Cutting 7075-T6 Aluminum

[Jon Matcho]

I needed to make a replacement part (a pushrod actuator bar) for my friend's Glasair III door.  After a fair amount of research I learned that a very popular method of cutting aluminum sheet is to use a table saw equipped with a special purpose blade.  After buying the most expensive blade I have ever purchased, and making a few practice cuts, I was able to break through and produce the part.

Here's the original stock with the template traced:

The yellow anodized part is the one that is being replaced.

In addition to the new part, I produced this 14" shard of death, and learned a new level of respect for my table saw and flying objects.

 

[Kent Ashton]

It's sort of unusual to see 7075 used.  Is that what's spec'd?   That alloy is a little more crack-prone

http://www.totalmateria.com/Article17.htm

I hate to throw shade my friend but your upper hole looks a little off center.  I presume 7075 was used because it's a higher strength alloy but with the smaller edge-distance on one side and the possibiiity of cracking, you might need to reconsider.  7075 is also a little less corrosion-resistant that the usual 6061 and 2024.  Maybe you can buy some 2024 bar and make one.

[Jon Matcho]

11 hours ago, Kent Ashton said:

It's sort of unusual to see 7075 used.  Is that what's spec'd?   That alloy is a little more crack-prone

http://www.totalmateria.com/Article17.htm

Good article, and here's another (see the table at the end):  https://www.metalsupermarkets.com/what-aluminum-grade-should-i-use/

I chose the 7075-T6 because I felt it was superior to 6061 (I think 6061 would have done just fine but the stock I had was a touch too thick).  I couldn't find anything in the Glasair plans regarding the material type, and their factory support wasn't helpful (I was told to contact the prisoner rehabilitation company they use that produces their parts!)  I resorted to making this part myself after attempting to get the factory to make 13/16" longer, and after attempting to find a local machine shop (why did I mention "airplane"?!)

11 hours ago, Kent Ashton said:

I hate to throw shade my friend but your upper hole looks a little off center.  I presume 7075 was used because it's a higher strength alloy but with the smaller edge-distance on one side and the possibiiity of cracking, you might need to reconsider.  

Yes, it's 0.01" off center (I didn't actually measure, but I did notice before posting).  I was just amazed at the time that I managed to produce the part using less than ideal tools.  I did go to bed thinking I might make a better one, but given the application (push/pull without much resistance at all) I am confident it will be fine, off center and all.

11 hours ago, Kent Ashton said:

7075 is also a little less corrosion-resistant that the usual 6061 and 2024.  Maybe you can buy some 2024 bar and make one.

I didn't know about 2024 until now, but according to the link I shared 2024 has "low corrosion resistance".  

The number 1 thing I learned from this is that I was not prepared for the amount of metal shavings that would be created AND how I now now that I do not have a machine shop.  I am going to buy everything I can from the Cozy Girrrls.  At least that's what I say now. ?

 

[aeroknot]

You don't need a fancy metal cutting blade for aluminum.  a standard carbide tipped blade,  I've cut 3/4" sheet in one of two ways.  both with stick beeswax on the blade.  one shop turned the blade backwards and cut sheet for tool and die use every day.  the next place only cut aluminum occasionally and left the blade in normal.

[Jon Matcho]

9 hours ago, aeroknot said:

You don't need a fancy metal cutting blade for aluminum.  a standard carbide tipped blade,  I've cut 3/4" sheet in one of two ways.  both with stick beeswax on the blade.  one shop turned the blade backwards and cut sheet for tool and die use every day.  the next place only cut aluminum occasionally and left the blade in normal.

I didn't spend fancy money, but the blade is carbide tipped and well-made from a reputable manufacturer (versus the crapshoot that can be with imports).  I was thinking to leave it in for basic woodcutting, but need to check its thickness.  Thanks!

[Jon Matcho]

On 8/7/2018 at 10:00 AM, Kent Ashton said:

It's sort of unusual to see 7075 used.  Is that what's spec'd?   That alloy is a little more crack-prone

http://www.totalmateria.com/Article17.htm

I did an informal test this weekend with that sliver of 7075 I had left over.  I wanted to see how it failed when quickly bent.  On my first attempt, it did not break.  I figured I didn't apply the force fast enough so I went to a thicker part and really went for it.  Same thing -- it just bent without any visible signs of cracking (I didn't get out a microscope).

The result shape holds its form quite nicely and even after subsequent attempts to bend or make the larger portions parallel, it returns to its original shape.  I could actually use this as a crank for some sort of small part.  Interesting material -- I could not get it to crack.

[Marc Zeitlin]

3 hours ago, Jon Matcho said:

... Interesting material -- I could not get it to crack.

 

Try a tighter radius. You're bending it at a radius of 3 - 5 times the thickness - go to 1 - 2 t and it'll start to crack.

[Jon Matcho]

It broke pretty easily that way, using needle nose pliers.  

Aside from that I beat on the rest of it a good bit and was impressed that it held position perfectly — straight as the original plate.