"Karl Townsend" wrote in message
...

On Sat, 23 Feb 2013 00:35:01 -0600, "RogerN"
wrote:


I have some Aluminum parts, 7075 T6, for machining and will anodize at
home
using the sulfuric acid / battery charger method, or a variation. For the
tight tolerance parts, do I need to machine, ream, oversize to allow for
the
anodizing? If so, how much? I've seen recommendations of .001"-.002" per
surface, is that about right? For example, one of the hole sizes in the
drawing is .251" +/- .001, the instructions by others that have built
these
parts say to use a .251 reamer, so that's what I bought. But now reading
the anodizing info I'm wondering if I need to ream to .253 or so?

RogerN


Roger, thanks for the heads up. I'm planning the same project and
didn't think of this. After watching eBay forever, I scored the tap.
Now you got me worried it will be undersize after anodize.

If you're interested, find me a piece of T7075. I'll drill and tap.
You can also drill and ream a couple holes in it with whatever reamer
you have. Check before and after anodizing the scrap part. Only way to
know for sure.

Karl

I did a little cad work to make it so I can bolt an AR-15 receiver to a
1-3/4 bar stock with a flat milled. I plan to have 2 dowel pin holes and 2
tapped holes in the areas to be milled out later. On the 1-3/4" stock, mill
off .246" leaving the thickness 1.504 on the D shape, this puts the center
of the buffer tube at 0.629" (0.875R - 0.246) above the deck per drawing. I
just have to make sure the piece of stock is running true in the lathe. I'm
thinking of running this on the CNC lathe, it threads fast and repeats.
Anyway, I can cut a little oversize to allow anodizing, since the buffer
tube threads shouldn't be subject to much wear, I wonder if it would be
easier to mask the area.

I'd guess running the taps and reamers back through the holes after
anodizing wouldn't be good for the cutting tools.

RogerN