vertical face mill

[mielke]

we have a large piece of stainless steel (15"x40"x5/8") and we are face milling the top of the piece. We only have the x and y corridinates confined with hex nuts, that sit below the surface of the plate against its walls,

if the we are only face milling the x and y plane of the piece of steel is it necessary to confine the z direction of the plate?

 

[ABritTurner]

You are asking for a disaster if you don't lock the plate to the bed in the vertical plane. Most importantly you could injure your operative and that could cost your company big bucks. It's just bad practice not to lock a job down securely when machining. There are a number of ways to do this, we discount magnetic clamping as most stainless steels have no iron.
Clamp in the vertical plane using:
1. vacuum bed arrangement, see propriety brands in the market
2. Use a wedge type clamp that exerts a downward pressure as you tighten down

If you are the supervising engineer and have no experience just ask your skilled workers and they will advise you. But you never never contemplate machining a plate unless it is locked on the three axis of possible movement. Being a machinist means you have mastered the basic art of understanding mechanics and how to apply these principles, they are not demanding a superior brain just a basic average intelligence with a common sense application of that knowledge.

Even using the 2 methods listed above great care must be shown in how heavy a cut you put onto the workpiece.

 

[ornerynorsk]

There are eccentric edge clamps available which do a fantastic job of holding workpieces like you just described. I'm curious, you do have an experienced machinist performing this work?

 

[btrueblood]

"most stainless steels have no iron." Well, not true - but Brit meant they aren't magnetic, which is generally true for the austenitic types.

Several swing-over clamps to hold down in the areas where the mill is not currently cutting, would be my choice. Swing the clamps out of the way as the cut progresses across the piece, and reclamp behind the cut.

Ornerynorsk also has a pretty good idea, I have had others tell me the cam-action edge clamps hold well.

 

[shawnpeter]

abritturner - "we discount magnetic clamping as most stainless steels have no iron"

more than 75% of the content typically would be iron...

 

[cloa]

And even the austenitic type develope some magnetism when welded or worked.

 

[ABritTurner]

The problem with top clamping is that the clamps have t be moved at some time during the process, this means there will be great difficulties i.n blending the cuts in and usually you get a stepped surface. Even when using side wedge type clamps the operator has to make sure that the bottom is shimmed so as not to force the material or to bend it. Clamps then have to bite into an area that has been wedged or shimmed so that the clamp doe snot bend the material.

When using stainless steel that has a small magnetic element in its composition then very light cuts have to be used, else disastrous events can occur.

 

[ornerynorsk]

Blanchard grinding is really the way to go on large flat surfaces. What grade of stainless are you working with?

 

[ABritTurner]

Even with grinding he still has to work out how to hold the job down on the table if the material is non-magnetic. He can sub-contract the job out but I guessed he is wanting to know how to do it if it is to be done in-house.

 

[mielke]

it is 304 stainless steel. The thing we want to avoid is having to facemill the top with top clamps and stopping the process and moving them out of the way half way through.

 

[ABritTurner]

Then you have to buy propriety side clamps that press into the sides of the work-piece and exert a downward pressure, you can also design them yourself, it's old technology.

If you have the room you can make up blocks to clamp to the table and use an M20 tapped hole with a bolt. Drill the tapped hole slightly downward, say 5 degrees and the bolt will pinch and press into the side of the work-piece, place adequate stops on the work-piece and make sure when you side clamp to shim so there is no bending introduced at that point. use a small diameter face mill rather than a large diameter,say 75 mm or 100 mm and take 1mm depth of cut at an insert loading of 5 thou per tooth per rev. Machine 316 around 100 metres peripheral speed. For final machining reduce the insert loading to 2 thou per tooth.

Use a suck it and see approach, if this loading and depth of cut works with no chatter or movement then you may increases the depth of cut. If the billet of steel is not very heavy then grinding is the best approach even if you have the additional cost of sub contracting out.

It is possible to purchase proprietary brands of side clamps similar to a vice, that you clamp to the bed with an adjustment similar to a one sided vice. Buck and Hickman may have them.

I hope this has been of help and can't think of any other advice to offer.