If someone is cutting seats without pilot what kind of seat cutter holder you are using in a mill?
Positioning can and will take a time but would it be possible to end up better quality with rigid machine vs. pilot during cutting?
Juhani
Re: Mill cylinder head/seat work without pilot
Posted: Sat Dec 28, 2019 11:06 am
by HDBD
I won't say it can't be done but have never heard of it. You could collet a ball head single point tool and turn it. It would be rigid if the machine spindle is. If the head holding fixture was rigid as well then it would cut a decent seat. The bigger question would be how would you get all the axes aligned to end up with a seat that is not tilted or out of x or y alignment?
Re: Mill cylinder head/seat work without pilot
Posted: Sat Dec 28, 2019 2:51 pm
by PRH
In my mind it’s as simple as this......
There’s a reason every available piece of equipment I’ve ever seen or heard of that’s designed specifically to do that job uses a pilot.
Re: Mill cylinder head/seat work without pilot
Posted: Sat Dec 28, 2019 3:51 pm
by tt911er
Thanks for your reply,
That is THE question.
Idea was at first to get the valve guide straight up (more or less) with a spirit leveler and then sweep inside the guide to verify that and also x/y.
I don't know is that possible to learn to do in a practical time but the idea was to minimize the moving parts that may cause the errors.
Probably ending up to do seats with a pilots and ball head but a bad habit inventing a wheel again raise it's head
Re: Mill cylinder head/seat work without pilot
Posted: Sat Dec 28, 2019 4:42 pm
by PRH
Many of the higher end machines don’t use a ball drive cutter body.
Even the programmable single point cutting systems use a pilot though.
Re: Mill cylinder head/seat work without pilot
Posted: Sun Dec 29, 2019 11:22 am
by dannobee
How could you possibly hold concentricity even remotely close without a pilot? It's hard enough to keep it within a thou or half a thou WITH a piloted cutter. And good luck if there's even a hint of chatter.
And if your handle suggests air cooled porsche 911 engines, those guides are short and wear out in no time anyway. Concentricity out by 5 thou or more isn't uncommon on used heads and seem to always have a low spot on the seats near the middle of the chamber (where the two seats are closest).
I don't think a spirit level will cut it. The valve included angles are 30.25 and 25.5.
Re: Mill cylinder head/seat work without pilot
Posted: Sun Dec 29, 2019 12:49 pm
by SchmidtMotorWorks
You can produce more accurate seats on a machine without pilots.
The clearances and taper involved in pilots are multiples of the accuracy of a good machine even if it is interpolating.
The main advantage of CNC milling seats is that you can have designs where the non-sealing faces have shapes or angles that change around the the perimeter of the seat. The best shapes in the center of the cylinder are different than the best shapes along the chamber walls.
I was doing this at Honda in the 90's with new CNC machines for that era, it wasn't fast but the work produced was excellent.
With modern CNC equipment the same work could be done in seconds to tolerances and finishes vastly superior to what a single edge cutter could do.
Re: Mill cylinder head/seat work without pilot
Posted: Sun Dec 29, 2019 2:43 pm
by WeingartnerRacing
I just don’t see how it would work. The guide has to be the exact level in all axis for the seat to be perpendicular to it. If you just cut the seats how do you know the angle of the guide is the same within a .002. The guide hole drilled could have been perfect but honing or sizing of the guide could be off.
Re: Mill cylinder head/seat work without pilot
Posted: Sun Dec 29, 2019 3:07 pm
by PackardV8
SchmidtMotorWorks wrote: ↑Sun Dec 29, 2019 12:49 pm
You can produce more accurate seats on a machine without pilots.
The clearances and taper involved in pilots are multiples of the accuracy of a good machine even if it is interpolating.
I was doing this at Honda in the 90's with new CNC machines for that era, it wasn't fast but the work produced was excellent.
With modern CNC equipment the same work could be done in seconds to tolerances and finishes vastly superior to what a single edge cutter could do.
New head casting for OEM production or used recons?
Re: Mill cylinder head/seat work without pilot
Posted: Sun Dec 29, 2019 8:56 pm
by ProPower engines
I am skeptical on how it can be set up with the concentricity level of +/- .0005" without being able to configure the guide angle accurately on a mill.
Yes I believe it can be done but at how much time spent from seat to seat. If a straight pilot was used to index the XYZ axis's that was a snug fit to the guide it would be easier but not sure on a manual mill how to probe the guide to get the angle correct and that every guide will be off slightly even on new heads and not to mention a used head that has moved around during its life.
The best VGS machines out there as mentioned use a type of piloted location system of some sort but the guide pilot size still plays a part of the seat runout based on clearance/deflection even on the most rigidly mounted heads.
Some use the 1/2 of the guide clearance as a base for runout of the seat they will accept with an OEM type interference valve job and while most here use tighter then a stock clearance we strive to get to a max of .0005" or less which in most cases can't be done using stock OEM guide sizes.
Re: Mill cylinder head/seat work without pilot
Posted: Sun Dec 29, 2019 9:33 pm
by SchmidtMotorWorks
With a CNC machine, you can probe the guide and then use a routine that adjusts the axis to align to the guide before running the program.
This kind of thing is not difficult to do with a modern CNC, it is ordinary in aerospace work.
SchmidtMotorWorks wrote: ↑Sun Dec 29, 2019 12:49 pm
You can produce more accurate seats on a machine without pilots.
The clearances and taper involved in pilots are multiples of the accuracy of a good machine even if it is interpolating.
I was doing this at Honda in the 90's with new CNC machines for that era, it wasn't fast but the work produced was excellent.
With modern CNC equipment the same work could be done in seconds to tolerances and finishes vastly superior to what a single edge cutter could do.
New head casting for OEM production or used recons?
Both, it doesn't matter, the guide locations and angles are probed automatically.
Re: Mill cylinder head/seat work without pilot
Posted: Sun Dec 29, 2019 9:39 pm
by SchmidtMotorWorks
For those that are not familiar with probing, here is an introductory explanation on a HAAS.
Higher axis machines have routines that can align the axis to what is probed and then set the work coordinates.
ProPower engines wrote: ↑Sun Dec 29, 2019 8:56 pm
I am skeptical on how it can be set up with the concentricity level of +/- .0005" without being able to configure the guide angle accurately on a mill.
Yes I believe it can be done but at how much time spent from seat to seat. If a straight pilot was used to index the XYZ axis's that was a snug fit to the guide it would be easier but not sure on a manual mill how to probe the guide to get the angle correct and that every guide will be off slightly even on new heads and not to mention a used head that has moved around during its life.
The best VGS machines out there as mentioned use a type of piloted location system of some sort but the guide pilot size still plays a part of the seat runout based on clearance/deflection even on the most rigidly mounted heads.
Some use the 1/2 of the guide clearance as a base for runout of the seat they will accept with an OEM type interference valve job and while most here use tighter then a stock clearance we strive to get to a max of .0005" or less which in most cases can't be done using stock OEM guide sizes.
A good modern CNC could add another decimal to that accuracy (actually a very good machine can add 2 decimals).
All of the probing could be done in one routine, probably run in less than a minute.
One of my clients has a Roders TEC 5-axis machine that can hold 0.0001" at 1000" IPM with 30,000 RPM spindle.
Re: Mill cylinder head/seat work without pilot
Posted: Mon Dec 30, 2019 2:27 am
by hoodeng
Hello TT911, what is the equipment level of your machine shop? Schmidt MW has some pretty trick facilities available to him that's for sure! i dream of having NC capability to cover what i want, but i am not at that level so its off to NC machine shops when i need one off's.
Why is it imperative to delete a pilot? As has been pointed out, guide condition is first and foremost to any seat work using a pilot, and has also been pointed out that in a machining operation that was not going to use a pilot would have to probe the guide for datum anyway, so regardless of what process is used a on design guide is needed anyway.
I would imagine if you are on Porsche engines you would not be running service wear limit parts in a performance job, a combination of parallel, round and on size guides with a carbide pilot surely wouldn't give that poor a job.
I would be interested to know, what improvement are we looking at for the projected equipment investment, and the performance gain?
