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

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.

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

I would think a loose fit with a light film of silicone would be
the fastest, quickest, cheapest, easiest. It would even be undone
if need be.

Clear Silicone should stick to both materials with enough
flexibility to allow for heat/cold issues.
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)




"Rob" wrote in message
...
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

Heat the PVC to about 212 deg, in boiling water. knurl the brass part, the
press them together, should hold tight. but I suggest that what ever you do,
make some samples first. If heated you might be able to get away without
machining the PVC, save time and money.
gary


"Rob" wrote in message
...
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

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

"Rob" wrote in message
...
I don't know if I could get away with more interference

Once assembled there will be no significant loads between the two parts.

Just a thought, if there are no significant loads between the parts, why do
you want to increase their interference?

Regards,

Robin

Rob writes:

Is there rules of thumb for the amount of interference used?

Given that PVC can have various degrees of plasticizer and filler, no. Can
be hard like pipe or soft like flex tubing. C'mon.

"Richard J Kinch" wrote in message
. ..
Rob writes:

Is there rules of thumb for the amount of interference used?

Given that PVC can have various degrees of plasticizer and filler, no.
Can
be hard like pipe or soft like flex tubing. C'mon.


Hi Richard, that's true but it's pretty hard machining flex tubing the fog
from the LN2 tends to obscure the view

I checked the suppliers website - the description is "Rigid PVC or
unplasticised PVC" and the the data sheet refers to DIN EN ISO 1043
designation U-PVC. Its the garden variety stuff that seems to be in
everyone's stock rack.

rob

"Robin S." wrote in message
...

"Rob" wrote in message
...
I don't know if I could get away with more interference

Once assembled there will be no significant loads between the two parts.

Just a thought, if there are no significant loads between the parts, why
do
you want to increase their interference?

Regards,

Robin



Sorry - perhaps I was unclear on that. I don't want to increase the
interference, I just wanted to be sure I was not overdoing it at 0.25mm in
24mm, or was there any rules of thumb or other ways of doing this.
cheers
rob

PVC will creep over time, so a larger press fit than that will
diminish. So a tighter press fit won't buy you much, though I think it
would be harmless if it is easier for you to make.

I think you could probably use about .040" interference in your hoop
size without risk of cracking the PVC. There are different grades of
PVC, some more tolerant than others.

It is common practice in industry to heat a knurled brass insert and
press it into plastic. The plastic will flow into the knurls and the
part is good and stuck. There is about .020" interference to the
outside of the knurls on a joint this size.

I think a good 2 part epoxy would work really well.

There is a CA glue called 3M Pronto CA40H that will adhere to PVC.

PVC cement is sticky and would probably adhere to clean brass pretty
well.

I had this design problem in the past, and I made the part that is
brass in your assembly out of PVC and screwed my sensor into it. Then
the PVC and PVC bonds to each other really well with PVC cement.


Thanks for the reply.

I like the idea of knurling the brass component and heating before assembly.
Unfortunately I cant make the brass part from PVC as it forms part of a
bearing mount assembly and needs to push quite firmly against a bearing to
locate it. I think I might try some adhesives and see what works - this or
simple press fitting is probably the best route.
regards
rob

"Gary Owens" wrote in message
...
Heat the PVC to about 212 deg, in boiling water. knurl the brass part, the
press them together, should hold tight. but I suggest that what ever you
do,
make some samples first. If heated you might be able to get away without
machining the PVC, save time and money.
gary



Thanks Gary - I'll try it. Heating the pvc in boiling water sounds like a
nice simple approach.
cheers
rob

"Gunner" wrote in message
...
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

Thanks for the ideas guys - with yours and the other guys replies I've got
some thinking and testing to do.

Glad you liked the ascii are Roy

regards
rob

"DanG" wrote in message
news:K%XQf.136277$0G.102272@dukeread10...
I would think a loose fit with a light film of silicone would be
the fastest, quickest, cheapest, easiest. It would even be undone
if need be.

Clear Silicone should stick to both materials with enough
flexibility to allow for heat/cold issues.
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)



\

Cheers Dan - I've got some black Sikaflex RTV - I know it sticks very well
to PVC. I'll try it.
rob