Trouble with slotting...

[Pcmaker]

I am using a 3/8" HSS endmill to slot a 1" 1018 round bar in a vertical position on the vise. I have a PM25MV mill.

I locked the quill, Z axis and X axis. I am using the Y direction to slot.

The entire mill, even the table was vibrating. My endmill eventually snapped. I was doing around .150 DOC on the first pass and it broke.

Was my DOC too high? I know that the general rule of thumb is not to go over half the diameter of the endmill.

I'm always having issue when slotting since it's both doing climbing and conventional milling at the same time, causing my mill to shake badly.


Any tips?

 

[mickri]

I have had lots of problems with slotting too. I think that slotting is the equivalent of parting on a lathe. I have a RF30 clone. This is what I have found to help. Use a drill just smaller than the slot to remove as much of the slot as possible. Use an end mill that is smaller than the width of the slot. For a 3/8 wide slot use a 1/4 end mill. My round column mill likes light cuts. .020 to .030 max. I tried to take a .050 cut once and the end mill snapped. I run my mill at 400 rpm. Use a 4 flute end mill. This seems to work for me.

 

[Pcmaker]

I wonder if larger knee mills have this issue as well

 

[Technical Ted]

If you were only taking a 0.150" depth of cut with a 3/8" OD HSS end mill and it snapped off, something is wrong. I'm not familiar with your mill, but here are some general suggestions.

- Check your spindle speed and verify it's in the correct range
- Make sure your feed is at a reasonable rate; not too heavy and not too light
- Check your gibs to make sure they are properly adjusted
- Make sure your setup is ridgid; verify your work piece isn't moving
- Make sure your cutting tool is properly sharpened and in good condition
- Make sure your spindle is turning in the correct direction
- Verify the material is what you think it is. Could it be something hard and miss labeled?

There may be more things to check, but that's a good list of items to verify.

A good end mill run properly should walk right through mild steel.

Ted

 

[projectnut]

We used a version of mickri's method for long slots in 316, and even 6061 from time to time. In our case however we used a center cutting roughing mill one size smaller than the slot. We plunge cut to within .020" of the final depth. The mill was moved 1/2 it's diameter on each plunge. Once the slot was roughed we used an undersized finish mill climb cutting one side at a time until the proper width and depth were achieved.

We also used either air or a vacuum to keep the swarf from building in the slot. The vacuum was the tool of choice when available because blowing down the machines was frowned upon.

 

[Tozguy]

I'm always having issue when slotting since it's both doing climbing and conventional milling at the same time, causing my mill to shake badly.

If you do a lot of slotting and you have the basics covered as Ted mentioned, I would try a different end mill that has some or all of the following features:
-roughing
-stub length
-high helix
-ball end
-3 flute

 

[Pcmaker]

I managed to get the job done by laying the round bar horizontal, securing it with a V block, sticking out the side of the vise about 2 inches. I used a 3/8" carbide end mill at around 800 RPM, taking .030 at a time. I don't have a 3/8 roughing end mill, which I think would've done a much faster job and I think I would've been able to take deeper DOC.

 

[Winegrower]

- Make sure your spindle is turning in the correct direction

While this sounds kind of impossible, it would replicate the symptoms the OP describes. I can attest to that, sadly.

 

[Logan Novice]

I am using a 3/8" HSS endmill to slot a 1" 1018 round bar in a vertical position on the vise. I have a PM25MV mill.

I locked the quill, Z axis and X axis. I am using the Y direction to slot.

The entire mill, even the table was vibrating. My endmill eventually snapped. I was doing around .150 DOC on the first pass and it broke.

Was my DOC too high? I know that the general rule of thumb is not to go over half the diameter of the endmill.

I'm always having issue when slotting since it's both doing climbing and conventional milling at the same time, causing my mill to shake badly.


Any tips?

How much distance between the top of the vise jaws and the end mill? When cutting slots in the end of round stock, I find it necessary to limit the height of my material above the vise/clamping device (especially round stock) to the diameter of the rod

 

[mikey]

I am using a 3/8" HSS endmill to slot a 1" 1018 round bar in a vertical position on the vise. I have a PM25MV mill.

I locked the quill, Z axis and X axis. I am using the Y direction to slot.

The entire mill, even the table was vibrating. My endmill eventually snapped. I was doing around .150 DOC on the first pass and it broke.

Was my DOC too high? I know that the general rule of thumb is not to go over half the diameter of the endmill.

I'm always having issue when slotting since it's both doing climbing and conventional milling at the same time, causing my mill to shake badly.


Any tips?

Cutting speeds vary with the depth of the slot. In mild steel, using a 3/8" finishing end mill at about half the diameter depth of cut, cutting speed is about 95 SFM. This works out to 965 rpm and a "decent" end mill should make that cut easily. Feed rate is 0.002" per tooth.

For slotting with end mills, getting the right speed is important. If you are feeding manually then knowing how to feed at a rate that allows the cutter to cut without deflecting is also important; push too hard and the end mill will deflect and then snap. Feed to slow and the cutter dulls and heats up. So, feed so that you feel a slight resistance to the feed and keep that rate going until you complete the cut.

It isn't about your mill; my little Sherline mill can easily make that 0.150" cut in mild steel. It is more about a rigid set up, accurate tool holder and then speeds and feeds.