Can I get a good TIR on my lathe? Is grinding necesary?

[pld0vr]

Alright... I'm going to be starting a project fairly soon... basically we are taking titanium engine valves and machining them down for another fitment.

It's all gravy except one thing that I have some concern with. Usually the 45deg angle on the valve head where it meets the valve seat is ground. A TIR of 0.001" - 0.002" is considered acceptable.

I'm using a Mori Seiki AL-2 to reshape the valves... it's a sturdy machine. The concern is that the head of the valve will move due to the stem being only about 8mm in diameter. I could however use my programmable tail stock for the final cut.

So let's say I do that... what is the best TIR I could hope for on a finishing cut? It is possible that I won't need to grind the valves after?

Unfortunately I'm waiting on some power requirements so my machine is down at the moment... and a good deal on a grinder came up.. but grinding is all manual and I want to keep the process automated if possible.

So should I buy the grinder? That's basically what I'm getting at here.

[neilw20]

When you turn you get grooves, however smooth.
When you grind, you knock the tops off the grooves.
Do you have a manual lathe?
Set up a toolpost grinder, even a die grinder will work.

[pld0vr]

No, its a cnc lathe with 8 position turret.
What if I used a cutting tool with a 45deg angle on it so it just needs to contact the valve to make the surface?
If I have to gring them so be it... But were talking 100+ valves

[neilw20]

At one of the tool holder positions mount a die grinder.
Mine had a threaded cover. I turned a large nut (easy piece of HEX) and threaded it to match the die grinder body-nose.
Now you have a CNC grinder. Good for small internal stuff too.
Cover the slides if possible.
Just run a slow spindle speed, and turn on the air before you hit cycle start. To easy.

[pld0vr]

Sounds nice but I can't see it working for me. So is that a no... No way I can cut it at those tolerences?

[ctate2000]

I see reason not to turn it. The 8mm titanium stem should be plenty stiff if you grip close to the chuck. I would use a single point tool and interpolate the chamfer. You are more likely to have issues by plunging with an angled tool.

Run out will depend on the set up and how much the part runs out when you put it in the chuck. I would use a collet if possible.

[MikeZee]

Take your valves to an engine builder, he will have the correct machinery, they will be "dead nuts" when done at a fraction of the time and cost you are thinking of putting in to this "project".

[pld0vr]

Originally Posted by MikeZee Take your valves to an engine builder, he will have the correct machinery, they will be "dead nuts" when done at a fraction of the time and cost you are thinking of putting in to this "project".

No. I am not making valves for one engine... I am doing batches of 100 valves.

I can do them "dead nuts" using the same valve grinder he would use... I'm just trying to see if I can avoid that step and be more efficient in my processes. Valve grinders are all manual machines... it's not a slow process but still, if I can get an acceptable finish on the lathe that's what I want to do.

[pld0vr]

Valve seats are often cut instead of ground these days, so I suppose I am asking why the valve surface could not be cut also?

[rock4xfab]

Well I will agree that I would grind them not machine them.. The valves would most certainly be lapped into the seats anyway. Try a couple and lap them in to see how the fit is.. If it is acceptable, then cut them if not grind them.

[pld0vr]

Originally Posted by rock4xfab Well I will agree that I would grind them not machine them.. The valves would most certainly be lapped into the seats anyway. Try a couple and lap them in to see how the fit is.. If it is acceptable, then cut them if not grind them.

Titanium valves can not be lapped as that will remove the dlc pvd coating that will be applied. Without this coating the valve life is very short.

[pld0vr]

Hmm, well I did find one company that sells a valve face cutting machine, which is basically a mini lathe with one purpose.


Surely my large CNC lathe would give a more accurate finish. I suppose I will cut a few and see what sort of finish I can achieve.