Difficult job. Need some advice.

[fomaz]

This is quite a difficult job that I have to do.

Pieces are from a oil pump, and the fit needs to be perfect. I am equipped with a CNC lathe, but I do not think that this piece is meant to be done in a lathe. I need advice on how to machine the piece on the photo. It is about 15 inches long. It works like showed on the picture.

If more info is needed, please let me know.

Any advice would be well received.

[HuFlungDung]

I would say that you need a 4th axis on a machining center to do that work.

When you say perfect fit how much tolerance does that permit? Is this some kind of a pump? How did one part wear out while the other one did not? Can you verify zero wear on the good one? It is very elusive to expect a perfect fit if some wear is present on the part that will be reused because all the reverse engineering in the world will not predict the wear factor that could be waiting to spoil the job.

Will you have to harden the new part?

[fomaz]

Thank you very much for the reply.

The central piece did not wear out since it is harden. The part that needs to be made is not hardened, in fact is made from a very easy to machine material.

Parts are from an oil pump. Perfect fit means to spin it manually without a great deal of backlash, that currently is present on the "old" part.

4th axis on a machining center could be arranged, but I do not find any tool that fits the expected end result. Could this be done with special tools ?

Once again thank you

[kling8]

On a 4th axis, For tooling I'd rough it out with endmill, and finish with a taper mill, or ball mill, probably both. Looking closer at your part, would it be possible to rough/run on lathe, with a groove insert. Setting your lead screw, about the same idea as o.d. threading.
I think if it does work to do some on the lathe you will probably have a milling op as well.
just thinking and typing. Let us know how it turns out

kling8

[fomaz]

I am keeping the lathe out, the lead is 60mm, that is more or less 2 1/4 inches. It would be to much material to remove with low revolutions in the spindle.
I will try the endmill solution passing through the part with a 1/2" endmill. It is the closer shape that I could test on the part. I think lot of time to be spent with a low probability of success... Some jobs are better not to start, but I never learn to say no.

I will say something when this will be machined.

[Fatboy]

Rather than machine an entire part, how about using metal spray to build up the worn sections and then lathe it between centers back to the original profile. That would save a lot of time, material, and machine/tool wear.
Plus it would be a lot simpler to set up and less prone to screw up.

It's worked on worn pump shafts for me in the past.

Fatboy

[307startup]

In your 2nd picture, top piece, left hand corner near the shaft end...you can see that there is a Z shape milling path.

This piece was definitely done on a machining center with a 4th axis, or a lathe with a Y axis and live tooling.

As to doing it on a lathe, it is possible. It is going to be a LONG cycle time without a Y axis and live tooling though.

Overly simplified, it is a very large version of a stub acme profile, with a long lead (twist).

It would be possible to do this with multiple starts, at the same index position each time, but say with a .200-.250" offset in Z each pass, until you get the width of each land correct. No need for really heavy cuts, just LOTS of little ones.

Once your rough out is complete, you would use a form tool to get the correct side profiles.

Again...this looks like a 20hr job on a manual lathe. Even on a 2 axis CNC lathe this would be a 10-12 hour job.

Maybe someone else could give a better description or setup?

From my experience, there should already be a rough forging or casting that has the basic profile on the shelf somewhere. I have done alot of oilfield work, and rarely does a wear part like this start off as a raw billet.

[wildwestpat]

Hi Fomaz

Take 'Fatboy's' advice - adding a thin metal coating to the worn parts is the traditional way of making good undersize parts. Either the flame dispossition or electroplating methods are good and the choice will depend on the base metal and the mating part.


If this is the helix out of a screw pump then the fit in the two bores is also important and will indicate how much build up of material is required. The wear on the bores may mean that full pressure cannot be achieved as the parts are no longer perfectly cylindrical. Assuming this is all for a screw thread pump then the two helical shafts in your picture have probably been lapped into the bores in the block and you may have to hone the built up part to fit by grinding between centers. It would be a good idea to check the bores prior to some expensive reworking as anciliary pumps are relatively cheap.

Regards

Pat