Tapped Holes in Welded Tube Ends - BIG PROBLEM

Gents, thanks in advance for any experiences you can pass along, I have to believe someone has dealt with this before.

We have support legs that consist of a 3 X 3 x 1/4 wall square tube that is essentially capped both ends. The bottom cap has a 5/8-11 tapped hole for a leveler, and the sides of the tubes have some 1/4-20 tapped holes as well. Note in the pic attached there are two issues, the pierce I think is being done on the hole without a lead in, but maybe what I see in that pic is just the end of the cut, and not the pierce? Also the threads lok flat, not sharp.

After welding by our fabricator these are sent for powder coat where they are sand blasted and powder coated with plugs for the tapped holes. Our powder coater states the sand they use is meant to break down when pressed hard against steel, and that he has not had problems like this before unless it was due to poorly tapped holes to begin with.

The issue we are having is the levelers will lock up in the holes. We have tried a very thick black anti-seize but this seemed to make the problem worse. We thought the problem was trapped sand and or metal shavings from tapping getting on the threads. We added a cut across the corner of the 1/2 in thick bottom plate to allow this junk to get blown out prior to assembly, but our guy spent a half hour doing two legs to get the tubes sufficiently cleaned out that the leveler could be installed by hand. We think material will continue to come out of the tube as long as we feel like trying to get it out, basically there will always be some crap stuck inside there.

We recently shipped legs to a customer that we thought we did a decent job cleaning out (note these legs had bottom plates without the corner cut off so it was difficult to get crap to fall out)..and after installation and adjustment the levelers locked up. The levelers in question are nickel plated.

Any ideas or experience on this would be appreciated. I have a pile of parts at our fabricator awaiting welding until I can come up with answers.

Is it feasable to tap them after sand blasting and powder coating, rather than before or to use serial taps, with the last tap run down the hole after the finishing work?

How are you making the holes in the plate? Are they drilled? Or laser cut? Are you tapping the threads?

If you're having problems with the threads jamming I suspect that there is a problem with the size of the holes. If you
use the correct tap drill size and a sharp new tap then you shouldn't be having issues. I assume you're just using
ordinary bolts for the levelers.

As for the sand inside, I would do away with the corner notch and use a (sacrificial?) bolt in each tapped hole to keep
crud out. Powder coaters have a variety of plugs and tapes available to seal holes but we've always had the best luck
with bolts in threaded holes--pretty much goof proof.

Just had another thought. Are you perhaps getting small grapes in the threads from the welding operation? Anti-
spatter will help but a bolt threaded into the hole assures that your threads stay clean...

Are you saying your tapping plasma cut holes? If so, that's always a bad idea.

Flat threads can be from wrong size hole being tapped or someone using the wrong tap when cleaning the threads. I have never had a problem with sandblasting parts. I also use a nylon brush on a drill in the tapped holes prior to shipping.

I always drill and tap or weld nuts on plates for steel and stainless adjusters.

Sent from my 2PS64 using Tapatalk

Why not drill the 1/4" 20 holes after the powder coat? Weld a solid end on the leg (no notch on one corner) with a shallow counter sink in the threaded hole and send to the coater with a flat head screw installed to keep the crap out of the inside. Once back remove the screw, drill + tap the 1/4" 20 holes and be done.
I just had another thought; If that is mill scale coming loose on the inside there will still be problems. From what I've seen, that is like hardened steel grit that's probably tougher than sand. If that is the case you may need to find a way to get the insides blasted before any other operation begins.
Dan

The "Crap" you show looks like mill scale, not tapping entrails, nor welding scat.

Are you having you tubes pickled ?

Additional comment about the clipped corner on the end plate... Very bad idea. With the bottom end open, every time the table gets jarred or dropped, another pile of crap is going to leak out on the floor, carpet, whatever.

Have the tube pickled (acid bath) to remove the mill scale, should be able to be done before the end plates are welded on, which will ensure all moisture and crud is out..Investigate if there is an anti corrosion coating they can finish with (I assume these are used in a dry environment, so shouldn't take much) and welding the plates on from the outside shouldn't add any swarf to the interior.

Dennis

Lots of good comments above. We do in house sand blasting and powder coating for small parts but the shop we use for the bigger stuff uses an etch wash which seems to give really good adhesion. I've specified sand blast for an outdoor application but the wash approach seems perfectly fine for normal indoor use.

At any rate, I've sand blasted lots of parts like this, indeed several types of table leg extensions, and not had any problem with threads or sand build up. You should be able to blow any sand out if the inside of the tube is dry. We water jet and you can tap perfectly fine threads right off the hole. If plasma was causing problems, I would think to cut a smaller hole and drill out before tapping. But regardless, chasing with a decent (newish) tap should fix any thread problems even if the tap wears out fast on mysterious hard spots. You certainly can have problems with worn taps. I had such issues once threading the ends of 8020 with the usual 1/4-20 tap and getting leveling feet jammed and nearly torquing the threads off. A new tap fixed the problem instantly.

Modelman said:

Additional comment about the clipped corner on the end plate... Very bad idea. With the bottom end open, every time the table gets jarred or dropped, another pile of crap is going to leak out on the floor, carpet, whatever.

Have the tube pickled (acid bath) to remove the mill scale, should be able to be done before the end plates are welded on, which will ensure all moisture and crud is out..Investigate if there is an anti corrosion coating they can finish with (I assume these are used in a dry environment, so shouldn't take much) and welding the plates on from the outside shouldn't add any swarf to the interior.

Dennis

Click to expand...

I agree.

to that point, if a simple blob of can foam was injected into
the tube end, it would end all the customers complaints ?

The fabricator is coming in this morning to review. I believe the pilot holes are laser cut, then tapped prior to welding. We don't like to drill holes in our shop.

Thoughts on remarks above,thanks to all for your help so far, this site is fantastic.

My main items to check thus far:
1. tap size wrong/worn tap
2. is material pickled
3. check on anti-corrosion options form fabricator

from reading the description my guess is that the holes are plugged before paint/powder coat but not before the sandblasting. Blasting media goes everywhere!

jhansen750 said:

The fabricator is coming in this morning to review. I believe the pilot holes are laser cut, then tapped prior to welding. We don't like to drill holes in our shop.

Thoughts on remarks above,thanks to all for your help so far, this site is fantastic.

My main items to check thus far:
1. tap size wrong/worn tap
2. is material pickled
3. check on anti-corrosion options form fabricator

Click to expand...

No, #1 is tap hole size wrong, if the tap hole is too large, you get interior threads with too large a minor diamter (i.e. "flat")

Why is the tapped holes on the tubing being done in a laser ?

digger doug said:

Why is the tapped holes on the tubing being done in a laser ?

Click to expand...

The pilot holes for the tapped holes in the tube MAY be done in the laser, not sure. However the hole we are fighting with sticking is the large hole in the plate that is welded to the bottom of the tube. This large hole is laser cut in the small square plate and then tapped. The plate is then welded to the bottom of the tube.

Rewt said:

No, #1 is tap hole size wrong, if the tap hole is too large, you get interior threads with too large a minor diamter (i.e. "flat")

Click to expand...

I think the laser hole size is too large. The fabricator is laser cutting this to the dxf which uses the standard drill size, but I suspect when lasering the quality of the cut and the width of the cut varies enough to cause issues.

jhansen750 said:

The pilot holes for the tapped holes in the tube MAY be done in the laser, not sure. However the hole we are fighting with sticking is the large hole in the plate that is welded to the bottom of the tube. This large hole is laser cut in the small square plate and then tapped. The plate is then welded to the bottom of the tube.

Click to expand...

O.k. so why are any holes being done with a laser, then tapped ?

digger doug said:

O.k. so why are any holes being done with a laser, then tapped ?

Click to expand...

...uh cost savings most likely...

jhansen750 said:

...uh cost savings most likely...

Click to expand...

Look smartass.....If you don't take the time to explain all your process, and why you are doing it this way, I can't take the time
(free time that is) to fix your problem.

GIGO

Wasn't intending to be rude, I am just a little embarrassed that our parts were being made that way.

I never like the idea of tapping lasered holes ,the material gets hardened and the hole is not a perfect circle ,I bet this is the root of the problem.