Question for machinist

[Dagny]

I keep all my knock out punches in a klien bag in the service van and needed a 3/4 hole today but must have gave my newest one away so tried to use the backup but the threads are not quite right .

I have several draw studs which are really just a 3/4 16 bolt but a very high quality bolt.

All the other punches thread right on but the 3/4 binds about 2/3 rd of the way on most of the bolts and almost all the way on on the oldest bolt.

Think it would pay to buy a tap and run it through there or get some lapping compound and run it in and out.

All the parts seem to be very hard steel. Greenlee made them when I was young.

 

[signcrafter]

I keep all my knock out punches in a klien bag in the service van and needed a 3/4 hole today but must have gave my newest one away so tried to use the backup but the threads are not quite right .

I have several draw studs which are really just a 3/4 16 bolt but a very high quality bolt.

All the other punches thread right on but the 3/4 binds about 2/3 rd of the way on most of the bolts and almost all the way on on the oldest bolt.

Think it would pay to buy a tap and run it through there or get some lapping compound and run it in and out.

All the parts seem to be very hard steel. Greenlee made them when I was young.

Guess it depends on how bad the threads are damaged, doesn't sound like they are too bad if it threads 2/3 of the way on. Also the condition of the knockout would play into my decision. Amazon has a new greenlee 3/4" knockout for just under 50 bucks. A century 3/4x16 tap is about 12 bucks. If the knockout is in good shape besides the threads I would order a tap and fix it and then you have the tap to fix any in the future. I didn't see a 3/4x16 thread chaser but I didn't look real hard. The threads are already cut, just got messed up and need to be reshaped. If the knockout is older or worn I might look into just getting a new one.

 

[whateg01]

Are you sure the one isn't M19-1.5? I would think the punches would be hard, so I wouldn't expect a tap to cut them. Can you file the threads with a small file? Or does a file skate over them?

 

[Dagny]

they are inside

 

[Firebrick43]

I always had luck with 5 micron diamond paste. Apply very little on the threads and screw it in until it almost binds and loosen, and repeat. Every time it will advance slightly, apply another small dab after 30 times or so, then afterwards clean very well

 

[signcrafter]

they are inside

I picked one of these up a few years ago at napa and have used it a few times. Might be an option for you.

https://www.amazon.com/Rotary-Thread-RTK1-1-Starter-Restore/dp/B085LRZZPS/?tag=atomicindus08-20

 

[whateg01]

they are inside

That's why I suggested a small file

 

[JABgj]

Could the stud be stretched from use making it bind up?

 

[Dagny]

The other punches use the same bolt and 3/4 doesn't load the bolt much.

 

[RoninB4]

Think it would pay to buy a tap and run it through there or get some lapping compound and run it in and out.

All the parts seem to be very hard steel. Greenlee made them when I was young.

-The following is JMO as a lifelong toolmaker accustomed to working with, and making, hardened steel components. Just the fact that Greenlee made this leads me to believe that good quality high carbon steel was used, which steel cannot be determined. The relative hardness of this component also cannot be determined. Was it case hardened or through hardened and to what Rc hardness? What can probably be guessed at is that buying/using a new tap in it will dull the tap cutting edges and maybe even not even make it all the way through the punch if it's hardened enough. A quick search shows that a 19mm is very uncommon and doubtful that Greenlee made one if it's as old as you indicate. Sounds like there's only a few .001's in thread form causing the fitment trouble and that happens with hardened steel sometimes. Some steels and/or the hardening process will either close up the thread pitch/form or will fuse some debris to the steel itself. What is SOP in most shops is to either use an oversize tap before hardening or use lapping compound after hardening to make threaded holes useable. Sometimes both were needed. Since your component is already hardened I'd suggest using some common lapping compound and some hardware store threaded rod so you don't abrade your existing draw studs any further.

-There's several types of lapping compounds available, some are more expensive and singular purposed than others. I don't see the need for using anything other than a very small, inexpensive tin of silicone carbide grease (Clover) that's available everywhere. Lower cost but also more of a mess than other lapping compounds. Would suggest a "medium-to-coarse" grit since you're not attempting a precision fitment, you just need the thread form corrected. You'll put a small dab on the punch trouble zone and run the rod in/out a few times. If you put too much on you'll have trouble getting the threaded rod started or it will abrade areas that don't need it so use some discretion about the quantity you'll use. It doesn't take much to be effective. The troublesome part of this is the abrasive particles tend to embed themselves in whatever is softer material and cleaning it all out of the punch will require some scrubbing with a brass brush and solvent to clean off the internal threads for test fitment to your existing draw studs. If the compound isn't fully cleaned off the punch it will begin to abrade your draw studs. You'll feel the grittiness as a sign that further cleaning is required. It will take a couple of tries (or maybe just once) to allow full threading on the existing draw rod. Thoroughly clean the punch and put a few drops of oil in the threads to finish.

-That container of Clover will last until your children inherit it so make it a very small tin. Or you can buy a 3/4-16 tap and proceed to ruin it for anything it's supposed to be for. Weigh the time/cost equation for what suits you. Report back if you have further problems with this. Good luck

 

[rlitman]

...Since your component is already hardened I'd suggest using some common lapping compound and some hardware store threaded rod so you don't abrade your existing draw studs any further.
... You'll put a small dab on the punch trouble zone and run the rod in/out a few times. If you put too much on you'll have trouble getting the threaded rod started...

You're always here with the best answers. Using a sacrificial threaded rod could be genius. It's a cheap source of a soft and more importantly undersized thread, so I'm confident that a threaded rod will fit loosely where the Greenlee draw stud may not, and saving the stud from the abrasive is an important point.

But I've never seen UNF threaded rod, and also, threaded rod is rolled, which may not interfere in the right places to get the job done with the minimum amount of work. Also, the cheapest chinesium taps I'm seeing on Amazon is $12. That's probably right around the cost of the threaded rod, and would work just as well as a lap, if you can anneal it.

If this were my project, I'd buy a 3/4"-16 brass inverted flare plug, grab the hex head in the side of my vise and hacksaw it off, and then I'd think about how I could stick something in the bore that I can chuck in a drill and turn it into a large metalworking q-tip. I'd probably jam a hex key shank in it, or maybe tap it for whatever all-thread is sitting in the scrap bin and stick that in there with some red loctite. Eureka! A straight flute screw extractor.