Building Questions

[Kandace]

Hi Everyone! I have a couple of questions, I hope someone can help. I decided to start with the keel tube, and the first thing I discovered was that my drill press won't go all the way thru the 2" tube! So I laid out the holes on each side and proceeded to drill away. I get all done and I have a couple of holes that do not line up perfectly, the bolt goes all the way thru but as it passes thru the tube the clearence gets a little less than the nominal 1/32".

I did not score the walls, so I'm wondering if I need to do this piece over. It has been awhile since I've done any metal working. I've been told I'm to picky but I want to make sure.

Also the 3/16" holes seem very tight on the AN3 bolts, is this normal?

And last, I'm being very careful with the material, but I've noticed some scrathces on it. Do I need to worry about those.

Thank you,

Kandace

[rehler]

As far as the tight holes are concerned, tight is good, but I recommend that you run a 3/16" bit (electric drill) through each hole before you put in the bolt to line the parts up and "clean out" the hole.

Always (when possible) drill all the way through from one side. If your drill bit it less than 2" long then buy a longer one.

If you don't score the walls then the aluminum is not damaged. Yes, you may be a little too picky.

[PW_Plack]

Ken,

It's not the length of the bit, it's the length of the stroke on these small, imported benchtop drill presses. I had the same problem. I got around it this way:

(1) Make sure the square tubing is clamped in place.

(2) Start drilling, but when you get to the end of the stroke, don't remove the bit. Just pull it up about halfway out of the hole. Stop the motor.

(3) Loosen the chuck, let the bit slide down in the chuck, re-tighten. You'll now still be in the hole even with the press at the top of its stroke.

(4) Hand-rotate the chuck to make sure the bit isn't binding in the hole, then restart the motor and finish the hole.

(5) You'll have to either reposition the bit in the chuck again, or drop the press table to get the bit out of the tube.

This is tedious, and you have to be very careful not to start the motor if the bit is binding in the hole, but it works. It might be more dangerous with aircraft alloys...I was drilling through softer two-inch stock for use in a custom antenna system. Having done it this way, I have to say I'd rather find a friend with a bigger press next time!

[Dean_Dolph]

Kandace, I agree with Paul, that if at all possible the hole should be drilled thru both sides with one pass.

It has been a while but in the past I always drilled slightly smaller than what the final size (not always possible but I always used a reamer to finish the hole) was supposed to be and then reamed to the final size.

Reamers are readily available from several sources. A reamed hole is closer to being round (in fact it would be unexpected if it wasn't!), is more precise and cleans up the hole nicely. The holes will still need to be chamfered (the reamer will take care of any burrs) by using a countersink bit or even a slight larger drill bit and lightly hand spinning it in the hole. The idea is to take the sharp edge off the hole and remove a stress riser.

Bolts, even AN ones, are not precision made. Consequently there are manufacturing tolerances. This means that some bolts will slide in nicely while others may be tight.

Oh yeah, there is nothing wrong with being picky. If you really want to be picky you can get reamers in different sizes and drill/ream each hole to fit the each bolt!

[Dean_Dolph]

...to add that while Ken R. agrees that you might be too picky; I think he sets a good example! I just don't think he sees his high standards of construction as being picky. The pictures of his machine(s) don't do it justice but the awards do.

[Kandace]

thank you all for your coments, I appreciate it very much. I've already ordered a new piece of aluminum, I'm going to make the part over. If I'm not happy with it........well after all it is my bottom in the seat.

Thanks again
Kandace

[Doug Riley]

My ancient bench press isn't imported, it's just small and has a stroke less than 2". I use the method Paul describes. Be extra careful when starting the hole in the second wall after you've "extended" the drill bit. Lacking a punch mark, the bit will tend to wander a little before settling in -- the flexibility of the bit will allow it to do so. Start that second pass with very light pressure to reduce the wandering. I use just a couple fingertips on the press arm, and barely touch the bit to the inside face 2-3 times to try to fake a punch mark for the bit to grab.

[Frank Zarzycki]

Kandace, I have used both methods with very good success. I set up a fence of either of a scrap 2x2 square tube or 2x2 angle and shimmed parallel to the drill and clamped to the table to hold my edge distance, and clamp my work to the fence.

If you have a scrap piece try a few holes to you are happy with you clearence.
I have found that on some extrusiond wall thickness may vary a few thousanths on each wall. AN bolts also vary anywhere from 3-5 thousanths.

Hope this is some help
Frank