First attempt of broaching with a hobby milling machine

[compact8]

The tool is a piece of HSS strip 2.5 mm thick x 8 mm wide. The result is OK but there are two things that I would like to seek some improvement :

1) The tool was advanced by just 0.05 mm between consecutive strokes but cutting only happened in every other strokes. When it cut the tool often bite into the metal making it necessary to use a lot of force to complete the stroke. Are there any ways to make it cut more smoothly ?

2) The face of the slot contacting the cutting edge of the tool is wavy as shown in the photo. The other two surfaces are very smooth. Function wise this is no issue but does it indicate anything wrong ?

 

[jwmelvin]

The way you describe the cutting action and the waviness suggest (to me) that your tool wasn’t sharp or didn’t have enough relief. Any chance you can get a close up of the tool (I know it’s really hard to get the right focus, etc.)?

 

[compact8]

The way you describe the cutting action and the waviness suggest (to me) that your tool wasn’t sharp or didn’t have enough relief. Any chance you can get a close up of the tool (I know it’s really hard to get the right focus, etc.)?

Here are the photos of the tool :

 

[Just for fun]

Following along to see what the pros say. My uneducated guess is the angle is too steep in your cutter.

Tim

 

[Janderso]

Flex?
The side cuts look great from the second pic. IMHO

 

[RJSakowski]

My guess is the problem is the cutter rake. Too much rake on a small mill would cause the tool to dig in. It looks like your piece is brass and brass is notorious for issues when drilling for the same reason, A neutral or negative rake should make for more controlled cuts.

 

[markba633csi]

My guess is your compound/carriage is lifting during the cut, then, once a ripple gets started it gets bigger.
Your workpiece is brass which is considered a "tenacious" metal and very grabby causing the tool to dig in more than other metals
As RJ mentioned, making a smaller rake angle on the tool may help reduce the tendency to dig in.
-M

 

[MrWhoopee]

I'm with @RJSakowski except I would suggest a neutral or barely positive rake. The fact that it only cut on every other stroke is simply due to the limitations of the rigidity of the setup. The waviness is most likely caused by the same. You didn't state what kind of hobby mill, but if it's a knee mill, I would suggest retract the quill all the way and lock it. Then make your cuts using the knee.

 

[jwmelvin]

if it's a knee mill, I would suggest retract the quill all the way and lock it. Then make your cuts using the knee.

That’s a lot of cranking! Do people really do that?

 

[compact8]

You didn't state what kind of hobby mill

It's an EMCO FB2