Best way to tap thick Cast iron.

A

Armor

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Well seems that we have to drill and tap about 5 ,2 speed gears boxes as a Customer wants some more places to add sensors and drains.

Had one guy drill and tap and broke the tap in the hole.

That got fixed.

But are being a real problem to drill and tap a large size plus 3/4 inch any hints.

All done with hand cordless drills.

Boxes are all put together, so have to watch the internal chip problem .

Thanks.

All Fuller 2 speed gear boxes.

Jeff
 
Jeff,

Sorry I can't help. Mind if I watch and learn. I had trouble with drilling and tapping a 1/4-20 blind hole in cast iron. The guys will jump in with help here soon. The did with I asked for help.

Benny
 
Armor said:
Well seems that we have to drill and tap about 5 ,2 speed gears boxes as a Customer wants some more places to add sensors and drains.

Had one guy drill and tap and broke the tap in the hole.

That got fixed.

But are being a real problem to drill and tap a large size plus 3/4 inch any hints.

All done with hand cordless drills.

Boxes are all put together, so have to watch the internal chip problem .

Thanks.

All Fuller 2 speed gear boxes.

Jeff
Click to expand...

Tapping by hand might reduce the risk of tap breakage. Also, how about taping a piece of 1/2" tube into the end of the ShopVac hose to concentrate the suction and allow it to be accurately positioned to catch the chips from the drilling and tapping?


M
 
I advise tapping by hand. First,drill holes that will allow 75% of the thread to remain after tapping. Drilling a VERY small amount too small in diameter will certainly invite breakage of the tap. Drill and tap cast iron dry.
 
I've done 1/4-20 and 10mm holes in cast iron using a small cordless drill, and things went great. Typically it's smaller size taps that you end up breaking.

I am kind of wondering how much force it takes to snap a 3/4" tap. Typically when I have broken taps it has been from lateral forces, not torsion. How the heck are you generating those forces, are you using a hammer drill? If that is the case, maybe just go by hand? If you get it started, it shouldn't be too bad if you throw a decent sized tap wrench on there.

Another thing to try is maybe increasing the pilot drill size and shoot for something less than 75 thread engagement.
 
Jeff,
are the boxes also filled with oil? As you are putting quite large holes in, you are going to get swarf inside. going to need an oil change afterwards.
How are you sure that where you are putting the holes will miss everything inside? Are they being tapped to tapered threads? You want to make sure that you have enough meat in the casing for a good seal. If they are being sealed on a flat face with a washer, how can you be sure that you have drilled and tapped the hole square?
Also warranty issues. What if you miss some swarf and it damages a bearing surface? If this is a customer request I would be recommending that he paid for a breakdown of the box to do the job properly, or signed a waiver.
Failing all that, maybe hook up a compressor so the box is positive. That may help to blow swarf out as you break through. Also if you use a tacky grease for tapping that may hold the swarf together so you can pick it out with tweezers. But on the other hand any that does dissappear in the hole wont want to come out easy either....
I think he, and you, are asking for trouble.

Cheers Phil
 
Tackle it in two stages. Truncate a taper or plug tap to about 60%, then run a full tap in behind it. Guaranteed. It cuts the forces required dramatically.
 
Thanks all , good answers and all done by hand as they won't but a large size T handle and don't think they make one for a 3/4 plug anyway.

It is two plugs really and bummer, using a heavy grease but as the Shop Assembly guy said do it , his butt on the line.

I do like Tony's idea two tries.

I think the biggest deal is the wrong size Drill, we go through about $3000.00 a month in drills all top quality but drilling stainless and well a bunch of holes they don't last.

Thanks will try some and see.

And yes gear box full of Oil as on the Trailer already.

Thanks

But good thing now down to 3 left to do.
:phew:

Jeff
 
Having a problem as why you are having this problem. I have done many many, from gear cases to
adding ports in block water jackets. As already said, but one more step, we do is to get a bushing for
the fill plug reduced for your common shop air. You dont need to much, put your air regulator down
to about 2-3-4 pounds small center drill until air hisses. I suggest if unsure I would drill and tap a
piece of scrap. No shame for that, there is a delicate sweet spot between the drill & tap. Most ports
if not all on gearboxes are taper tapped. As far as lubricatant we use carb or brake cleaner while
tapping cast. If all is correct it should tap like butter.
 
Not me doing the tapping but a few guys on different teams.

Broken Taps and all gets me worried as we have two more to do after the others last night were done.

All gear boxes now come with the holes tapped and plugged from the manufacture.


Saves a bunch of time and by the looks of it a lot of ' Lead folks' some serious explaining as they are the ones who broke the Tap.:lmao:
 
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