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Straight edge materials and stiffness

avivz

Cast Iron
Joined
Jan 28, 2009
Location
Israel
I read few discussions regarding straight edges and I have left with some questions.
I understand that ultimately a selection of a specific SE selection depends on the specific use. E.g., SE used for inspection might have different consideration compared to SE used for hand scraping. What I’m mostly puzzled about is the stiffness considerations which seems to be barely discussed and I wonder why. The most common materials for precision SE (and other shapes) are cast iron and granite, having young’s modulus of 80-140 GPa and ~70 GPa respectively. By comparison, mild steel has elastic modulus of ~210 GPa. I tend to think that in particular for SE (considering its geometry), the elasticity modulus is a critical factor for its stiffness. Then why steel is not a preferred material over CI and granite? What I’m missing here?
 
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Thermal stability is a big consideration and why granite is used so much. Also why there are carbide gauge blocks. Cast iron second is far more thermally stable than steel and why it's preferred where precision is desired.
 
Stiffness seems like it should be of great importance in SE design. However, stiffness is rarely actually tested in use of a straight edge. Straight edges are practically never used as a bridge even though many of them look like a bridge. In use they are really usually spanning extremely short distances between hundreds or thousands of support points. So, the question the SE answers is not usually how much of a gap is there from a straight line some support point at one end and the other end to the surface midway between the ends. The question they answer is how well do the many many support points line up. That seems like the same question as the spanning question but it is not. A straight edge should be fairly stiff for convenience, but ultimate stiffness of one material over another is not a deciding factor for practical use of a straight edge. Thermal stability is also a consideration but usually thermal deflection can be minimized by avoiding temperature fluctuations either through reduction of major environmental temperature fluctuations or localized heat input with local input commonly being due to prolonged local contact with the users hand or even radiant body heat.

The important considerations for straight edges is stability, ease of manufacture, and ease of scraping. Scraping steel can be done and we occasionally hear reports of someone successfully making steel straight edges. But scraping iron is much more convenient than scraping steel. Historically, it has been much easier to cast iron than steel though it is obviously possible to do both. Both materials are stable. Both materials will retain internal stresses which can be largely eliminated through thermal stress relief. Both materials will develop stress from machining. But, at least in the case of cast iron, machining-induced stress induction post stress relief is usually not a problem as the item iis scraped or ground. (Everyone knows that grinding long thin sections of iron or steel can certainly cause major warping especially if poor techniques is used)

Side note: I cast a grey iron 36" bridge-style SE yesterday in my little foundry. I have cast hundreds of straight edges of my own designs.

Denis
 
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Steel gives you slivers and you get a lot of burrs, so ou need to use a dull smooth file to deburr it. Granite SE is nice as I own 3 of them butthey chip if your not careful plus they do wear and need to be factory lapped. I would buy or use a cast iron parallel as they can be used for inspection and scraping. Gary Martin of Martin Models makes one and Here is one made up in Canada. You can see more info by searching youtube under NYC CNC John Saunders scraping parallel as he brought one to a scraping class.
 

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The one instance where stiffness might be applicable is in use as a Planekator to map a surface plate relative to a verified flat plane.

In theory at least one could use a known flat straightedge, calculate the sag at a specific span, then map the surface plate and compensate for the sag error. Or if one had a parallel of similar quality, tracing both top and bottom could be used to calculate the actual sag and by extension the accuracy of the underlying surface plate.
 
The one instance where stiffness might be applicable is in use as a Planekator to map a surface plate relative to a verified flat plane.

In theory at least one could use a known flat straightedge, calculate the sag at a specific span, then map the surface plate and compensate for the sag error. Or if one had a parallel of similar quality, tracing both top and bottom could be used to calculate the actual sag and by extension the accuracy of the underlying surface plate.
No argument that stiffness to some extent is necessary. But as you point out, sag can be compensated for and will occur no matter what steel, iron, or aluminum alloy is used. When I carefully measured the sag of one of my grey cast iron 36" Featherweight Straight Edges supported on the ends only like a bridge and then loaded it with its own weight at the center, it sagged less than a tenth. It would be reasonable to expect similar performance from most camelback designs. In other words, the sag approaches measurement error for most of us.

Some reading here will not be familiar with the design I tested. For reference, here is a pic of a raw 36" casting with the sand brushed off and some rough grinding done to remove flash and gates.
1715440025676.png

But, to the OP's question, even for the setup you suggested, I do not think the small stiffness difference between steel and CI would not be enough of a factor to make choosing steel a good option considering steel's generally inconvenient scraping properties and casting difficulty.

Denis
 
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I see this as an argument about who's straightedge is better. Makes no sense to me. There are several brands out there
Brown & Sharp is the famous one. I make SE castings, Martin Models, Bush Precision, Challenge, etc. Arguing over Stifness is like a kid Arguing, mine is bigger than yours. I've taught classes where students brought the SE Denise makes and when we Vibration Stress relieved they moved. Not alot, but they moved. All cast iron moves no matter who makes them. Especially new castings. Some say cast is like rubber. That's why we prefer aged Iron. It's know on here Dennis and I don't like each other. That's why I don't write in his threads. Also EG as he always likes to argue with everyone accept it seems Dennis. They must be bbuddies. I support my knowledge with facts and my over 40,000 students over a 55 year career. You can see several youtube shows customers and students did on my classes. Search "Richard King Scraping Biax " on YOUTUBE. or leave off Biax. The pictures are my or our family made castings and photos of students "ringing" their parts. Moderators please close this thread!
 
Photos of King-Way brand Straight Edges. Foster SE. Ring stress relief.
 

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I added Bourn & Koch in Rockford IL who are one of a handful of new machine builders left in the USA who have had me teach several scraping classes there. I can back up my credentials. *Comment edited by moderator*
 
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I see this as an argument about who's straightedge is better. Makes no sense to me. There are several brands out there
Brown & Sharp is the famous one. I make SE castings, Martin Models, Bush Precision, Challenge, etc. Arguing over Stifness is like a kid Arguing, mine is bigger than yours. I've taught classes where students brought the SE Denise makes and when we Vibration Stress relieved they moved. Not alot, but they moved. All cast iron moves no matter who makes them. Especially new castings. Some say cast is like rubber. That's why we prefer aged Iron. It's know on here Dennis and I don't like each other. That's why I don't write in his threads. Also EG as he always likes to argue with everyone accept it seems Dennis. They must be bbuddies. I support my knowledge with facts and my over 40,000 students over a 55 year career. You can see several youtube shows customers and students did on my classes. Search "Richard King Scraping Biax " on YOUTUBE. or leave off Biax. The pictures are my or our family made castings and photos of students "ringing" their parts. Moderators please close this thread!
Now that is the goofiest response I have seen in a long time. Did you even read my post? Did you notice the line that said " It would be reasonable to expect similar performance from most camelback designs." And it is certain no one questions your often self-cited scraping credentials.

Do you have something to to add to the discussion that might be pertinent and helpful to the OP and most importantly fact-based backed up by something more than "personal experience" and not at odds with metallurgical research carefully done and well-documented by the likes of ASM?

Such comments would be welcome I am sure. Personal attacks not so much.

Denis
 
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I never read your posts thats why I had hoped you AND your bubby would stay out of mine. I didn't attack you. Just pointing out a few facts. You always argue with anything I say. I'm honest on here. Have you ever told the members what you did before retirement? How many lathes, milling machines, surface grinders have you completely rebuilt? You always comment. Please enlighten us on your scraping and rebuilding experience?
 
I never read your posts thats why I had hoped you AND your bubby would stay out of mine. I didn't attack you. Just pointing out a few facts. You always argue with anything I say. I'm honest on here. Have you ever told the members what you did before retirement? How many lathes, milling machines, surface grinders have you completely rebuilt? You always comment. Please enlighten us on your scraping and rebuilding experience?

So, do I respond to this public personal attack or not? Hmmm. If I do, am I stirring the pot? If I don't, does it look like you have something on me? I am not sure as I thought personal attacks were not supposed to occur on PM. Note to most members: The Following Post Should not be Needed on PM and You Can Skip It Without missing Anything Related to The OP's Question ;-) But if you are in the mood for some popcorn...

Rich, Had you actually read my posts would know that I have posted many times about my 33 year career as a Board Certified Family Practice physician and have offered numerous members medical suggestions based on personal experience and scientific evidence. I have invariably cited published articles from respected sources to back up those opinions along with the advice as I think unsubstantiated personal experience should be taken with a (big) grain of salt especially when it is counter to well-documented scientific research. BTW, that career that was quite rewarding and intellectually stimulating. But, not wanting to be a one-trick pony and seeing the need for something new in straight edge design, in retirement from that career I designed and started casting straight edges nearly ten years ago. That has also been a very challenging and stimulating pursuit---really a hobby and certainly not a money maker. I feel good about the work I have done and the mentoring I have provided for up and comers in the casting field. And it has lead me to do much reading and much labor to perfect the art of casting iron straight edges. That has NOT made me an expert in all things metal-related nor even to have broad experience in casting iron. But I feel I do have something to offer concerning straight edge design, fabrication and machining.

I rarely wade into rebuilding questions as I have very limited experience in rebuilding and always so state if someone asks me my opinion on rebuilding questions. I will say again (is this the tenth or fifteenth time that you have made this same attack and I have made this same request?) if you find fault with the factual basis of an opinion (any opinion) I have offered and can cite reasonable evidence to back it up, please do so. I will then set the record straight and make appropriate apologies. But, I am sure you will respond as previously with .......... nothing.

If you have a special beef with me, you should probably just PM me and not attempt to embarrass me. It's not working well for you and you are simply pooping the punch bowl and wasting members' time. And please, have the courtesy to at least read a post before you come on here and find fault with it.

Denis
 
Rich, give it a rest! Denis said nothing about you or your straightedges. And admitting that you jumped in with a long comment without actually reading what he wrote does your credibility no good at all.
 
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I started this thread and his buddy said the OP and he said I didn't know about Stiffness and he agreed. Dennis can comment in his own threads. I read his info, I said that to get his goat and it worked 💪
 
I started this thread and his buddy said the OP and he said I didn't know about Stiffness and he agreed. Dennis can comment in his own threads. I read his info, I said that to get his goat and it worked 💪
So, Rich are you doing OK?


Thank you. Now everyone knows. How many. You Tube shows have people made about you? I have several . The members can decide who they can trust or believe. I contribute to this forum as I was one of the organizers or contributors from the get go. I have 55 plus years in the rebuilding, way scraping, straight edge making, etc. I have taught al over the world to new machine builders, machine rebuilders, machinists. College Professors, etc. I can comment on many forums on PM. Some people have way to much time on their hands. Pics L to R. MIT professor, scraping test bar, Member Sip who took Boston class, Imts show pic. I am worldwide instructor for BIAX, class held at Kieth Ruckers shop in Tipton GA. students: Tom Utley, Adam Booth, John Saunders, Lance Baltzley, several YouTube people,
Rich are you well?
Cuz
1) You did not start this thread. And even if you had, you would still not own this thread.
2) No one said you don't know about stiffness.
3) No one made claims of one SE being better than another. In fact just exactly the opposite was stated.
4) You got my goat? Really??? I guess I did respond in a calm and civil way to your repeated unfounded attacks. If you want to see my goat sometime, you'll have to do better than that. And I try never to go there no matter how silly the provocation.
5) Once again you only seem to attack me personally but fail to actually point out any errors I have made or false information I may have provided.
6) So if that is winning, you're winning alright. 😂
7) Important question: how did any of your remarks other than the first one you made help anyone on PM. Or is that a factor? Are you trying for a Donny and Thermite circus. I ain't goin there. I am finished addressing any attacks from you in this thread. But I am more than interested in further discussing this OP's question in this thread which brought up a subjects that are of interest potentially to a few people and are worth discussing, civilly. Cheers!

Denis
 








 
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