Working 6 mm steel to dimension and a fine finish. How to ....

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Eugene:
Title of the thread says it all really.

In a sparsely equipped workshop I need to bring some 6mm x 185 mm x 125 mm mild steel plates (and other bits) to size, with a good edge finish that won't nick fingers; how do you guys do this from a sawn blank? Accuracy isn't an absolute, I'm not talking tenths, the nearest 3-4 thou is OK, but looking nice and being handleable is important. I've tried milling with a small milling slide on the lathe but the big overhang on the crosslide allows a bit of movement so the finish isn't anything to write home about and it takes forever. Linisher? What?

I have a feeling the answers will damage the workshop bank balance!

Eug

PekkaNF:
Do you have caliber, some sort of surface plate or a straight piece of steel (linear/parallel) and engineering blue? If yesh, then draw filing.

http://chestofbooks.com/home-improvement/workshop/Machine-Shop-Work/images/Fig-57-Draw-Filing.jpg
http://chestofbooks.com/home-improvement/workshop/Machine-Shop-Work/Files-Part-3.html#.VABHfBDV7cY

There might be better link, but this is pretty good way of getting plate edge pretty straight and pretty.
http://www.technologystudent.com/equip1/hfile1.htm

It's pretty easy to get edge straight. A little harder (more measurement) to get it parallel and square.

Pekka

bp:
I agree with Pekka. Trot off to your nearest suitable shop, get yourself a good quality 10" or 12" flat second cut file and handle, a good straight edge (solid, as in not flexible, steel rule) a scriber, and a square. At the newsagent get a broad tip marker aka felt tip pen, I like red or black, but anything is fine really.
Do you have an engineering vice? If so good, if not that will be probably the most expensive thing you have to get, a good 3" one will be better than a cheap 4" one.
Select an edge of your piece of plate, using the marker apply some ink to one face. Using the straight edge and the scriber, scribe a line through the ink, as close to the selected (sawn) edge as possible. Put the plate in the vice and start filing, try and keep the edge as straight and square as possible whilst working the whole edge down towards the scribed line. When you get pretty close, so that you can still see a tiny bit of ink, that's the time to start draw filing, as shown in one of the links in Pekkas post. This will, given practice enable you to get the thing dead straight, dead square. Check straightness using the straight edge and a light, hold the plate up to the light, place the straight edge on the filed edge, and try and see if there's any light showing, check squareness using....you guessed the square. With patience, and no little effort you can get this edge to being straight and square fairly quickly, BUT DO NOT HURRY IT!! Especially if you haven't done much or any filing. This first edge becomes the datum edge. Select an end to become your second edge, apply marker ink and use the square with the stock against the datum edge, scribe a line as close as you can get to the sawn edge. I'm guessing that you can work out what to do next!!
To remove the sharp edges a couple of strokes of the file will ensure that no blood is drawn.
Don't panic if it doesn't go brilliantly straight away. Filing is an art, the only way to learn how to do it, is to do it, and be fairly critical in your assessment. I learn't how to file 50 years ago, and I still get pleasure and a nice warm inner glow (as well as the hot outer glow!) from doing exactly what you are trying to do.
best of luck
Bill

Pete W.:
Hi,

To hold something that has lots of area but not much thickness, a woodwork vice is sometimes better than an engineer's metal vice.

Alternatively, sandwich the workpiece between two robust square or rectangular bars and grip one end of the sandwich in the metal vice with a clamp on the other end.

Just my two penneth!

Lew_Merrick_PE:
Eug,

1) Make friends with a local machine shop that has a milling machine!
2) Set up a bench grinder with a large pivoting table (there have been several posted here over the years) and add a "rip fence" to it that allows you to take off a couple of "thou" at a time to avoid overheating the bar. Then finish with a large file.
3) Same as (2), but using a disk grinder/sander.

More on item 2: My set-up is a piece of 1 X 6 (inch) HRS bar that is 20 inches long. I made cut-outs such that the (8 inch) grinding wheels fit into the table about an inch. Using angle (L3 X 3 X .250 inch) that was dressed to square, I mounted a pair of pivots reamed to a ø.500 bore and carefully line up. Mounted to the bench upon which the grinder sits, I made and mounted a pair of "angle-base uprights" with tapped holes into which shoulder screws mate. A pair of "round shims" that assure that the shoulder screws properly clamp the table completes the set-up.

OK, I spent a lot of time assuring that my "angle-base uprights" line up with the shaft of the grinder within .001 inch. Being "close" (say within .030 inch) is good enough for most applications. When I (ab)use my grinder in the manner you request, I "dress" a (call it) 10° angle on the outboard edge of my wheel and do my grinding there to avoid interference with the other wheel on my grinder. In the horizontal position, my table lies approximately .400 inch (call it 10 mm) below the centerline of my grinding wheels.

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