Quick-fitting screw into plastic

[Mark FryParticipant @markfry71618]

[Mark FryParticipant @markfry71618]

Hi all,

I wonder if there's a good way for quick-fitting a M5 screw into a piece of 2mm-thick, 10mm wide plastic tube. That is, the screw could be inserted and removed by just pushing and pulling the screw into/from a hole in the plastic piece.

The connection won't sustain high stress, as the screw part will be held fixed and it'll always be under the plastic piece.

I'm thinking of fitting a rubber sleeve over the screw, but I wonder if popping the plastic piece (with a 7mm hole, suppose the rubber is 2mm thick?) in and out would put too much stress on the plastic and eventually create cracks in it.

Any thought will be much appreciated.

Thanks

[JasonBModerator @jasonb]

If the rubber is 2mm thick you will need a 9mm diameter hole.

Risk of cracks etc will depend on what plastic teh tube is made from.

Easiest way to get a M5 screw to push in and pull out of a hole is to drill say 5.1mm which will maintain max strength of the tube

Edited By JasonB on 08/05/2016 20:34:26

[Mark FryParticipant @markfry71618]

@JasonB I think I forgot to mention that I'm hoping to achieve a tight fit. I was thinking a 7mm hole because I thought the rubber should be compressed a fair bit in order for it to grip on the plastic tube.

So I think a M5 in a 5.1mm hole would give it a somewhat loose fit.

Is ABS prone to cracks? Will PC be better?

Edited By Mark Fry on 08/05/2016 20:43:26

[pgk pgkParticipant @pgkpgk17461]

I don't know what the purpose is here but wouldn't it be simpler to turn a smooth rod with a 2mm groove just behind the tip so the tube wall has something to sit in?

[John McNamaraParticipant @johnmcnamara74883]

Hi Mark

Not sure what sort of plastic it is ? Could you heat a turned blunt spike then press it into the plastic, Maybe the plastic would flow into the tube forming a thicker section that might hold the screw firmer?

This process is used to reinforce holes in steel tube see link below.

**LINK**

Regards
John

Edited By John McNamara on 09/05/2016 12:31:16

[Jeff DaymanParticipant @jeffdayman43397]

As with many similar enquiries it would be far simpler to tell us what you're trying to do with the device. There may be a far simpler way to make it or possibly a low cost solution already exists.

Define the problem and solutions become apparent. JD

[Tim StevensParticipant @timstevens64731]

One problem that is likely with a tight fit in a thin plastic component is cracking around the hole. A sort of 'plastic fatigue' if you like. The smoothness of the hole surface will be critical. And if the tightness is to resist gravity, or shaking, oh dear. Unless perhaps the tube is flexible – eg PVC fuel and oil pipe, perhaps.

Tim

[Tim StevensParticipant @timstevens64731]

There is another factor which I have just remembered: Migration of plasticiser. Put two plastics or rubbers next to each other – as you are proposing here – and if either of them includes a plasticiser, the soft material will become harder and the hard softer. Even to the extent of going like very soft cheese.

So, be very careful how you mix plastics and rubbers.

It might be helpful to offer an example –

Old vehicles with inner tubes and wire wheels need rim-tapes to stop the heads of spokes cutting the tube. A common dodge is to use insulating tape instead of traditional rubber. PVC insulating tape, with plasticiser. After some time, the plasticiser moves into the rubber making it softer, and the tape becomes harder. This provides a sharp edge on the tape next to a soft part of the tube, and with the fidgetting movement of driving, the tube can be cut to ribbons. And not repairable, either.

How do I know?

Cheers, Tim

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