End Milling the Lock Bar Cut Out

[ldsabinadi]

Just need some advice. I am testing out the lock bar cut out on some T6061 .187 aluminum. I have a Carbide 12mm flat 4 flute end mill and as you can see below, am trying to find the right RPM's for my Drill Press to perform the cut out. Basically I am plunging the end mill vertically into the aluminum. The RPM's that I wrote on the block are what the drill press instructions say it should be. I am not so sure that the settings on my Ridgid are accurate to be honest. I noobed out and didn't check the speed on the first pass (the 400 RMP cut.) At 600, the cut came out more square and the 700 rpms even more so. I ended up doing what was stated to be 2k+ (I wrote 1000 on the metal since I don't think it was doing 2k...) The mill didn't look like it was spinning that much faster than it did at 700, so I have my doubts, but the cut did come out a little better than the 700. I just couldn't stand the drill marks in the cut at any speed however.

The last cut was at the highest speed but I did this laterally instead. I did it really, really, slowly. I like the results but it took several minutes to complete it and I am worried about lateral pressure, even if I go slow, on the chuck.

My question is for those that use a drill press for your cut outs... any suggestions? Angles, speeds, lubricants, do it at 2k+ and sand out the cut out to make it smooth, etc. (other than find someone who has a milling machine and have them do it unless that really is the only viable way for me to do this!)


If it looks this rough and takes this long with aluminum, I am assuming it's got to be exponentially harder with Titanium to get good results with what I am doing.

 

[Frank Niro]

Did you know that a flat angle cut on the blade cut out of say 10 - 11 degress works well? As well this is usually cut from one side right through to the other. I cit these with 120 grit on my belt grinder. The liner I cut with a slight relief with the leading edge going into the blade cut out being the long side. Frank

 

[ldsabinadi]

Frank, I appreciate the response. I, however, can not visualize what you are suggesting. Pics might help if you have an example. Thanks for taking the time to respond!

 

[Sandow]

Most of that looks like chatter from the workpiece being unsupported. If your end mill is center cutting, you could clamp a piece of soft metal (like the 6061) flush against the workpiece so you are cutting through both with your plunge. Think of it as putting scrap wood behind something you are drilling through.

Using a drill press for a lateral cut is asking for it. If the press uses a chuck on a tapered arbor then it may pop loose under lateral load.

-Sandow

 

[ldsabinadi]

Most of that looks like chatter from the workpiece being unsupported. If your end mill is center cutting, you could clamp a piece of soft metal (like the 6061) flush against the workpiece so you are cutting through both with your plunge. Think of it as putting scrap wood behind something you are drilling through.

Using a drill press for a lateral cut is asking for it. If the press uses a chuck on a tapered arbor then it may pop loose under lateral load.

-Sandow

That actually makes a lot of sense. I think that would give me a few more options too by way of which bit to use. (i.e. cobalt drill bits to plunge cut two scales facing each other at the same time. Gonna give that a try tonight.)

 

[ldsabinadi]

That did the trick to get something that is consistent and workable. Plus, I can create two lockbars at the same time... Even better. The pics below show the results of using some scrap aluminum and an old drill bit.

The edges of the cuts were just a tiny bit ragged but pretty good otherwise. The thickness between the four drill points was between .065 and .070. With some better bits, I can probably shore that up some. Some paper debris is still on it in the pics but it looks much better in person. Going to test with some new bits tomorrow to see how much cleaner it comes out.

Now I just need to figure out how to clean up where the drill bit bottoms out to make it look more consistent...