Cheeseholing suggestions

[Alex1072]

Does anyone have experiance cheeseholing 2x2 1/8th wall Aluminum? I'm sure people have done this before and I was wondering if anyone had suggestions or recommendations on the most efficient way to cheesehole it. We're a little screwed in terms of weight at the moment. Thanks.

[Bill Gold]

The lower and upper arm of 258's 2004 robot was 3"x3" aluminum with a .125" wall...

http://www.markrobot.com/gallery.php...ncoln%2F30.jpg
http://www.markrobot.com/gallery.php...ncoln%2F26.jpg
http://www.markrobot.com/gallery.php...ncoln%2F31.jpg
http://www.markrobot.com/gallery.php...ncoln%2F34.jpg

PM/IM/Reply if you have any questions.

-Bill

[Raul]

We usually have the students do it with a step drill for holes 1.0" or smaller or a hole saw for larger holes. It does keep them busy for quite a while though.

[BillCloyes]

Just a few words of caution...

For the hole saw rookies:

Expect to get a hole LARGER than the hole saw is marked at.
How much larger depends on the condition of the hole saw (old and mangled = much larger hole)

Also...
Keep in mind the possible loads that these members will experience (use a healthy safety factor- depending on location, it could be very difficult to replace at Competition). Run some stress and strain calculations with the proposed reduced cross-sections before you start going completely crazy (2.75" hole in a 3" wide tube ) with the hole saw...

No one wants to have the piece that they spent hours swiss-cheesing break in half...

my two cents

-Bill

[ChrisH]

Originally Posted by BillCloyes

Also...
Keep in mind the possible loads that these members will experience (use a healthy safety factor- depending on location, it could be very difficult to replace at Competition). Run some stress and strain calculations with the proposed reduced cross-sections before you start going completely crazy (2.75" hole in a 3" wide tube ) with the hole saw...

No one wants to have the piece that they spent hours swiss-cheesing break in half...

my two cents

-Bill

If Alex1072 can provide a better picture of how the aluminum member will be used, then I can probably give a good idea of just how far you can take the speed holes. But I'd hate to give a number, say for a simply supported beam, and then find out you were actually cantilevering the load. They are different problems with different answers.

[Alex1072]

We're using it as a vertical support. Actually you can see the 2x2 in one of the teasers i posted. The other places we want to cheese hole are at the base of our arm (cross bar), and as a vertical tower for cabling purposes.

[ChrisH]

Originally Posted by Alex1072

We're using it as a vertical support. Actually you can see the 2x2 in one of the teasers i posted. The other places we want to cheese hole are at the base of our arm (cross bar), and as a vertical tower for cabling purposes.

The moment generated by the arm needs to go into whatever is holding it up. You also need to consider side loads (like impacts with other robots) that can create torsion around the 2x2. I typically assume a 1/2g side load in addition to the normal gravity load.

Assume that the 2x2 is at the "back" of the robot and the arm swings up and down pointed towards the "front" If you knew it was only going to resist the moment from the arm and gravity, you could probably cut 1 1/2 inch diameter holes in the left and right faces of the tube and space them 2" apart without compromising the strength of the tube in the fore and aft direction. However, I have not investigated the effect of such holes on torsional strength and stiffness. The bolt on rails will also have some effect, but since I know little about them, I can't estimate how much.

[sanddrag]

Lasercutting or Waterjetting or CNC milling are the only real "professional grade" solutions. The only other alternative would be a hole saw but you will have lots of filing and sanding to do, it comes out ugly. Also, prepare to go through lots of hole saws.

[Holtzman]

Ideally, equilateral triangles water jetted, or cnc'd or whatever into the 2x2 would be great. Assuming you don't have these resources, I would suggest 1 inch holes every 2 inches with 1/2 inch holes every 2 inches in between the 1 inch holes, 1/2 an inch from the outside. Its difficult to picture from my description, so I've attached a model. Also, make sure you offset the sides by an inch so you make sure you have the most material possible at the edges while still removing the same amount of material.

If you going to drill one set of holes down the middle, MAKE SURE YOU OFFSET THEM. I've seen many teams that don't do this, and their just throwing strength away. See attached jpegs for more info. The pictures can explain it better than I can. Offsetting the holes doens't change the weight, but you conserve strength considerably when they are offset.

Sorry for any vagueness. PM me for more info

[Bill Gold]

Originally Posted by sanddrag

Lasercutting or Waterjetting or CNC milling are the only real "professional grade" solutions. The only other alternative would be a hole saw but you will have lots of filing and sanding to do, it comes out ugly. Also, prepare to go through lots of hole saws.

I disagree with your theoretical "professional grade" statement (not that perfection is required on FIRST robots). Check those 2" holes in the pics I linked earlier (I can take other pictures tomorrow, if you're not convinced). All done with a single hole-saw, deburred by hand, and then sanded with fine sandpaper. It looked/looks great.

<edit>
Also note the offset holes, like Holtzman mentioned earlier.
</edit>

[BillCloyes]

Originally Posted by Bill Gold

I disagree with your theoretical "professional grade" statement (not that perfection is required on FIRST robots).

I agree completely... A hole saw used on a vertical mill (or even a good drill press with either a 2 axis bed, or really good marking/measuring and center punching) will produce a very good hole. (if you were that worried about it being a 2.000" hole, it wouldn't really be cheese hole...)

As for the wear on the hole saw itself....
* Generally speaking, hole saws are made to be run slowly (bigger diameter the slower spindle speed).

* The use of Cutting Fluid (not just oil (lubricant) or coolant) will quicken the process and also extend the life of the tooling.

-Bill