combo square repair

[hobby]

Hello,

This is a build blog for fabricating a new combination square clamp, it is that part of the square that gets bent and finally breaks after normal usage, usually the pin breaks, this is because the whole square is built rigidly with a cast aluminum body, and a stainless steel blade, beautiful small 6" squares to work with, but the clamping mechanism is cast aluminum too, and always wants to bend and break at its pin location.

The first one broke, I went to town bought a new one, but when this one broke as quick, I knew I had to make the clamps out of steel.

So here is a quick build blog on how I built new ,combo square, clamps.

The square at the top left has been fixed with a new clamp and is completed, it works fine, but because both squares have different manufacturers, I need to fabricate the second square clamp, from new measurements, as one square differs from the other in widths of the clamp.



　

Here is the original clamp piece from one of these squares, it has the guide pin broken off, I'm not using this as a template for the new builds, rather I'm going to set this aside, and fabricate new ones using the square parts themselves, and do emperical measurements and calculations, to get the best fit possible.



so I cut off about 1-1/2" length of 3/8" drill rod.



step one is to turn down the dia. to around 0.250", for a length of around 0.400"





　

　

Then using a die, thread it to 1/4-20.





Here is the resulting piece ready for the milling process.



Now comes the fun part of machining parts, I need to first secure the dimensions of the opening this piece will fit into, it turns out to be around 0.270" square.



So now I have the workpiece in my spin jig, so I can maching all four sides easily, to make a square around 0.260" the 10thou. less is for some clearance, in the hole.



Now after doing some additional measurements and a lot of basic math, I was able to determine the amount of material to take off,for the beginning of this next procedure.

The material left over, is the clearance thickness of the clamp in its hole, plus the plus the thickness of the blade, plus the depth of the slot in the middle of the blade.



Now securing the last dimensions, is to determine the half blade width to the edge of the pin, plus the pin width, and finally the pin depth, which this depth turns out to be around 0.035"







with all this determined, I machined a pin 0.080" wide by 0.035" high and situated the edge of the pin 0.355" from one end of the clamp so the blade can nestle into the pin, and the clamp can slide properly on the blade in its slot.

here is the piece still attached to its parent material.



continued next thread.....

 

[hobby]

and the fun math that was involved.



Lastly the pin is machined with square corners, the slot in the blade is a concave half round deal, so the clamp does not fit properly yet,



Therefore some needle file work to shape the pin is in order.


now thats better, it now fits snugly yet loose enough to slide on the blade.



Now I have both squares repaired and working properly again, so with two squares I can have one set for (1/8" and 16") and the other is set for (1/16" and 1/32").



These clamps are made of steel so I do need to tighten them a little tighter then the original, because steel against steel needs to have more friction then aluminum against steel, but they tighten and loosen very easily and slide properly in there blade slots, and they wont break as easily as the aluminum ones did.


Have fun in the shop.

　

　

 

[Sshire]

Nicely done. The steel should be a definite improvement.
When the swarf gremlins took my Starrett square locking bolt, I got one from Starrett for $4.50. Of course, a few days after it arrived, the gremlins returned mine.

 

[hobby]

Thankyou, Stan.

 

[SilverSanJuan]

Thanks for the great write-up, Stan. Very informative.