Kiwi Mk II

[Richard P]

Guys
I am struggling!!!
I am trying to machine the Kiwi crank and so far I have failed to find the correct cutter. The picture shows the tools I have used all of which have an overhang of around 35mm. The tipped parting tools seem to "wobble" and I fear the carbide insert will spring out. The parting blade isn't really suited to the task and the tool in the rear tool post chatters badly at all speeds. I have cut a relief into the center of the cutting edge. I have tried the tipped parting off blade in the read tool post but it wasn't stable. I believe the tool height is correctly set.

I am sure it can't be that hard but so far I have failed to find a workable solution. I don't know the grade of the rolled mild steel but it came from a very reliable supplier some years ago and was used for general machining is a development model shop. I annealed it before use. It drills very easily.

Any insights would be appreciated.

Many thanks

Mike

View attachment 138966

Hi Mike, having recently built this engine I've just had a look in the workshop and found the cutter that I used. In the end I went for a pretty sturdy and solid parting blade rather than using an insert cutter. I shaped the edges to give the stress relieving corner radii and then created the central notch with a diamond hone.

By working the cutter from side to side with each cut only a small area of the blade is cutting at any point in time time. I first roughed out the material and then was able to get a very good fine finish cut with this method.

 

[Mike Ginn]

Hi Richard
Thanks for the info and indeed all the other Kiwi photos you have posted. I did find this crank small end bearing difficult to machine. I should have removed more material on the mill to reduce the interrupted cut which was my main issue. I found that I needed to use the rear toolpost to provide rigidity and I ground the 5.5mm wide tool to have 2 spurs about 1mm wide. Using small cuts and traversing I was able to get to an even cut when the journal was less than 0.5 inch. I then used a tipped parting tool with an overhang of 35mm to complete the journal. I very lightly ground the top off the insert to provide a sharp edge (maybe controversial but it worked). Thanks for the picture of your parting tool. I tried to get a similar profile but I completely failed to grind the shape using either a Hemmingway grinder or a drimmel. I also could not get the 2 cutting points to be square with the shank of the tool.

How did you achieve the profile????

I now need to machine the main journals and I will try to mill as much material away as possible before cutting on the lathe.

Thanks for your help

Mike

 

[Mike Ginn]

So you retire – in my case at 75 – and rekindle your interest in model engineering. Maybe resurrecting that model you started 10 years ago. It’s all very relaxing and time slips by!

Then I have to make the crank shaft for the Kiwi. Seems simple but has taken ages with every operation having the potential to wreck the work to date. I normally fabricate the shaft but this time, as per ETW words and music, I started with a bar of unidentified steel. I have finished the shaft and it runs smoothly in the crank case but I have to say that drilling the 2.3mm hole through the shaft to a depth of over 2 inches was stressful to say the lease. It probably wasn’t helped by the radio discussion about the UK economy - which is a very British disaster!

I used a new Dormer long series drill at the Myford S7’s top speed of around 2000rpm and using the Cowell rack tail stock I was able to quickly retract the drill about every 0.25mm to brush on cutting oil.

I wouldn’t describe it as fun but at least I didn’t break the drill! I am now letting the headstock bearing cool down while I finish the bottle of wine.

A relaxed Mike