Thread: Machining head surface in lathe

How do I achieve a better finish, the tool cuts small grooves when it passes over the head bolt and coolant holes

Ken

You might have to snug up your gib's and maybe a little more nose radius on your tool.

Spindle end float might be worth looking at also, interrupted cuts can cause things to bounce around a bit if you haven't got a solid machine, a different speed might also help.

Interesting that the finish is good on the outer part of the head where the alloy is solid.

Could it be that the tool is being pushed back whilst machining the solid part and as soon as it hits those coolant galleries it is springing forwards and taking a deeper gouging cut?

Not sure what to suggest...is your tool razor sharp?

What speed and feed are you running,what is your depth of cut.
It looks as if the tool is not very sharp.
Are you feeding in or out.
How much more can you take off.

That tool doesn't look anything like a facing tool , to my eyes anyway .

I think you want more of a large radius on the cutting edge , rather than the sharp end you are using

Mike

Thanks for the fast replies, just checked the spindle bearings by holding one end of a bar in the chuck, and the another in the tail stock, I can get .04mm axial movement on the dial gauge
gibs are snug
machine is Hafco AL-320G
cut started on the outside


Ken

Ken try putting your indicator on the face of the chuck and try to measure for end float, you might need to adjust that.

The bar in the tailstock will be putting load on the spindle brgs and you won't be able to measure any freeplay

Originally Posted by 19brendan81

Interesting that the finish is good on the outer part of the head where the alloy is solid.

Could it be that the tool is being pushed back whilst machining the solid part and as soon as it hits those coolant galleries it is springing forwards and taking a deeper gouging cut?

Not sure what to suggest...is your tool razor sharp?

I think you hit the nail on the head

What depth of cut were you taking?
What was the feed rate?
What was the speed/rpm?

The surface speed is not constant either..

I totally agree with Morrisman - that is not the correct cutter for this job.

You should be using a facing cutter with a blade or semi rounded edge to get a smooth finish.

Definitely not the cutter that you are using, it's way too pointed.

To do the inside part of the head you should be using a small boring bar with a semi rounded edge.

Rob

Apart from what others have asked. Thats a brazed carbide tool right? To me is seems to have very little or no rake.*

Stuart

*which is fine for carbide but wont help with the finish. Do you have any HSS?

I think the tool angle looks wrong . It is hard to tell from the funny angle of the photo though. Seems to me to be angled toward the centre of the spindle. It would be better for facing to have it angled back the other way .
Try a carbide indexable insert at higher spindle speed instead of tungsten . The interrupted cut might be chipping the tungsten edge .
I don't know if you have power cross feed but that would help finnish also.
Depth of cut can cause a problem with interrupted cuts . A heavy cut for the lathe setup can cause some spring in the tool setup . so when it encounters the hole it drops in for a deeper cut and can chip the tool edge or load up the tool edge with smeared material that blunts it for a while . Try making a real fine cut at a higher speed.

Is is feasible to grind the last couple of thou to get a very smooth surface,
if so what would I use

regards,
Ken

[QUOTE=Gringo;1548924]Is is feasible to grind the last couple of thou to get a very smooth surface,

You can, but it will require coolant and the stone to be dressed after each pass to prevent alloy clogging.

A tool post grinder would do it, but it would be a damn messy job as it would spray coolant everywhere.

I've never done it, and I doubt that I would deem it necessary for a head, but a quick Google shows it can be done successfully - check the Practical Machinist site.

All the refaced cylinder heads I've handled have never had a mirror finish.

I have successfully fine finished alloy crank case halves (two stroke) using a sheet of glass and grinding compound, and LOTS of elbow grease, but it's a slow and tedious job, and only suitable for external mating surfaces.

If you used a decent facing cutter to begin with, you wouldn't even consider such measures.

How do you face off ends for basic round stock normally? Just use the same profile.

Rob