Cheap Cylinder Head Mill!

[Pullstart 67,563]

Check this out!  It all starts with a clothes hanger 

 

 

[lynnmor 8,009]

That type of machine was available for many years.  I took a pair of heads to a shop and after they were sanded I could get a .012" feeler gauge between them when placed face to face.  I all depends on how flat the platen is.  Just because it is glass doesn't mean that it is flat.

 

[Handy Don 14,414]

2 hours ago, lynnmor said:

I could get a .012" feeler gauge between them when placed face to face

Ok, school me please ‘cause I’m now really curious! 

 

Of course .000” would be perfect in this case, but maybe face-to-face isn’t the best way to test (additive and subtractive variances and all that...)

BUT, what is a reasonable tolerance for a head measured from dead flat?

[ri702bill 9,797]

OK kids, my 2  cents.

First - that is not a milling process. It is sanding. Milling the mating surface of a head usually involves precision fixturing and linear motion of either the part or the head of a rotary flycutter.

No switching belt grits from cut to clean to finish pass as most of us do with K series heads??

Material removal is one thing, but what is the surface finish that is the end result?? This ties in with Don's reply - part of the tolerance will be taken up by the microscopic peaks & valleys. The rougher the surface, the more of the allowable tolerance is eaten up....  

 

Edited Tuesday at 04:29 PM by ri702bill

[lynnmor 8,009]

59 minutes ago, Handy Don said:

Ok, school me please ‘cause I’m now really curious! 

 

Of course .000” would be perfect in this case, but maybe face-to-face isn’t the best way to test (additive and subtractive variances and all that...)

BUT, what is a reasonable tolerance for a head measured from dead flat?

 

Of course I could have checked the heads on a surface plate using feeler gauges or an indicator, but I did a quick check right at the machine shop and handed them right back.  They were better than that before he sanded them.  He has a proper milling machine that was used to get them right.

 

These cast iron heads use a thin metal gasket so they need to be right.  It is surprising just how bad a head can be and still be pulled down with the head bolts, but I didn't want to be a test case.  I have read various tolerances for aluminum, iron, 6 cylinder, etc. but there is no excuse to have the flatness out more than a couple of thousandths. 

[Handy Don 14,414]

47 minutes ago, ri702bill said:

The rougher the surface, the more of the allowable tolerance is eaten up....

Yeah, I can see that.

During one of my summer jobs I was given grunt work in a quality control department--measuring surface roughness on ceramic high-voltage insulators. We used a clever gadget that we ran across the surface--it had a phonograph needle and a wheel in a housing. The device calculated “frequency vs. speed” as a numerical index that we compared to the required specs for that piece. 

Why, you might ask? Turns out that too rough a surface allowed moisture and dust to accumulate which let electricity “short circuit” across the insulator. Not good. 

[ri702bill 9,797]

"Profilometer". to measure the profile of a surface..

[adsm08 3,513]

8 hours ago, Handy Don said:

Ok, school me please ‘cause I’m now really curious! 

 

Of course .000” would be perfect in this case, but maybe face-to-face isn’t the best way to test (additive and subtractive variances and all that...)

BUT, what is a reasonable tolerance for a head measured from dead flat?

 

From the shop manual of  the 96 Ford Explorer, spec sheet for the 4.0 V6:  0.003 in any 6 inches — 0.006 overall.