I was reading the thread on panel preferences, and thinking about the comments about preferring a blank end panel, because the KOs are often the wrong size, in the wrong place.

It sounds like some folks just punch new holes in the pre-punch boxes, right though the existing KOs. Or I may have misinterpreted, and they're carefully placing the punch to cut virgin metal.

So, I'm wondering what it is people are really doing. Can you actually make a new opening that, say, takes out a third of a non-punched-out KO?

[This message has been edited by SolarPowered (edited 03-15-2006).]

The difficulty with doing that is more with drilling the pilot hole for the KO than actually punching it. They always seem to end up right in the ring of a concentric KO. If you get past that part, the rest is easy

When to KO's don't match the conduits that may already be in a wall, I often do this... Jamb the panel in the wall where it will be, find all the hole that can be used, or manipulated to be used, and then.... Very carefully holesaw the pilot for the KO punch, and try to position it so you can cover 2-3 of the offending prepunched KO's as much as possible. Then punch it, hoping that not too much of the un-needed KO came out around the hole you really need, if so reducing washers, and ground bushings. Big PITA!

Rather have a solid panel to work with and just use carbide hole cutters....

[This message has been edited by e57 (edited 03-15-2006).]

I have had reasonable luck using the Greenlee "High Speed Cutters." In technical terms, these are "rotary broaches," rather than hole saws.

Nevertheless, in replacing some panels I have had to resort to removing the bottom of the old panel and attaching it to the new panel. Or, when I simply need to place a small hole where there is a big knock out, I will make the "small hole" in a blank 4-sq cover, and attach that over the large knockout.
In either situation, pop rivets are my fasteners of choice.


By now, I sometimes feel that, if you're not fully equipped to make holes for pipe in a variety of materials- maybe you shouldn't be working on panels! A pox on panle knock-outs!

" if you're not fully equipped to make holes for pipe in a variety of materials- maybe you shouldn't be working on panels! "

My sentiments exactly - obviously not enough room to slam the trunk closed... A 1/2" -1 1/4 KO set (At least) is a standard issue item for anyone who takes themselves seriously.

Has anyone else used these hole cutters ?
Don

Don, those are the type I was talking about. Cut metal real good, little burr.
Very important to keep RPMs low, and use cutting lube.
Also important to wear glasses...big sharp chips...and the chips are hot!

I have gone through a few different brands of them in 7/8", one in particular has a spring on the pilot that keeps the cutter from crashing into the surface, (and knocking off the teeth) which does really seem to prolong life...

Speaking of which, 'long life', I usually use them at high speed and lubed which gets me through 200-300 holes on a single sitting with the average un-caring underling assigned the task. (Except for the one with the spring, still going on over 800 holes...) Should they be at low speed?

FYI I seem to buy one every sizable job... And give away the nearly toothless item when it's over. (Except the one with the spring...)

John,
I tried the Greelee version and their is no comparison. They just don't do the job or last near as long as the Blair cutters.
Don

Suggested speeds.

In response to the cutters, I used the Greenlee and really liked the clean holes they cut...however I have several in different sizes that have bad tips (broken by the "careless underlings" who try to force or twist the cutters. I have tried finding someone who can re-tip these cutters since they have carbide brazed on them. I haven't found anyone who can do it yet. Generally the problem is that these are in a radial configuration unlike a carbide saw blade. I guess it is too difficult to do this properly without charging an arm and a leg. Didn't know about these others...what is the cost for these...say a set for 1/2 - 1 1/4"????

Have you guys tried using a washer, like a 3/16 fender, on top of a panel to keep the tool from crashing into the work and preventing tooth removal? Works well and extends tool life a lot.

Best hole saw tip I ever got from an old timer: take the hole saw off the mandrel, drill the pilot hole, put the hole saw back on and saw the hole.
Stops snapped bits, busted teeth (saws and yours) and broken wrists.

Second best hole saw tip from an old timer: Take the pilot bit out of the mandrel, cut a #2 phillips screwdriver shaft (they are usually 1/4 inch make sure first), set screw that into the mandrel. Drill the hole with with the pilot bit in the drill, switch out for the hole saw with screwdriver bit.
Stops broken or bent pilot bits. Tempered steel and its smooth.

Third best hole saw tip from an old timer: When drilling into a live panel or even a dead panel with wires, wrap electric tape about a half inch from the saw teeth. It needs to be thick.
Stops from punching all the way thru the panel and maybe cutting something important.

I should mention one little detail, I hate hole saws. They make ragged sharp holes, they bind and twist, they throw shavings all over the place and they are next to impossible to center. When I started in the trade I worked for a rather cheap contractor who would not buy KO sets, hole saws only. Got laid off and got a job with a contractor that had varibits and KO sets, what a difference. That became my preferred method, but hole saws have a place and I have a kit on the truck.

As for the OP, I do commerical work and prefer panels with blank ends so I can cut my own KOs. It takes no more time to cut the KOs to line up with the pipe then it does to bend the pipes to fit the factory KOs which are NEVER cut at standard unistrut sizes off the wall for some reason. I have cut holes in prepunched panels to line up, just make sure to invest in some chinese money first, aka reducing washers.

One last tip, this is from me: if you are cutting a lot of holes in plaster or tile or cement backer board, get a carbine grit hole saw. Goes through easy and makes a clean hole. They have no teeth but rather look like they are dipped in carbine grit.

drillman,
The Blair bits make a hole as clean as a knock out punch. We don't use punches for 1" and smaller conduit. The hole saw is much faster.
You are correct that you have to watch out for the chips, but other than than I have no issue with them. However if you are talking about some of the other types of hole saws, I would fully agree with your comments.
Don

The problem with cutting into panels with a standard hole saw is that they will drop through into the panel if you don't ease up on the pressure at the end of the cut. A hole cutter (any of the major brands ) have a shoulder that prevents this from happening. As for breaking teeth and pilots, that's what the washer is for. You drill the pilot thru the washer hole and when it drops through the cutter lands on the washer which spins and doesn't grab. Remove the washer and finish the hole. Much faster than all that mandrel and pilot bit swapping.

The one with the spring...LENOX
The best hole cutter yet.
Clean fast holes.
Slug comes out on its own. The spring.
I have used my 3/4 (1-1/8") cutter for hundreds of holes.
These things are the best.

It looks like this thread has pretty well wound down, so I'd like to say "Thanks!" for all the good information here. I'm often amazed at how much one can learn from everyone on this forum.

WhiteRook, regarding your question about how much the hole cutters cost, I saw a 1/2"-2" set of the Blair cutters online for $160 at www.autotoolmart.com . Search for "Holcutters" (with no "e").

Edited to add URL


[This message has been edited by SolarPowered (edited 03-25-2006).]

I have seen guys setting a trough right on top of the old panel. Now you have virgin metal over the whole top of the panel...no need to worry about being half in half out of any open knockouts in the panel, and you can make holes exactly where you need them in the top of the trough for the pipes.