Shear Modification

Modification to increase the capability of the "Central Machinery" Shear.
By Cullen Bennett
March 2003

A few months ago, I was visiting Harbour Freight looking for some safety wire. While I was there, I saw a store special for a 30" shear/break/roller combination for $279.00. I had been looking in the catalogs for several months at an identical unit for $289.00 plus shipping (approximately another $80). Seeing this unit in a local store at a less than catalog price caught my attention. The spec said it would shear 20 Ga mild steel. I had a project on my back burner that needed some 0.022" #304 stainless steel sheared. I asked the salesperson if it would do the job. Oh Yeah.... No problem! I decided to chance it. So, I bought the unit and pulled my pickup around back to have it loaded. It was in a crate from China, all 340 pounds of it. I got it home and unpacked it.






















The excitement wained when I tried to cut the stainless steel. This was after I got some instructions from the machinist bretheren on how to set it up (I am a confessed total newbie when it comes to shear alignment). It would cut paper and 20 Ga mild steel as advertised. Stainless is, however, another animal! It cut nicely for about the first 5" and then started to just pull the material between the blades and mutilate it. Back to the adjustments and try again... More of the same. At that point I walked into the house in total frustration and told the wife that my purchase didn't do what I had intended. She just said, you'll figure it out....and went on.


After a few days I ventured back into the garage shop. Tried to shear another piece of stainless (hoping for a miracle) and got a consistent result....garbage! I looked at the configuration and surmised that the blade must be tipping over toward the middle of the cut. So I set about to mark off a couple of new support bolt slots in the blade.






















The blade is approximately 3/4" thick and it amounted to about a 4 hour milling operation for me. (I take small light cuts, the mill is old and small).






















Next was to drill and tap the blade back support so that a couple of 3/8x16 bolts could be used to keep the blade from tipping over. The shear bolts are 10x1.5mm, but I don't have one of those taps.










































This resulted in:






















that still would not shear the stainless steel. So, I had to conclude that the blade tipping was not really the root cause of the problem. I was really getting frustrated at this point and stayed out of the garage for almost a week. But, being of a mind that I will not let a "machine" get the best of me, I waded back into the fray.


The only thing remaining was that the blade support must be bending with the loading from the stainless. This blade support is 3/4" cast iron. After looking at it for a while, it dawned on me that if the manufacturer intended for the truss bolt (center back) to "bow" the cast iron to make sure that it cut across the total 30" that it "MUST" be able to bend. The following Saturday I went to the local metal salvage lot and purchased a hot rolled piece of bar steel. It was 1"x3"x31" and must have weighed about 30 lbs. I drilled and tapped 5 holes (3/8x16 1" deep) in the narrow side of the bar evenly spaced around the center line. The bar was cut to the exact length of the inside dimension between the end braces of the shear. I cut a small notch out of the back side edge to clear the chamfer on the casting. I then drilled and tapped 2 holes (3/8x16) in each end so that it could be secured to the endplates with a couple of cap head allen bolts.






















I re-assembled the blade support in front of the new "support bar" as seen it next.






















Next, I went through the same alignment procedure as before, adjusting until it cut paper nicely. This requires adjusting the front screws until the ends of the lower blade just "kiss" the side of the upper blade, and then adjust the backside center "truss bolt" until it cuts paper at the ends and the center. Now, I unscrewed the bolts in the "support bar" brace until they just kissed the back side of the blade support (no real pressure applied, just snug).


I then tried to cut the stainless and the sound was that of paper tearing. The result was a clean, beautiful cut across the entire length. I was a Happy camper!!!






















I have since sheared up to 0.089" T6 aluminum, but it was a strain all the way. It will do it, but its a job. I plan to add a couple of large pulleys and a cable on each end to a pedal underneath the table to help distrubute the forces, but, that will be another project...






















Completed shear on the table.






















Hope this helps someone else. It is posted in the metalworkers website; March 2003 Cullen Bennett (Tempe Arizona).