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Advice for a small cut in aluminum

IndyGunworks

Cast Iron
Joined
Feb 11, 2010
Location
Indianapolis, IN
I know this would be a super easy job for most of you, but I want to make sure i do it right.

material is 7075 aluminum anodized. Its the side of an AR-15 billet lower reciever. I am machining some improper engraving (not atf related) off the side.

it will need to be 2.5 inches long, and around .20 deep.

A 5/8 end mill will cover the width i need it to cover.

What speed feed would you use, what lube?
is a HSS 5/8th endmill going to be an appropriate tool?

I plan on taping the rest off when finished and blasting the machined area and trying some aluma black to recolor it. If that doesnt take then the whole reciever is going to be recoated.

I have been struggling w/ the whole machining aspect of gunsmithing so i want to make sure i get this one right, it will be a huge confidance booster.
 
Use a 3-flute HSS or carbide end mill. If carbide, run it at the highest speed (rpm) your machine has. If HSS, close to that. ;)

It's hard to screw this up, really.
 
Hmm, if using a bridgeport I think I'd machine around 500 rpms, lowest speed in "open belt"/high speed. Thats just me, I don't run my tooling screaming like its a VMC under full spindle load ;) and trying to save seconds per part. In my shop I'd use CoolTool2 or Tap Magic as that's what I have for lubricants but I believe it will finish fine dry. You don't have to take the entire .200" depth off in one pass, i would leave say .005" depth for the final pass. You can also get some practice taking lighter "slices" of the .200, say go .050" deep at a time, you can even try some .005" cuts to simulate how the finish cut is going to work.

I would not step all the way down with .005" depth cuts as that's wasteful, but its a good confidence booster to start with light cuts and move to deeper cuts as you get more experience.

Also, as a sense check, .200" seems like a lot of material off to remove engraving. If you told me .020" deep or until it cleans up (guessing around .010" would get it) I would feel thats more in the ballpark.

Last is if you have to plunge (drill, with the endmill) to depth (closed slot both ends rounded) then a 4-flute endmill is likely the improper tool and a 2-flute would be better.
 
Since you are not looking for production speed the RPM and feed is not really a problem.1000-1500 RPM with hand feed so you can feel the cut should work fine for you,squirt it often with WD-40 and you shouldn't have a problem.WD-40 works great for a lube to cut aluminum with.

Crank the handle till you feel a slight load,you do not wanna go to slow feeding it,going to slow sometimes can be as bad as going to fast.
 
Pretty easy stuff..

Get under that anodizing quickly, it's hard on the cutter ... NO .005 steps...

A 2 or 3 flute will work fine, RPM up a bit, as posted above.

Some coolant/lube to wash chips away, and prevent recutting, will help surface finish...
 
I did mean .02 deep.

what about a 4 flute carbide endmill at around 1500 RPM, plundged to the depth that will get rid of the engraving (probably not even .02) then moved laterally to clean it up?
 
Plain cutter in a horizontal mill is the ticket for this. Won't smear the center like an endmill.



I used a two flute and plunged to depth then cleaned it out latterally... was super easy no issues, but it did have a few marks in the middle that i blasted out before i recoated it.

whats a "plain" cutter?
 
One thing I didn't see mentioned is that hard anodize is a crystaline layer of electro-chemically applied aluminum oxide that's very hard but thin. It will wear a notch in an HSS cutter depending on the time in cut. The notch telegraphs as a ridge to the wall on successive cuts. Carbide is a better choice for anodize even though HSS is usually preferred for cutting aluinum.

If I can exercise my preferences I remove the anodize by barely breaking through it with a carbide cutter or an HSS cutter ready for the "dull" box. That way a fresh HSS cutter use subsequently will enjoy normal working life.

Once through the anodize the cutter selection is not critical. However 7075 is a chrome and silicon bearing alloy and is abrasive in rough proportion.

Naturally the underlying metal exposed by machining is not protected by anodize and so will wear and corrode.
 
Quoting my earlier posts Forrest.... :)

#7 and #9....

" Pretty easy stuff..

Get under that anodizing quickly, it's hard on the cutter ... NO .005 steps...

A 2 or 3 flute will work fine, RPM up a bit, as posted above.

Some coolant/lube to wash chips away, and prevent recutting, will help surface finish.."

" That will work fine.. It really is not hard to machine stuff... Not gummy.

The anodizing is the toughest part..."
 
Naturally the underlying metal exposed by machining is not protected by anodize and so will wear and corrode.

Thats why I blasted the aluminum and coated it w/ a thick airbrush coating of Norrels moly resin, baked it and its protected and blended in to be a pretty close match to the original colored finish.

I did have some small tool marks that even going deeper did not remove them so i media blasted as many of them away as i could.

TO ME, it wasnt PERFECT, but the customer was VERY happy and i made 40 bucks in about 15 minutes so i guess its win win. but i am still wondering if their was a better way.
 
The photo attachment shows the type of problem involved here.

Notice that the surface is curved and recessed.

I would probably approach this by masking off the surrounding rims and using an 80-grit flapwheel grinder with a rotary tool like a dremel.

The main problem is that most flapwheels use aluminum oxide, but it would be better to use diamond. You could probably make do with the aluminum oxide which will work very slowly. On the other hand slow might be an advantage here.

If you use a mill it will look like shit and you risk smearing.
 

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