greenlee 13/16" knockout punch problems

np3 · Joined: 18 Feb 2012 Posts: 1

I used a 13/16" knockout punch to cut a hole in a stainless 1/2 barrel keg to install a weldless thermometer. Drilling the pilot hole was a pain, but cutting with the knockout punch was surprisingly easy. The problem I ran in to is that the ss slug the punch cut out got stuck around the threaded rod inside the base of the punch. It looks like as the slug was being punched out, it got bent so that it scraped along the threads. Unfortunately this did quite a bit of damage to the threads, and made the slug really difficult to get off the punch, so the punch is not usable anymore (after one use!), unless I find a die to straighten the thread out. Even so, this seems like it should not happen. Has anyone run in to this problem before? Found a solution? The only thing I can think of is making a pilot hole bigger than 3/8" next time so when the slug gets bent it doesn't ruin the threads. Any advice would be great, thanks.

Castermmt · Posted: Sat Feb 18, 2012 1:23 pm Post subject:

I think you answered your own question by drilling the pilot hole a little bigger. I never had a problem with my knock outs.

stickyfinger · Joined: 04 May 2014 Posts: 176 Location: hudson valley, NY

I was just going to ask if I REALLY need to drill a 1/2" pilot hole in order to use the 1-1/4" punch and the 13/16" punch. It seems so large and then it won't be possible to get the hole exactly where I want it. I guess you just have to suck it up not being able to get the hole exactly where you want it with such a large pilot hole compared with the shaft size of the punch? I certainly don't want to F-up the threads on my pricey new punches!! Guess I'll have to head to HD to get a 1/2" cobalt bit!

Aaron

Castermmt · Posted: Sat Jan 24, 2015 1:57 pm Post subject:

You only need to drill a pilot hole slightly larger then the bolt being used. It's pretty hard to screw up the threads. I used my step bit for the 1-1/4 holes. As for getting it where you want it, I used a center punch to create a small dimple to hold the bit centered. Hope this helps, Castermmt

barryhannah · Posted: Sat Jan 24, 2015 8:50 pm Post subject:

You have to drill the pilot hole the correct size or you can't locate the punch properly.
The slug always bends, that's how the punch cuts. It always gets stuck on the bolt, often within the cup of the punch. To remove, unwind the bolt, take off the cutting head and wind the bolt up through the bottom of the punch cup. Push it out, then unwind the slug off the bolt thread.
I'm very surprised the threads were that damaged, it's machine hardened steel. If it's hard enough to cut the material it should be hard enough to not get wrecked by it.
Getting the slug out can be a pain but take your time.

stickyfinger · Joined: 04 May 2014 Posts: 176 Location: hudson valley, NY

I guess I'll try a practice punch in some metal I have lying around or get some scrap. I have several cobalt bits, and I can try using my 1/2" titanium bit to make the final hole before using the punches. Hopefully I can use my drill press for several of the holes. It's kind of akward positioning the kettle on it though! It should work fine for the holes that are near the top and bottom of the pots at least.

barryhannah · Posted: Sun Jan 25, 2015 7:57 pm Post subject:

Dude you can't drill a 1/2" hole as your pilot if the punch bolt is significantly smaller than that. The punch won't work, it may move position as you tighten the punch and make an oval hole or worse tear and leave a complete mess.
Drill your hole just big enough for the bolt and use the punch as it was designed to be used. Then deal with the fact it's sometimes challenging to get the slug out after each hole.

stickyfinger · Joined: 04 May 2014 Posts: 176 Location: hudson valley, NY

That's what i thought, but the manual specifie
A 1/2 inch pilot hole, unless i'm misinterpreting.

stickyfinger · Joined: 04 May 2014 Posts: 176 Location: hudson valley, NY

barryhannah · Posted: Tue Jan 27, 2015 12:26 am Post subject:

Fair enough if that's what the manufacturer states. The bolt mustn't be significantly smaller in that case.
All I was saying is the pilot hole shouldn't be significantly bigger than the bolt.

Kevin59 · Posted: Tue Jan 27, 2015 4:52 pm Post subject:

stickyfinger · Joined: 04 May 2014 Posts: 176 Location: hudson valley, NY

OK, guys, thanks for the feedback. I just got scared by the OP's first post about ruining his punch. I thought 1/2" pilot hole sounded kind of crazy. I'll see what I come up with. Maybe I'll try a 1/2" hole in some sheet metal for practice and see how it goes. Thanks for the input!

stickyfinger · Joined: 04 May 2014 Posts: 176 Location: hudson valley, NY

OK, I finally cut all but one of my holes in my pots this weekend and during the snow storm. My observations are the following:

1) Using my drill press for all of the holes made it super easy to get the pilot holes going. If you don't have a drill press, buy one on craigslist or something. you will love it. I just had to put a 2x4 into the pot for the holes near the top of the pot lip so the pot didn't bend when trying to drill the holes.

2) I drilled around 1/8" or a little less hole first and then went up a little bigger and finally to 3/8", which worked perfectly with cobalt bits and cutting oil.

3) I tried doing 1/2" pilot holes with my titanium dewalt bits, and they don't work well at all. they won't go through all of the way and jam up. I had to dremel out the hole to get it big enough to do the punches, or you could just use a smaller hole punch first.

4) I tried using my Greenlee 1-1/4" and 13/16" punches with a 3/8" hole (slightly enlarged with a dremel) and found that i messed up the threads a little bit so don't do that. They recommend a minimum 1/2" pilot hole, and that is what works best.

5) I tried using my 9/16" hole punch in the 3/8" pilot hole and it worked perfectly. They recommend a minimum 3/8" pilot hole for that punch. If you then use your larger hole punches in the hole produced by the 9/16" hole punch, you will have effortless holes.

6) If you use a step bit, you will probably be able to position the holes exactly where you want. using a drill press and separate drill bits, I wasn't able to get the holes perfect, but they are perfectly adequate.

7) You might not be able to get the holes perfectly aligned using the 9/16" hole punch first, but you will not screw up your hole punches at all. If you draw a big cross before drilling your holes you can use that to align the hole punches from the outside when you make the holes and get closer to perfect (when you have a larger pilot hole.)

It was overall a lot easier than I thought. The hardest part was cleaning out all of the cutting oil and metal chips from the pots after the cutting. I took a couple showers with my pots to do that, oh la la.

marsch77 · Joined: 06 Feb 2015 Posts: 8

I've seen a lot of people talking about using the Greenlee punches here. Would using a step bit to drill to one step to what's needed and then running it on the inside for the last step to debur work? Just for reference this is the kind of thing I'm asking about.

http://www.amazon.com/s/?_encoding=UTF8&camp=1789&creative=390957&linkCode=ur2&rh=n%3A256287011%2Cp_n_feature_seven_browse-bin%3A5485702011&tag=theelectricbrewery-20&linkId=YWNT2N6G74J36O3B

Just wondering if it's worth spending over $100 when I can get the step bits I need for less than $100.

foomench · Posted: Sat Feb 07, 2015 12:16 am Post subject:

I used step bits in keggles, which are thicker than Blichmann and many other pots. They worked for me, but there is some concern about a step bit deforming a thinner pot.

stickyfinger · Joined: 04 May 2014 Posts: 176 Location: hudson valley, NY

**kal** · Posted: Sat Feb 07, 2015 3:13 pm Post subject:

stickyfinger · Joined: 04 May 2014 Posts: 176 Location: hudson valley, NY

If you are very limited for cash, you might be able to get by with the step bit. However, I think it was worth the price of at least one of the punches just to see what they can do in action. As you turn the hex head from the outside, with very little effort whatsoever, you look on the inside and see the head just slicing through the stainless pot like it is made out of cardboard or something until it pops out and a perfect hole is left in its wake. It is an incredible sight to see, very nice engineering and very simple in design. I plan to use my 9/16" punch anytime I need a 1/2" hole in any kind of metal in the future. I'll probably keep the 13/16" so that I can install a ball valve into any new piece of brewing equipment I dream up. the 1-1/4" is probably the most frivolous investment, as you only need it for 2 holes in the pots, but you can probably sell that pretty easily to another homebrewer.

marsch77 · Joined: 06 Feb 2015 Posts: 8

Yeah, I would love to buy some of the Greenlee punches but I just can't justify the expense when something cheaper will do the job. With that said I'd feel far safer deliberately putting a hole in my pot using the Greenlee punches though.

Thanks for the example Kal, I'll probably end up using that when I can afford all the pieces to get pieces I need for my 20 gallon pot.