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

Pcmaker

Pcmaker

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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?
 
You should be able to bury that end mill with no problems . They like to cut , the heat should come off with the chips . 1200 rpm sounds a bit fast also . Coolant ? I'm not familiar with the PM machines , is it rigid enough for the aggresive mill ?
 
Never used a cobalt end mill but have used HSS mills
Never ran a 1/2 inch that fast.Milled keyways in shaft using a deeper cut using coolant around 300 to 400 rpm
Is 1018 hard or did it work harden
When you first start machining the piece the chips should give an indication if something is amiss
 
I concur Dave and Nigel. On my RF30 I’ve done many a slot in steel and usually around 600 rpm and all my bigger end mills are HSS that I grind myself. I creep up on DOC like start at .020 to make sure I know what’s going on with the bit, the metal and my setup. Then work my way up with successive passes up to .050 to 070. DOC. Also for slotting I use tool holders instead of regular collets as the setscrew will absolutely keep the bit from moving as the heat and pressure of the cut work on the cutter and collet. I’ve quit cutting tapers since going to tool holders for big stuff. Also use coolant/oil.
 
What I have learned after ruining a couple of end mills on my RF31 clone cutting slots in 1018 is 1) drill out as much of the slot as you can first. 2) light cuts .020 to .030, 3) 200 to 300 rpm, 4) conventional milling and 5) the end mill should be smaller than the width of the slot. If you just use the end mill one side is doing conventional milling and the other side is doing climb milling. This creates a lot of vibration because I believe that the end mill is constantly switching back and forth between conventional and climb milling.
 
1200 RPM is a bit fast. Around 600 on a 1/2'' end mill in mild steel may be a good starting point. Air or a coolant mist would also be a good thing.

I have buried a 1/2'' cobalt rougher 1'' deep in mild steel and cut just fine. So 0.070'' DOC on your machine should work with no problem. You do normally need to drill a starter hole at least 0.375 for a 1/2'' end mill, many roughers are not center cutting so you can not plunge with them without a starter hole.
 
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
 
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I got my end mills at a garage sale. $10 for a box full.
 
Again, too much speed, I'd say 800 RPM tops with coolant, and I'd be with much more DOC. Sometimes, I use a 2FL end mill more like a boring bar, and make a initial hole through the stock, then step the tool over sequentially until the length is reached, then take a central cut all the way from one end to the other and possibly step over laterally and clean up each side to finish width; this spares the end mill taking full width cuts on its full face.
 
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