[TheForge] Re: smoothing hammer guides

Mon Apr 7 09:23:01 2003

Message: 7
    From: "Paul Hewitt" <[email protected]>
    To: <[email protected]>
    Subject: Re: [TheForge] Air Hammers
    Date: Sun, 6 Apr 2003 20:09:49 -0700
    Reply-To: [email protected]

    The problem with UHMW is that if "cold forms"  UHMW is actually Ultra 
High
    Molecular Weight Polyethylene AKA Milk Jugs....  which are LDPE low 
density
    Polyethylene.  high load forces, speeds and impact cause the material to
    deform, the larger the tolerance gap the move "slamming: it will do, 
thus
    the faster it will deform into an unusable state.  Also UHMW prefers a
    ground and polished surface in bearing type applications, which is hard 
to
    accurately do on the slide of a hammer.  The hammers I have built in the
    past are not even brass, just simply greased steel on steel.

Dear Paul,

a polished surface is actually very easy to do on the slide of a hammer, I 
have done hundreds of them.  For a home built hammer, can use a drum type 
sander lke those for polishing stainless steel.  It is actually called 
"graining" and you just use progressively finer grit down to about 150 then 
Scotchbrite medium and then fine and the sliding surface will be plenty 
smooth, even for plastic guides.  Just make sure that the grain lines run 
parallel with the movement of the slide, that is, the grain runs longways.  
A disc grinder will not work, the scratches will alrays run across the 
surface to some extent.  You may be able to put a nice looking polish on 
your ram slides with a side grinder, but it will not be smooth enough. You 
can also just draw file longways, then sand longways and polish by hand.  
This is my personal preference and you can get the same exact finish, maybe 
better as the filing levels out the surface by taking off the high spots and 
leaving the divots. Thouroughly degrease the steel. Use a brand new mill 
file, and clean the file with a file card after each stroke so absolutely no 
crumbs will catch and gall the surface. Hand sand with 100 grit, then 150. 
then scotchbrite.  You can sand finer if you want, but 150 is good enough 
for hammer guides if you are careful.

The most important thing to remember is that flat, shiny, and smooth are 
three completely seperate attributes of a surface, and hammer guides mostly 
just need to be smooth.  If you put your hammer together and immediately get 
black sludge forming on the brass, take the ram out and polish it some more, 
until you can run the hammer for several minutes without the sludge forming. 
Then it is smooth enough and the guides will last 10 or 100 times longer. 
Another test is to scratch the edge of your thumbnail down the length of the 
slide surface.  If you leave a white line, or feel anything scratchy, polish 
some more, and always polish longways.  I hope this is useful.

Tom Troszak

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