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Tapping/Threading aluminum
- Thread starter The_Apprentice
- Start date
- Joined
- Jun 14, 2017
- Messages
- 263
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.
- Joined
- Feb 13, 2017
- Messages
- 2,138
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 Threading, long compensated for.
I probably was more confusing than helpful. But, I gotta try.....
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 Threading, long compensated for.
I probably was more confusing than helpful. But, I gotta try.....
- Joined
- Sep 28, 2013
- Messages
- 4,395
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.
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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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