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Greenlee punch set ~ Tool / tip of the week

Started by Brian Mc Cullough - BMC British Automobile, July 10, 2009, 01:45 AM

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Brian Mc Cullough - BMC British Automobile

Following others on the "tip of the week".

Put down the disposable hole saw manufactured for a one or at best two times through sheet metal. We purchased a set of Greenlee 7238SB Slug Buster knockout punch set with 6 different hole sizes.

These are useful for two types of shops:

1- original. If your replacing a panel that does not come with a hole that should be there, you can get it very close and grind the last out with less time than using that silly one time hole gnawing thing that was manufactured for wood.

2- modified. We use these to pull wiring through places that were never there but should have been. When rewiring for fuel injection or something radical, we cut holes with these in 15% of the time it took before. The mess is 10% of what it was and the holes are Spot On!!!

Original use: Conduit.
Problem? Conduit sizes are kind of like NPT. It measures the inner hole, NOT the hole size cut. That said, some of the standard size rubber grommets can be found to fill. For instance- MGB firewall wiring plugs or best- MGB gearbox fill plugs (in body behind radio council) are teh perfect fit for one of the larger sizes and allow you to pull a large plug through a hole such as a computer harness plug which we do often. "It even looks professional"

Actual hole cut sizes according to my measurements:

One of my guys kept twisting my arm until we purchased one off evilbay. Instead of $350 new, a used set was less than $120 shipped. Best money I have spent this year on a tool! Worth the $350 but I'm cheap. Already used on 1 project 5 times. Hmm. Didn't use 3 size hole saws up. Didn't leave those horrible metal shavings. As they say- No brainer.

The other guys have used the set for a number of projects around the shop as well. If you have to rebuild or fabricate anything in your shop, you need these.

Worried about warpage? I have no or little warpage. I worry more about warpage and run out on hole saws!

If you want a demonstration of what a Greenlee does, check this video out and fast forward it to 3.30:
(from 3.30 to 6.00 for them to drill/punch)

Restoration, Modification, Driveline Conversions and parts for British cars https://bmcautos.com

Carl Heideman - Eclectic Motorworks

I've had a Greenlee set for years and agree with everything Brian has said.

I've also got a Rotobroach set and it's very useful for putting smaller holes in sheetmetal.  Rotobroaches are sort of like low-end end mills that you can run in a drill.  The company has been sold several times and the most common manufacturer name I've seen is Blair, but the tools are usually called Rotobroaches.  In the past few years, they've also been marketed in smaller sets as spot-weld drills (we use the 5/16" size for spot weld drilling).  My set goes from 1/4" to 3/4" in 1/16" increments--costs about $80 and replacement bits are about $5.


Brian Mc Cullough - BMC British Automobile


I will have to try the Rotobroach set out for the smaller holes. I did have one size of the 'spot weld drills' but they were horrible for actually drilling spot welds out. If they are one in the same then i will try them for punching holes. I suspect they are different from the units we currently have in the tool collection.

Restoration, Modification, Driveline Conversions and parts for British cars https://bmcautos.com

Jim Allen - Southside British Cars

There is no "reasonable" substitute for any Greenlee tool set!  I've used them for years and always get a clean, ready to use hole, right where you want it.  And because they are designed for the professional (electrical) contractor, for punching holes in commercial switching panels they last forever and replacement parts are easy to get from large electrical jobbers and wholesalers. I haven't looked at their catalog in some time but they have a broad selection of punch tool types and other products, which have cross-over applications.   

Jim A.

Carl Heideman - Eclectic Motorworks


It looks to me like the tool they sell as a spot weld cutter is the same one as the one from their set.  I've used and own every spot weld cutter in the world including the big-bucks Snap-on with the $30 bits and I've found that the Rotobroach is the fastest and the most effective for the money.  There are similar knock-offs on the market, notably like the ones Eastwood sells, that don't work at all.

I've found the Rotabroach work best if you drill a 1/8" pilot hole for the guide pin instead of just dimpling with a punch.  I always use two drills, one for the 1/8", one for the Rotobroach.  I also lube the bits as I'm going to keep the cutting fast and keep the bits sharp.  It's fast and does little damage.

As long as we're on the topic of drilling spot welds, I'll mention I rarely do it.  The only times I will is when I've got to save the panel.  If I don't have to save the panel (like when I'm doing MGB floors), I weaken the spot welds with a cutoff wheel, then chisel the panel off with an angled "panel splitter" air chisel bit.  Really fast and no tears like if you don't weaken the welds first.