Another MoFo

[Nick]

Yep, though better if you ground the face flat on a wetstone first.

[pre65]

Yep, though better if you ground the face flat on a wetstone first.

Indeed, but I might be better making one from 6mm aluminium, I've got loads of offcuts.

I'll make some M3 studs so I can tighten it down with a hex nut.

[Nick]

Why? If you tighten it too much you will cut through the insulator.

[pre65]

Why? If you tighten it too much you will cut through the insulator.

I appreciate that.

I've not got any M3 setscrews long enough, so stud and nut is more convenient.

[Ray P]

Why? If you tighten it too much you will cut through the insulator.

and possibly pull the stud out of the soft heatsink. Anyway, the device datasheet tells you the recommended torque.

[pre65]

Why? If you tighten it too much you will cut through the insulator.

and possibly pull the stud out of the soft heatsink. Anyway, the device datasheet tells you the recommended torque.

Soft heatsink ? What makes you say that Ray ?

Mine are certainly not "soft".

As for too much tightness, I'm not a gorilla.

[Paul Barker]

Well the good news is that that will work as a reservoir, but the bad thing is it will take some time to charge back up through the resistor if you pull a peak from it. But unlikely with your music collection

cheered me up

[Ray P]

Heatsinks are usually of a soft material, normally aluminium but sometimes copper. M3 is a fine thread and not the easiest to get really tight when tapped by hand. Steel bolts are hard. It doesn't take much over-tightening to strip the thread or pull a stud out of the thread. I speak from experience!

[pre65]

Heatsinks are usually of a soft material, normally aluminium but sometimes copper. M3 is a fine thread and not the easiest to get really tight when tapped by hand. Steel bolts are hard. It doesn't take much over-tightening to strip the thread or pull a stud out of the thread. I speak from experience!

I'm familiar with "soft" aluminium, and how it reacts to machining and drilling/tapping. I've got some cheap heatsinks for the 833a A2 buffer project, and again, they certainly are not soft, if they were I could bend them by hand, and I can't.

I generally use engineering grade (6082) aluminium for most things, or HE15 (2014) for anything special.

I'd say my heatsinks are very similar to 6082 spec.

[pre65]

Perhaps you have seen 1050 based heatsinks ?

"Which Aluminum Alloy Should You Use for Your Heat Sinks?
If your first thought is to find the alloy with the highest thermal conductivity, think again.

For example, 1050 aluminum offers a thermal conductivity value of 229 W/m•K. However, this alloy is mechanically too soft for heat sinks.

You should generally look at the 6000 series alloys for heat sinks. These alloys are widely available, are fairly strong, and tend to extrude well. The following chart shows a comparison.

Alloy Thermal Conductivity Values (W/m•K)
1050 229
6061 166
6063 201
Alloys like 6061 and 6063 are some of the most common in the 6000 series. They are common for extrusion in general. And either one will actually work quite well for heat sinks."

[pre65]

Generally speaking one would use a more coarse thread in an aluminium material, as like using UNC instead of UNF, but I'm not sure what the metric equivalents would be.


I know some Japanese motorcycles used a more coarse thread form on alloy engines which can catch people out when replacing fixings.

[Nick]

You are both creating a problem where one doesn't exist. Use a 8 or 10mm m3 screw, drill with a 2.5mm drill and tap with a newish m3 tap with some lubrication. tighten up as fits the screw size and material. There is NOTHING to be gained by having it too tight. use a suitable insulator, If you can use a washer on top of the device all good. Fix the PCB so there is no movement of the device, tighten it up after the PCB is fixed in place. Measure with meter to make sure its isolated and solder to the PCB. Done.

[pre65]

What is the best easily acquired lubricant for tapping aluminium ?

My old engineering books say paraffin, but I use VMD20 spray on, Italian off Ebay. Some say WD40 is good.

[Ant]

I usually use tygris r214 cutting and tapping fluid for most things, either that or wd40 in a pinch. It's crap for steel but fine for aluminum.
I also use the drill press when tapping, stick the tap in the chuck and turn it by hand. hold down the handle to put the required downward force on the tap and you will get a straight thread. Much easier and more accurate than a tap wrench

[Nick]

I tried using a drill press, found it more of a problem than a solution. You shouldn't need any downward force once its started, and I find its much easier to feel how the cut is progressing by hand. Ad of course you have to keep a hand on the thing to stop it trying to pull the tap back out.

I just use a old tin of engine oil and dip the tip of the tap in before starting, its only a m3 thread so hardly much work