Face milling cutter uneven surface

[taydin]

I have used an 80 mm face milling cutter to machine the surface of a 200 x 170 x 30 mm aluminum plate. This is going to be a vacuum plate so it is very important that the surface is completely flat. So I have machined this in two steps, with three passes each. The last step was a pretty shallow cut.

But once I was done, I can feel that there are "steps" between each machined area. Why would that happen? Is it because the workpiece heats up and I need to cool it down for each cut? Or do I need to flood it with coolant? I hope not cause my mill isn't set up for that and it would be a huge mess. The milling machine is a manual 50 x 14 bridgeport type machine.

[MattiJ]

Head is not trammed right. Can be difficult to get "perfect" head tramming for 80mm face milling cutter in a bridgeport style machine, especially if there is any wear on the machine.
"feel" can be also deceptively sensitive, fingertip or fingernail can detect really small differences.
So is it 0.1mm or 0.01mm?

You might get better results with large fly cuttter that covers entire width at once.

[taydin]

Ok, I will measure the difference. But it really was a substantial step, probably in the 0.1 mm ballpark.

And good point about the head tramming. But I hope that's not the case, because the head of this machine can't nod down or up, it's fixed there. It can only be turned clockwise/counter clockwise. And when I machined this, the workpiece moved from left to right, which means the machine head would be out of tram in a way where there isn't any adjustment. I would have to shim it to correct.

[CCWKen]

If it's that important the surface is flat, it should be ground. Yes, tram is most likely your problem. The head needs to be in tram, in the X and Y, to the table. I hear (read) many say it needs to be in-tram within .001-.0015" over the width of your milling vise but that's not good enough for large cutters. That might be ok for a 1/2" (12mm) cutter but move out to the end of a 3"+ (80mm) and that out of tram grows significantly. Also, you need some type of lubricant. In the US, it's common to use a product we call WD-40. It's basically a solvent reduced oil. It's close to Diesel.

[taydin]

Also, you need some type of lubricant. In the US, it's common to use a product we call WD-40. It's basically a solvent reduced oil. It's close to Diesel.

I brushed a layer of kerosene before the cut. But WD-40 is available here, I'll try it next time.

[CCWKen]

I think you're fine with kerosene too. Check your head tram in the X and Y. Also check to be sure the inserts in your cutter expose the same amount. That is a big problem with the Asian cutters. What style of cutter and what inserts?

[CCWKen]

Out of tram in the Y-plane will leave steps in the X-plane. Out of tram in the X-plane will leave peeks at the ends of the cut. The center of the cut will be lower. This, of course, is when cutting in the X-plane or L-R, R-L.

[taydin]

I think you're fine with kerosene too. Check your head tram in the X and Y. Also check to be sure the inserts in your cutter expose the same amount. That is a big problem with the Asian cutters. What style of cutter and what inserts?

Here is the cutting head. Unlike the picture there, the head has 6 cutters mounted on it. The milling machine has an ISO40 mount.

http://www.imc-companies.com/Tungalo...p=515&GFSTYP=M

The vendor also gave me aluminum specific inserts. They have a very sharp edge. But I don't have the insert code at the moment. I will take picture of it when I go to the shop. I'll also check the tram of the head.

[old mart]

That Tungaloy shell mill is a quality industrial product, it won't be to blame. Can you mount a dti on the spindle to measure the exact error? It should reach the front and back of the table, with the spindle directly over the centreline.
Are the jibs on the knee adjusted ok?

[CCWKen]

That Tungaloy shell mill is a quality industrial product, it won't be to blame.

That one with the SWMT/SWGT13 inserts takes a lot of horsepower. A less than tight and sturdy mill will have that thing bouncing all over the place.

If the tram is off, a flycutter won't help either. Do you have a picture of the finish? Or did the cutter leave a trail as the leading edge came off the part? A tram problem will show up there. Or the finish will look great going one way but rough going the other way.

[enginuity]

Checking your mill tram is the proper first step.

For that size plate I'd probably try my hand at using a large fly cutter. For a vacuum plate I would then take it over to the surface plate and lap it flat (provided you have a plate large enough - but even a small surface plate should work).

[loose nut]

It can also be other things beside the tram.

Tool digging in under load, for one, will pull one side down slightly and leave that ridge. The type of material can affect that. I have had the same problem with some types of metal but not others, without adjusting the tram.

[CCWKen]

Yeah, those high-rake inserts like to bite. My 5" face mill with APKT inserts is that way. (But man, does it ever lay-down a shine.) That's why I mentioned the OP's 45* setup will take more horsepower and a stiff machine.

[dalee100]

Hi,

Most like cause as already stated, is that your head tram is off. If you are doing something that really matters, you MUST verify the tram before you begin EVERY TIME when using Bridgeport style mills. They hold zero worse than my dovetail mill/drill does. But insert cutters are always a bit off also, (manufacturing tolerances are not as tight as you think on insert pockets).

Personally, for a vacuum plate, I would have purchase a piece of pre-ground tooling plate and then simply drilled the hole pattern I needed. But I've learned the hard way to not ever trust a Bridgeport to be super accurate when needed.

[MattiJ]

Cutter or insert height problems would show up in a different way, not step between passes. (Unless you crack or wear down the cutting edge..)