how to machine angle iron flat on all sides. (2024)

I need to mill some 3/8 angle Iron flat on the back sides and at least one of the insides of the bend. the angels is 4" x 4" and 24" long. The outsides needs to be square or perpendicular to each other. the inside part should be parallel to the outside machined surface.
I was think of clamping the angle upside down to two angle blocks on the milling table and indicating it in, but the surface is really rough and rusty.
i suppose I can try to get it close and take a shallow cut first then indicate the newly cut surface and re-cut, and then flip the cut surface against the angle plates and star the other side. Another idea I had was to clean up as much rust as i can with an angle grinder and abrasive pad. Then clamp that part to the table, and then mill just the 3/8 edge and then flip that 3/8 edge over and rest it on the table when I clamp to the angle plates, this will at last get me close to fat to table.
I have not had to do anything like this on the scale so any incite will help.

3 vises with 4" tall soft jaws
Mill outsides flat and perpendicular
Switch to short jaws
Mill one or both insides flat

Take the head of your mill off.Put your clarkson chuck in the nose of machine put a stub arbor in chuck.Two side and faces one smaller diameter than other.(Say 9ins dia+7.5 diam) or as long as dias have at least half inch difference in diameters. Then a spacer thickness of finished wall,The smaller dia cutter goes on right then spacer then other cutter-So that means the big cutter will be maching the outside face of the angle iron, whilst the smaller cutter will be maching the inside face.Then clamp job down to table, and straddle mill the 4 faces will have no taper on and be dead square-Obviously you will be clamping the job close to edge of table-this will allow you to drop the larger cutter into water channel-or until you have set the smaller cutter to finished thickness of wall-which both are the same thing

I have to do that kind of thing all the time. You got a Bridgeport? Or a horizontal? Tolerances? All that makes a big difference how you do it. Angle iron is never a perfect 90 degrees. You need something that is 90 degrees to your cutter face. Back jaw of vise(s) or angle plate(s). Let's say you use vises. Since the stationary jaw is your datum , put the angle iron in the vises with a small block of material between the part and the moveable jaw. You don't know how true to each other the inside and outside surfaces are and you want it registering on your datum surface. Cut the top surface to a bare minimum clean up, preferably with a sharp tool like a HSS fly cutter. ( to minimize the stresses you are going to put in the angle iron.) use an end mill to skim a flat along the narrow edge of the part. turn part over and cut put machined side against the back jaw and put the same block between the angle iron and the moveable jaw. Skim cut the face with a fly cutter and again cut the edge with the side of the end mill. After you cut the second side, you will have a much closer to 90 degree angle. Now you can set the angle iron up in the vises with parallels under it so that the surface of the inside of the angle iron is above the jaw. Tap it down until both parallels are in contact. Fly cut the inside face. Turn over and repeat. Depending on how flat and true you need, you may have to recut the angle iron until you like it. Every time you cut it you will release more stresses. Depending on your tolerance, you might need to stress relieve it before your finish cuts.

Is Angle Iron available "Cold Rolled"?

^ not sure about that large, but over here i can easily get it upto 50mm from th local supplier the further afeild ones website is always down over night.

Check the head on the mill to be 90 degrees to the table vise.
Machine cuts should be taken with very small depth of cut.
Backing up the angle iron with wood or other scrap to avoid deflections.

lf you did it the way I suggested-straddle mill the job,you will be maching the 4 faces in 2 passes.Will be square and if you wanted +/-.001 with no taper you would get it.Easy set up clamped to table-no need to butcher knee plates,its a simple job.You should already have table stops which are just bits bar machined to fit in your table slots-put 4 of these spaced out the length of your job and tap the job up against these-if you cant get the length of travel on your m/c go as far as you can,loosen the clamps(leave the cutter in posistion)Put your hand on job and hold it to stop it moving. Now travese your table along so you can get the extra length-tap job up against stops and reclamp and finish-Whats hard about that

I have stood angle clamped to 123 blocks going long way on the chuck and cut the throw away off with abrasive wheel on the surface grinder. Then set flat on chuck to grind top of inside flat and with dished back of wheel the inside side of the short leg. Then clamped to 123 block to get out side of the short leg.
Grinding can seem slower than milling but because set up is so quick , accuracy so easy and with little stock to remove can some times be faster that milling.
Angle is full of stresses but should stay in .010 and can be ground true with going back for a skim.
Often made SG back rails and end bump rails of split angle..46 H to k is a good wheel running wet. With a 36 wheel and not looking for a super finish one can full wheel the job for very fast grinding.