Judging Broach Marks

[Lynn H.]

Re: Judging Broach Marks

Lyle,
I do apprectiate your experience as an inspector, but I do not believe I have my description backwards. The inspection tool you refer to is call a profilometer and measure surface finish in micro inches. While surface finish does worsen as the tooling dulls, I believe the conditon we look for on the blocks is one that is caused by the broaches being "too sharp" if you can believe that. The chattering condtion can return as the broach dulls as well as the finish going away. Many shops use the surface finish as a way of determining broach life. This discussion can get way more technical than I can write on this board. I was just attempting to try to describe why it is so difficult to give an "absolute" in determining what to look for when describing the stamp pads. This seem to be a subject that many find interesting. That seems to be proven by the length and detail of this particular posting. This may be a good topic for a seminar, as I do not believe most of our members understand the broaching operation itself, therefore have a hard time understanding what to look for, and how to describe it. I do consider myself to be one of the very best in when it comes to any type of broaching as I have "done it all" and even some things thought impossible by many when it comes to broaching. I am sure the input on this subject could be endless.

[Michael W.]

Re: Judging Broach Marks

Gilbert,

Thanks for your first hand observations and background in the industry, very valuable.

This is all acedemic, but my own experience (ref post about about broaching slots in turbine disks) is similar to Lyle's with respect to dull tools leaving more marks than sharp tools.

I can relate very well to the chattering effect from a new tool, but believe that this would leave different machining marks from the longtitudinal 'gouges' that are seen on many stamp pads. Several times I observed a series of 'waves' running perpendicular to the machined surface with the distance from paek to peak roughly equating the distance between any two teeth on the tool.

[Lynn H.]

Re: Judging Broach Marks

I am sure this could be debated in length, and I too have had some experience broching the turbine dics (for the aswan dam in Egypt) like I think you are refering to. While I do agree that you can also get similar markings from dull tooling, you have to ask your self to you believe the tools were always dull in the engine block broaching application (or more times than not). This is a condition that is way more prevelant in flat broaching than forms when it comes to the broaching operation and new or sharp tooling. I cannot tell you how many times I have had to stone the finish teeth on new tooling worth tens of thousands of dollars in order to eliminate these type of tool marks (very risky at times). They are not acceptable in most high tolerance broaching applications. I am not attempting ot be the "know it all" when it comes to this, but I can attest to broaching millions of parts of all designs and feel very confident in my evaluation of these tool marks. One of the biggest factors in these marks on the engine block is the material itself. Cast iron is not one of the most favorable materials for broaching in general. Nothing like a good debate !!

[E S.]

Re: Judging Broach Marks

Faulty logic EJ. Have you ever seen a cylinder case with original broach marks and NO stamp at all? They do exist. As do cylinder cases with original broach marks and only an assembly stamp -- no VIN. So original broach marks are no assurance that you are looking at the factory original engine.

Beyond that, no judging organization has factory authenticity as their judging standard. ALL of them state the APPEARANCE of factory authenticity. You are seeking a standard that exceeds that of every Corvette judging organization.

(1) Clarification-I'm referring to engines in cars(1960-1967)with vin#s.
Are you saying you have seen engines in these cars that have ORIGINAL broach marks, but NO stamp at all?
How would the dealership order eng/trans. parts for warranty/service work?
How did you determine that the blocks you are looking at have ORIGINAL broach marks when you also say "no judging organization has factory authenticity as their as their judging standard. ALL of them state the APPEARANCE of factory authenticity".
Did You mean to say that the blocks you were looking at have the APPEARANCE of original broach marks?
By the way -I was replying to the member who said "there are several in our organization who can judge a stamp pad at a glance"
Personally,I hope someday there is a way to judge authenticity as well as the "appearance" of authenticity. Regards-EJ

[Michael W.]

Re: Judging Broach Marks

Many over the counter short and long blocks had no stamps whatsoever on the pad.

[E S.]

Re: Judging Broach Marks

Hi- My comments/opinions/observations only refer to engines that were installed in '61-67 corvettes.

[Dick W.]

Re: Judging Broach Marks

In the past few years E. J. I have purchased a '64 block, a '67 and a '68 block that had never been stamped. As Mike stated that there were many blocks across the counter that never had anything stamped on them. For audit purposes all engines installed in vehicles had the suffix code and VIN stamped

[Terry M.]

Re: Judging Broach Marks

No EJ, I was not suggesting that cylinder cases without assembly or VIN stamps were factory installed in cars (Corvettes or otherwise), however given the millions of Chevrolet produced vehicles I am sure there were some which escaped the usual processes. Let's ignore those anomlies for this discussion.

I have seen many cylinder cases, presumably built as partial engines of bare cases, without stamping on them -- as others have mentioned. My point was that your statement:

"Hi Mike-Do I understand you to say that there are several in our organization who can positively identify factory original broach marks?
If yes- then that would also prove that the vin#, engine assy. date,and hp suffix are also factory original to this vin# car, since they are stamped on top of these factory original broach marks. Correct?"

is not correct in that one of these bare cases with factory correct broach marks could be stamped with a "correct" engine assembly date and code and the vehicle VIN derivative and be presented for judging. So the factory original broach marks do not prove the factory originality of the cylinder case to that car. So your statement is not correct.