"Composite" straight edges?

[Andre]

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.

 

[Mike Gibson]

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.

 

[TroyO]

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.