newb questions: how to hold workpiece and mill?

[Vavet]

So imagine a 8" x 1" piece of steel 3/16" thick. I need a 1/4" hole centered 1/2" from each end and a 3/8" wide slot starting 1" from each end. I made this by first squaring up the edges of the material with a 3/4" end mill, then using the parallels, I clamped it in the vise along the long edges.

I used a 1/4" drill bit to drill the holes on the ends and a series of holes 3/8" apart where the slot will be. I then enlarged the holes with a 3/8" drill bit. Then I took a 3/16" end mill and went down to center to connect all the holes. Finally, I used a 3/8" end mill to make one continuous smooth slot.

Is this overkill? Could I have started with a 3/8" hole and used that as the starting point for my end mill and cut my slot with the 3/8" end mill in one pass?

I also have a question about climb vs conventional milling. I understand that conventional milling is preferred, but if I'm cutting a slot straight through the material, it seems I am performing climb and conventional milling at the same time. My workpiece is moving to the right. My end mill is turning clockwise. It's cutting on both the ingoing and outgoing part of it's rotation if it's cutting a slot in virgin material, right?

 

[Andre]

When cutting a slot, you are climb and conventional milling. When conventional milling, the endmill gets pushed away from the work, and when climbing it gets sucked into the work. This means there is cutting pressure to one side, probably a few thousandths depending on the endmill and your machine. If you need more precise slots, use the next size down endmill (5/16" for a 3/8" slot) and rough it with the 5/16" then run a finish pass of 1/32" to open it up to 3/8".

 

[maineshops]

So imagine a 8" x 1" piece of steel 3/16" thick. I need a 1/4" hole centered 1/2" from each end and a 3/8" wide slot starting 1" from each end. I made this by first squaring up the edges of the material with a 3/4" end mill, then using the parallels, I clamped it in the vise along the long edges.
right. My end mill is turning clockwise. It's cutting on both the ingoing and outgoing part of it's rotation if it's cutting a slot in virgin material, right?

SNIP


you shouldn't need to drill for the slot. juse use a 3/8 end mill if the tolerances are sloppy, and plunge down with the quill as you move back and fourth in the x axis. as mentioned if tolerances are close use a 5/16 and do the same thing and widen it out to your correct size.

 

[Andre]

SNIP


you shouldn't need to drill for the slot. juse use a 3/8 end mill if the tolerances are sloppy, and plunge down with the quill as you move back and fourth in the x axis. as mentioned if tolerances are close use a 5/16 and do the same thing and widen it out to your correct size.

Just a note, you have to use a four flute center cutting endmill or two flute to plunge. If you use a cupped endmill, you have to "ramp" the cut down. No big deal, but I just wanted to point that out in case you didn't know.

 

[Hawkeye]

I've had good results in roughing out long slots by plunging with an endmill overlapping the previous plunge by about half the diameter. Using a cutter one size smaller than the finished slot allows the most precision for the final size.

 

[retmac]

I've had good results in roughing out long slots by plunging with an end mill overlapping the previous plunge by about half the diameter. Using a cutter one size smaller than the finished slot allows the most precision for the final size.

You are trying to cut a 6ins. slot in a 8ins.piece of bar stock. In order to do this safely your mill vice should be at least 8ins.wide.
If your vice is narrower say 6ins. wide the material will collapse on your cutter possibly breaking it or possibly throwing your work across your shop hopefully not hitting you
Another way of holding your bar is to clamp it on your mill table on top of a piece of sacrificial material.
Find your center and one end of your slot, using a 5/16 center cutting end mill plunge through the bar now mill the slot to the length now move the cutter 1/32 sidewise cut to the other end of the slot move sidewise 1/16 in the opposite direction cut to the other end.
You have a finished slot to size with a good finish.
RETMAC

 

[markknx]

As far as the conventional vs clime milling Goes the forces center act each other so this is one time it doesn't matter. The issue with clime milling is it tends to pull the cutter into the cut faster than you are feeding do to among other thing back lash.
MarkMark

 

[Walt]

As far as the conventional vs clime milling Goes the forces center act each other so this is one time it doesn't matter. The issue with clime milling is it tends to pull the cutter into the cut faster than you are feeding do to among other thing back lash.
MarkMark

The cutting forces on the end mill at the sides of the slot cancel out, but most of the cutting action is happening at the leading side of the end mill as it advances into the slot, I'm pretty sure this will push the mill sideways.

Widening an existing slot by feeding an end mill exactly down the middle should result in zero net sideways pull assuming a reasonable depth of cut. (But probably results in a lot of vibration!)

Pushing an end mill into the side of a chunk of metal tends to push the metal sideways in the same direction that the end mill rotates.

Seems to me that cutting a slot by plunging in an end mill to start is more like pushing the end mill sideways into the metal than widening an existing slot.

If the slot doesn't have to be cut to a precise width, it doesn't matter anyway!

Walt

 

[Vavet]

I'd like to thank everyone for their help. I made a second specimen out of 1/4" aluminum and just drilled the start and end holes. I used a 3/8" end mill and started it in one of the holes. I then cut the slot. It actually came out 0.002" undersized, which I don't understand.

I'll post some pictures of the fixture I made with this later so you can see what you helped me create!

 

[markknx]

As far as the conventional vs clime milling Goes the forces center act each other so this is one time it doesn't matter. The issue with clime milling is it tends to pull the cutter into the cut faster than you are feeding do to among other thing back lash.MarkMark

Sorry guys that was meant to say "Counter act each other" Walt, you are correct about an end mill pluging and making a slot wider than the end mill. This is why as somebody stated earlier that if the slot needed to be right on or pretty close it should be cut with a smaller end mill, and then widened by taking cuts on either side