Set-up question

tourtelot

tourtelot

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Hi-

Came to this site looking for a specific answer but it seems I am in the right place for other learning as well.

I am a home-hobbiest and have been punching holes in aluminum for 30 years, mostly electronic boxes (think "stomp-pedals"). Every thing I build is a piece or part to be used in my (now retirement) business as a location audio recordist. But I really like working metal and a table-top mill is on the list in my "golden years" :)

Okay, now for the specific. My only real big metal-working tool is a floor standing drill press. I have been (mostly) successful in doing what I need done with this machine, step-bits, drills, reamers, etc not to mention knock-out punches, abrasive wheels, Dremmel, etc.

I have 2-3-4 blocks, v-blocks, a (nice) sliding table, table clamps and the like. My table is flat to the chuck (within .0005) in both x and y axis.

I need to cross-drill a piece of aluminum bar stock. The piece is 5" long and the stock is 2x1. I want to bore a centered 1/4" hole though the long dimension. Right through the middle.

My set-up was to make a right angle jig with the two 2-3-4 blocks, clamped to the table. Find the centers of the 1x2 faces with a steel rule on the diagonals, light center punch. Clamp the piece in the 2-3-4 block jig. Drill a pilot with a 1/8" drill. flip the piece and repeat with the 1/8" drill. Drop the table and chuck up the 1/4" drill. Center it on the pilot and drill 2/3 deep. Flip the piece and drill through.

I tried this on a block of wood and it worked perfectly. Tried it on the aluminum and the hole somehow wandered, maybe, a 1/16" or so where the two bores met.

What happened? I was pretty careful and expected perfect results but something went amiss.

I'd love a talking through befoir I run to On-line Metal and pick up another piece of stock to get frustrated by again. :)

Thanks for helping someone trying to up their skill level. When you quit learning, you die.

Doug
 
This would be real difficult to do on a drill press...

You might try using a two flute end mill to bore a 1/4' hole after the pilot drill. This will stay true on center better. probably can only go an inch or so before out of end mill. Then switch to a drill bit.
 
An interesting problem. I think I would setup as you did, but forget about the 1/8 pilot drill. Just center drill and then drill with the 1/4 inch as deep as you can. Then given that you don't have enough drill press stroke to drill through, I would clamp the material down by any convenient method and use an electric drill and a long drill bit to finish out the hole. The original hole will guide the long bit and hopefully it won't wander too much.
 
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Yeah, I tried that in a Chinese lathe on steel & got the same results. Drill bits wander & the longer the bit / hole, the further they wander. 1 possible cause is uneven tip sharpness, dun no. I do, however watch my professors on UTube. That's what I call Adam Booth, 2 Keiths & Tom Lipton + many others. Just a beginner in machining myself. Anytime I see anyone start a drill bit into a center cut hole, the bit starts it's little gyration as if it started off center - even on their big fancy machines. They, however, are just getting a hole started that is big enough to accept a boring tool or in smaller instances a reamer. Just gotta play with ideas to get close enough sometimes. It's like centering hot rolled steel in a 4 jaw chuck - in practice it's good to see how close you can get, but in the end it wasn't round to start with.
 
tourtelot said:
Hi-

Came to this site looking for a specific answer but it seems I am in the right place for other learning as well.

I am a home-hobbiest and have been punching holes in aluminum for 30 years, mostly electronic boxes (think "stomp-pedals"). Every thing I build is a piece or part to be used in my (now retirement) business as a location audio recordist. But I really like working metal and a table-top mill is on the list in my "golden years" :)

Okay, now for the specific. My only real big metal-working tool is a floor standing drill press. I have been (mostly) successful in doing what I need done with this machine, step-bits, drills, reamers, etc not to mention knock-out punches, abrasive wheels, Dremmel, etc.

I have 2-3-4 blocks, v-blocks, a (nice) sliding table, table clamps and the like. My table is flat to the chuck (within .0005) in both x and y axis.

I need to cross-drill a piece of aluminum bar stock. The piece is 5" long and the stock is 2x1. I want to bore a centered 1/4" hole though the long dimension. Right through the middle.

My set-up was to make a right angle jig with the two 2-3-4 blocks, clamped to the table. Find the centers of the 1x2 faces with a steel rule on the diagonals, light center punch. Clamp the piece in the 2-3-4 block jig. Drill a pilot with a 1/8" drill. flip the piece and repeat with the 1/8" drill. Drop the table and chuck up the 1/4" drill. Center it on the pilot and drill 2/3 deep. Flip the piece and drill through.

I tried this on a block of wood and it worked perfectly. Tried it on the aluminum and the hole somehow wandered, maybe, a 1/16" or so where the two bores met.

What happened? I was pretty careful and expected perfect results but something went amiss.

I'd love a talking through befoir I run to On-line Metal and pick up another piece of stock to get frustrated by again. :)

Thanks for helping someone trying to up their skill level. When you quit learning, you die.

Doug
Click to expand...
There was a thread about a month ago with suggestions on drilling deep centered holes. If you follow all the suggestions you will get a straight hole( within several hundredths of an inch.) https://www.hobby-machinist.com/thr...-made-a-suppressor-adapter.82383/#post-717373
 
There was a recent thread about drilling holes straight.
Part of it was about using a gun drill.
These are known for keeping straight into deep holes.

This explains it --> https://en.wikipedia.org/wiki/Gun_drill

The thread was here --> How do I drill small holes straight? (I made a suppressor adapter)

The problem is these things are expensive - likely much more than the parts you are likely to make with it.
If the rest of the item was circular, it becomes possible to "make the hole first", but in your case, drilling bar stock with a drill press limits that option. Also, much of the previous thread assumed a lathe was involved.

I have seen it suggested here that starting carefully with a center, and then using the right kind of (new) drill, and a technique of "small pecks", + cutting oil, and frequently clearing the chips and swarf, can give good results.
 
Thanks for all the replies. I am going to try it again and just ordered the stock. I talked to a machinist friend here in town yesterday and in addition to all the great ideas on the forum, he suggested that I use a larger bit as a pilot. Maybe start at 1/4", this because he reckons, a larger bit will flex less. So with a careful layout, a clean center punch, a spotting drill, a new 1/4" drill and patience (all of which I possess, except for maybe the patience) , I might do better. Perhaps just a bit (sorry!) cocky on my first attempt.

Doug
 
Lot's of good input here Doug.

I just stopped by to say .....Welcome to the site!

-brino
 
Thanks. Always wonderful to find user groups like this one with so many talented and giving members on-board to pass their knowledge on to others. I am so grateful for the kind welcome and the help.

D.
 
2.5" for a .125 drill is a high aspect ratio hole. It doesn't take too much to have the drill start to wander. Done on a drill press, there is even more tendency to wander.

When faced with a problem like that, I drill the pilot holes from either end as you have done and follow with a slightly large drill, say 9/64" from either end and going about 3/4 of the way. This will tend to merge the two holes. Follow this with successively larger drills. By the time you have reached your final diameter, the two holes should be close to aligned.
 
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