Subject: Re: Brass bearings

From: [email-masked]
Date: Sun, 18 Aug 1996 13:11:25 -0600

I agree with you Hollis on the use of different materials for "bearing"
surfaces but on an air hammer we are talking about a ram "guide" rather
than a bearing. There has to be .010-.015 clearance between the ram and the
guide for it to move. If this is kept well lubricated it will last a long
time.

The older Little Giants used a cast steel ram and a steel ram guide
(wraparound style). The pins that hold the ram and the pins connecting the
ram to the links are steel. The links are steel. These old hammers do show
some wear but only after many, many years. I'm not sure whether the ram
guides on later hammers are cast steel or cast iron.

Having said all that I do agree that using brass wear surfaces will last
longer, I'm just not convinced it matters.

Just my opinion, Bob

>In many types of applications, the brass acts as a "sacrifice", so
>theoretically, the harder to machine steel would not wear out and the brass
>could be easily replaced.  Something else I have seen before is the tendency
>of like materials to "gall" so similar grades of steel on steel might end up
>with scored surfaces (especially if they get hot).  Toolmakers commonly use
>different grades of tool steel if bearing contact is a requirement, e.g., S7
>and H13, both hardened to 48 Rc or the same grade at different hardnesses
>(maybe 52Rc and 46Rc).  If you are going to the trouble to build a hammer, I
>would definitely install some sort of wear plate - I don't think you will
>regret it.
>
>Hollis

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From: Peter Beky <[email-masked]>
Date: Mon, 19 Aug 1996 10:56:48 +1000

I have a 2cwt pneumatic air hammer, the stuffing box has wear plates to
stop the tup (ram) from rotating, and these are grey cast iron, as they
wear they are shimmed.  The other material that can be used is Tobin
Bronze.  These peices are consumable in any case.

Secondly the wear plates are attatched to the stuffing box with brass 
rivets, again a consumable item.

Go with the brass.

Pater.