More on straight edges

Argh! It ain't fair. Here's three 8 ft B&S cast iron straight edges in two auctions.

Two here:

And one here

Someone with more money than sense needs to scoop all three straight edges and send them to me. I can scrape and calibrate them to generate a NIST qualified reference and make stout boxes for them. Then we could sell them and only lose about $200 apiece. Like I said, more money than sense but it's criminal negligence to do less. Where is a nice ditsy wallet man when I really need one?

[ 09-24-2006, 08:07 AM: Message edited by: Forrest Addy ]

Had a ten footer, too much for even two guys.

Seller on the pair is Dewaynne Tackett, a member here.

He is the one with the ancient 25" Sidney we discussed some time back.

Forrest you should try making the URL function work for you and cut down those insanely long links.

John

John: Kinda like that? I could never get it to work in the past. I just now discovered you have to remove all the spaces between brackets or the URL thingy fails.

Two guys? It is to scoff. By the time they rassle the tool onto the work and taken a rub on it, they've had they warm sweaty mitts all over it. For tooling like this you need a nice bridge crane and a suitable low rate extension spring.

Betting that reliable will get more for the one then xtrucker will get for the pair.

I've been gazing wistfully at those, but have two problems. No make that three.

1) I need all three as I have no other reference to true them to, and

2) I can't pick them up anyway (damn contractor got cheap and apparently omitted the bridge crane from garage)

3) Not enough spare cash


I think about a 5' edge would be about right; long enough to cover most of my work, and maybe can be moved around. I'd need to find a friend with a long enough edge or plate to true it to, but then would at least have a reference for whatever follows next.

My current philosophy on scraping is, scraping isn't that hard, but finding all the ancillary tooling to tell you what you're doing is a PITA.

Still having fun though, have had to halt scraping practice while I re-arrange the shop to shoehorn the new lathe in.

Rob

Forrest: I'm not sure whether your intial post is in jest or not. I'm not willing to bet against Mebfab, the one at reliable wouldn't shock me to go higher than the pair.

I'd buy the pair, but fear shipping will double the price.

Someone else want to step up and grab the third?

Forrest gonna do all the scraping for free?

Maybe someone's driving the right direction and could help us save on the shipping?

Of course when it's all said and done, I'd want one of them.

Not trying to be a smart-a$$, but don't know if we could really put something together out of all this or not.

If anyone has any thoughts, I'm listening; there's a little under 7 hours to figure it out.

Rob

John: Kinda like that?

Click to expand...

You done good FA Skinnied the thread right up.

As to owning these, long ago here I proposed a
"circuit" master precision level to be furnished by me and passed around as needed.

This was rightly generally scoffed at.

These long straight edges would be even more impractical to send hither and yon.


John

Moving an 8 ft straight edges across country costs $300 coast to coast. If cost me nearly that much to ship my 5" DT straight edge from MI to my nearest shipping depot. It would have been nearly $100 more from depot to my house. As it was the stout 2 1/4 x 4 3/4 full dimension lumber and 3/4 ply case I built for it was nearly destroyed in shipping from CFS and back.

While I'd scrape a circulating reference for group use in a heart beat I don't know how we budget conforming types could separately fund the shipping.

Rob, you looking for a good 5 ft DT straightedge? I have one to spare. Email me.

please forgive my ignorance here, but why not use the aluminum tool grade straightedges? or is there some issue that makes them unsuitable for scraping? can you calibrate an aluminum one Forrest?

I've noticed that the Scraping Class has caused a big spike in Ebay prices for scraping-related paraphernalia. I realized yesterday (after the auction closed) that I was bidding against Blackboat for a Brown & Sharpe straight edge -- sorry about that Rob!

We should make some kind of mutual "Friends of Scraping" bidding agreement

Betting that reliable will get more for the one then xtrucker will get for the pair.

Click to expand...

Yeah, no kidding -- our buddy "smonros" (who only bids on Reliable auctions) is the high bidder right now. It's about time for cvwest and 1cableart1 to show up.

Anyone want to place bets on how high the Reliable straight edge will go? I'm thinking $800

It's alright lazlo; I knocked out Forrest & Bruce on one little plate, Forrest got me on another, etc.

I bid what I was willing to pay, based on cost of new, and what my CC can stand.

It goes against my grain to "out" an ebay auction before it's over, especially if I'm bidding, or think someone here might be on to it.

However, I'm willing to discuss a little bit of who needs what, and where it is in regard to scraping tools.

Forrest: thanks for the info on shipping, kind of what I was afraid of. I'm at work now; I'll email you this evening; would like to hear more.

All good fun; can be a little tough somedays being a poor boy trying to play with a rich man's toys.

Rob

It's alright lazlo; I knocked out Forrest & Bruce on one little plate, Forrest got me on another, etc.

Click to expand...

I try to avoid an auction if I notice one of our PM brethren bidding on it, especially if it's not unique. I backed off on a cast iron box parallel when I noticed Bruce was bidding on it. Unfortunately, neither of us ended up with it, and the same guy (Phuzzy2) sold another for $11 that I just completely missed.

Did a buy it now on the pair. Will get freight quote Monday thru the contact info in the Ebay listing.

Forrest - can send them along if you want to go ahead and see what we can do group wise.

If you will scrape and document (and make cases), we will have some valuable property of which we would be joint owners.

If some of you want to be involved like helping with shipping I would welcome that and you would become a "group" member. To me you should not become a group member unless you can forsee needing these in your shop within the forseeable future.

If nothing comes of this Forrest, I would be pleased to pay the going rate for your efforts and get them back to Houston when you are done.

Your collective input on how to proceed is welcome.

John

Sad thing is I my not have enough in the checking to capture the B&S 96" striaght edge at Reliable Tools. It's at $177 now. People have a way of sniping Reliable's sales up through the roof - and then there is shipping.

I gotta look at the checkbook.

By the way guys, how do you scrape-in a 96" straight edge? Do you have a 96" surface plate?

Lazlo,

There's several tricks to scraping flatness to the limits of the technique. If you can find a copy of Porter's "Engineering Reminiscences" there's a good discussion of making flats (and straights incidentally) by a sequential process of scraping three aproximately equal sized plates together. When all three argee in their bluing pattern then thy satisfy NIST recognized proof of flatness for scraped fletness references.

This is not done by a process of strict rotation but a process of test and cancellation.

Forrest, you know I'm quite familiar with Whitworth's Systematic distribution of Errors

My question is when you, or John, get that 8 foot straight edge in, how the heck are you going to scrape it flat?

You really need a 96" surface plate, or a Talyvel and smaller surface plate, and do it in segments?

I posted an 8' bridge type cast iron straight edge about a week ago, that was on the Sacramento, CA Craig's list. I think he wanted $400 for it. Went back to check and the listing has expired.

No one showed any interest when it was posted in the tools and acc forum here in PM. The seller also had an 8' black granite straight edge and a 3' by 5' cast iron scraped table for sale. The straight edges were in wooden cases and looked to have come from military surplus, or aerospace.

Laslo

The system used by Whitworth was invented long before him by experimentors in the glass industry. Whitworth adapted it for use in generating flatness and linearity references for the then nacent machine tool industry.

The hand of a twist does not change with inversion or reversal. Straightedges are essentially long skinny surface plates. The problem with using three straightedges in an adptation of the Whitworth system is there's is no way real sensitive way to check for twist using indications from the straight edges themselves.

There was some discussion a few months ago about what I call "the Whitworth system" (that illustrated in Porter's "Engineering Reminiscences") for generating intrinsicaly flat reference surfaces. In the discussion I demurred when the topic of twist came up and expressed skeptacism about rotating the flatness references 90 degrees face to face to reverse the sense of the twist and thus detect it (call it helical error if that's a more vivid rendering of the concept).

I declare now, my position was mistaken and you guys were right. Without face to face rotation, twist is undetectable error when using the Whitworth system. I'm in the process of winnowing through all my writings to correct this error. I was going to write my revised position up fancy but now is as good a time as any to 'fess up. Some of you look up to me for presenting straight info; goes to show the truth about "feet of clay."

We can use a careful set-up of the work on some very rigid support and cross-check with a precision level to detect twist across the reference edge. Naturally any four point in a plane restraint of the work may have an effect on the twist of the reference edge. Given that the level is 0.0005" in 10" and the bubble can be easily interpolated via bare eye inspection to 1/5 that, 0.0001" error in 10" across a 2 1/2" wide straight edge is pretty damn accurate.