Interferance fit on Slug to case.

[marcopolo]

I don't know if this is a good idea, but here goes:

Whilst i'm waiting for my bFlex and LEDs to arrive from cutter I was going to start on the light housing. I am going to use a round aluminium slug about 15mm deep as a heatsink on the back of the MCPCB and the slug a close fit with the round aluminium tube it will sit in but I have had a better idea:

What if I were to make the slug say 0.01mm (on my lathe) larger than the I.D. of the tube, put the slug in the freezer, heat the tube with a heatgun, insert slug into tube then I should get a very tigh fit once they go back to room temp - maybe even without any artic silver 5.

Any thoguhts on this?

thanks,

Marco.

 

[LukeA]

I think that would work very well.

It'll heat up faster with a torch than a heat gun.

 

[trout]

Yes it works great I did that on saturday . you have to work fast with the insertion as the slug will suck the heat from the tube quite fast .and then you are stuck half in and it then wont come out either with out brute force.

I was also then going to screw it into the maghead but after inserting the slug it altered the tolerence of the threaded bit and I then had to recut the thread

but a successfull method

 

[marcopolo]

Thanks for the info.

Just out of curiosity Trout, do the have the OD/ID micrometer measurements for the tube/slugs...or does my 0.01mm sound reasonable?

Marco.

 

[trout]

Thanks for the info.

Just out of curiosity Trout, do the have the OD/ID micrometer measurements for the tube/slugs...or does my 0.01mm sound reasonable?

Marco.

Sorry Marcopolo nothing as acurate as that just a bit of Yorkshire engineering.

cool it down - warm it up - does it fit /no then machine a bit off
and repeat untill a result .

it took 5 of the above processes to achieve a snug hot cold pressfit .
but when it cooled / warmed man is it tight .

 

[Anglepoise]

I don't know if this is a good idea, but here goes:

Whilst i'm waiting for my bFlex and LEDs to arrive from cutter I was going to start on the light housing. I am going to use a round aluminium slug about 15mm deep as a heatsink on the back of the MCPCB and the slug a close fit with the round aluminium tube it will sit in but I have had a better idea:

What if I were to make the slug say 0.01mm (on my lathe) larger than the I.D. of the tube, put the slug in the freezer, heat the tube with a heatgun, insert slug into tube then I should get a very tigh fit once they go back to room temp - maybe even without any artic silver 5.

Any thoguhts on this?

thanks,

Marco.

In many cases, this is a great way of making sure you have a perfect metal to metal contact and the parts stay together.

However in our application, there is bound to be a situation in the future where you might need to separate the two parts for future mods, repairs, upgrades etc. It has been my experience that a well machined sliding fit with Arctic Silver grease, will wick the heat away almost as well as a press fit.

 

[LEDobsession]

In my experience, using liquid nitrogen will help get the shrinking done faster than just putting it into the freezer but that is all your call. It should also shrink it a little bit more (maybe .010" inch). Your decision.
Trevor.

 

[will]

I have done a number of press fits on Mini-mag bodies. One thing I noticed is that if the fit is too tight, the outside anodize will craze very slightly. You have to look very hard to see it, but it is there. With the thickness of the head this might not be a problem.

 

[gadget_lover]

I would think that the fit does not need to be so tight that it will not fit without force. The heating / contraction should take care of that.

The formulas are readily available that will tell you the expansion rates at various temperatures.

Dan