Er40 collet wrench modification

[PT Doc]

So I want to add a square hole to my er40 collet wrench. This will allow me to use a torque wrench. The collet wrench width and thickness is beefy enough that this subtraction shouldn’t weaken the wrench. I have another identical wrench that will not be modified so that can be used when not needing to torque it down.

I have a few questions.

What size drive, 3/8” or 1/2”? Max torque for er40 Techniks nuts are 140ftlbs.
How would you create this square drive hole?
How does the distance of the square drive hole to the center of the nut effect my actual torque application compared to what is dialed in on my torque wrench?

The tightening of the collet nut will be in a CAT40 fixture. I think I will mount this fixture to a board and that will be clamped in a vise. Hopefully the torque application doesn’t tip the vise and stand over. But that’s another issue.

Thanks in advance for the help.

 

[darkzero]

I would use 1/2 drive for ER-40 but it depends, what torque wrenches do you currently have? If you don't currently own any torque wrenches, some things to consider.

Most 3/8 torque wrenches have a max torque of 100 ft/lbs. 1/2 torque wrenches are generally longer than 3/8 torque wrenches so they'll have better leverage.

1/2 torque wrenches are commonly are available in 150 ft/lb max or 250 ft/lb max. Many of the inexpensive clicker type torque wrenches available these days with max 250 ft/lb have a resolution of 2ft/lb. But the more expensive or older ones are available with 1 ft/lb resolution. Many not matter much in this case though.

It's good practice not to store clicker type torque wrenches while tensioned. So if you do buy this style torque wrench & use it often, it gets old very quick having to wind in the torque setting to the max end of the scale. If you buy a digital torque wrench there's no worry of storing while tensioned.

Will you be using the torque wrench for other uses? I own both clicker & digital in 3/8 & 1/2 from my automotive days. I still prefer to use my clickers over my digital. You get what you pay for in quality when buying torque wrenches.

 

[PT Doc]

I’ll likely be using a harbor freight 1/2” for this. Affordable and I likely don’t need to actually get to 140ftlb. I always store my clickers at zero, it’s just the right thing to do.

 

[darkzero]

How does the distance of the square drive hole to the center of the nut effect my actual torque application compared to what is dialed in on my torque wrench?

Oh and yes, it will affect the torque reading anytime you use a spanner extension/adapter like this or a crows foot. Only socket extensions won't affect the torque reading. You can find the formula & calculators online.

 

[rust rescue]

If the torque wrench is kept at 90 degrees to the line from the drive to the nut it is considered a wash.

 

[darkzero]

Oh yes, forgot about that.

If you use it like this no need to worry.

 

[PT Doc]

Oh yes, forgot about that.

If you use it like this no need to worry.

View attachment 292488

If everything is at 90* then all is ok. What if it was at 180*?

 

[darkzero]

It's the same thing, still 90° to the handle & on centerline with the drive.