# "Composite" straight edges?



## TroyO (Apr 14, 2014)

I was mulling over straight edges and just can't see spending too much on one to scrape in my hobby level machine tools. I have a small prism I made form some windows weights, and it turned out great and the price was perfect, LOL. (Free). It's about 1.25 x 11. 

I will need a couple of larger ones for the G0704 though, so I set about pondering cheap alternatives. 

(1) What about casting JB weld against the surface plate? Using a clay "mold" you could cast right on the plate (After several coats of wax) and it should be a mirror of the extremely flat reference. You could insert some "ribs" while it cures to give it some additional stability... granite perhaps? The cool thing about this one is you could still "scrape it in" using traditional methods.

2) Combining granite tile cuts to create a straight edge and joining them with epoxy..... you can test the flatness of it before continuing and if you assemble it on the surface plate it should maintain it's flatness pretty well I'd think. There would have to be some vetting of the tiles as you went to make sure the cuts didn't throw it out of wack.

In the end, as long as it's stable(ish) and flat.... does it matter how/what it's made of? (Well... at least in a hobby setting.)

It's certainly inexpensive to try it out..... maybe $40 for both to give it a whirl.

Am I completely nuts? I don't see any drawbacks IF it works as expected... one key fact I'm off to research is if I can find any thermal expansion rates for JB Weld (Or any other epoxies.... I keep mentioning them but I swear I'm not a shill, LOL!)

CoC Pics attached


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## DMS (Apr 14, 2014)

I think that much JB-Weld is going to cost more than the rough straightedge 

For a straightedge, the material does matter. You want something that is fairly stable dimensionally, as well as something that transfers the blue well. Cast Iron is typically the preferred material. So how cheap are you trying to get away with? Durabar is somewhat expensive IMO, but it's not that bad, especially if you can find a drop big enough.

FYI, I have seen people "re-purpose" old cast iron surface plates into usable straight edges. If you can find one at a scrap yard, or on CL, that may be an option. Old cast iron table saw table might also work too, if you can find one with few enough holes. Just add a handle and scrape flat.


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## TroyO (Apr 14, 2014)

Surprisingly you can get JB pretty cheap, LOL. I filled the base of the X2 with it for ~20 from Ebay. I guess I was thinking cheap in comparison to $350-$500 for a 24" Camelback casting. It's a combo of cheap and time-saving compared to scraping in a rough camelback too. 

I actually have a big chunk of durabar I can make a wider prism from.... but it won't be tons longer. I figure I can cut some granite tile I have already (18x26) down and make a long/narrow edge for the table ways. I suspect granite, even in that form will be pretty stable.... maybe not enough to last for seasons of use, but enough to get a set of ways done.

I'm just shooting ideas out..... I was also looking at optical glass prisms too.... but they seem to only go up to about a foot.

I hadn't thought about scrap tables etc. I'll have to ponder that one.....


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## cjtoombs (Apr 14, 2014)

As for alternate materials for a straightedge, I would think aluminum would be the next choice down from cast iron.  It is relatively cheap, cheaper to ship if you have to order the piece you needed, realtivliy easy to cast if you have that capability (and a good casting aluminum alloy would likely scrape easier than 6061).  It's fairly easy to scrape, if all the Gingery builds out there can be counted as evidence.  I think the big problem with alumium would be more rapid wear, which would be less of a problem for a hobby scraper than it would be for a pro machine rebuilding shop.  As for composites, I think the wear problem with aluminum would be even worse.  Also, on a piece that size, there would likely be some shrinkage deformation, so casting it on a surface plate may not buy you much.  You may still have to machine it flat before you scrape it in.  Scraping something soft like that is doable, but it takes a different touch, or you gouge too deep.  Good luck.


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## DMS (Apr 14, 2014)

That's a pretty good idea. MIC-6 is a cast plate, and comes pretty flat as is. Might be a good start.


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## TroyO (Apr 15, 2014)

Good point on the.... errr..... points. The cast mirror may be slightly inferior but it would still be darn close. Luckily anything cast like that should be able to be given a quick pass with a  scraper.

I think I may try the idea in the second pic..... at least just to cut a slice off a tile and checking it for flat by basically just spotting it like any other. I could even dress out minor issues with diamond hones maybe. If it passes that test the rest seems like it would work.

I have the tile and a small wet saw so it's free to give it a swirl.

The Mic-6 cast plate is interesting too... for some reason it never occurred to me that you could scrape AL. FYI it's about $35 shipped for a 1x2x32.... not too bad. I might need to find a slightly larger hunk but it's a start.

Lastly, some of the casting resins would also be $35ish for 3.something pounds of it, which should cast something that looks an awful lot like a camelback.

Will it save money? Probably not..... but it's starting to sound like fun. LOL.


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## DMS (Apr 15, 2014)

A place near me sells drops of mic-6 by the pound. You may see if there is a similar place near you, the "drops" can be pretty large.


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## astjp2 (Apr 15, 2014)

cjtoombs said:


> As for alternate materials for a straightedge, I would think aluminum would be the next choice down from cast iron.  It is relatively cheap, cheaper to ship if you have to order the piece you needed, realtivliy easy to cast if you have that capability (and a good casting aluminum alloy would likely scrape easier than 6061).  It's fairly easy to scrape, if all the Gingery builds out there can be counted as evidence.  I think the big problem with alumium would be more rapid wear, which would be less of a problem for a hobby scraper than it would be for a pro machine rebuilding shop.  As for composites, I think the wear problem with aluminum would be even worse.  Also, on a piece that size, there would likely be some shrinkage deformation, so casting it on a surface plate may not buy you much.  You may still have to machine it flat before you scrape it in.  Scraping something soft like that is doable, but it takes a different touch, or you gouge too deep.  Good luck.


Nope, it expands and contracts too much to be an effective straight edge.  I can get rough iron castings for around 100 including shipping each new....from Greg Dermer.  Do a search on here for contact info.  
Tim


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## cjtoombs (Apr 15, 2014)

astjp2 said:


> Nope, it expands and contracts too much to be an effective straight edge. I can get rough iron castings for around 100 including shipping each new....from Greg Dermer. Do a search on here for contact info.
> Tim




The whole point is to maintain the work area and straight edge within a fairly narrow temperature range.  That's why even cast iron straightedges have wooden handles, to keep your body heat from warping them from diferential heating of the area where you touch it.  Also, if you do a symetrical parallel design heating/cooling should have very little effect on the flatness of the surfaces.  Bush Precision makes a line of aluminum straightedges with cast iron wear surfaces bonded to them:


http://machining.buschprecision.com...a6100-series-aluminum-parallel-straight-edges?


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## DMS (Apr 15, 2014)

The Busch Precision site is interesting. If you want a laugh (or fright?), take a look at the prices on their camel backs. The small one is about 3x what I paid for my first car 

I also want to add that both the previous posters have good points. Aluminum will move more than cast iron (coefficent of thermal expansion for aluminum is about double that for CI), but cast iron will move too. The thing you need to avoid in use is differential heating (getting one side at a different temp than the other) as this will cause the item to warp. Camelbacks have additional structure to prevent this, so if you can integrate ribbing into your design, that would probably help keep things flat.

Personally I am a little skeptical of the Busch design with cast iron facing. It looks like the design is balanced (cast iron on both sides) which will help, but it seems like a bad idea in general to mix materials like that. Maybe that line of straightedges is not meant for machine restoration?


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## cjtoombs (Apr 15, 2014)

DMS said:


> The Busch Precision site is interesting. If you want a laugh (or fright?), take a look at the prices on their camel backs. The small one is about 3x what I paid for my first car
> 
> I also want to add that both the previous posters have good points. Aluminum will move more than cast iron (coefficent of thermal expansion for aluminum is about double that for CI), but cast iron will move too. The thing you need to avoid in use is differential heating (getting one side at a different temp than the other) as this will cause the item to warp. Camelbacks have additional structure to prevent this, so if you can integrate ribbing into your design, that would probably help keep things flat.
> 
> Personally I am a little skeptical of the Busch design with cast iron facing. It looks like the design is balanced (cast iron on both sides) which will help, but it seems like a bad idea in general to mix materials like that. Maybe that line of straightedges is not meant for machine restoration?



I expect the secret sauce for their ironclad aluminum straightedges is either very precisely balanced thicknesses, or the glue has very specific quality’s (it allows the iron to slide a bit on the aluminum, maybe), or a combination of both to give consistent performance. I also expect a lot of attention is paid to process, i.e. making sure that the glue on both sides is laid down very consistently and to a uniform thickness. I also expect for the price and the fact that these come hand scraped that they are intended to be every bit as accurate and consistent as their cast iron predecessors. It's actualy a great idea, considering how heavy a long straightedge can be. I don't think this would work well on a camelback design, at least not without some serous engineering going into the shape and composition of the backplane.


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## astjp2 (Apr 15, 2014)

The cats Meow is the ceramic ones that weigh next to nothing and are not as affected by temp gradients.  They come in a variety of sizes and shapes and are not as expensive as the granite/Cast iron ones.  Tim


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## TroyO (Apr 16, 2014)

I haven't runin to ceramic ones.... do you have a link by chance? I'm definitely curious!


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## astjp2 (Apr 16, 2014)

*Re: &quot;Composite&quot; straight edges?*

The Mazak installation guy was telling me about them, they have one that they use for installations.  I have not done any research beyond that yet.  So I don't have a link.  Tim

- - - Updated - - -

The Mazak installation guy was telling me about them, they have one that they use for installations.  I have not done any research beyond that yet.  So I don't have a link.  Tim


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## TroyO (Apr 20, 2014)

I got a chance to give this a try this weekend. Results were actually pretty promising overall. I cut out the basic shape and glued it up using JB Weld marine epoxy. (No particular reason, it was just what I had.) The tile saw I used was ones of those super cheap ones I got years ago, a simple plastic tub and a motor that spins a 4" diamond disc. I think it was $40-ish.

Overall it's 24x2" (Surface plate is 18x12)

So, after cooking overnight I got to playing around with it.... it didn't spot well at first, just the two ends. It was bowed.... but not by much as a .001 gauge wouldn't slip in under the middle.

I decided to go after it with a diamond hone and it actually cleaned up pretty quickly. I have some areas that "light spot" still, but for less then 2 hours total time investment and less than $20 (Way less for me as the granite tiles were leftovers.) I think this little venture will end up a winner. I may try minimize the light areas but really they are missing by tenths.

Pics attached, some showing the pattern I am at now. One problem is that it wrings to the surface plate and "sucks down" even with a very transparent layer of canode on there. That's a problem I can take, LOL. I may try Prussian blue next time, thinned with WD40.

Anyway..... only time will tell on stability. I'll post back next time I get a shot at it.


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## davej (Jun 22, 2014)

This seems like an interesting idea, although I have no familiarity with marble or marble counter-tops. Is it easy to obtain pieces of this size? What is the weight? I didn't understand the earlier idea of using something like JB Weld against a surface plate -- if you were going to do that wouldn't you simply apply a layer of it to something like this?

I suppose granite counter-top edging or door threshold or window sill would probably be closer to our desired dimensions.

http://www.lowes.com/pd_484570-25497-G024BTHR436_0__?productId=50157548
(apparently Lowes doesn't really have these)


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## The Liberal Arts Garage (Jun 23, 2014)

davej said:


> This seems like an interesting idea, although I have no familiarity with marble or marble counter-tops. Is it easy to obtain pieces of this size? What is the weight? I didn't understand the earlier idea of using something like JB Weld against a surface plate -- if you were going to do that wouldn't you simply apply a layer of it to something like this?
> 
> I suppose granite counter-top edging or door threshold or window sill would probably be closer to our desired dimensions.
> 
> ...


What you ought to try working with is a granite bathroom door lintel- in tile dept. glue a pair of
elegant drawer handles on the back. Diamond will let you touch up as necessary.  ....BLJHB


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## george wilson (Jun 26, 2014)

I definitely would NOT use diamond on a straight edge that is made of material that can readily absorb some of them. Diamonds are FOREVER. I keep them strictly away from my machine ways.


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## Mike Gibson (Jul 17, 2014)

Has anyone done any machining on an as cast camelback straightedge?  I have one 18" long and another coming that is 24" long.  Before I screwed them up I thought I would ask if any of you had Machined them and then scraped them or were they Blanchard ground?  Any ideas of what the cost for Blanchard grind would run.  I checked with one place here in Houston and they said $600.
  Any thoughts would be appreciated.


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## cjtoombs (Jul 17, 2014)

I machined and started scraping a square, but have not completed it yet.  It was already annealed, and I rung it a few times with a rubber mallet as I was scraping it to help relive and stress and promote movement.  It seemed to be settling down pretty well before I wound up moving to another project.  The 600 quote sounds like a "we're not interested in the job" quote.  I would think you should be able to get that done for 200 or so.  Why are you set on Blanchard grinding?  Surface grinding would likely be cheaper and easier to find someone to do it.  If I were going to scrape it, I wouldn't bother with the grinding.


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## Andre (Jul 17, 2014)

Not a bad idea, but straightedges are made from CI or granite for a reason. Cast iron and granite are very stable, they do not move much after being seasoned, and they are very hard. Obviously granite is very hard, and cast iron with all it's carbon acts like glass, protecting it and giving it a self lubricating effect.

The problem with epoxy is that it is not stable, when it dries it shrinks, and warps. Even after scraping, it keeps warping. And even if you could keep it flat it is too soft and will wear itself away during the scraping process. 

I wish you the best of luck on scraping, get some more elbow grease while it's on sale at MSC.


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## Mike Gibson (Jul 17, 2014)

cjtoombs said:


> I machined and started scraping a square, but have not completed it yet.  It was already annealed, and I rung it a few times with a rubber mallet as I was scraping it to help relive and stress and promote movement.  It seemed to be settling down pretty well before I wound up moving to another project.  The 600 quote sounds like a "we're not interested in the job" quote.  I would think you should be able to get that done for 200 or so.  Why are you set on Blanchard grinding?  Surface grinding would likely be cheaper and easier to find someone to do it.  If I were going to scrape it, I wouldn't bother with the grinding.



Thanks for your reply. I'm not set on Blanchard.  I'll probably check with some shops on the surface grinding.


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## TroyO (Jul 18, 2014)

A little update... the composite straight edge worked very well, actually. 

It did meet it's unfortunate demise when I had it resting upright against something and it fell down and struck something and it basically broke in to two pieces, about 1/3 from one end. Luckily, that was as I was cleaning up from the job, LOL. It was intended as a disposable tool anyway and served it's purpose. I also still have an 8" and 14" one now, I guess.

The door lintel may indeed work, I'd want to see one though as it sounds like it has beveled edges?

I'm not too worried about using diamond on the straight edge.... it's possible some embedded, but I find it unlikely. IF it had embedded it likely wouldn't transfer either.  It's not like I was sanding the ways with the straightedge anyway... any wear on the ways would be negligable.

I like the idea of trying the epoxy as a layer on a surface plate with a granite backer.... I think I may try it next time.

I realize epoxy may shrink and/or move over time, but if the work is theoretically done in a short time scale and not something you expect to keep true for years.... who cares? If it keeps a certain level of accuracy over a couple of weeks (And can be verified by surface plate) it just doesn't matter.

Anyway... I consider it a huge sucess, especially for oddball/one time/hobby use. I wouldn't suggest it as prefferable to old school iron/granite references but it's a heck of a lot cheaper and good enough for most people.


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