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Quote:
Originally Posted by Henry Schmidt View Post
Generally speaking, 911 heads are cut on a lathe not a mill.
That said: there are many ways to skin a cat.
Maybe out in the field they are. But obviously not in production!
Another way on a Bridgeport knee mill after traming the head is a automatic boring head.
But I think you will appreciate Henry that its way faster in a cnc than in a lathe or manual mill especially when you find a head that needs a .001" more to clean up and you have the other 5 to redo.

Old 04-06-2021, 09:55 PM
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Originally Posted by dtxscott View Post
drgouk,
Curious.... What happened to the spot next to the valve stem on the far-left one?

Nothing happened, it was a little bit of carbon I missed when bead blasting, more discoloration .
Old 04-06-2021, 09:57 PM
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Originally Posted by drgouk View Post
Maybe out in the field they are. But obviously not in production!
Another way on a Bridgeport knee mill after traming the head is a automatic boring head.
But I think you will appreciate Henry that its way faster in a cnc than in a lathe or manual mill especially when you find a head that needs a .001" more to clean up and you have the other 5 to redo.
What I actually appreciate is that with the proper fixture, machining the heads accurately on a lathe is quick and easy without the shop wasting footprint of a CNC mill. The proper fixture allows for repeatable results days, weeks or even months later without the need to remove studs and cam tower locator dowels.
What we do to avoid the necessity of re-machining the heads is to accurately measure all the heads, make an informed decision based on experience as to the head with the greatest deficits and machine that head first.
This method allows for a clean mating surface with the least amount of material removed.

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Last edited by Henry Schmidt; 04-07-2021 at 07:11 AM..
Old 04-07-2021, 06:24 AM
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Studs are removed yes and whilst they are out, they are plated, cam tower dowels no, that would be dumb. I think it would be foolish to buy a cnc to re face 911 heads, But when you have one due to your other engine work developing race engines for Single Seaters and making hundereds of parts. I have refaced heads using all 3 methods and adside from removing the the studs its the superior method if you happen to have a CNC
Old 04-07-2021, 12:06 PM
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Milling machines are higher precision than lathes too.....
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Old 04-07-2021, 01:58 PM
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The tolerance for machining heads is +or - .02mm or .00078".
If your lathe can't hold 8 tenths you might as well have a beaver chew on it.


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Old 04-07-2021, 03:50 PM
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It was a factual statement, Henry, not an opinion......
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Old 04-07-2021, 05:02 PM
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Both machines are capable of accuracy far better than needed on machining engine parts.

My good machinist friend who works in aerospace has a CNC lathe that can make parts to 2 micron tolerance. Is that precision needed for engine parts? Nope.
Old 04-07-2021, 06:08 PM
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Oh my God....all I said was that milling machines are higher precision than lathes. That's a simple fact. You know, like 2 + 2 = 4.
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Old 04-07-2021, 08:48 PM
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Oh my.....
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Old 04-08-2021, 07:24 PM
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Originally Posted by Jeff Alton View Post
Oh my.....
I'm sure you meant "Oh my god".
Reading some of these posts is like listening to my 14 year old grand daughter.

Absolutes vehemently proclaim as factual.
It's as simple as 2 diamonds plus 2 radishes equal 4 diarads.
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Old 04-09-2021, 12:41 AM
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https://www.usimn.com/cnc-lathe-and-mill-difference/

I was not arguing suitability.....if you have a CNC milling machine and don't have a lathe, like drgouk, a milling machine is a reasonable choice.
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Old 04-09-2021, 12:56 AM
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Relax. I just wished that some day I could be as good as this guy with a hacksaw.

https://www.youtube.com/watch?v=-KPWEG_O9M4
Old 04-09-2021, 03:43 AM
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Originally Posted by winders View Post
https://www.usimn.com/cnc-lathe-and-mill-difference/

I was not arguing suitability.....if you have a CNC milling machine and don't have a lathe, like drgouk, a milling machine is a reasonable choice.
I do have a lathe, I just choose to do heads on my Hardinge Bridgeport V1000, for reasons noted above.
I don't think any method offers better accuracy, as you should have the suitable equipment to do the job in the first place, in good serviceable condition. The accuracy of this procedure will largely be down to the clown driving it. My remark about doing the heads on the CNC, being superior, relates to the speed at which the heads can be re faced, and re done if required to clean the sealing face. The accuracy also comes down to the clown driving it, as firstly you must clock up a jig and probe the head to get Z zero. Get those things wrong and it be worse than the other 2 methods.

Henry, do you measure your heads prior to machining with a clock on the sealing face, heads on parallels on cam tower tower sealing face? To determine the lowest head? or another method?
Old 04-09-2021, 04:07 AM
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Originally Posted by drgouk View Post
I do have a lathe, I just choose to do heads on my Hardinge Bridgeport V1000, for reasons noted above.
I don't think any method offers better accuracy, as you should have the suitable equipment to do the job in the first place, in good serviceable condition. The accuracy of this procedure will largely be down to the clown driving it. My remark about doing the heads on the CNC, being superior, relates to the speed at which the heads can be re faced, and re done if required to clean the sealing face. The accuracy also comes down to the clown driving it, as firstly you must clock up a jig and probe the head to get Z zero. Get those things wrong and it be worse than the other 2 methods.
Quote:
Originally Posted by Henry Schmidt View Post
Generally speaking, 911 heads are cut on a lathe not a mill.
That said: there are many ways to skin a cat.
"There’s More Than One Way to Skin a Cat"

Definition: There are multiple ways to accomplish a goal.


Quote:
Originally Posted by drgouk
Henry, do you measure your heads prior to machining with a clock on the sealing face, heads on parallels on cam tower tower sealing face? To determine the lowest head? or another method?
I'm not sure what "measuring with a clock" means but we measure from the sealing surface to the mating surface with a micrometer. Then access any anomalies to determine which head might need the most material machined to make them reasonably clean. Quite often the CE ring will leave a deep impression but only an experienced builder can determine the need to completely remove that impression. There is a limited amount that can be removed and removing an unnecessary amount for simple cosmetics can compromise the stack and combustion chamber.
One clear benefit to using a mill is the ability to modify the chamber cto produce a custom chamber or repair anomaly (IE: damage from an explosion).

Now a question for you: how many 911 Porsche head have you machined and what do you charge?
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Last edited by Henry Schmidt; 04-10-2021 at 10:11 AM..
Old 04-10-2021, 09:53 AM
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Originally Posted by Henry Schmidt View Post
"There’s More Than One Way to Skin a Cat"

Definition: There are multiple ways to accomplish a goal.



I'm not sure what "measuring with a clock" means but we measure from the sealing surface to the mating surface with a micrometer. Then access any anomalies to determine which head might need the most material machined to make them reasonably clean. Quite often the CE ring will leave a deep impression but only an experienced builder can determine the need to completely remove that impression. There is a limited amount that can be removed and removing an unnecessary amount for simple cosmetics can compromise the stack and combustion chamber.
One clear benefit to using a mill is the ability to modify the chamber cto produce a custom chamber or repair anomaly (IE: damage from an explosion).

Now a question for you: how many 911 Porsche head have you machined and what do you charge?
henry, DTI or finger clock, which is better as the stylus is smaller and can probably give a more accurate idea of what's lower as it will go into smaller pits. This could be done on a mill with clock mounted on the quil and heads sitting on parallels. Alternately on a granite table following the same method. On a badly pitted/loose heads, Its going to be a guess. Obviously a mic won't come close to the root of the low spot and in reality it will come down to an educated guess as you do.
For QC, I use the above method to check my work and establish if a barrel shim is required.

I haven't been keeping a tally on how many heads I've machined to date. As far as price, I charge by the hour and I normally only do internal work. Its not the main focus of my business, Its a sideline. As I mentioned, I build a lot of single seater race car engines, Hence why I have a CNC making race engine parts or I would be beavering away on a lathe :]

Last edited by drgouk; 04-10-2021 at 02:30 PM..
Old 04-10-2021, 02:21 PM
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Originally Posted by drgouk View Post
henry, DTI or finger clock, which is better as the stylus is smaller and can probably give a more accurate idea of what's lower as it will go into smaller pits. This could be done on a mill with clock mounted on the quil and heads sitting on parallels. Alternately on a granite table following the same method. On a badly pitted/loose heads, Its going to be a guess. Obviously a mic won't come close to the root of the low spot and in reality it will come down to an educated guess as you do.
For QC, I use the above method to check my work and establish if a barrel shim is required.

I haven't been keeping a tally on how many heads I've machined to date. As far as price, I charge by the hour and I normally only do internal work. Its not the main focus of my business, Its a sideline. As I mentioned, I build a lot of single seater race car engines, Hence why I have a CNC making race engine parts or I would be beavering away on a lathe :]
Nice dodge
The answer is: you haven't done many Porsche heads and you don't have Porsche customers or quoting a price would be simple.
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Old 04-10-2021, 02:42 PM
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I bet I have more New Porsche inventory in my shop currently for customers, How many new Porsche cases do you currently have in your shop?
Old 04-10-2021, 02:57 PM
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bragging rights

What tool do you measure this with for this moment.PEKKER on the table.What is the size for this argument?Ciao
Old 04-10-2021, 03:09 PM
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What tool do you measure this with for this moment.PEKKER on the table.What is the size for this argument?Ciao
Im only winding up the old boy!

Old 04-10-2021, 03:14 PM
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