Accurately centering holes with drill press?

[dicej32]

I just got a new drill press. Having problems accurately drilling marked holes. I tried center drilling first but then the table has to be lowered to fit the drill bit so all positioning is lost. Tried a few holes yesterday on some 1/4" aluminum but locating by eye on a marked location I still come up off center. Any trick to doing this? I tried using a center finder with needle nose probe but when I center it in the punch mark its hard to keep it from moving off center. Any suggestions would be greatly appreciated.

Jenaro

 

[Loose nut]

When you use a wiggler/wobbler, how ever you want to call it, start by running the drill press fairly fast and then with the end of a pencil push the end of the needle towards the center axis, until it is running true, takes a bit of practice to keep from going to far. Then lower the tip until it is just a few thou. above the work piece, get your magnifying glass out and adjust the table until the tip is lined up in both directions, then use your center drill, you can get within a few thou.this way

 

[te_gui]

I realize most home drills don't have a reverse, but if you are one of the fortunate ones you can run in reverse until you feel the center drill or bit drop in to the punch dimple, then while keeping presure down with the quill switch to forward and drill as normal.

Brian

 

[mklotz]

It's very difficult to locate a center pop with a larger (say > 1/4") drill. Small drills will easily guide themselves into a center pop. (Try it on some scrap until you get the feel.) A center drill is intended for drilling center holes for lathe centers. As such, it's made purposely stiff and can't bend enough to guide itself into a center pop easily.

So, for the larger drills, drill first with a smaller (~1/8") conventional drill. In addition to helping you hit the mark, the pilot hole will make drilling the larger hole appreciably easier.

Also note that it's hard to start a drill on a punch mark made with a *prick* punch. After marking your hole location with a prick punch, re-punch it with a real center punch to create a pop that the drill can easily find.

 

[gilessim]

You could try turning a point on the end of a piece of drill rod about the same dia. and length as your drill bit and locate your centre first using that, even pressing lightly with the point may be enough to help the drill go in , otherwise solder the smallest centre bit you can find into a hole drilled in the end of yet another piece of drill rod and use that as an extension , I use a magnifying glass to locate the spot and just touch on, that should be enough to guide the drill bit.

Giles

 

[Mcgyver]

99.9% of the time I let the work 'float', in other words it is not clamped or fixed to the table. this way a spotting drill (or centre drill but a spotting drill makes subsequent drilling easier) will pull a centre punch mark into alignment with the spindle. This is perfectly safe and is standard practice however you have to have a sense of the relationship between the inertia of the work (or if small, work in the DP vice) and the potential torque.

At the same, the DP is the most dangerous machine in the shop so you have to be intelligent about it. you can get large amounts of torque from large drills going slowly, or all of a sudden by a drill grabbing in very thin stock or when drilling brass and bronze without the correct drill geometry. For large drills, if you are worried that a job that could get away from you, spot drill then drill a small dia. With small dia's there is little chance of the torque being so high it runs away from you. then with a pilot hold drilled, if you feel it necessary to clamp to the table for successive drills, even if your alignment is not prefect they will tend to follow the already drilled hole. lets say you're putting a 3/4 hole through a piece of steel - I wouldn't hand hold that - but i would for the 3/8 hole i'd made as pilot - then clamp for the 3/4 hole

For brass and certain bronzes grind or stone on zero rake and they won't grab and for thin sheet stock, well, pick a different type of drill (brad point or step) or sandwich it. if the work piece is small, use a drill press vice or finger place to increase the mass - its impossible and very unsafe to hand hold small parts for drilling.

As a safety I keep a short chunk of large (may 3 or 4") angle iron clamp to the table. I often use this as a stop when drilling larger pieces.

 

[compound driver 2]

Hi
Buy a decent set of Slocomb Centre Drill's from numbers 1 to 6 and use a well ground centre punch to start out.
Small drill bits should NOT guide them selves into the punch mark/centre spot but rather drop straight in. Allowing the drill to wander onto the mark can cause a drill to goo of line and in the worst case snap. Its no trouble aligning a drill bit to a punch mark and even less trouble if you have used a Slocomb Centre Drill with the work clamped to the press table.

cheers

 

[GeneK]

One other method is to use a bit of Rodico, blue tack or other stick on type stuff to hold a sewing needle to the tip of the drill bit.(or milling cutter) run the drill and 'milk' the needle to run true and use that to line up with the pop mark. Remove the needle and stick on type stuff and drill the hole.

GeneK

ps I think this is in one of the Machinist bedside readers, well worth the money for all the tips and things in them.

 

[raym 11]

At last resort I sometimes use an edgefinder with a pointed end. Spindle not turning .I can move the part until the index prick mark or small location hole is on the point with a light pressure and I cannot feel any offset of the edgefinder with my fingernail.

If you want to see the spindle runout, if any, turn the spindle by hand and note any change in offset of the edgefinder.

 

[Bernd]

I have done several large plates of aluminum that have several holes in it. I first prick punch the scribed lines. Then I use a center punch to enlarge the prick punch mark. I use a #2 center drill. The drill is small enough to pull the work on center while running. Then I just apply pressure to make the center drilled hole. The holes will be within tolerance of your marked lines. Hope this has helped.

Bernd

 

[raym 11]

Gene K

I cant figure out how to insert a partial quote in a reply so I'll just say I agree the Bedside Readers are very worth while. I have learned a lot from them and made several of his projects.
I wonder if Guy Lutard is still around. ???

Ray M

 

[Lew Hartswick]

Gene K
I cant figure out how to insert a partial quote in a reply
Ray M

Just highlight the part you dont want and delete it. Just as I did on your post.
...lew...

 

[raym 11]

Just highlight the part you dont want and delete it. Just as I did on your post.
...lew...
[/quote]

Thanks Lew,

Ray M

 

[Bernd]

I wonder if Guy Lutard is still around. ???
Ray M

Yes he is. Here's his website: http://lautard.com/
Bernd

P.S. I'm waiting from him to publish the forth Bedside Reader.

 

[DickDastardly40]

One other method is to use a bit of Rodico, blue tack or other stick on type stuff to hold a sewing needle to the tip of the drill bit.(or milling cutter) run the drill and 'milk' the needle to run true and use that to line up with the pop mark. Remove the needle and stick on type stuff and drill the hole.

I was taught an alternative to this which we also called 'sticky pin', which works on larger holes where the chisel tip of the drill won't fall into the pop mark. If you are confident that your centre pop is accurately located, scribe the biggest circle you can with a pair of dividers on the job in layout blue or marker pen.

Set the job on the table with the drill in the chuck and a pin stuck to the side of the drill with blu tack or gum and the point of the pin below the tip of the drill. hand rotate the drill adjusting the pin until you get it set to the radius of the large scribed circle and then move the job until when you rotate the spindle the tip of the needle follows the scribed circle. Nip up the clamps and recheck, remove the gum and drill.

God I hated that method, but it did work.

Best Always