[SEL] Question for the Machinists - Advice Needed - OT

[Listerdiesel]

On 29/10/2008, fero_ah at city-net.com <fero_ah at city-net.com> wrote:
> Folks,
>
> I need a little advice on dimensioning some parts I'm designing for one of
> my
> measurement applications.
>
> I'm using commercial titanium pipe for a number of pieces in the assembly to
> keep the total weight down.  In this application, aluminum isn't an option.
>
> When I assemble the whole rig, I'd like for the parts to be a smooth-running
> slip fit without being too sloppy.  I need to dimension the following:
>
>   - A hole bored in a block that needs to slip onto a length of
>     3/4" Sch. 10S titanium pipe.  The nominal OD for 3/4" pipe is 1.050".
>     Depending on whether it's welded or seamless pipe, there will be
>     normal "commercial tolerances" for that OD (and for the ID).
>     But I'll be damned if I can find that data on the net.
>
> So given the (presently unknown) tolerances in the 1.050" OD, what diameter
> and
> tolerances would you specify for a smooth-running slip fit?
>
> Thanks.  Any help would be appreciated as the hole is presently dimensioned
> 1.080 +.015/-.000 and that "feels" too sloppy in my mind.
>
> See ya,  Arnie
>
> Arnie Fero
>

I've just turned the CAD system off, but you can do the simple stuff
fairly easily.

A smooth hand-running fit with both parts having a good surface finish
is only a few of thou or so, assuming a light film of oil,  5-10 thou
starts to feel sloppy.

You need to find out the actual size of the pipe you are going to use,
and if it is +-15thou tolerance, then you're not going to know what
size it really is until you buy it.

Ground OD tube is usually within a thou or so, and all you need to do
is to make sure your hole don't go undersize at all and tie the
oversize to something that will allow you to take the commercial size
tolerance and use it.

I've just been drawing up a stainless steel adapter connector that
allows our customers to plug a 100A charger (2-pin, unequal pins) into
a 200A train socket (2 equal pins with polarising pin)

The connector has to be in two parts as there is a large 75mm
retaining collar on the front which mates with the threaded socket on
the train, and that same threaded socket is replicated on the back for
the other connector to screw to.

The two body parts have a 0.0025" free running fit and are held
together with 3 X M4 stainless cap head screws, retained by Loctitie.
Tolerances are set up on both parts so they can actually be made and
any pair will fit together. Stainless and Titanium will wring together
horribly, so if you have any parts that are these materials, be
careful with fits.

Peter
-- 
Peter A Forbes
Email: listerdiesel at gmail.com
http://www.oldengine.org/members/diesel
http://stationary-engine.co.uk
http://www.oldengine.co.uk