Any advice for slotting or is it generally a practice you don't do?

[C-Bag]

The rule with steel is slow it way down at first, till you see how it's cutting. Use oil, and good quality endmills.
To save money when I was starting out, I would buy used endmill lots from Ebay. Estate sales, etc. One lot in particular was a goldmine. Many new and nearly new USA made cutters for pennies on the dollar, plus some unusual sizes and shapes that would have cost a fortune to buy separately
-Mark

Prices on estate/garage tooling lots are all over the place. My experience has been lots are way cheaper than singles. It’s best to check the prices of new USA quality bits then you can better gauge what your getting. I ran into a gold mine here and wish I would have checked it out months before. But waiting till the end has it’s benefits too because they are blowing stuff out but it’s not the cream of the crop. He was selling stuff on CL for almost 6mo for friends who had closed their machine shops.
Te surprise for me was finding out my reground foreign bits compare quite nicely to the high $$ HSS I picked up. They were not well ground from the factory.

 

[MrWhoopee]

As others have stated, rpm was about double what it should be. When you are cutting into a piece of material with the side of the cutter, the rotation causes it to deflect towards one side. If the feed is too light, it will deflect, recover, deflect again etc., causing chatter. Heavier feed is the cure, just like a parting tool on the lathe.

 

[westerner]

Heavier feed is the cure, just like a parting tool on the lathe.

I am a permaNoob, but I can certainly attest to the validity of THIS concept. My parting issues were cured when I became comfortable with INCREASING feed rates as the chatter built, instead of REDUCING said feed rate. Ain't broke anything 'YET'. Gimme time......

 

[Old Rivers]

I was using a 1/2" cobalt roughing endmill to slot a piece of 1018 steel with a .070 depth of cut. I have a PM-25MV, locked the Z and X axis.

I was pushing the workpiece towards the endmill and the vibration was really bad. I was feeding in pretty slow at 1200 RPM.

Is slotting in generally something you don't do? I decided to start cutting in the middle of the workpiece instead of the side like I normally do, doing conventional milling.

The endmill became red hot and something moved, not sure what. The endmill ended up going up, and the workpiece has a sloped cut instead of straight. Ruined it.

Any advice?

This video has some good tips:

Bill

 

[Mitch Alsup]

I was using a 1/2" cobalt roughing endmill to slot a piece of 1018 steel with a .070 depth of cut. I have a PM-25MV, locked the Z and X axis.

I was pushing the workpiece towards the endmill and the vibration was really bad. I was feeding in pretty slow at 1200 RPM.

Is slotting in generally something you don't do? I decided to start cutting in the middle of the workpiece instead of the side like I normally do, doing conventional milling.

The endmill became red hot and something moved, not sure what. The endmill ended up going up, and the workpiece has a sloped cut instead of straight. Ruined it.

Any advice?

If you are trying to make a slot precisely 0.500 wide, you do NOT do it with a 1/2" end mill !!
You do the slotting with something at least 20-thou smaller than the slot and the back cut the walls to precise (and smooth) dimensions.

Secondly, since the end mill is engaged to 1/2 of its diameter (in the direction of travel) you use a slower than normal RPM.
Also note: the long engagement creates more heat than edge milling requiring either slower RPMs or coolant or both.
On my G0730 8×30 mill I would not slot with a 1/2" end mill faster than 270 RPMs (3/8ths at 450 RPMs)

Thirdly you need a means to continuously remove the chips from the slot. {Coolant or vacuum cleaner or blowing air.}