by Richard Braithwaite

[BANYAN]

Hi Richard.  This is one (home-made) that I use with my Sherline.  The idea is to cut a profile (template) in metal that is used as the master profile for as many duplicates as you need - works best with more complicated shapes but will work with a simple flat/tapered profile also.  However, I usually use a compound slide to cut tapers on the Sherline, but that only works well over shorter distances.  Hopefully the photos are self explanatory, but essentially, the cutter (top) will only cut as deep as the profile follower (bottom bar) and the template will allow.

 

cheers

 

Pat

[Richard Braithwaite]

Very neat. Rather more elegant than the graph paper plot followed by tricky manal dial turning i have used for complex machined shapes!

 

I did think of making this jig from brass/ aluminium. But, so far, my quick wooden effort seems to be stiff and durable enough...

 

Have you had any success turning tapers on long slender wooden shafts such as oars and spars?

 

If  i could make that work it would be much better than what im doing ( machining to a square taper and then manually " octagonalising" and rounding).

 

However, whenever ive tried turning this sort of thing it fails due to vibration/ flexing. 

[BANYAN]

Hi Richard, I actually do all my spars on my Sherline (long bed) lathe. I first cut the required square and hex shapes slightly oversize, the (very roughly) shape them to a hex taper using a plane and then set it up in the lathe and use small machinist jacks and a follower rest to shape the final profiles.  I use a combo of rasps, files and sandpaper for that process constantly checking the profile with calipers etc.  For shorter sections I sometimes use the duplicator, especially about the hounds and masthead doubling.  I then refine the squared and flat surface manually using a file rest and fine needle files to get them to the final dimensions. You can see some of my earlier dings (collision scars) between the Y cross-slide and the chucks before I made a stop for it  Well, one has to learn some lessons the hard way; I put it down to the experience of learning.

 

PS: Sorry, I should mention that I mainly work at 1:72 so, at your scale you might have some difficulty setting up spars etc.

 

cheers

 

Pat

Edited Monday at 11:26 PM by BANYAN