Press fit clearance for brass into PVC?

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.

Gett> I'm pressing a cylindrical brass part into a turned PVC part. The Brass

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) snipped-for-privacy@7cox.net

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

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.

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

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

- Proverbs 22:3

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

Regards,

Robin

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

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

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

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

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

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

On Sun, 12 Mar 2006 22:46:05 +0800, with neither quill nor qualm, "Rob" quickly quoth:

I would think that the standard would be to mold the PVC around the existing metal parts, with a lip on the end of the metal part to ensure that they stay together during the changes in expansion rates of the two materials as they go through temperature changes.