Ideas on Approach to milling particular part

I would like some help and ideas on the best approach to remove a part from steel stock. I'll receive in square and round stock from 1.5" to 3.5" diameter that I need to remove a 5" long and .875" diameter round bar for tensile testing purposes. Unfortunately the center point of the .875 round is supposed to be on the center-line between the edge and the center of the original bars stock.

In the perfect world the .875 diameter bar would be undercut allowing the center to be narrowed as far down as .5", otherwise a second lathe operation will be needed.

Tolerances are pretty loose +/-.01, possibly greater.
Surface finish doesn't matter except the inside diameter (.5") has to have a very nice finish.
I can get the rough stock in whatever length I'd like.

I currently have a small Milltronics CNC machining center.
I also have access to a small manual lathe from our sister company. I couldn't use it all day, but if I just needed a cleanup pass to put the final finish on the end part that would be acceptable.

I will need to be process 2-10 of these the same day that they arrive in addition to other standard work so ideally tooling setup should be easily repeatable.

The good news is I can probably afford about $30k for initial tooling/machine costs to help make that happen.

The current ideas that I've thought about.
1. Fixture the original part in a vise. and plunge mill the area around the sample with a long end mill. Use a Keyseat cutter to perform the under cut.
(I think this will take a long time, and I probably don't have enough mill time to do so without purchasing another mill).

2. Fixture the original part in a vise and face mill around the part.
(I believe this will take a long time but haven't gotten the programming exactly figured out... Possible)

3. Attempt to add a 4th axis to the cnc mill and mill with an carbide end mill as the part rotates
(Current mill is small and I don't necessarily think I could do my other parts without creating changing up the fixturing for it. I do not have the software to program this.)

4. Purchase a CNC Lathe and turn it offcenter
(Turning a 3.5" diameter bar that far offcenter seems like it creates issues as well as interrupted cuts would shorten tool life. I also expect that operator would have to be watching it extremely closely to stop the machine if there was any issue such as tools breaking without creating a massive crash).

5. Purchase a vertical/horizontal saw in order to help with any of the above. (Great with square stock but little worried about dealing with semi/quarter rounds.

6.???

Last Caveat. I am not a machinist and would like to get the final solution to be relatively simple so even a laymen could hit the right buttons. I'm hoping that someone might be able to put me on the right path for a solution.

Thanks

Could you post a drawing of the thing you're trying to make? It sounded simple enough until you started talking about "undercuts" and "inside diameters", which I'm having a hard time visualizing from your description.

Hi TJB - I'm not a machinist either but it sounds like you need to do the following:
1) Set up the bars and end drill them with centres. The trick here is to correctly register the centres. You may have to mill a flat at each end for this purpose
2) Place in lathe between centres, use a dog and turn the part

or
Use a 4 jaw chuck to set it up offcenter then centre drill the end then fit live centre and go for it. Once the 4 jaw is set the rest is easy....

Personally I'd contract the part to someone with a double chuck cnc lathe so it can be done in one hit.

And a dwg would help.

Peter

Find a Local Job Shop to Design your Tooling/Machines...if you are not a Machinist. If, you still want to try to make this Tooling yourself in House hire a Machinist, a Programmer, and a Tooling Designer or a Mobile Sub-Contractor.

If I understand your scenario correctly, this has to be turned on a lathe, any inconsistency in the surface will result in inaccurate data with regards to the tensile strength of the material.

Re: interrupted cuts on a lathe.

Don't use carbide for this. Use a good quality High Speed Steel tooling blank, and don't run it too fast or deep. You (or somebody in your shop) will need to learn how to hand-grind a lathe tool bit. Fortunately, we live in the era of YouTube, and there's lots of videos showing how to do this... it's not that hard to do, really.

I agree that a face plate, drive dogs and centers is probably the way to go for this.

Or, outsource it to somebody already set up to do the job. What you are asking for doesn't sound very complex, so just about any general machine shop should be able to knock it out rather quickly...

Is that 2 to 10 figure total parts to be made, or is that how many you need to make per day, on a repeating basis? If it's repeating, I'd probably look to doing it myself, in house (and accept the fact that there will be a learning curve involved); if it's just a one-time thing, and ten is how many you will make, ever... then outsourcing it starts to sound like a much better (and lower-cost) idea.

:)