Problem- Cutting T section and sqealing

[chris123]

Hello,

I have a CNC taig desktop mill and I have two problems cutting up aluminium.

First is when I cut a slot a few mm deep the mill starts to squeal
What's causing it?

Second is I'm having trouble cutting one of the sides off a piece of T section. What's the best way?
I've tried putting it in a vice and either cutting a slot with an endmill, would it work better if I used a slitting saw?

[ImanCarrot]

What diameter of end mill you using?

How many flutes on it?

Are you using coolant or air to get rid of the chips?

What RPM and feedrate you cutting at?

What's the end mill made of and how new (sharp) is it?

What do the chips look like that come off? are they gummed up and stuck together or are they free flowing single chips? How hot are they? are they warm or too hot to catch in your hand?

[chris123]

Originally Posted by ImanCarrot What diameter of end mill you using? How many flutes on it? Are you using coolant or air to get rid of the chips? What RPM and feedrate you cutting at? What's the end mill made of and how new (sharp) is it? What do the chips look like that come off? are they gummed up and stuck together or are they free flowing single chips? How hot are they? are they warm or too hot to catch in your hand?

I've tried
6061 and 6060 aluminium
DOC .12" - 0.066"
tool diameter 6mm, 8mm, 10mm all 2 flutes
kerosene and/or air for coolant, will try flood coolant soon
15-20ipm
4000 & 5600rpm
HSS, brand new and fairly new
Chips freely fly off, they do not gum and they are hot, from memory they look like tiny curled flakes

What about cutting the top off of a T section of aluminium, any hints, ideas?

[christinandavid]

Originally Posted by chris123 What about cutting the top off of a T section of aluminium, any hints, ideas?

If you hold the T section with the centre upright vertical, and try to Z-level machine it, you may run into problems as the end of your cutter will get battered by the material flexing and vibrating - especially if you are running the cutter straight down the middle.

If you have no choice but this kind of setup, use a cutter with adequate flute length, go straight to depth in the Z, and climb mill the upright from one side, in multiple passes. As the upright gets thinner and weaker it will start to be pushed out of the way by the cutter. You may possibly do this in a single pass with a larger cutter, but watch the waste material at the end of the pass - it may get dragged into the cutter. Of course you may not have to take it off completely - you may be able to break off the remainder by hand and give the part a bit of bullsh!t to make it look nice...

Another approach would be to clamp the part in a vice so that the upright is horizontal. You could even incorporate a thick support plate to help stop the part from flexing. If you put a few dowels into this plate it becomes a fixture that locates the part at the correct height/position. Again, full depth (thru) multiple or single pass is down to you and your tooling.

However, I fear that the advantages of this approach (rigid setup/swarf evacuation) may be negated by tool reach limitations?

As for the squealing, maybe that's high pitch vibration from the thin part flexing (although I would describe that sound as 'screaming' rather than 'squealing'). Slowing the feed down/speeding the spindle up will likely make that worse. Turning the feed up may improve the noise factor - especially if your cutter snaps

DP

[chris123]

I currently have the upright horizontal and cut it off that way as its quicker. But not as quick as Id like
I havnt tried it with a support plate.

I shall try feeding faster until it jams or snaps, then slow it down a bit

[christinandavid]

Another thing to try is putting two components back-to-back in the vice so they help support each other. Locating the pair with stepped jaws or a nice block to sit on and up against you would save some loading time at least.

DP

[roninB4]

Unless your squealilng is something else, I migh suggest that the noise may be due to vibration. Aluminum doesn't take much to cut and the speeds/feeds are higher than for ferrous materials. This also means that the vibration occilations are at a much higher frequency. Add to this a thin cross section and you have a splendid opportunity for high speed squealilng (test by putting your finger on the workpiece while cutting but AWAY from the cutter). Whether ferrous or non-ferrous, any felt vibration in the workpiece means the material is bouncing into/away from the cutter. In HSS this isn't as much of a problem but for carbide it can induce micro-fractures at the cutting edge and render a carbide cutter dull way before it should. I prefer using HSS on aluminum, especially if machining it dry. If it's a T in cross section you could try clamping the "leg" to an angle plate or use several small toe clamps that you move out of the cutter path. Thin sectioned parts are always a candidate for excessive vibration that can render poor accuracy and bad surface finishes without proper clamping/fixturing. At the very least, try putting a sandbag or something on the workpiece to dampen/absorb vibrations. Hope this was of some help, we all struggle with this in machining at one time or another.

[chris123]

I'm a self taught machinist. I'll have to look up certain things youve mentioned.
I've just made up an enclosure for flood coolant and have made several parts in it.

For the screeching I've now sped the machine feed rate up to its maximium, no tool breakage and it sounds the same as when it was going at 15ipm.

As for the T section I will try clamping it better,
I've tried drilling 30 odd holes to break it off, works with out any issues but is a lil bit slow, I could possible drill faster with the coolant

[davewoods]

I was going to suggest increasing the feed, but you said that made no difference. You might consider cutter geometry as a source of squealing, especially in Aluminum. Look for an end mill with 40+ degree helix, and a small circular land (.002-.004) vs. an off-the-shelf 30 degree primary/secondary tool. If that's not doable, try a very light hone on the cutting edges.

[chris123]

Originally Posted by davewoods I was going to suggest increasing the feed, but you said that made no difference. You might consider cutter geometry as a source of squealing, especially in Aluminum. Look for an end mill with 40+ degree helix, and a small circular land (.002-.004) vs. an off-the-shelf 30 degree primary/secondary tool. If that's not doable, try a very light hone on the cutting edges.

refer to post #8, i have some idea with the helix angle, but dont know what you mean with the rest
I get pretty much off the shelf cheapest tools I can find
I dont see the point in buying "special" tool bits for over $30 when I can get over 5 for that same price where each does the job and lasts for a rather long time. I do live in Australia and the options arnt that great or cost effective, well none that I have found

[christinandavid]

If you have gone to the limit on the feed you can start reducing your speed, see if that reduces the noise. I remember when I used to do a fair bit of thin aluminium parts and the shrieking was worse during full engagement in the corner of pockets etc.

We used to play with the speed until we achieved a nice pitch/volume that the turners moaned least about (we made the most of it though - the boot was usually on the other foot. Some of their looooonnnng whiny cuts roughing out inco were ear-piercing...really not nice at all... )

As has already been suggested the issue is sometimes the keenness of the tool. Try running the cutter through a bit of steel first (hint - that double-sided set-up support plate you're gonna make )

DP

[chris123]

Originally Posted by christinandavid If you have gone to the limit on the feed you can start reducing your speed As has already been suggested the issue is sometimes the keenness of the tool. Try running the cutter through a bit of steel first (hint - that double-sided set-up support plate you're gonna make ) DP

Changing the feed seems to have no effect
I can change the rpm one more pulley or down several
Clamping it to the support plate will require some work as I use most of the base of the T section