# How big would a reference surface be for a 120 inch straight edge.



## Peyton Price 17 (Oct 30, 2020)

I am thinking of getting a 120 inch brown and sharpe camel back straightedge. How long would another surface have to be to have it rescrape it?


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## benmychree (Oct 30, 2020)

Somewhere nearly as long  ---


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## graham-xrf (Oct 30, 2020)

I think, with care, there are some methods that allow to confidently scrape in something that is longer than the test surface. From memory the surface needs to be a bit more than half the length. This surely must be a thing so common, it be well known by now.

In theory, if you flattened 1/3, then moved attention to the next third, and so on, the tolerance extrapolated would be worse than if you had a huge surface to begin with, but still good enough for you.  Maybe it is mentioned in Connelly's book.

[Edit: In Connelly's book "Machine Tool Reconditioning" 8.15 on Page 48, there is reference on what to do about having a surface plate that is too small, though the stress is how to use it in combination with a straight edge to overcome the problem when working a a big piece. This is not the same situation as how to make the straight edge straight in the first place.]


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## graham-xrf (Oct 30, 2020)

There may be some mileage in what this guy did with .. hand tools only!
It is longer than his surface plate - but not by much. Surface plate looks at least 3/4 or more

--> Hints on making Straight Edges out of Steel


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## Dabbler (Nov 7, 2020)

Q to  @Peyton Price 17 :  Do you really need a 120 inch straight edge?  Will it make 2 good 58" ones?  Is that overkill for what you need?

-- you can easily scrape in a 58" straight edge on a 48" surface plate.   As mentioned by @graham-xrf , the basics are in Connely's book.


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## MontanaLon (Nov 7, 2020)

Dabbler said:


> Q to  @Peyton Price 17 :  Do you really need a 120 inch straight edge?  Will it make 2 good 58" ones?  Is that overkill for what you need?
> 
> -- you can easily scrape in a 58" straight edge on a 48" surface plate.   As mentioned by @graham-xrf , the basics are in Connely's book.


Well, a 48" surface plate is usually 36" wide so the diagonal would be 60". You could scrape in a 58" straight edge easily on that. 

But a 10 foot straight edge? What are you working on? Most of the stuff in my shop would have trouble supporting the weight.


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## matthewsx (Nov 7, 2020)

Theory vs. practice.

Guys who need a 120" straightedge probably aren't in the "hobby" machinist category. 

@Richard King 2 knows this kinda stuff and if you really want to learn I strongly suggest listening to him. If it's just an academic question then simple arithmetic should answer the question.


John


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## Richard King 2 (Nov 7, 2020)

There is an easy way to first test it to be sure it needs scraping.  Flip it over and brace it with the originally scraped surface up.  It must be solid.  Place a precision level .0005/12" in the middle and level it.  Then using a tape measure and sharpie marker measure out 1/2 the length of the level, stop align the edge, wait 10 seconds, light pressure on each end.   It should be .00005" to .0001 per 12" .


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## Richard King 2 (Nov 7, 2020)

If it is bad, then you locate the lowest spot or area and scrape that area to your short master not moving it more then a 1" or 2 when rubbing.   Once that area then move out 1/2 the distance of your short master and scrape the high area until it starts to blue in the finished area., etc. etc.  This called step scraping.  Also use the level to test as I described before.


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## Peyton Price 17 (Nov 8, 2020)

Dabbler said:


> Q to  @Peyton Price 17 :  Do you really need a 120 inch straight edge?  Will it make 2 good 58" ones?  Is that overkill for what you need?
> 
> -- you can easily scrape in a 58" straight edge on a 48" surface plate.   As mentioned by @graham-xrf , the basics are in Connely's book.


because it is huge and who doesn't want one. I think i might be getting a big metal planer so it would be good for testing the wear.


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## vtcnc (Nov 8, 2020)

Peyton Price 17 said:


> because it is huge and who doesn't want one. I think i might be getting a big metal planer so it would be good for testing the wear.


If you are getting a 10' or larger metal planer, then this would make a lot of sense.


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## Richard King 2 (Nov 8, 2020)

Why do people always try to re-invent the wheel?  It is so much easier to scrape a long way as Keith Rucker, Adam Booth show on You Tube with 1 long straight edge. You are doubling or tripling the time it take in my opinion of 55+ years of scraping machine tools and getting paid to do so.   Yes this is a forum called Hobbyist, but many here are not hobbyists like myself, vtcnc, John York, etc, etc, .  Those 10 and 12' straight-edges are not made anymore and to even talk about cutting one in 1/2 is sacrilege.  A bit like saying lets cut in 1/2 the Basilica in NY because not as many people attend it anymore or that 120" lathe is only used 2 times a year so lets cut off 60" off the back end.  Sorry to sound silly, but that's the way I feel.  

I'm not a big fan of the guy showing the steel fabricated SE, who is he? if steel was so easy why have they been making cast iron straight-edges for  hundreds of years.  He uses it to check his press brake or sheer.  How accurate does it need to be, .002"? 

I am here to answer questions to improve the accuracy of machine tools.  I don't guess.  People pay me a lot of money to help them and their industry improve.   There are other books to quote besides the collection of opinions that Edward Connelly put into a book.  My Dad, Herman King met him, when he asked my Dad to write the section on scraping as Connelly lived in St. Paul, MN and my dad lived and worked in Minneapoils, MN.  

Connelly  was not some genius rebuilder, he was a trade school teacher who organized information others who were professionals in the field gave hin.  Look at the first few pages of the book where he acknowledges them.  The inspection drawing in the book were copied from the George Sleschinger book at the top of this forum. That book was written by a German engineer and all the standards of the ASME and SME are based from it, copied into that Connelly book. . The Moore book "The Foundations of Mechanical Accuracy is another great book, again is at the top of the forum.   Nelson our founder was a hobbyist at first, but I would call him a great man and professional for what he has created.   G'day


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## matthewsx (Nov 8, 2020)

Peyton Price 17 said:


> because it is huge and who doesn't want one. I think i might be getting a big metal planer so it would be good for testing the wear.



One of the best things a forum like this can do is connect people that can help one another. If getting such a rare and possibly useful tool is a possibility for you it would be good to consider finding a mentor who has experience in the area. We have such a section on here and it may be useful to put out a call on it.









						MENTORS & MENTEES - SIGN UP HERE!
					

H-M is all about HELPING OTHERS. If you are willing to MENTOR someone less experienced in your area, please sign up here!




					www.hobby-machinist.com
				




As @Richard King 2 noted this is something which can be done but probably best accomplished by someone with experience. If tools like this aren't made anymore then acquiring one would be more of a "caretaker" situation than simply owning it. For a young person to have it, and care for it appropriately, and possibly make it available to others in need would probably be an excellent outcome IMHO.


John


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## Richard King 2 (Nov 8, 2020)

Thanks John.... I have to laugh now....I was once the head moderator of this forum.  Nelson asked me to write in here until one of my crabby times I got fired and I quit.   Since then I missed the forum and re- joined as Richard King 2....lol...I bet you could find me in the archives as Richard King...... oh well we all make mistakes and hopefully we learn from them...


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## matthewsx (Nov 8, 2020)

I enjoy reading your posts almost as much as I enjoy fixing up old machines. Hopefully one day my experience and machine selection will warrant actually learning how to scrape in a surface, right now I'm just struggling with replacing the leadscrew and feed rod on my Bolton 13 x 40 project.

Thank you for sharing all your experience on here, we have much to learn....

JOhn


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## graham-xrf (Nov 8, 2020)

Agreed that a 3m long straight flat, especially if as much as 75mm or 100mm wide is a reference to be taken care of - and cutting it is bound to rub the wrong way among those who appreciated what it took to get that way. An extreme version of "parting out". If another fabulous antique cartographer's atlas is discovered, it's fate is to be unbound, and the pages sold as separates. I guess humans are like that.

For the hobbyist, even a short straight edge reference is really expensive! Just a raw rough casting for a 12" little camel-back is *£165 ($217)*. A used 18"x1.5"x 3" ex Brown & Sharpe is *£485 ($637)*. I can fully understand the motivations of guys like Alex (the fabricator) to go against the traditional ways. He made it for a press-break, which may not need to be as accurate as might be needed for, say, lathe ways. Even so, everything he did to indicate measure it, and what he did with it seems sane.

Traditionally, a particular type of cast iron is used because it is known to be very stable. Support castings shapes, with motive to keep the weight down, became received wisdom from the beginning. If Alex found a steel structure that compensated such as to match the performance of the traditional build, then good for him!

In a different application I knew that carbon fibre composites had exceptional stability. It had me thinking that maybe a carbon fibre support structure under a final scraped metal surface could be stable. Unfortunately, the temperature coefficient of carbon composite, while well enough constant for a given single layup build , can be chosen over a fairly wide range, and pretty much all  are considerably less than for cast iron. Even then, making it that way is unlikely to be cheaper than the traditional way - though possibly much lighter.

Likely there is no comparative critical study that would give us a clue as to exactly how good is the Alex fabricated SE, compared to the, by now very well known, performance of traditional cast iron standards. His SE was knocked up in a hurry, used, and then stored for 2 years before he made the video. Maybe, if a USA-based HM member brought one to one of @Richard King 2 's classes, it could be spotted against something known.
Alternatively, just build one and keep a check using a surface plate.

We still need all the skills and effort and time to get it flat as taught by Richard, and a laser-cut support + two chunks of carbon steel, plus welding and scraping effort is not doing it on the cheap. This kind of accuracy always costs, and these skills are still around as a labour of love. My dabbling with actual scraping is likely to be limited. Getting to acquire the references is first. Only then I might get to scrape on the stuff that really needs it.


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## Peyton Price 17 (Nov 9, 2020)

graham-xrf said:


> Agreed that a 3m long straight flat, especially if as much as 75mm or 100mm wide is a reference to be taken care of - and cutting it is bound to rub the wrong way among those who appreciated what it took to get that way. An extreme version of "parting out". If another fabulous antique cartographer's atlas is discovered, it's fate is to be unbound, and the pages sold as separates. I guess humans are like that.
> 
> For the hobbyist, even a short straight edge reference is really expensive! Just a raw rough casting for a 12" little camel-back is *£165 ($217)*. A used 18"x1.5"x 3" ex Brown & Sharpe is *£485 ($637)*. I can fully understand the motivations of guys like Alex (the fabricator) to go against the traditional ways. He made it for a press-break, which may not need to be as accurate as might be needed for, say, lathe ways. Even so, everything he did to indicate measure it, and what he did with it seems sane.
> 
> ...


The person selling it only wants $600 us dollars. He was proud that i was interested in old tools and machining even though i'm 12 years old. The planer will be cheaper since they sold one of the same size for $150. It also has 2 heads that work independently. the table is 12 or 14 feet long. It has the motor for running it too.


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## Peyton Price 17 (Nov 9, 2020)

vtcnc said:


> If you are getting a 10' or larger metal planer, then this would make a lot of sense.


the planer is a 12 or 14 foot long one.


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## Peyton Price 17 (Nov 9, 2020)

Richard King 2 said:


> Why do people always try to re-invent the wheel?  It is so much easier to scrape a long way as Keith Rucker, Adam Booth show on You Tube with 1 long straight edge. You are doubling or tripling the time it take in my opinion of 55+ years of scraping machine tools and getting paid to do so.   Yes this is a forum called Hobbyist, but many here are not hobbyists like myself, vtcnc, John York, etc, etc, .  Those 10 and 12' straight-edges are not made anymore and to even talk about cutting one in 1/2 is sacrilege.  A bit like saying lets cut in 1/2 the Basilica in NY because not as many people attend it anymore or that 120" lathe is only used 2 times a year so lets cut off 60" off the back end.  Sorry to sound silly, but that's the way I feel.
> 
> I'm not a big fan of the guy showing the steel fabricated SE, who is he? if steel was so easy why have they been making cast iron straight-edges for  hundreds of years.  He uses it to check his press brake or sheer.  How accurate does it need to be, .002"?
> 
> ...


That is what i thought. My dad wants to get the straight edge too. if i told him if people wanted to cut a straight edge that big in half he would go on and on about how useless it is. here is a picture of one and how big they really are.


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## graham-xrf (Nov 9, 2020)

The design of the arch is to keep the surface supported with a stiffener girder that has height appropriate to to the distance from the edge. The central portion so much needs this that there was no attempt to cut out a weight-reducing circle out of the the centre two section between the ribs.

Any attempt to "cut it in half to make two" upsets all the design of support for the surface itself. Clearly it is a fine reference as it is. What can be made of it's metal to contrive two shorter straight edges is hardly better than starting from scratch.


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## Dabbler (Nov 10, 2020)

Long straight edges come in a different format as well:  I was assuming it was a parallel type, the kind I used when I was learning.  The biggest one I used was 80 inches long, and had a parallel depth of around 12":  when one of the other guys dropped and broke it, it was turned into 2 separate ones if different lengths, hence my question.

I've never used a camel-back version even though they are the most popular kind.


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