Plugging large holes in 1in plate

[Asm109]

As a caveat we never admitted to making mistakes. If a component needed to be moved it was because it was called out wrong on the print, not because the print was read wrong. That's my story and I'm sticking with it.

A toolmaker once asked me: What is the difference between a machinist and an engineer?
Answer: When a machinist makes a mistake its called a f'up. When the engineer does same, its a design revision

 

[projectnut]

The nice thing about a machinists f’up is that if it gets corrected before the boss sees it, it never happened.

 

[jmarkwolf]

OP here:

I mis-poke, my apologies. The existing holes aren't 0.375in diameter. Two are 0.485in and two are 0.520in. So the plot sickens. Now I'm not sure how I should proceed.

Yes, I do not have a welder.

The only welder I know charges $85 to flip the switch on his welder.

After plugging the big holes I will be drilling new smaller holes on a grid that may overlap the edges of the old larger holes, so I think adhesive (either JB Weld or LocTite) along the entire length of the threaded plug would be more solid vs welding at both ends.

I have a Procunier tapping head to help tapping the holes once I determine which size holes to tap.

 

[piper184]

Old joke.
"machinist....making engineers look good for generations"

Machinist to engineer during an argument: "I know I can do your job, the question is, can you do mine?"

Just jokes guys, no offense meant to anyone. Besides as hobbyist, we often are both.

 

[Jake M]

I have an 8in x 8in x 1in steel plate I want to use for a project. It already has four 0.375in holes I want to plug, to make the plate "contiguous".

I'm thinking of drilling and tapping the four holes to 1/2-13 (0.4219in tap drill), then "slathering" JB Weld on bolts (or studs) spin them into the holes, sticking out a little proud on each side, then once the JB Weld cures, milling or fly-cutting down the surface of the plate.

That's the hard way... That's very doable, but it's an inch of threading with a lot of "diameters" engaged, you'll need a dead straight start and some elbow grease, and you'll want to be generally on your A game. It'd work for sure though. I'd prefer to use a locking compound over JB weld for something like that. In either case the end use must be considered.

Same threading idea, but different (and way easier). Drill from both sides and tap each side for an quarter inch NPT plug. Way less effort due to the shorter tapping distance, and WAY less risk due to a much "beefier" tap with much less engagement. (Make sure to leave it tight enough to leave a thread or two of the plugs showing after it's tight... Oil the threads of those plugs, thread one in. Yarn it right down until the square head rounds over. You're gonna mill it flat anyhow. Plenty tight. All you can give it. Turn over and repeat. Depending on how you're gonna use this- It's clearly not this, but brass plugs made flush are kinda reminiscent of an old timey braised repair. If that doesn't entertain you (and fair enough, it's a pretty visible detail), cast or steel plugs are quite stout, and "almost' go away when you make them flush.

Or depending on what you're doing, ream the holes (or drill and ream) for a heavy press fit to a standard pin, and rail a pin in there.

Or, if you have welding equipment and you're not afraid to use it... With holes that small? Don't weld in plugs, drill the whole dang thing out to a half inch so you can get in there, or if you don't need "solid", just burn some weld right in the top of each hole and dress it up.

 

[SLK001]

Try using a force fit. Machine studs 2-4 thousands oversize about 1.5" long, then press them into the holes. Machine off excess.

 

[piper184]

A good welder is easily worth that $85 startup fee as long as you are willing to pay for his skills.
With that said, a few jobs at $85 for us hobby users will go a long way towards getting your own welder and learning how to use it. A welder was one of the first tools I got after an air compressor. Both have been upgraded in the last 40+ years, but I have never regretted a dime spent on welding stuff. Even though I got priced out of the rental/refill oxy/acc market, my torches and equipment still have value. A plasma cutter replaced 99% of my needs for oxy/acc. If I used it more (or was abundantly wealthy) I would keep the tanks rented and full.

We don't know your situation but what you are needing done is something I wouldn't hesitate to do with my meager welders and skill level. Something you might want to consider. Filling in those holes could be your inaugural project and open up a whole new world for your future projects.

I understand the need to move a hole, having done so several times. The treading a bolt in and milling flush is a workable solution but will not be as invisible as pressing a pin as the threads will have voids visible depending on where the milling falls against the turn of the thread. If appearance is not that important it should be plenty strong for your needs.

The tapered NPT pipe plug idea is a good one as the threads will deform at full torque and help hide them in the final product.

Best of luck in what ever you decide to do.

 

[mattthemuppet2]

If you lot are worried about taking 1/2-13 in steel the very last thing you would want to consider is an npt thread. I’d rather punch myself in the nuts all day and all night than tap 1/4” NPT threads in steel.

To the OP, make some plugs a thou or two under size and to the correct length. Slather them with the 24h jb weld and push them in. Trim off excess. Jb weld as a glue sucks, but when you have a large surface area to diameter like this, it’s perfect. Drilling and tapping into the edge of a plug isn’t going to move it. I’ve done it myself multiple times.

 

[Eddyde]

The existing holes aren't 0.375in diameter. Two are 0.485in and two are 0.520in.

Obviously too big for ½" but you could do 9/16-12. Both hole sizes should work, the .485 holes just one thou over for 75% thread and the .520 holes being just over the range of 50% threads by.004" being you plan to fill with JB weld anyway the oversize shouldn't matter.

After plugging the big holes I will be drilling new smaller holes on a grid that may overlap the edges of the old larger holes, so I think adhesive (either JB Weld or LocTite) along the entire length of the threaded plug would be more solid vs welding at both ends.

I disagree that adhesive would be stronger than welds, even if only at the ends. However it probably wouldn't matter, unless the new hole considerably overlaps the plugged one, leaving say a partial, crescent sliver of the plug, I could see that loosening if there were repeated cycles of bolting into that hole.

 

[Eddyde]

If you lot are worried about taking 1/2-13 in steel the very last thing you would want to consider is an npt thread. I’d rather punch myself in the nuts all day and all night than tap 1/4” NPT threads in steel.

Yeah, that would be tough especially, in a straight hole. to properly thread NPT, you need to use a taper-ream first then tap. You may get away without the taper in softer metals but steel, I doubt it.