PDA

View Full Version : squaring the sides of a thin steel plate...Question?



krems
01-26-2008, 08:35 PM
What is the proper technique for squaring / shaping the 4 sides of a 3/16" steel plate. I've never worked w/ steel before only aluminum and never played around w/ thin plate material. I've got a piece of 4142 pre hard (hardness 28-32) steel plate that I need to square the sides w/ my manual milling machine.

How would you go about clamping the plate and squaring up the sides?? Would you lay the plate flat or upright in the vise?? What type and size of tooling would be best for this. What about RPM and feed rates??

I know this is a basic milling project and I have just about enough machining knowledge to be dangerous...........Thanks in advance

Krems

aboard_epsilon
01-26-2008, 08:46 PM
you don't Say how big your plate is ...

or what milling machine you have

anyway if its large

take the vice off.

put an angle plate on the table .

place steel plate (your work) against it ......so that plate edge runs down centre of t-slot...or a gap big enough to get your endmill in with plenty of clearence ...

dial in the angle plate so that it is square to the table.

this is done with a lever type dial indicator in the quill.

tighten bolts on angle plate

clamp down your work in as many places as possible using the t-slots .

mill away .......using the angle plate for all sides

krems
01-26-2008, 09:00 PM
I'm working with the flate plate material 3" by 2" +/-...........Maybe the term plate was a poor choice. I've got a basic 9 x 42 " milling machine. I don't have any angle plates yet so I will be limited to the kurt vise for now.

Krems

aboard_epsilon
01-26-2008, 09:14 PM
all i can suggest then .

thats if your Kurt will open up 4 inches or more

is you lay a parallel down in the vice ...on its side
one parallel each side of the jaws.

put workpeice on top of the parallel....and between parallels that are standing upright

put a hold-down-clamp running into the vice from the left of it to act as a stop....this is to stop the milling cutter pushing it sideways out of the vice.

push plate against the stop

don't over-tighten or you will distort the plate.

plate should stick out beyound side of vice no more than an inch

aim a couple of smacks with soft hammer on the workpeice ...because it will lift at the front side of the vice, when you tighten it...the side parallels let it slip down when you do this ...and protect your vice jaws.

speed......... plus 400 rpm with 4 flute has endmill.

feed gingerly

mill on the right side of the vice ..important!.......front to back

and off you go .

all this is asumming the plate is pritty square to start off with ....if it not then it wont hold in the vice right ..


all the best.markj

barts
01-26-2008, 09:52 PM
3" x 2" plate will fit in mill's envelope, so I'd use a hold down clamp from one size to hold the plate down against a a piece of scrap alum. on the table. Square it up as close as possible to the t-slots, then run around the 3 sides of the plate you can reach w/ the mill. Add another clamp from the opposite side, then remove the first clamp and finish the remaining side.

- Bart

darryl
01-26-2008, 10:41 PM
Much like what Barts said- cut a piece of flat scrap a little smaller than your plate. Straddle the center t-slot with it, lay the plate over it, square up fairly close by measuring from one edge of the mill table. Clamp down using t-slot nuts and some hardware. Mill one long edge. Run a file along that edge to knock off any high spots, (chip reweld) then have another piece of scrap with at least one straight edge- bring that up to the first machined edge, but not overlapping a second edge of your plate, and clamp it down. Now you have one good edge on your plate and a reference edge clamped to the table. Then add another clamp over your plate such that you can remove one of the other clamps. Put this second clamp in place before removing one other. Now you have a second side clear to mill true. If your mill can do a precise 90 using x, then y, you now have two good sides. If a third side is free, mill that also, and machine it to the wanted dimension. Add another clamp so you can remove one other and free up the last side. You might have to move the plate so the final edge doesn't tuck behind your reference, but that's ok now because the reference is known to be square to one axis because it's been referenced by the first milled edge on your plate.

Pay attention to backlash and play in the gibs because the table could move on you due to cutting forces. I find it's best to always bring the table with the workpiece attached towards the cutter with the feed handle, stopping at the desired spot. If you overshoot the mark, back up at least half a turn, then dial in again to the correct point. This way the backlash in the leadscrew area will be taken out and in theory the table can't move away from the cutter during machining. For best control of cutting forces, you need to make sure the cutter is not trying to pull the work towards itself, in other words not climb cutting. Climb cutting works well, depending on a lot of factors, but it can so easily push a workpiece out of position because you usually have very little control over the size of the bite the cutter takes. You need to have a tight machine and considerable knowledge of climb milling before you should do this.

You don't really need the reference piece to be there, but it helps to control the workpiece from shifting as it's being worked on. If your clamping is tight enough, the cutter is sharp enough, you don't move the workpiece while changing the clamping around, and you don't go too deep on a cutting pass, the plate should ideally be in the same position as when you started, and it will have all 90 degree corners. Obviously there will need to be some extra length and width on the plate to start with.

torker
01-26-2008, 11:25 PM
Am I the only one here who would just clamp this lil' piece standing up in the vise..mill the top flat...flip it over a quarter turn..square up with a machinists square in the vise, tighten, mill it off. The next two cuts are a no brainer.
I've done a pile of "platelets" like that.
Russ

Al Messer
01-26-2008, 11:31 PM
And I'd just clamp it in the bench vise, draw file one edge, rotate 90 degrees and check the squareness every few strokes until all four sides are done.

Mcgyver
01-27-2008, 12:03 AM
if i didn't have an angle plate, then, well I'd get an angle plate....they'er not much dough and are just the ticket for secure set ups of awkward pieces like that. couple of heavy c clamps and away you go. Otherwise what Russ said if dimensional tolerances are tight or what Al said if not.....when what you're filling is only 3/16 it'll come off fast and you'll surprise yourself how square you can get...just keep checking with a square as you go.

you will mill steel basically like you would aluminum except the cutting speeds are much lower. use 80-100 sfm instead of the 400 or so you'd use for AL....remembering to drop the feed rate to keep it around the same chip load