Question on proper workholding

[mrcodewiz]

I am trying to do a run of several parts and cut down on operations. I have it down to 2 right now but I am getting some chatter and I am wondering if it is due to my workholding setup.

My first operation is just milling out 2 countersunk holes in a vise. For the second operation, I have an aluminum jig with two steel dowels in it that fit into the countersink and through holes made in the first op. the dowels are threaded 1/4-20 on both ends and I just tighten a nut down on either side. The second op itself consists of milling another countersunk hole and then running a profile around the entire piece. This is on a mini mill so I am running a 3/8 cutter at maybe 2k RPM taking .05 cuts at around 6-7 IPM. Here are a few pictures of the setup - is this setup OK or should I do it differently?







This is what the final piece looks like:


thanks,
Kevin

[Geof]

Your setup looks pretty good; except for one small point I would not do anything different.

It looks like you are clamping an unmachined extruded surface to another unmachined extruded surface. If you check your extrusion you may find the sides are not flat; extruded aluminum flat bar often has slightly convex sides and if you hold two together you can rock them slightly because they only make contact along the center. This rocking can lead to chatter.

Slightly relieve the fixture in the vise so that when you clamp on the part it only makes contact via a land about 1/8' wide all round; this will remove any rocking.

Even so you may still get chatter, the material is quite thick for a small machine so you are taking a very wide cut with a small diameter cutter.

[DareBee]

Good pictures and explanation Kevin.
Rocking is a possibility.
Your machine is small and the overall rigidity of it and the spindle could be an issue.
It could also be your toolholder or cutter length (long series cutter are a bugger and holders/collets need to be as short as possible).
Are you using carbide?
If not switch, the extra cutter rigidity will make a big difference.
You didn't mention coolant. Aluminum is bad for clogging up cutters if they are not lubed.
One of my rules of thumb (now) is never to use HSS cutters for diameters smaller than 3/8. Carbide cutter pricing in small dia is very inexpensive these days.

[JWB_Machining]

Yea, i'm no expert but that looks good. The only thing I might recommend is using a wider vise if you have it. If not it looks like you have ample material underneath your work piece to stop it from deflecting downwards as your cutter pushes in.