Being thrifty (cheap) I would probably try using a 1/4 inch square tool bit. I would grind one end round for a distance of about 1/4 inch. Then drill a hole for the round end to pilot in. Insert tool, push with hydraulic press or heavy vice. Adjust as needed.
Another way to get a 1/4 inch square hole is to weld in a scrap 1/4 inch socket or extension and cut to length. Everyone does save their broken/unusable tools, don't they?
Don Young
punching 1/4" square holes?
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Rich_Carlstedt
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Calculating Shear requirements, for those wanting to know
Here is a quick way to get the required force to shear steel.( or any other material)
You have to realize, that there are many variables, like predrilling the holes, whether there is a "shear angle" on the punch, and what the clearance is between punch and die. For example, a .250 square die (hole) with a .245 Punch gives .0025 clearance..this is tight !
While a .220 punch has a .015 clearance (per side) and is loose.
Loose makes sloppy holes, while tight requires LOTS of force.
Since we are hobbiests and want 'Tight" tolerances, lets take a look at the problem.
First refer to "Machinery's Handbook" if you have one and look up "Strength Data" for Iron and Steels, under Strength of Materials.
Look up the Tensile strength of the steel you have, which for this example, we will say is 1018 or 1020 ie mild steel.
Note that the Tensile Strength (T) is listed as 60 to 70
That means it has a tensile strength of 60,000 pounds per square inch.
Just to the right of that column is the term "Shear"
Note, that ALL STEELS are rated .75 T, which means you take 3/4 (.75) of the Tensile to get shear. So the shear for mild steel is ( 60,000 x .75=) 45,000 pounds.
now think of a square steel bar , 1 inch wide by 1 inch tall clamped in a vice.It has a cross-sectional area of one sq inch .. instead of sawing it in half, it would take 45,000 pounds of force to shear it square as it is 1 square inch in cross-sectional area....assuming you have the tooling.
If the bar was 1/2 by 2 inches wide, it would require the SAME force, as it is still one inch in cross-section !
Now in the case in point, a 1/4 by 1/4 square hole, by 1/4 deep is eqaul to one inch of perimeter (4 sides @ 1/4 =1) by 1/4 deep.
So the total cross-sectional area is .25 Square Inches ( 1 x .25= .25)
Therfore, Area times Force required gives us the answer.
So .25 square inches times 45,000 PSI = 11,500 pounds (6 tons) to perforate the plate with a square die and punch with no shear angle on the punch
Hope this helps.
Rich
Here is a quick way to get the required force to shear steel.( or any other material)
You have to realize, that there are many variables, like predrilling the holes, whether there is a "shear angle" on the punch, and what the clearance is between punch and die. For example, a .250 square die (hole) with a .245 Punch gives .0025 clearance..this is tight !
While a .220 punch has a .015 clearance (per side) and is loose.
Loose makes sloppy holes, while tight requires LOTS of force.
Since we are hobbiests and want 'Tight" tolerances, lets take a look at the problem.
First refer to "Machinery's Handbook" if you have one and look up "Strength Data" for Iron and Steels, under Strength of Materials.
Look up the Tensile strength of the steel you have, which for this example, we will say is 1018 or 1020 ie mild steel.
Note that the Tensile Strength (T) is listed as 60 to 70
That means it has a tensile strength of 60,000 pounds per square inch.
Just to the right of that column is the term "Shear"
Note, that ALL STEELS are rated .75 T, which means you take 3/4 (.75) of the Tensile to get shear. So the shear for mild steel is ( 60,000 x .75=) 45,000 pounds.
now think of a square steel bar , 1 inch wide by 1 inch tall clamped in a vice.It has a cross-sectional area of one sq inch .. instead of sawing it in half, it would take 45,000 pounds of force to shear it square as it is 1 square inch in cross-sectional area....assuming you have the tooling.
If the bar was 1/2 by 2 inches wide, it would require the SAME force, as it is still one inch in cross-section !
Now in the case in point, a 1/4 by 1/4 square hole, by 1/4 deep is eqaul to one inch of perimeter (4 sides @ 1/4 =1) by 1/4 deep.
So the total cross-sectional area is .25 Square Inches ( 1 x .25= .25)
Therfore, Area times Force required gives us the answer.
So .25 square inches times 45,000 PSI = 11,500 pounds (6 tons) to perforate the plate with a square die and punch with no shear angle on the punch
Hope this helps.
Rich
How to Broach a Square Hole
You might also look at rotary broaching tools. Check out the square broaches at: www.rotarybroaching.com
They may also be able to be used as a punch.
They may also be able to be used as a punch.
Re: punching holes
As you don't need a great deal of holding power on the square hole, maybe you could counterbore the pilot hole large enough to clear the punch?spectrumacoustics wrote: I guess I should have clarified that I don't need a massive amount of holding power on the square hole. The material is fixed at 1/4", I can't change that.
Counterbore about 1/8", leaving 1/8" to punch - should reduce the force required to about half..........
Cheers
Barry