# Drilling Concentric Holes



## dusty (Oct 25, 2009)

I am a wood worker trying to work with metal (aluminum, actually). I need to drill a number of concentric holes and need some advice.

Should I drill the larger hole first or the other way around?

How do I keep the drill bit from running? I have drilled a small starter hole thinking that would help but I don't believe it has.

It is OKAY to laugh. My feelings will not be hurt. After being inept for 70 years, I have gotten use to it.


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## GWRdriver (Oct 25, 2009)

Dusty,
Tell us a little bit more about what you are trying to accomplish, including hole size. Are you by any chance trying to make countersunk holes for recessing screw heads or some such?


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## Tin Falcon (Oct 25, 2009)

dusty:

First of all(UP on soap box) an intro please tell us about yourself and why you are here etc.(off of soap box.)
No laughter sometime the even simple operations can be a pain and give undesirable results. Drilling can be a challenge things can grab and the drill bit gets stuck. Try drilling out a broken grade 8 bolt with a hand drill and try not to damage the parent metal. This with a Black and Decker(Yuck)hand drill . 
Anyway back to your question 
Specifics would help. 
The size of holes 
Number of holes
grade/type of aluminum(some grades are quite gummy)
what machine(s) are you trying to use.

there are lots of variables to consider
speeds /feeds
drill bit grind geometry.etc. 
Tin


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## dusty (Oct 25, 2009)

In response to your questions: I am a wood worker but I have started building a number if aluminum jigs. It seemed as though it would be the same as working with wood but it is not.

I am using a Shopsmith Mark V Model 520 that provides a lathe, horizontal boring, vertical drill press and saw.

I am installing bolts in an environment where the heads need to be buried; thus the need for concentric holes. I am also drilling and tapping a number of holes. The taped holes will be 1/4" (1/4, 20). The balance of the holes are 5/8" counter bores with smaller through holes.

You ask, why am I here. Well, I thought "Home Machinist" - just what I need. Looking a little closer, I see that you guys are really into engines so I am probably in the wrong place. For that I apologize and if you want, I will cease.

If not, I do appreciate your responses....and I find your forum most interesting even though it is not in a discipline that I follow.


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## Dave Sohlstrom (Oct 25, 2009)

Dusty

I believe you are fine asking your questions here. Jigs are jigs be they for building engines or other things.

For the 5/8 counter bore. Go to Enco and look up piloted counter bores. You drill your hole for the bolt to a standard clearence diameter. then run a piloted counter bore in to the depth that you need to have your bolt clear the surface of your part. The pilot keeps every thing concentric. you will also have a flat bottom for your bolt to set on.

Dave


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## GWRdriver (Oct 25, 2009)

Dusty,
Had your holes and c'bores been relatively small I was going to suggest that you could make your own bits from drill rod but for 5/8" diam counterbores . . . what Dave said.


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## Deanofid (Oct 26, 2009)

Hi Dusty;

First, I don't mean to put words in Tin's mouth, but I don't think he was asking "what are you here for" to insinuate that you were in the wrong place. More like what are your interests and such.

I don't really know the capabilities of the Shop Smith, but you say "horizontal boring". You can get the counter bores you want if you are willing to pop for one in 5/8", but that one alone will run about $35. If you can do horizontal boring then you can probably make the counter bores using a flat ended boring bar. 

To start your hole, no matter what kind of machine you use, start with a centering drill. It's a short, plain shanked drill bit with very short flutes and a small stiff starting point. Just use it to make a dimple to keep the drill bits from wandering off the position you want to start them. Then continue from there. 

From there I would drill through with your bit for 1/4-20 tapping and then drill or bore the next bigger bore you need. By boring you can make a flat bottomed hole. 
When you tap aluminum, it can be tapped dry, but it is much easier if you use some kind of tapping aid. I use paraffin wax, rubbed on the tap. One of the few things that WD-40 is good for around machine tools is tapping aluminum, so you might try that too. Clean your hole out often to keep chips from plugging the tap.

I didn't catch how deep you need to go with these holes. If they are fairly shallow, I would drill the smallest hole clear through the piece and then do the larger hole. If they are pretty deep, start with the smallest size and just drill a short way, then do the larger bore. Finish up by completing the smaller hole through. If the hole is not deeper than the full length of the flutes on the drill, just drill the small hole clear through to start with. Clean the drill flutes often by backing out the bit and then going back in, (pecking).

Dean


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## dusty (Oct 26, 2009)

Thanks for your replies. I do believe you have answered my major questions. What I am missing is a centering drill. I have been attempting to do what you instruct but with a simple "small" bit followed by a larger; this sorta works but the bit tends to walk thus I loose the center.

I'm going to have to spend my operating budget this month for metal working tools. That's a bummer - for a wood worker. I have to though, I can't stand looking at those jigs with the bolt heads off center in the counter bore.

BTW, I thought the flat bottoms only came with a milling machine. ;D


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## Tin Falcon (Oct 26, 2009)

> You ask, why am I here. Well, I thought "Home Machinist" - just what I need. Looking a little closer, I see that you guys are really into engines so I am probably in the wrong place. For that I apologize and if you want, I will cease.


Dusty sorry if you felt put off. While the focus here is building model engines we are certainly willing to help interested folks with machining questions. 
It helps the folks here help the newbies if we know a little about you ,your interests and where you are from. We are not mind readers. 
While I do sometimes question the motives of newcomers who post something for sale or to buy etc in there first post that was not my intent in your case.I do see you as sincere and wanting help with machining. You are welcome here.
Tin


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## Deanofid (Oct 26, 2009)

dusty  said:
			
		

> BTW, I thought the flat bottoms only came with a milling machine. ;D



No, you can get them with the lathe or even the TV! (smartypants!)


By the way, let us know how you make out with your drilling/boring chore.
DW


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## joeby (Oct 26, 2009)

If you need 5/8" counterbores and have a spare 5/8" drill bit lying around, you could grind a flat-bottom drill and finish your counterbores with that. You need to drill almost to depth with a conventionally ground drill first, and just finish with the flat-bottom. The hole being roughed in like that will keep the flat-bottom drill from wandering.

 You can get away without centerdrilling, sometimes, with a stub drill. Just a drill with very short flutes, easily made by cutting most of the flute length off and resharpening.

 My $.02 toward saving the budget.

Kevin


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## Captain Jerry (Oct 26, 2009)

Here's 2 cents worth from a woodworker. I know a little bit about Shopsmith, having worked for the company in the sixties. I also did a few years with DeWalt when the only product was radial arm saws, pre Black&Decker. 

Be careful what you say to a woodworker about boring. Woodworkers bore holes with a drill bit. As much as I like the Shopsmith as a woodworking tool, it is NOT! a horizontal boring machine. It is a horizontal drill press! The spindle bearings are fairly tight but there is no controlled micro feed. Be sure to set your depth stop on the quill feed. and CLAMP your work piece to the table!!! Particularly for anything ove 1/4". The Shopsmith has a very powerful motor with lots of torque, particularly at low speeds. The table is ridgid enough for woodwork but not anything like a metalworking mill or lathe. Aluminum can be gummy to machine and can grab your drill bit before you know it. For woodwork, it is fine to put a piece against the fence and hold it down with your hand. Not so much with aluminum.

One of the key issues on this forum is safety, and it should be so in all our shops. (Particularly for us older guys). Woodworking procedures that you may have gotten comfortable with may not translate directly to metalworking. Just takes a little shift in your thinking.

Jerry


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## dusty (Oct 28, 2009)

I want to thank all of you for your assistance. I have not been totally successful in my endeavor but that was certainly not the result of your inputs. I have drilled six of the holes somewhat successfully and five of the counterbores. I stopped on the last counterbore because the machine didn't sound quite right. I found that the drive belt was about to give out. Had to stop and change that.

I bought a new 5/8" counterbore. I had the other drills that I needed.

The only real problem that I have had has been getting everything lined up properly. I really need to be able to see better than I can and I need accurate x/y control. Most times while doing wood work if I get to within 1/32" I am close enough. That does not seem to be the case with these screw holes.

I am going to make some sort of x/y control for on my drill press that can be used either in the vertical or horizontal drilling mode. (yes, Captain Jerry - I realize that I do not have a "real" horizontal boring machine".)

The other thing I don't have is an accurately setup drill press. I really though that I was properly adjusted but when I found that some of the holes did not line up properly, I checked. The drill bit is not perfectly vertical to the table. Close enough for most wood work but not for what I am attempting.

Too bad I didn't start this learning endeavor many years ago (before I retired and went on fixed income). If I had, I probably be in the market for some new machinery.

Thanks for your help. I post later with the final results. I'll include a couple pictures if that can be done here. I have not checked that out.


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## dusty (Aug 18, 2013)

Thanks for all of the replies.  I took no offense from any of the comments and I found them very helpful.  I have not been active here for reasons that have nothing to do with the forum but rather my personal health.  It is hell getting old.


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## MachineTom (Aug 18, 2013)

Welcome back Dusty, I was just about to respond when I noticed the thread was 4 years old. So has you Metal illness grown since you last post? like most hobbies interest shrinks and grows like so many things, this growing old part seems to be the trail we all must follow.

Since you returned here I assume the "metal Illness" is currently growing.


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