[TheForge] Delrin hammer guides?

Mon Apr 7 13:00:05 2003

All hands:  Could you use Delrin (acetal) in this application?

                                        Grant
----- Original Message -----
From: "Tom Troszak" <[email protected]>
To: <[email protected]>
Sent: Monday, April 07, 2003 5:40 AM
Subject: [TheForge] Re: UHMW hammer guides

> Message: 4
>     Date: Sun, 06 Apr 2003 21:59:29 -0700
>     From: Ian <[email protected]>
>     To: TheForge <[email protected]>
>     Subject: [TheForge] Air Hammers
>     Reply-To: [email protected]
>
>     Instead of using brass bearings for the hammer and slider, has anyone
> used
>     UHMW ...
>
> Dear Ian,
>
> I have made dozens of power hammers using UHMW for guides.  The most
> important thing is that the steel side has to be smooth at lease a 60
> microinch finish or better.  I have built some hammers that strike
> 30,000,000 blows per year, and the brass guides had to be replaced every
> three or four months as the brass needs constant oiling, and most guys oil
> about once a day. The good thing about brass guides is that even after
> 100,000,000 blows, the rams still looked like new.  When the brass guides
> were replaced with UHMW, there was no appreciable wear on the UHMW after
> even six months.  However, in a solid fuel shop, (coal or coke fires), or
a
> place where you do a lot of grinding, microscopic particles of grit get
> "bedded" in the plastic forming a "lapping tool" which actually eats the
> steel. there does not seem to be a good cure for this, but the grooves in
> the steel do not seem to impair the performance, they just look "bad".
>
> Brass guides can be tightened up to a very "crisp" alignment with only a
few
> thousanths play and still slide well, UHMW guides always feel a little
gummy
> by comparison. You have to make a fairly tight fit, almost pinching to get
> rid of the "wobble" but the UHMW is so slippery that it works well. The
UHMW
> has virtually no structural strength at all, so in any application it
needs
> to be "backed up" structurally some way. UHMW is very spooky stuff. An
> unsupported bar will deform from it's own weight, yet it is virtually
> indestructible in many applications, but rough surfaces will erode it
fairly
> quickly.
>
> Another plastic that I have used successfully for hammer guides is
> oil-filled nylon, also called Vecton (and other names I'm sure)  It is
olive
> green in color and is structurally much stiffer and tougher than UHMW.  I
> have used it in fully automatic applications where no lubrication is
> allowed. It is not usable for food grade applications, however. You just
> "prime' it with a little swipe of light oil as you assemble the machine
and
> then it runs for years with no further oil.  The steel side needs to be
> smooth, as with UHMW.  Believe it or not, regular nylon works pretty well
> even without constant lubrication, but I would not recommend it for high
> speed applications.  I discovered this by accident when a supplier
> accidently send plain nylon instead of the oil-filled stuff, the hammer
ran
> great anyway.  It is more expensive than brass, but very cool stuff.  The
> caution about dirt applies here as well. It is not as slippery as the
UHMW,
> but perhaps a little more slippery than bare brass.
>
> I hope this is useful.
>
> Tom Troszak
>
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