On Sun, 12 Mar 2006 15:42:07 GMT, RoyJ wrote:

Nice ASCII drawing!

.25 mm interferance (about .010") is getting close to the max you are
going to be able to press in PVC. ABS would be much higher. I think I
might do some experimenting with some samples at .5mm, .75mm, etc, see
where it fractures, and run about half that. Heating both parts to 200F
to 250F (100C to 125C) might allow an easier fitup as well as a much
tighter press.

Getting sealants/glues that like both PVC and brass is somewhat
problematic. If press fitting will do it, stick with that.


One might also consider knurling the part with a straight knurl as
well. This acts as teeth of course and helps keep the part from
spinning in the future.

Gunner

Rob wrote:
I'm pressing a cylindrical brass part into a turned PVC part. The Brass
component is 24mm OD and is pressed about 10mm into the PVC until a shoulder
on the brass part is reached.

Is there rules of thumb for the amount of interference used? I've been
boring the PVC to 23.75mm (diameter is 0.25mm smaller than the inserted
brass part. The OD of the PVC part is 40mm

It seems to work ok but I don't know if I could get away with more
interference (read less accurate machining!) or will this lead to the PVC
failing and cracking with time.

Once assembled there will be no significant loads between the two parts. The
PVC is just a cover for an electronic sensor that mounts on the end of the
brass part.

Would it be better to have a loose sliding fit and use some sort of adhesive
/ rtv to assemble the parts?

Any advice welcome.


-- |-----------------------
| | PVC 23.75mm ID
------ |-----------------------
\
BRASS |
24mm OD |
3mm wall|
/
-----
| |----------------------
-- |PVC OD = 40mm
|----------------------
|10mm|


regards
rob






"A prudent man foresees the difficulties ahead and prepares for them;
the simpleton goes blindly on and suffers the consequences."
- Proverbs 22:3