Why a mechanical shear, isn’t hydraulic better?
In the 70s and 80s, the legendary John Heine 108B Guillotine dominated Australian sheet metal shops. This beauty cut at a rate of 55 Strokes per minute (SPM), today if you aren’t careful, some of the cheap machines on the market are as slow as 12 SPM. That is like watching grass grow!
Hydraulic rather mechanical drive systems and increased rake angles are mostly to blame.
Rake angle is the angle between the upper and lower blade. The bigger the rake, the easier it is for the machine to cut.
The steeper rake reduces the cross-section of material needing to break under strain. It, therefore, requires less power and the manufacturer can then lessen the structural rigidity in the guillotine and offer for a lower price. However, the compromise is the steeper the rake angle is, the slower the SPM due to the moving beam needing to travel further to complete the length of the cut. A typical 1.5-degree rake guillotine has to stroke 80mm down then back up to complete a 3.0m cut. It would be 110mm each way on a 2.0-degree rake machine.
Also, the steeper the rake angle, the more twist and bow is generated in the offcut strip. Twist and bow might be critical if the offcut strip is the piece required for the job. You usually need it flat and straight!
Something else not typically mentioned in the brochures is the distance from the front of the finger guard to the cutting line. On heavy capacity machines that often look attractive due to the small price premium from the lighter gauge models, need to allow enough room under the finger guard to maneuver full-thickness plate, even when the plate is slightly warped. So, a 6.0mm guillotine might need a 10mm or 12mm space.
Since you can fit your fingertips into that space, they then need to set the guards far enough back not only so that your fingers can’t reach the blade, but so they can’t reach the hydraulic hold-down cylinders in front of the blades. This can result in the front of the finger guards being more than 200mm from the cutting line. So visually seeing the cutting line is very difficult and if you want to trim cut narrow cut strips, you need to use a scrap piece of material to push the metal.
Floor space is also a consideration. Can your new machine offer a return to sender function so that you can optimise floor space and position the back of the shear closer to a wall?
Sheet support systems, to utilise your new power-operated backgauge system you need a mechanism to ensure the sheet metal is kept flat and doesn’t droop and miss the back gauge bar. There are different sheet support systems available some are excellent, some are terrible.
Blade gap adjustment, benefits of full-length clamp bar, safety, programmable back gauges, so much to discuss to help you get the best solution for your sheet metal shop.
