Flatness achieved by conventional milling

i believe that this question is very dependent on what type of machine your using, how old it is, the kind of tooling your using and how the machine is mounted eg what kind of foundations it has. it would be easyer if you gave an indication of what your trying to achieve!

hi, i posted the last coment before i joined.

What is the material your cutting and how big is it?

How much material are you removing per pass, how is it secured, clamped, fixtured, does the machining have a CAT50, a CAT40, or a Morris taper?

I have to ask, you do know there is a difference between conventional milling and climb milling, right?

just some information needed to project, not to mention feeds and speeds...

On a vertical manual milling machine such as a Bridgeport in good condition with the head indicated in very well (total indicator reading of .0002) with a properly ground flycutter or good quality insert tool 2" to 10", you can mill an aluminum plate flat within .001". With the smaller cutter you must overlap your cuts by at least half of the cutter diameter. You may have to cut both directions in a cross pattern. With the larger cutter you can do it in one cut, but the head must be nearly perfectly level to the table. If you are trying to flatten a plate larger than say 8" it is best to use a rotary table and spin the plate under the cutter. Also very important is the shape of the cutter especially if you are using a flycutter. The tip radius of the flycutter should be no more than .03" otherwise the cutter may lift and or chatter. Take cuts of .010 or less. The material must be held in a stress free state either gently in a good vise or held down with double sided tape. The tape is tricky and if you don't know what you are doing it can be dangerous. If you want to know the rules for machining with double sided tape you can contact me and I will share them with you.

Are you asking about flatness or surface finish?

Hi !!

Your question is very general & enough has been contributed by other friends. I just want to add that Give more specific information to get specific answers to your question.

You have to furnish

1. What is the material ?
2. What is the size of the job , LX W & thickness ?
3. What type of cutting tools are deployed ? Are you using Face Mill with Carbide Inserts , If so, are you using wiper insert ? or is it a Fly cutter ?
4. How much is the stock removal in final pass ? Are there multi pass to cover larger area using small dia Face Mill ?
5. How are you clamping the job ? If you stress the job too much with hold down clamps after declamping there would be error in flatness. For better results It is recommonded to to take final finishing cut with very little stock removal and clamping force shold be reduced to avoide stressing of the job if it has ductile properties and put stoppers at either end.
6. Fianlly how do you propose to check the flatness ? By straight edge and filler gauge ? Or by using Flatness checking gauge ? Or by using Electronic levels for flatness analysis by scanning grid of 50 X 50 mm or 100 X 100 mm

As you are aware when ever face milling is done for larger area using small dia cutter there has to be an overlap of 5 mm between the pass and there shall always be slight variation in flatness between the pass .For all practical purpose if you get flatness of 0.1 to 0.15 mm / 300 mm , you should be happy but this depends on many parameters which needs to be controlled and you have not indicated anything what so ever in this regard.

Best is to carry out actual trials and have experiance to get a fair idea about flatness that can be achieved by milling on your specific milling machine for your specific type of jobs.

---Udayan---

Hi,

what is conventional?

If you measure the straightness of the axes (with an autocollimator) and renew or enhance the quality you can do anything you like.

If you make the vertical spindle in the true vertical (if the x-y stage is true horizontal) you will get nearly perfect flatness.

If you do perfect balancing of the tool (in the machine, not the tool as standalone) you will remove many of the uncertainties in tool markings.

If you remove your gearbox and attach a DC direct drive you will make it one more step better because the gears are neither circular nor noneccentric.

The asynchronous motor is bad too.

If you remove then the main bearing and add a hydrostatic (or aerostatic) or hydrodynamic bearing to the main spindle this will be near perfect.

Next step will be the guideways to be changed to hydro- or aerostatic.

Last will be the ballscrews to be removed and replaced by either direct drive or hydraulics. (Unless you can get these old fantastic quality spindles from the Moore jig grinder.)

Then add some temperature control to the room, remove the operator to a remote location and shield any heat sources and add stabilised cooling to all motors.

Last add an interferometer to the machine and a very scilled operator.

Try natural diamond tools.

With all this you can achieve flatness and roughness below 1 microinch .

Residual flatness is determined by nonorthogonal axes of main spindle to x,y. So you are then looking to temperature gradients and stability of these.

Residual roughness (0.5microunch) by material (only non ferrous material and some plastics work in this extreme situation).

We do similar experimental machining since many years.

So first define what you want to do in which material.

Good luck

RHABE