Bad chatter

[keithmcelhinney]

OK I have my mill mostly running like a top but have a strange problem. I have been using 3/8" hss tooling for a lot of my cutting (.1 - .14 DOC/ slotting/ 35ipm). Runs like a dream. I chipped a bit and decided to throw on a carbide 3/8" bit I had. Both had same stickout (~1"), same cuts, same number of flutes(2) and the carbide SCREECHED. I had tried 3fl 3/8" carbide endmills and had the same problem but I thought it had to do with it being 3fl. I use a 1/2" 2fl and 1/4" 3fl with very little problems. My long 1/2" isn't the quietest but it is sticking out 2.5".

I know we can talk about harmonics and get into math that makes my head spin but is there things a non-professional guy can check? I have had issues with the spindle motor pulley slipping down the motor so I have fixed that but it was real finicky with belt tension. If it was were I thought it should be (barely any slop) the motor ran at 20% without being under load. I loosened it up and then the spindle would "hesitate". I got it where it doesn't hesitate and runs at 10% when not under load. When I start work for the day I have to run the spindle for at least 10-15 minutes to get it to come down. It usually starts at 18-20% and then warms up and drops down. Is this normal? Could it be that I the gibs aren't tight enough and this is causing it?

Any help would be appreciated.

-Keith

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[AUSTINMACHINING]

I've found endmills can be very different depending on manufacture/type. I had one rougher that shrieked like crazy and I just quit using it. It just seemed horribly dull. For HSS the YG-1 hi helix endmills have been fantastic and cheap. For coated carbide, Zrn coating is super slippery and leaves that mirror type finish, but $$$. The main issue I noticed with loose gibbs was a wavy looking walls on the finish. I never thought about belt tension, but my load meter is higher under no load at low RPMs(30% at 1000) and the load drops the faster the spindle turns.
Of course work holding can have a huge impact on chatter as well.

[SCzEngrgGroup]

If it was were I thought it should be (barely any slop) the motor ran at 20% without being under load. I loosened it up and then the spindle would "hesitate". I got it where it doesn't hesitate and runs at 10% when not under load. When I start work for the day I have to run the spindle for at least 10-15 minutes to get it to come down. It usually starts at 18-20% and then warms up and drops down. Is this normal? Could it be that I the gibs aren't tight enough and this is causing it?

Any help would be appreciated.

-Keith

Spindle "load" meters aren't truly load meters - they are simply ammeters. When the spindle is cold, friction is much higher, due to thicker grease, and other factors, so more power is required to turn the spindle, which means higher current. So, what you describe is to be expected.

As for the chatter - it IS a resonance issue, and every combination of tool, toolholder, machine, and workholding is different. Sometimes you can compensate by changing feeds and speeds, using different tooldholders, and/or changing your work holding. Other times, you can't. So, you just have to find tooling that works when uses as you need/want to use it. My experience is carbide often does often chatter more on these smaller, less rigid machines, which is part of the reason I use carbide only for smaller tools, and then only to get the extra tool stiffness. In terms of MRR, surface finish, tool life or any other measure, carbide will give you no real benefit over HSS on these machines for tools over 1/4".

Regards,
Ray L.

[LeeWay]

I have one part that I cut that is 6061 aluminum. 1.5" depth. I have not ever had a problem cutting the slotted holes at that depth, but I also profile the back side. It screamed on the Torus, so I lowered the feed and speed just a little. From 4500 RPM down to 4200 and from 20 IPM down to 15 IPM. That stopped the screaming.

3/8" 4 flute carbide end mill. 1.75" flute.

On the Pulsar, I tried the same original feeds and speeds. I got the screaming. I switched to a 3 flute and the screaming went away. There is more than one way to do it.
I haven't ever done a finish cut on these parts, but may try it just to see how it comes out.

These parts get powder coated, so finish is really irrelevant.

I now have SolidWorks to play with and HSMXpress. I want to see how that HSM does on those parts.

[engnerdan]

I just had a similar problem. I have been buying YG1 endmills too, I get the plain 4 flute uncoated carbide endmills for steel and the 3 flute "Alu-Power" for aluminum. Anyways I was using a 1/2" 4 flute on some 1018 cold rolled and chipped it due to bad settings in HSMxpress (my fault). So I put a 4 flute coated from Maritool in as a replacement. For the life of me I could not get the Maritool cutter to take a 0.100" DOC slotting pass without chattering like hell. I turned the speed up and down and the same with RPM's, the best I could do was cut my RPM's down to about 1,400 and my feed to half of what the YG ran. It still chattered but to my amazement that cutter made several cuts like chattering and never chipped the flutes. The only think I can think of is it was a combo of the length of my tool holder, the direction of the cut (Y-) and the particular angles of the Maritool cutter.

keithmcelhinney - What brand endmills are you having problems with? Are you using coolant (flood, mist, MQL) or air?

-Dan

[keithmcelhinney]

Lakeshore carbide 3fl and 2f. The 3fl endmills were my goto endmill on my little 135. Cut way better than anything I tried. Now with the pro they chatter. I have to try some different types though. I use carbide for my long endmills but had to go to 2fl as the 3fl chattered a ton. I use flood coolant.

-Keith

[AUSTINMACHINING]

Lakeshore carbide 3fl and 2f. The 3fl endmills were my goto endmill on my little 135. Cut way better than anything I tried. Now with the pro they chatter. I have to try some different types though. I use carbide for my long endmills but had to go to 2fl as the 3fl chattered a ton. I use flood coolant.

-Keith

Weird...
I've LSC are my favorites so far. I've used their 3 flute in .125, 25, .375 & .5" sizes with no issues. I don't do a lot of slotting, but when I do,no problems yet. All my roughing passes are HSM type toolpaths at 12-20% step over. My last run with the .25" end mill was .04 step over .5 deep at 90 IPM. The only chatter I get is doing something I really shouldn't be doing, like cutting a .15 interior radius with a .25" end mill. I also use the shortest "stick out" end mill I can. I'm using high pressure mist coolant.

I punched in some #'s into HSMadivsor for a HSS .375 EM and cam up with....