My 48" Straight Edge

[graham-xrf]

It arrived today wrapped up in an extravaganza of thick cardboard, miles of brown plastic sticky tape, and strapped down onto a pallet. All except the last 5cm or so at one end seems usable. I can see the scrape marks everywhere, and it's now the straightest thing I own.

It has dovetail bevels!
Underneath, it stands on three little steel balls set into the casting. One thing that I don't remember being in the description is that one edge is 45° beveled on the underside, and the other edge is beveled at what looks like 30°.

The rusty end.
A bit tragic, but the last two inches at one end seems to have been left exposed. Once the rust is knocked off, the pitting looks too deep to fix, unless it can be repaired with epoxy, and scraped back in. To do anything to the straight edge as a whole will require a granite at least 48" diagonal, but I may not need to do that yet. The rest of it looks OK to check out the ways on a 36" South Bend.

It's heavy!
I can just about pick it up, but not so easily move it about. I protected it at the edge of the (steel) benchtop with cardboard, and then lifted the other end. Clearly I have to contrive some sort of "dangle it" arrangement to be able to gently set it onto, or up against, anything one wants to check out. Given I can actually pick up the 36" South Bend lathe bed, I kinda wondered if it would be easier to dangle the bed onto it. Duh! Silly notion, surely!

So, such as it is, I now have a main reference for most of what I want to be doing. One day, it might get a refurbishment makeover, but for now, I can just use it.
I don't know how deep that rust pitting is on the end, and I am open to any suggestions about what one does about stuff like that, short of a regrind and a scraping in.

 

[JRaut]

Now you just need a 48" granite plate to check that it's flat!

 

[Ulma Doctor]

a wipe with phosphoric acid on a rag will take care of the rust

 

[graham-xrf]

a wipe with phosphoric acid on a rag will take care of the rust

I get it that rust volume expands up higher than the surface, and once we dissolve it away, the pits depths will be below the original surface, but there seem to be some areas between the pitting that might be up to the level of the original scraping. I had thought I could put some JB-Weld on it, very like the way one would put filler on a car, then scrape it back, as a kind of "repair".

At least for now, 36" fits onto 48" without needing to use near the rusty bit at the end.

 

[woodchucker]

I would put a paper towel with evapo rust on it.

 

[FOMOGO]

I think just the fact that you know it's there solves most of the problem. There are bound to be areas left after cleaning (as you mentioned), that are at, or so close to original, that it will have little, to no effect on it's use. Cheers, Mike

 

[Ulma Doctor]

thankfully low areas are not of much consequence, unless there are vast areas of lows
40% bearing is all that is required for most work as i remember

 

[C-Bag]

I know it never ends but you need a set of tool room stones to get rid of any present or future burrs.

 

[graham-xrf]

I know it never ends but you need a set of tool room stones to get rid of any present or future burrs.

As it happens, I did stone it gently with my medium grade slip-stone, In the first seconds, I found two "events" near the edge which fortunately rubbed off straight away, and the stone then started that no-cutting feel sliding action where it was only shining up micron high regions.

I know the stone was not one of a precision ground pair, like Robert Renzetti makes, but I had made flat by it rubbing against a flat diamond hone. The diamond plate is about 3/8" thick. I had checked the stone against a 6" glass flat. The stone, of course, clogs up immediately on the rust at the end, but when I got it to slide about, and clearing the rust with an alcohol wash, I could see the extent of the pitting at the one end.

My quick-n-dirty test using a 0.0005" indicator on a base, checking across a local gap of about 100mm (4") to the DTI shows no real movement as I slide it about, leaving me guessing the local flatness is somewhere around a tenth and maybe two tenths, but when we get into the rust pits at the end, the DTI moves about over a 0.001" to 0.003" range. If that's how deep the pits are, it is fixable by scraping, which, for me, would require a granite big enough to spot the whole surface.

I do have a variety of stones, flattened against the diamond plate, and they act exactly as precision-ground tool room stones would, except they were not from a session on a surface grinder. I tried one on a 123-block ground surface, and all that happened was it showed up the micron ripple from when the 123-block was finish ground. I know I got there using hand-made kit, but by now, I do trust the result.

From the design of it, obviously arranged to sit on three ball-bearing mountings, with flat side up. it clearly is mainly intended for stuff to be brought onto it, rather than it being put up to a machine. Basically, it seems like a long surface plate. It is 48.8" long and 5" wide. The design is not "camel-back" style. How exactly it is going to be used to check out the ways on my South Bend is not yet fully clear to me.. Sure, if scraping the ways, then use it for spotting, but diagnostics might be something like moving a DTI along, using the straight edge as a base.

 

[casey.little]

Looks like a piece of train rail!


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