# Tapping/Threading aluminum



## The_Apprentice (Feb 26, 2018)

I am going to practice with my cheap carbon tapping set on some aluminum roundbar soon. I the problem is I do not have any standard tapping lubricant (yet). But I do have standard cutting oil /machining coolant. Is this ok to use instead for just aluminum, or still bad idea?


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## David S (Feb 26, 2018)

Not sure what size you are considering, but when machining aluminum, if I didn't have any of the specific fluids, I would use WD-40 or kerosene.

David


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## f350ca (Feb 26, 2018)

As David said WD40, or if Im out straight kerosene.

Greg


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## pdentrem (Feb 26, 2018)

Same as the rest! WD40 or Kerosene.


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## The_Apprentice (Feb 26, 2018)

Seems I have another problem here on my first attempt at using dies.

As I understand, if I am making my own M8 nut, I need to drill about %20 smaller than the tap size. However, I am confused when it comes to using the M8 die to thread an M8 bolt. Should I start with an 8mm roundbar and just thread, or am I supposed to change the size of the shank. I ask this, because it seems damn impossible to get the M8 die on an 8mm roundbar.


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## Dave Paine (Feb 26, 2018)

It is not easy to get a die to start on the bar unless you file or machine a taper.   This may mean tapping the thread longer than needed and machining off the excess.   I make a taper for aluminium or steel.    If I do not make the taper, the die tries to bite but then the small thread breaks off before the die is able to get a good hold.

The taper ideally begins about the base diameter.   The length of the taper in my work depends on the material and diameter.


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## T Bredehoft (Feb 26, 2018)

Even in aluminum, I chase threads to about 70% of depth then run a die on them. The die always starts straight.


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## brino (Feb 26, 2018)

The_Apprentice said:


> it seems damn impossible to get the M8 die on an 8mm roundbar.



......and since this is the "beginners forum" one side of the die starts much better than the other! 
-brino


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## benmychree (Feb 26, 2018)

Tap Magic works fine on aluminum and does not stink like kerosene.


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## mikey (Feb 26, 2018)

The_Apprentice said:


> However, I am confused when it comes to using the M8 die to thread an M8 bolt. Should I start with an 8mm roundbar and just thread, or am I supposed to change the size of the shank. I ask this, because it seems damn impossible to get the M8 die on an 8mm roundbar.



8mm = 0.3149". You want to turn the blank down to about *0.310" OD*, put a 30 degree taper on the end and you'll have about a class 2 fit.


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## Bi11Hudson (Feb 26, 2018)

I am not really the best person (not even pretty good) to get involved in this conversation.I have been a maintenance man in steel mills for years. And part time boss where having to think on my feet was a primary function. With several hundred tons of hot and molten steel in play, there isn't time to think about the problem. Just cobble it together it and keep the mill running. Certainly no spills...... messy!

A few points on your threading: 

For external threads, tapering the shaft such as mentioned above is applicable for all metals and all grades of dies. I often turn a starter shaft to the smaller diameter of the thread to give the die a place to start true. This in addition to the taper. It *helps* on the lathe. *Mandatory* if the threading is going to take place later in a vise or whatever.

For internal threads, starting with metric is easier to describe. Imperial works the same, just harder to figure. 

Start with a 10mm tap. The usual thread is 1.5mm pitch. Take the 10mm bolt minus the 1.5mm pitch and there is the size to be drilled. 8.5mm. This may not deliver the optimum 86% thread tooth engagement, but it is close enough to hold an automotive engine assembly together. And get you up and running without worrying about a chart or wires.The diameter minus the thread pitch.....

For imperial threads, think 3/8-16. It would be 3/8 (0.375) minus 1/16 (0.0625) for drill size. 5/16" as I recall.... And 5/16 is a good starter size for a 10mm tap as well. A letter drill a few thou larger would be better, of course.

I happen to be able to juggle numbers in my head pretty good so it's easy for me to juggle imperial and metric. Comes from model building. Some folks not so easy..

Hope that helps in your endeavers,
Bill Hudson​


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## The_Apprentice (Feb 26, 2018)

Alright, decided to give another M8 die a chance in case it was a die issue. I switched to the fine thread, and got it to finally go. Though something seems off here, wayyy off. After threading, the size of the shank is now almost a whole mm smaller. That doesn't sound right at all?

Used more than one caliper just in case my measuring was off... I'll post photos tomorrow maybe.


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## Ken from ontario (Feb 27, 2018)

Hey King, here are two very useful charts for external threads, I have a copy of each chart on the walll in my shop, you wouldn't believe how often you'll need them:
https://www.engineersedge.com/hardware/metric-external-thread-sizes1.htm
http://www.diecasting-mould.com/dat...t-Screw-Socket-Thread-Specification-Sheet.pdf


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## RJSakowski (Feb 27, 2018)

The major diameter is the nominal diameter of the thread. i.e. an M10-1.5mm would have an unthreaded rod diameter of 10mm.  For tapping internal threads with about 75% thread, the tap drill diameter is the major diameter less the pitch. i.eo, the M10 1.5mm tap drill would be 10-1.5 =8.5mm.  

This also works for SAE threads if you convert tpi to pitch.  A 1/4 -20 thread has a major diameter of .250" the pitch = 1/tpi =1/20 = .050" so a .200" tap drill is used.

When threading rod with a die, I find it useful to turn a short lead to the tap drill diameter. There is a slight interference with the die which helps to get the die to bite in and the lead helps to getting the die to thread straight.

As Brino said, there are two sides to the die.  Most dies are labeled"start this side".  If the die isn't labeled. look at it closely.  On side has more of a chamfer than the other and it is the start side.


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## The_Apprentice (Feb 27, 2018)

I tried both sides but still things are just fail. To be honest, I've heard the cheap Pittsburg Dies at HF are crap, so that could be part of the reason. Though naturally, I don't want to start blaming tools when I am the newbie at play here.

In any case, it seems I'm having the issue of the teeth just digging in, and then stripping. So far it's still a fail, with standard and fine dies for M8 no different.  What I will do is some more research on this during March, and just maybe I'll eventually get myself up to a master-thread cutter. LOL.

I will also experiment with some hot-rolled steel, may that will be easer.


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## agfrvf (Feb 27, 2018)

Chuck it in a drillpress and give it some feed pressure and clamp the die and turn the pulley by hand. It may help to cut a groove witha dremel or jewlers file.


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## rwm (Feb 27, 2018)

Your die is slipping and stripping the threads. I have had this problem with large diameter taps. You may be starting with too large of a shaft. Forward pressure on the die holder will help as AGFRVF stated above. Others may have some good tips.
Robert


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## Tozguy (Feb 27, 2018)

Those 'entry' level taps and dies are part of the problem. Have you inspected the die closely to see if you can see an obvious problem with it? If you ever need to cut a full quality thread then spring for a reputable brand tap or die of the size you need.
But for now to make those HF dies work you have to make it easy for them, by cutting start tapers and other things as mentioned above. If that does not work then pitch the die.

BTW This chart has two different thread engagement choices that is my favourite for quick reference.
https://littlemachineshop.com/reference/tapdrill.php


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## ttabbal (Feb 27, 2018)

Good tips. I'm just going to put this here though. You owe it to yourself to try one known good tap and die. I am in a similar place with HF stuff I already had. I was trying to run a 3/8 tap and just couldn't get it to cut past the starting threads. I ordered this and it came in today. 

https://www.amazon.com/gp/aw/d/B00F8RFEZ6

OMG. This thing cut 304 stainless like butter. The HF tap couldn't cut 12L14. I know part of it is that this is a brand new tap, while I did use the other on mild steel before. But I was shocked at the difference. I struggled with the other one for about an hour trying to get it to work. I was done with the new one in about a minute. 

Sure, the one tap cost about what the HF set did. But it's worth it. I do this stuff for myself, so I can just standardize on a few thread types. And I'm planning on doing more threading on the lathe than not going forward.


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## rwm (Feb 27, 2018)

Aluminum will be easier than steel. What size shaft are you starting with for the 8mm die? Do you have a method to exert forward pressure like a lathe or a drill press?
Robert


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## Tozguy (Feb 28, 2018)

An 8 mm thread should be easy to cut with a die even in steel as in post 19 above. You should not have to do headstands to accomplish that. Get a quality die and see for yourself.


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## The_Apprentice (Feb 28, 2018)

> What size shaft are you starting with for the 8mm die?


8mm, and just a fraction less, as I read in most cases M8 bolts are actually undersized.

In any case, I found some old cold-rolled steel round-bar around the house... a bit rusty but I will polish it up and try to see if using a die on that works any different.


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## Bi11Hudson (Feb 28, 2018)

King; Some after-thoughts on your trials and tribulations. 

Aluminium is what I refer to as a "tenacious" metal. While it is softer than steel, it is also "stickey" and stringy. With HSS taps in a hand drill for electrical base plates, I have found aluminium will much more easily break a tap than steel. I don't know the proper terms for the characteristics, just how I have to deal with them. Usually I am dealing with Nr 10 or quarter inch screws. I drill the clearance holes a little loose, one number size drill larger.

Now, to taps and dies;  Carbon steel is OK to use for very soft material, plastics and the like. It even works with "mild" steels. Hot rolled is _*not*_ mild off the shelf, it needs to be drawn somewhat. Cold roll has often work hardened during production and should be treated similar to hot rolled. For those, you would want "High Speed Steel" for cutting clean. Carbon steel is a poor choice for aluminium. Good in it's place, but poor for aluminium.

Now, to Harbor Freight; I have many tools from there. But it is stuff that I can control or where quality doesn't matter that much. Examples would be paint and sheetrock mud stirrers. I won't comment on their precision (or lack of) tooling but it's not good on the best of days. Look to HSS from known good vendors to get good cutting tools.

Many decent dies have a setscrew to adjust diameter, class of fit, by spreading open the die. If your's has this, you might try it. If not, get a better one from a supply house. Amazon is fine for books, but has no business selling tooling to machinists. Real or "wanna-be" (like me) Stick with people that speak the language, not salesmen that have memorized the finer points to peddle a product.

Now, on lubricants. Many above refer to kerosene, the petroleum product. *Kerosene and coal oil are not the same product*. But kerosene is a pretty good cutting oil for aluminium. Coal oil is better, but harder to find. What you need to look out for is stuff like *Tap Magic*. It can't be bought any more in the old formulation. But it was magic on steel. I have a few cans of another solvent that also contains* trichloroethane, tech. 1,1,1*. The chemical, added to the usual tapping oil, will work magic on steel. Today it's outlawed, for good reason. But I still use it occasionally. The finer points involve a deep discussion. It does something that nothing else will. But, it is a _known HazMat_.

The thing to watch out for is using such cutting fluids on aluminium. The trichloro will turn aluminium to powder. And, it's sorta hard on your lungs, too. Works fine for brass and bronze and the like. But keep it away from aluminium.

On thread sizing; _theoretical_ "V sharp" threads come to a fine point on the (triangular) thread form. After a few hundred cuts, that sharp point tends to dull a little. Male(outside) threads trim off the very point of the thread form to form a flattened edge. That's why you don't cut your fingers when you grab a bolt. It also causes the diameter of the screw to be a few thou under. Measuring a small screw, it might only be a thou or two undersized. On larger screws, it makes a noticeable difference. With a 1/2" screw, it almost looks like a 7/16" on the threads. Dies cut this small trimmed area down so it will be more likely to fit a nut from the latter part of a run. This is from the days of *Unified Thread*ing, long compensated for.

I probably was more confusing than helpful. But, I gotta try.....


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## mattthemuppet2 (Feb 28, 2018)

I haven't done much work (successfully at least) with dies, but I've done a ton of tapping and the best thing I ever did was get some decent taps. Started with spiral point, ended up with spiral flute too in all the sizes that I use, typically the smaller end of the range. What a difference, like night and day. The taps and dies in those Pittsburgh sets, which are what I started with, are fine for cleaning up threads, but they really struggle with cutting new threads. the dies just won't or if they do, they won't cut straight. The taps aren't so bad but you'll spend all day turning it CW 1/2 a turn, then CCW 1/4 turn, then CW and so on, then backing it out all the way to clear the flutes then doing the same again. Spiral flute (or point) tap - bzzz pft, done.

if you look for taps on Amazon by % discount, you can get name brand taps for $5-7 each, often as an Add on Item. Can't say no at that price.


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## umahunter (Feb 28, 2018)

I started with cheap harborfreight taps and eventually have picked up better taps here and there as I need them but if your careful and take your time you can get good results with Chinese taps I think the smaller the tap the harder it will be that being said I've successfully tapped aluminum  steel and even stainless with my cheap set just take it slow and be patient


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