Filing a metal block to true squareness

[ThinWoodsman]

It's not the same sort of flatness as you are thinking of it. Consider a bearing surface, like the ways of a lathe. Getting anything truly flat is impossible, so what you try to do instead is to get as many points on the same plane as possible. When you start out, you have (for example) one high point per square inch. The more you scrape, the more high points per square inch you have, because removing a high point results in all of the slightly-lower points now being high points. Carry this process to infinity, and you will have a perfectly flat surface, but nobody has that sort of time - so you set yourself a "good enough" point, say 30 points per square inch, and stop when you achieve that. The "points", by the way, are identified by putting some blue dye on a surface plate, and rubbing the workpiece against it: the number of blue points in an area 1" square are counted.

For your metal block, this sort of thing is less of an issue: you have one high point you are trying to get rid of in order to be able to measure squareness accurately. But if you want to learn scraping, get a surface plate and some dye, and attempt to get the flatness down to a specified number of points per square inch.

Note that this is flatness, though, which is different from squareness. Something can be flat and not square, or square and not (sufficiently) flat.

 

[Winegrower]

Koi, I think you are going to be very successful as a craftsman.

 

[Koi]

Koi, I think you are going to be very successful as a craftsman.

Nah handwork has pretty much no place in the modern world though it seems useful in a zombie apocalype scenario where machine tools are too heavy to carry around or have to move around constantly xd.

 

[ThinWoodsman]

What is obsolete changes the further you get from infrastructure and convenience.

A run to the hardware store can turn into a 3-hour trek for me, depending on what I need and how many roads have fallen trees on them. Being able to make parts saves me a lot of driving around (though not any money).

Likewise, manual machining work lets you bypass time-consuming setups and so forth. I was reminded of Koi's manual-machining threads tonight when I was bandsawing some steel channel, and needed a cutout that was just too delicate for the bandsaw. Cut two sides in the saw, went to the vise, used a cape chisel to cut a groove and some perforations, then used vise-grips to twist the metal so it snapped at the groove. All in less time than it would have taken to set everything up in the mill, let alone do the actual cutting. Files cleaned the part up enough for a test fit.

It's useful to know this sort of thing is an option, and to have the ability to carry it out.

 

[Koi]

I got paid all during my apprenticeship and making a square block was a 1st year test, We were encouraged to do rabbits in our lunchtime and if the shop was open and we weren't officially working we were allowed to come in and do our own projects. The use of draw-filing is a good way to finish as it removes very little material with a single cut file. Use a micrometer regularly to check across faces dimensions. A good solid vise with square jaws is a must.
Have a look at some of Clicksprings videos - he's even made his own files just to show how!

Clickspring

I'm Chris from Clickspring, and I create home machine shop project videos with a focus on clock making technology. Join me as I make an authentic replica of ...

www.youtube.com

A scraper blade holder i made within 0.02mm in dimension tolerance and is as square as my machinist square is .Had to weld both together too.

 

[Koi]

For a larger spot, I have often been able to use the edge of a file like a scraper, but 0.02mm (0.007 in?) is pretty small. You should make a small scraper, perhaps from a large nail or a small lathe toolbit. Just has to be flat across, and sharp enough for the one use. Make a wooden handle for it as you do not want to be using a hammer on the scraper.

I did use that method with high spot blue i made from ink pad refiller mixed with a tiny amount of automotive grease and it sure made the surface flat .

 

[C-Bag]

I did use that method with high spot blue i made from ink pad refiller mixed with a tiny amount of automotive grease and it sure made the surface flat .

I’ve yet to use it, but I got off youtube where the guy used cement coloring powder and motor oil to make his spotting tints. One brownish red and one orange. Just haven’t done some more scraping like I expected. I would love to find the water based spotting tint to use instead of Prussian blue but not run into it.