ETW Oil Pump

[Roger B]

In Westbury's book 'Model Petrol Engines' is the description of a valveless reciprocating oil pump described as suitable for engines up to 30cc. Has anyone made one or an engine that uses one?

The drive is from a worm on the engine shaft coupled to a pinion on the pump shaft that reciprocates with the plunger. As the pinion moves axially it obviously cannot be a 'proper' worm wheel. I have found a commercial 0.5 MOD pinion that is long enough to allow for the plunger movement. My lathe clains to have a screw cutting setting for 0.5 MOD. I think that I should be able to cut a worm that will work with this pinion but am unsure on a couple of points (I could just try it and see what happens but I always like to ask first  )
1) What sort of thread profile should I use?
2) The thread on the worm will have a pitch angle. Should I angle the pump pinion and pump shaft to match?
3) As it will be very lightly loaded do 1) and 2) really matter.

I think that Jo's Kiwi or Kitti used a screw thread based worm drive for an oscillating oil pump but I can't currently find the details.

[steamer]

I built the pump that goes into the Wallaby which is 29cc if I recall but it's a gear pump.

Do you have a picture?

Dave

[Roger B]

This is the pump

[Jo]

If you turn the page you will see the pump fitted to Kitty.

Just checking my Westbury designs

Jo

[Jo]

That type of pump is fitted to the Atom 5  .

The MAP drawings don't give details of the oil pump but clearly it is one of those. It says 26 TPI worm... Westbury was not very original on his gears and worms: he had one or two that were a common size back in those days and he used them for everything...

Edit: On the Dolphin drawings he mentions that the worm should have an Acme form thread. Really it just needs to be adequate to go round.

Jo

[Bluechip]

Baffled ...   

Can't really see how it works. I suppose the lever sticking out is the clue, but ...

Vincents had a rotary / reciprocating pump somewhat like that but there was a track-cam  / pin arrangement to give the reciprocation?

Dave

[Jo]

There is a cam above the gear, the other cam is attached to the lever, sticking out the side.

So the pump plunger rotates and reciprocates at the same time, at the end there is that little finger that acts as a rotary valve to control the suction and discharge ports.

Jo

[steamer]

I get it....that's a brain teaser........YIKES!

Dave

[Bluechip]

Ah yes!   Cheers Jo ... 
 
Cryptic bit of drawing. I can see now where the hashing changes direction on  #3... ( hatching ?? ).

Not keen on making it     obvious, was he ???

Dave

[Roger B]

Thank you Jo    A 20 tooth 0.5MOD gear will be 11mm diameter and the drawing shows a 20 tooth gear 3/8" (9.5mm) diameter so that will be close enough for my metrification. The plunger will be 5mm diameter which matches the bore on the commercially available gear. If I make the ports 2mm diameter and the finger thing on the end 3.5mm it seems to match the original geometry.
Without deep complications (trying to grind my own tool  ) I can either cut the worm with a 60° threading tool or a 55° DCMT tip. As it will be at least 15mm diameter (12mm shaft) the pitch angle will be fairly shallow. I think some test pieces are required 

[Roger B]

I had a go at cutting a worm on a piece of 18mm diameter brass rod. The tool was a standard 55° DCMT tip and cut to a depth of 0.75mm. The quick trial with the pinion seemed ok  Seems to be heading in the right direction 

<a href="https://www.youtube.com/watch?v=4Gl8to9JKzc" target="_blank">http://www.youtube.com/watch?v=4Gl8to9JKzc</a>