How to machine lobed oil pump?

I'd like to make an oil pump on my small mill. Its a special project for a car and its okay if it doesn't work right or blows up the engine, the car is practically disposable and is meant for experiments like this.

The rotor design is pictured below. Apparently this is called a positive displacement, lobe style, rotary pump. Its very typical of automotive oil pumps, and apparently, can also be made in aluminum (yes, the rotors and housing).

I'm wondering if anyone knows where I can find the geometry for this style of pump? It looks pretty simple, but I'd rather not guess at it. It must be a very old design, maybe there is some engineers handbook with geometry?

Has anyone made a lobe pump for a mini engine?

http://www.turbododge.com/forums/att...have-pump4.jpg

The name they go by is a "gear rotor" pump. https://www.google.com/search?q=gear...client=firefox

Makes more sense to build small gear pump. It will do the same job and much easier to make.

Quote:

---

Originally Posted by bluejets

Makes more sense to build small gear pump. It will do the same job and much easier to make.

---

What makes the gerotor hard to machine? It looks like you can make both rotors and the housing without tool changes and maybe just flipping the part over once to surface the back.

Wire EDM......

Quote:

---

Originally Posted by gabedrummin

Wire EDM......

---

why would wire edm be appropriate for this?

Maybe I am not seeing this but most pumps I have seen like this have a housing that has a sleeve with a gear type of rotor cut through it . This sleeve is driven with a rotor with a gear shape .. The rotor can be wired through then a shaft can be pressed in on center to make the shaft and rotor one piece . And if this is not what your talking about how about posting a pic. of the indivigal parts you want to make , soory for the spelling errors.

Quote:

---

Originally Posted by gabedrummin

Maybe I am not seeing this but most pumps I have seen like this have a housing that has a sleeve with a gear type of rotor cut through it . This sleeve is driven with a rotor with a gear shape .. The rotor can be wired through then a shaft can be pressed in on center to make the shaft and rotor one piece . And if this is not what your talking about how about posting a pic. of the indivigal parts you want to make , soory for the spelling errors.

---

Yes thats exactly what I'm talking about!

I actually found some incredible software which designs the rotors for gerotor pumps based on performance requirements, and even exports solidworks files, so I no longer need any help figuring out how to make the actual rotors.

The part i need help on is figuring out how to attach the shaft to the inner rotor. Im not familiar with press-fit clearances or what that might take to machine, so I need to research that. Have you made press fit parts?

If there is no too much tourque on the rotor and say the shaft was .500 I would ream the rotor to to.4985 . If you are worried about it slipping tig weld it then grind the end flush . If you have a big press you can ream it -.005 . You can also freeze the shaft and bake the rotor then the shaft will drop in .

Quote:

---

Originally Posted by gabedrummin

If there is no too much tourque on the rotor and say the shaft was .500 I would ream the rotor to to.4985 . If you are worried about it slipping tig weld it then grind the end flush . If you have a big press you can ream it -.005 . You can also freeze the shaft and bake the rotor then the shaft will drop in .

---

very helpful info thank you! i will be making the rotors out of aluminum because I cant machine steel at the moment. can i press fit a steel shaft into aluminum?

All of the original equipment manufacturers simply machine a channel in one face of the internal rotor making sure it does not go all the way to the working surface of the actual lobes, then bore a hole in the shaft and use an appropriately sized hardened pin as normally found in needle roller bearings as many sizes and lengths are available ex stock from decent suppliers.

In the case of the picture posted the shaft would be fitted from the bottom the view being from the top with a second stage rotor held in place by the locating pin being fitted after the non visible rotor is placed on the shaft, Then when the shaft is inserted the pin drops into the slot in the other rotor to lock it to the shaft and as well retain the rotor to the shaft.
Then yet another pin is fitted to the shaft which in this case is underneath the visible internal rotor, This then stops the shaft from falling out the other end and gives a drive pin for the visible upper rotor to connect and be driven by the shaft.

The whole assembly is then either bolted into a machined register in the engine which seals off the visible rotor with part of the engine casing or block forming the end plate for the pump assembly and at the same time supplying both inlet and outlet ports to the pump,If not done in that fashion then it would connect from the non visible side and be sealed with a bolt on end plate.

Pretty easy and tough design that has proven to be reliable unlike some later setups where they run a much larger diameter gerotor pump off the snout of the crankshaft the drive being two flats on the crankshaft the pump engages with internally, These often seem to crack the inner rotors and have proven not as reliable as the older setup as in the photo the Acannell posted.