Max torque for M4 bolt into 8mm Aluminium

[triplej]

I could probably Google this but thought I'd go to the forum

I'm tapping an M4 thread into 8mm thick Aluminium. What would be a sensible torque setting for mounting TO247 devices? Its a Class A amp so max thermal coupling is needed.

 

[Andrew Eckhardt]

About half newton meter. Not sure you can get M4 through the transistor.

 

[grimberg]

I suggest you follow the manufacturer's recommended mounting torque for the specific device you are using. The information can be found on the device's data sheet, as the example linked below:

http://www.vishay.com/docs/94391/70tpspbf.pdf

Look for "Mounting torque" on page 3.

If the data sheet of your device does not have that information, look for the manufacturer's publication containing the guidelines for device handling, lead forming and mounting.

 

[triplej]

thanks!

The particular devices are 2SK1530/J201 and do not have mounting info so thanks for the link.

Andrew E: Well spotted! I've taken the standard M3 mounting hole out to M4.

So you think the torque will be governed by the device and not the tap?

 

[grimberg]

So you think the torque will be governed by the device and not the tap?

I do. You can damage most TO-247 devices with less torque than it would take to damage the thread, even if it is tapped in low grade aluminum.

 

[triplej]

I do. You can damage most TO-247 devices with less torque than it would take to damage the thread, even if it is tapped in low grade aluminum.

Exactly what I needed to know. Thanks again.

 

[Andrew Eckhardt]

Yes, the program has really nothing to do with the title. If you have tools to measure torque that small, believe them.

 

[triplej]

Yes, the program has really nothing to do with the title.

Ture, mainly because I thought the tap would be the limiting factor.

 

[Andrew Eckhardt]

Only if you break it off in the sink.

 

[AndrewT]

Using a clamping bar usually gets a more effective heat transfer.
Then you can use two M3.5, or two M4, or two M5, instead of one offset M3.5

 

[AuroraB]

Tapping treads directly in alu can be a problem - use lots of cutting oil.
Screws and bolts also have a tendency to 'weld' themselves in alu. Using helicoils or similar inserts is recommeded if screws are to be removed several times....

 

[grimberg]

Tapping treads directly in alu can be a problem - use lots of cutting oil.
Screws and bolts also have a tendency to 'weld' themselves in alu. Using helicoils or similar inserts is recommeded if screws are to be removed several times....

These are the products I use to deal with the issues you mentioned. Tap Magic is great for lubricating while tapping.

Enco - Guaranteed Lowest Prices on Machinery, Tools and Shop Supplies

During assembly, I dip screws in this product to avoid seizing.

Enco - Guaranteed Lowest Prices on Machinery, Tools and Shop Supplies

 

[triplej]

Using a clamping bar usually gets a more effective heat transfer.
Then you can use two M3.5, or two M4, or two M5, instead of one offset M3.5

Thanks Andrew. I may try that. Rod Elliot suggested a U shaped Ali bar.

I find mounting the power devices one of the more frustrating parts of prototyping hence why I'm going to try taps. I'm over nuts blu tacked to the end of a screwdriver .

 

[Rundmaus]

Using helicoils or similar inserts is recommeded if screws are to be removed several times....

+1 for the helicoils! Great stuff for tapped holes in aluminum. During my years at a physics lab, I used them for almost any tapped hole in soft materials like alu.

Rundmaus