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Re: [PSUBS-MAILIST] viewport surface finish



Brian, 
 
A-516 shouldn't be any more difficult to machine then standard off the shelf A-36 or 1018 steel you find.  There are some steels that are freer machining but not by much.  There are a lot of steels that are much tougher and sticker to machine.  If your machining any 316 stainless for sub parts, you'll find that much more difficult. 
 
I imagine you could etch with acid but I've never heard of anyone doing that.  It would probably just give you a coating of corrosion under the paint.  All you need to do is, after your done machining, sand the surfaces your going to paint a bit right in the lathe with some, maybe 180 grit emery paper, or sand blast it after your done machining if you have a sand blaster.  Use a two part, self etching primer after that.  The primer will bite into the surface and hold the paint.  Also, the primer will protect the surface until your sub is all welded together and painted. 
 
You may want to run some tests of how thick your paint will be when your finished.  I'm guessing one layer of primer and one layer of paint will average about .010 of an inch but it depends on how you put it on and how heavy you apply it.   
 
Dan H.
----- Original Message -----
From: Brian Cox
Sent: Monday, March 06, 2006 9:36 PM
Subject: [PSUBS-MAILIST] viewport surface finish

Hello All, 
                       I've got another couple of viewport questions for some of you savy sub builders out there.  I've been machining my first flat disk viewport flange .  That A516 grade 70 steel is really hard stuff !!  I was surprised how much more difficult it is to machine,  in that you can't take off as much metal at a time.  Anyway I have been doing some of the final cuts and facing and getting a very smooth surface finish with higher speeds on the lathe and I have my tolerences very close.  But what I'm wondering is if those surfaces are going to be painted with epoxy will the very smooth suface finish make it hard for the epoxy to stick?  Should I treat it with muriatic acid before I paint it?  And how many thousandths does the average epoxy paint add up to?
 
Thanks
 
Brian Cox,  Ventura