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

[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.

[bp]

Lews #1, is probably the most pragmatic solution!!

I recently got two small angle plates ground spot on flat and square, having milled them approximately flat and square, but I wanted them really accurate, a bargain!
cheers
Bill

[Eugene]

Thanks lads,

I've already done some draw filing on the exterior of gun barrels and the curved surfaces of gun locks. None of this was to dimension; in the first case I was removing rust spots, in the second just producing a nice profile by Mk. 1 eyeball. I'll give draw filing a whirl and let you know how I get on.

Eug

[Eugene]

Thank you for the advice; draw filing after a good deal of faffing about is going well.

I've improved my sawing technique which has helped no end; filing a 2.5 mm waste to dimension isn't any fun at all, by the time I approach to line I'm too knackered to work neatly and the results are all over the shop. Also I've found out how to get a face cutter working reasonably accurately; I'm getting a run out of -.0015" along a 4 inch length using a milling slide, which I don't think is too bad for a beginner. The finish isn't anything to write home about, but if I'm right careful with the file I can get all the tool marks out plus get a bit closer to parallel. So it's saw to around near enough, face cut to within a couple of thou, then file square, flat, and more or less to size. It takes a dogs age, but I'm pleased with the results.

I'm making some tools to make some tools to make ... well you get the picture. When I've actually nailed something together I'll post a "proud parent" pic and you can all have a laugh at my ugly duckling which of course I shall see as a magnificent swan! Again, thanks.

Eug

[awemawson]

Angle grinder with thin 1 mm disk and finish on a linisher saves all that elbow grease !

[Jonny]

Eug I never saw the need to draw file precision fitted stuff that had to be sanded and smoked up, just wasting your time.
Lockwork rarely draw filed you will waste time fetching the marks out and go undersize, two weeks work down the pan.

5" width should be able to strike down the length acting as a draw file in strike mode, easy. Then just hold 45 degrees and knock edge off, one strike job done. Of course the best files prevail but hard to find and don't last long. Give you some idea used to go through the best quality 3 sq bastard in a day if filing up 20 ejector springs from flat 1/2"x3/8"x6" leaving 125 thou turn point and two tapers 75 and 65 respectively ether end 9 mins each. Backs were flat and struck off down the 6" length.
Must say it was entertaining watching apprentices roll the file no matter how hard they tried.