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Old 21st July 2006, 03:36 PM   #1
vax9000 is offline vax9000  United States
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Default My experience: the cheap punch set VS Greenlee punch

Here is my experience.

I bought the cheap punch set from ebay. It has two bolts, 4 dies and 4 nuts. From the photo I guess it is the same set as that from HaborFreight. I punched six 7/8" holes and three 1 3/32" holes on a electric break box. The bolt used with the 7/8" punch was worn to a point that the nut was not straight with the die, and when I was punching the 7th hole the nuts stuck on the edge of the die. I did not notice and I kept turning the bolt. I heard a big sound and the bolt was broken into two pieces.

The bolt used with the 1 3/32" punch was severely worn after three holes. Fortunately I need only 3 big holes for my EL34 amp. I guess it may be able to punch another 3 holes before it dies.

I could not wait 1 week to buy on ebay, so I went to home depot and bought a 0.89mm(roughly 7/8") punch with $30. It is very good. I needed less force to punch the same break box. After 4 holes I observed the bolt and there was no sign of wearing.

This is my experience that might be useful to you guys. I guess the much better cutting edge design is the reason why less force is needed with GreenLee. Maybe the bolt quality is higher too. It well worths the price.

Edit: The break box is made of 1/16" steel sheet. It is the soft type steel often seen with break boxes, not hard steel or stainless steel.
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Old 21st July 2006, 04:22 PM   #2
EC8010 is offline EC8010  United Kingdom
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As you've discovered, cheap tools are more expensive in the long run - you have to replace them with proper tools. In the UK, we have Q-Max punches. Some of mine are twenty five years old.
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Old 21st July 2006, 05:22 PM   #3
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I just checked the Harbor Freight knockout punch set I got and it does indeed have too much slack in the bolt threads. I have used them for a few holes in aluminum and thin steel (baking pans) so far without problem, but looks like they will likely fail on something heavier. I just tried some Greenlee bolts in them, but they do not fit. Wrong thread pitch, so no help there. Its a shame the H-F knockouts aren't made right. I think I will try using a smaller punch (backwards) as a security nut behind a bigger punch, next time I use them, to distribute the forces.

Only other option I can think of would be to bore out the punch thread and use the Greenlee bolt with a big nut behind the punch. (Mouser sells spare Greenlee bolts by the way. $20 for the big ones. Even the Greenlee's break bolts occasionally, but I never had the thread strip out on them.) Likely need a tungsten carbide boring bar to machine the hardened steel punch though.

Another problem with the H-F knockout punch design is that it has four points on the punches, this means 8 cuts occuring in the sheet metal simultaneously (very high forces required). The Greenlees only use two points and they also have a newer (and even more absurdly expensive) design that uses a spiral cutter with only one cutting point. Finally, the H-F kockout punches are not really the right sizes needed for tube sockets anyway (conduit punches).

Don
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Old 21st July 2006, 05:34 PM   #4
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GREASE the threads before using ... even on a Greenlee. It'll reduce the torque required and maybe save the bolt a little longer. I've broiken a few Greenlee bolts too...

With the cheap ones, I wouldn't even TRY punching steel - only aluminum.
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Old 21st July 2006, 05:36 PM   #5
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Default Greenlee punches

I've got Greenlee punches my dad got for me when I was a ham in the 1960s plus I've bought used Greenlee punches at swap meets that look like they came from the 1930s. They all work great, and I never have had to sharpen them. I do occasionally put new grease on the threads and bearing surfaces. I mostly punch aluminum, but have used them on soft steel, too.

A friend turned me on to something new, which works much better than punches: the "Rotabroach". This is a drill-type tool with changeable cutters than comes in sizes from 5/16" to 3/4". My friend got it from Sanp-On, but they should be available other places, too. They make very smooth holes quite easily. I still use the Greenlee punches for the larger sizes.

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Old 21st July 2006, 07:52 PM   #6
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Rotabroach?
I assume you mean these things:
http://www.rotabroach.co.uk/cutters/opening.htm

They do look nice. But they are even more expensive than the outrageous Greenlee prices.
Also it appears that they do not have 3 flats on the shank for a standard drill press chuck (I see a set screw type flat in their picture, may only fit their own special drill presses). And it will take a strong drill press to drive them for the bigger diameters (up to 60 mm, 16 cutting edges).

For up to 3/4 inch I would suggest using stepped drill bits. Some cheap titanium coated ones here:

http://www.northerntool.com/webapp/w...3494_200313494

H-F sells them even cheaper, I haven't tried theirs yet, (plastic?)

Don
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