Precisely drilling aluminum square tube question

[Erich_870]

Here's the question.

I'm working on a little suspension project where I want the tightest tolerances I can achieve with my meager tools. I have a small table top drill press and an assortment of drill bits, including a 7/8" uni-bit.

I need to make two identical parts by drilling a 3/4" and 1/2" holes in two 2.5' long sticks of 1 1/4" x 1 1/4" x .130" aluminum square tube.

I need them centered on the long axis.

I'm looking for specific steps to prevent the bits from walking, the hole going egg shaped, etc. and making both parts identical to each other. How would you go about doing this?

Here are my normal procedure:
1. Use adjustable square to mark center of each axis for each hole.
2. Punch center with spring loaded punch.
3. Adjust drill press to allow proper drill depth.
4. Drill pilot hole with small drill bit (usually 3/16") [Here might be the start of problems I've had as this bit walk or bend]
5. Move up to 1/4" then up to 3/8 then 1/2" After that I have to go to the Uni-bit. [What is the correct size increments to move up each time?]

I guess this question falls under "what are the proper machining techniques" category, if that makes sense?

Thanks!

Erich

[4x4mike]

I think you have the right idea but I'm not sure it's neccesary to make so many holes. I'd start with a larger pilot hole especially if you have problems with the smaller hole. Why are you having trouble with egg shaped holes. Is it the drill press? Bits? Maybe slow it down, go a little bigger and go slow.

As far a duplicating the holes; you can drill both at the same time if you have a way to clamping them together and keep them from moving. Once you drill one hole through both pieces you can put a bolt through the hole to keep them lined up and together. You can also use transfer punches. I don't have any but always use something I have lying around (depending on the size of the hole) to get the job done.

What are you making? Aluminum isn't used in suspension much especially in 2.5 foot sections.

[4x4mike]

This one only goes up to 1/2" but you get the idea.
http://www.harborfreight.com/cpi/cta...temnumber=3577

[Erich_870]

I think you have the right idea but I'm not sure it's necessary to make so many holes. I'd start with a larger pilot hole especially if you have problems with the smaller hole. Why are you having trouble with egg shaped holes. Is it the drill press? Bits? Maybe slow it down, go a little bigger and go slow.

As far a duplicating the holes; you can drill both at the same time if you have a way to clamping them together and keep them from moving. Once you drill one hole through both pieces you can put a bolt through the hole to keep them lined up and together. You can also use transfer punches. I don't have any but always use something I have lying around (depending on the size of the hole) to get the job done.

What are you making? Aluminum isn't used in suspension much especially in 2.5 foot sections.

I think your right about starting with a larger bit. I want a bit that will ride the punch hole to get started, but not be too thin, and thus create flexing problems. I'm also thinking I'm having troubles because the bits are dull. That's probably 95% of the problem.

I'm working on Phase III of my Kayak Trailer. So it's a super light weight suspension.

Here's Phase II.

This one only goes up to 1/2" but you get the idea.
http://www.harborfreight.com/cpi/cta...temnumber=3577

Oh man! I totally need a set of those!! Thanks for posting that, I didn't know those existed.

Keep the suggestions coming

Erich

[4runnerchevy]

To make tight tolerance holes, I usually use an undersized bit, then go in with a precision reamer. To start the hole I would use a spot drill, machinist use these to spot a hole before drilling. If your making precision stuff with drill press, then I am truly impressed.

[MTL_4runner]

Erich, you might want to pick up a set of these bits so you can go right to a larger size from the center punch alone and they won't flex if you're using the larger dia bits at the start. Also be sure to use lots of oil (motor oil, WD40, etc) when drilling because nothing dulls HSS bits faster than heat (if you see the oil smoking, there's not enough so add more.....you'll see the bits cut better and stay sharp longer).

[4x4mike]

Some sharp bits will go a long way. Maybe look into the quick start ones that are like 135 degree. You could always sharpen them as well. My bench grinder has a guide but before that I used to do them by hand all the time.

[Erich_870]

To make tight tolerance holes, I usually use an undersized bit, then go in with a precision reamer. To start the hole I would use a spot drill, machinist use these to spot a hole before drilling. If your making precision stuff with drill press, then I am truly impressed.

You got me, I'm using the term "precision" very loosely. I just need them to line up and be within 1/64" of each other

Erich

[Erich_870]

Erich, you might want to pick up a set of these bits so you can go right to a larger size from the center punch alone and they won't flex if you're using the larger dia bits at the start. Also be sure to use lots of oil (motor oil, WD40, etc) when drilling because nothing dulls HSS bits faster than heat (if you see the oil smoking, there's not enough so add more.....you'll see the bits cut better and stay sharp longer).

I'll be adding these to my Christmas list as well

I'm going to look into one of those Drill Dr. Sharpeners too.

Erich

[glenyoshida]

When I have to get my holes dead on I'll draw a circle with an ultra fine tipped marker or scribe just larger than the hole I need to drill. That way I can see if the drill hole is drifting as I step up in bit size before I finish. It often means that I'm hand finishing the last part of the hole but if ya have limited tools to work with like I do then it's a way to trade labor for equipment. Isopropyl (rubbing) alcohol is an excellent solvent to wipe off the permanent marker. Using a split tip drill bit helps to prevent walking and by all means use a sharp bit.