Lubricant for tapping upward into aluminum

[BruceMystic]

I'm asking because my search found this old thread here, on tapping aluminum:
https://www.eevblog.com/forum/reviews/your-favorite-aluminium-millingdrilling-lubricant/
I'm starting a new thread because that one is from 2017.
I need to tap (upward) 3/8"-16 threads into an existing 5/16" hole in an aluminum casting.  I'll be tapping 1/2" into a blind hole, so the shavings will not come out the back.
The interesting part, is that I'll be tapping upward into the hole.  The casting is part of the frame of an aluminum bodied car, so I can't remove the casting and put it on a workbench, to tap downward into it.
So liquid will run down out of the hole, away from the cutting edges.

What lube would be good here?
Most of the lubes I've seen suggested for cutting aluminum are quite thin and will run right back out the hole.
WD-40 has a good reputation for use in cutting aluminum, but it's runny.
One suggestion in the linked thread was Vaseline, another was KY jelly (really!).
Any other suggestions on this?

Thanks!

I already know I need a sequence of taps: taper, plug, bottoming, to put threads in the bottom of the hole.  Depending how that goes, I also will have some self threading bolts, which should cut all the way to the very bottom (top!) of the hole.  And I know I need to cut in about 1-2 turns, then back out, to get the shavings out.

[langwadt]

ethanol, it doesn't really matter that it is runny, the tap just need to be "wet"

[PartialDischarge]

Super Tapping Fluid from CRC is a spray with foamy texture. Of course if you apply too much it turns liquid

[Stray Electron]

  It's not going to really matter if the cutting fluid is runny or not, just as long as you get it up inside the hole where the cutting action is taking place. The reason why it doesn't matter is because that you need to back the tap out (about once per revolution?) and clear the cuttings off and re lubricate the tap.  Kerosene is a good lubricant for tapping aluminium. WD-40 is mostly kerosene and will work also. I would get a small container of kerosene and dip the end of the tap in it and get the threads started and then periodically back the tap out and wipe or brush the cuttings off of it and then redip it in kerosene and then go back to tapping the hole. 

   As your tap gets deeper in the hole and the nearer that you get to the bottom of a blind hole, the more that you need to clear the chips from the tap.  The LAST thing that you want to happen to jam the tap with chips and have to it seize in the hole!!   If some chips cling up inside of the hole you could use something like WD-40 in a spray can with one of those long thin tubes on it and spray that up into the hole to relubricate the material and to help blow some the chips out of the hole.

  I would use WD-40 or kerosene before I'd use Vaseline!  Vaseline is sticky and will probably make the chips cling to the inside of the hole and to the tap.  You want them to fall out and get out of the way of the tap.

  Do NOT use any kind of chlorinated solvent for lubricating aluminium when you're using steel tools! 

[coppercone2]

I think that foam stuff is good, IDK if they have it for aluminum but the one that CRC sells for drilling is excellent. But it does drip you put a bucket under what you are doing because it makes a mess

I used it to drill aluminum without problems and probobly tapped some holes too, I don't think it was a problem. I would only worry about it if you are doing alot of holes like in production

I bet even that wd40 foam gel spray would work

its like shaving cream that is less stable (the CRC one), the wd40 gel spray might even be a bit less stable, I think the CRC holds foam shape better

if its upside down I would just spray it into the flute of the tap while working periodically

[abeyer]

Anchorlube is a pretty good choice in a more viscous paste-like form, and less mess/easy cleanup compared to some options.

[langwadt]

1/2" of threads for 3/8" in aluminium is marginal, rule of thumb is minimum 1x diameter in steel and 2x diameter in aluminium

[jpanhalt]

1/2" of threads for 3/8" in aluminium is marginal, rule of thumb is minimum 1x diameter in steel and 2x diameter in aluminium

That depends.  Try a Whitworth 55° profile and/or finer threads.  As an example, look at the threads for 60+mm camera filters.

[Someone]

Tap Magic is thick enough to coat surfaces, and they sell an extra thick version...

[langwadt]

1/2" of threads for 3/8" in aluminium is marginal, rule of thumb is minimum 1x diameter in steel and 2x diameter in aluminium

That depends.  Try a Whitworth 55° profile and/or finer threads.  As an example, look at the threads for 60+mm camera filters.

sure but they are not that size for strength

[Zoli]

Sheep tallow IS the traditional cutting/threading lubricant; not surprisingly solves the problem.

[Martian Tech]

They do make solid & paste lubricants.

https://www.mcmaster.com/products/lubricants/solid-tapping-and-threading-lubricants/
https://www.amazon.com/Lubri-Cut-Cutting-Drilling-Tapping-Lubricant/dp/B017C0HZA8?th=1

[hubi]

If this is a repair for a damaged thread, a helicoil might be an option. I don't think the cutting fluid matters all that much in aluminum for a single hole done by hand. With the shallow hole, the taper tap might bottom out quickly and if you keep turning, there is a risk you might damage the little bit of thread you have already cut. If you have not done this type of work before, do a few practice runs to get a feel for it.

[BruceMystic]

Thank you all.

Having read everything here, my plan now is to use WD-40 as the cutting lubricant.
WD-40 apparently is one of the best "lubricants" for cutting aluminum, and I already have it, can easily get more if needed.
PartialDischarge suggested Super Tapping Fluid from CRC, which probably would be even better - but I don't see it available here in the US.  It seems to be marketed in Europe.

Anyway, I can use the thin spray tip that's supplied with WD-40; the lube will go all the way up into the hole and should help wash the shavings down and out.  I'll have a drain pan below, to catch it.

As for the depth of the hole - I might drill it very slightly deeper than it is (currently 10 mm, just under 1/2").  Maybe an additional 1/8 to 1/4 inch deeper.  If I drill more than about 3/4" deeper, I'll hit the bolt that supports a suspension bushing (car's front lower control arm).  I'm sure the roughly 3/4 inch of non-drilled aluminum material there, is needed to properly support that bolt.

I agree that for steel bolts in aluminum, the length of thread engagement should be about 2x the nominal bolt diameter.  But for this application, I don't need superb strength; a 1/4" or 6 mm bolt would be enough.  The only reason to use a 3/8" (approx 10 mm) bolt, is that the existing hole is the perfect diameter to be threaded for that bolt size.  So I don't need a lot of torque on the bolt.  I've checked the specs on what torque the aluminum casting should be able to take; I'll give it 1/3 to 1/4 of that torque and it should all hold very nicely.

I don't expect all my tapping tools to be here until next weekend - so I have to hold off until then.

[geggi1]

I have good experience with 3M polywater and ethanol or isopropyl spirit.
The polywater to spirit rate equal parts but if needed more polywater can be added.

[Someone]

But for this application, I don't need superb strength; a 1/4" or 6 mm bolt would be enough.  The only reason to use a 3/8" (approx 10 mm) bolt, is that the existing hole is the perfect diameter to be threaded for that bolt size.

Glue a press nut or helicoil in the hole?

[Gregg]

Anchor lube is exactly the product you are looking for.  It is available at any supplier of machining / cutting tools or even Amazon.  It is water based and the consistency of mayonnaise.
https://www.amazon.com/CECOMINOD047769-Anchorlube-8oz/dp/B00FQQ3JWY

[G7PSK]

Go to an engineering suppliers and ask for cutting paste/compound, not sure what brands are available in the US but I always use "trefolex" here in the UK been using it since the 1970's never given me trouble Paste has the advantage that the swarf gets stuck in the tap flutes so that the swarf come out with the tap, I also use it for drilling, just dip the end of the drill into the tin.

[Wallace Gasiewicz]

I worked where we manufactured transmissions. The housing of course is Aluminum. The cutting fluid was almost all water with minimal lubricant which was high quality oil and surfactant.
Off line repairs were done without additional fluid and were done with a tap in a hand held slow drill. Like a DeWalt. You don't need much cooling to tap Al, so a little WD 40 or any oil is just fine.

[pcm81]

tapping fluid does 2 things: cooling of the tool/hole and prevent galling under high loads. If you are tapping slow, like with a hand tap the cooling is not an issue, so anything that lubricates will work. just go slow and periodically back out to clear the chips.

[james_s]

You don't need the tap to be submerged in fluid, it's a lubricant, just brush a bit onto the tap and go. A lot of people use waaaay more fluid than is needed.

[Wallace Gasiewicz]

Industrial Tapping / Cutting Metal Working Fluid does four things.
Cool the tool and the part     
Lubricate the tool   
Wash away the cuttings   
Cause all sorts of problems

[artag]

Like G7PSK, I usuualy use trefolex. I think it's for steel but it works well enough and stays where it's put.

Isn't milk sometimes recommended as a cutting fluid for aluminium ? Not that surprising as it's an emulsion.
So if you want it to stay where it's put, maybe use clotted or whipped cream ?

And you can add 'goes rancid' to Wallace's list - though that's a feature of some soluble oils too.

[nctnico]

I'm still using Relton A9. It is excellent for machining aluminium. It is also not super thin so it would be a good choice for using a tap upside down. Maybe apply it with a brush so it can wick in between the thread. Biggest 'problem' with machining aluminium is sticking to the cutting surfaces so you don't need huge volumes of fluid. Just a thin film.

[coppercone2]

You don't need the tap to be submerged in fluid, it's a lubricant, just brush a bit onto the tap and go. A lot of people use waaaay more fluid than is needed.

i feel like I definitely noticed that the tap goes in easier if like half way you take it out and relube it