Spotting/drilling question

[jgarrett]

If one has several holes of the same size to drill in a piece what is the best procedure to use? Center/spot all of the holes and then switch to the drill bit an go back over them or spot and drill each one at a time?? This is using a DRO. Holes are <.125"

Also is there and difference in whether you use a center/spotting drill or a combo drill/countersink??
Thanks,
Julian

 

[Ken I]

Personally I centre / spot - change to drill if I'm working off the dials - when working with a DRO I spot all the holes then drill them (I sometimes do this off the dials as well if depth is an issue on multiple holes).

So I would guess its a matter of choice and to some extent how confident you are of getting back to exactly the same place twice.

For deep holes I would tend to spot / drill / bore etc. to keep the exact same centre.

If I understand you correctly - using a drill c/sink combo - you still need to spot / centre first - the combo drill still has a chisel point and cannot be relied upon to find centre (unless it has been accurately thinned and is short - like a spotting drill).

Another personal preference when working off dials / DRO is not to centrepuch the work as this can drag the bit off centre (because your punching wasn't spot on) - I'm sure there will be a bunch of guys who are going to disagree with me on this - not much accounting for personal preferences.

By the same token I don't drill bolt clearance holes - I drill them bolt size - if you get everything spot on it fits (a point of personal pride perhaps) only adding the clearance size later or (horrors) if needed.

Similarly I'm not big on marking out if I'm going to be working off the dials / DRO anyway - when working off the dials in particular you can easilly be a whole rev out and ruin the job so marking out can save you from yourself here. Quite often I will print a self adhevice lable 1:1 instead of marking out - my 1200 dpi printer is more accurate than I can mark out - and serves to show you the error of your ways if you have miscalculated or miscounted the handwheels etc. etc.

Whatever floats your boat.

Ken

 

[Mainer]

Whatever you like. If I'm doing a bunch of holes the same size I would probably spot them all with a centerdrill, then drill them all, to save multiple tool changes. Since I hardly ever mark out, it also gives me two checks on locating the holes. If, when going back to drill, I end up located not over a spotting hole, I know I screwed up either when spotting or locating for drilling.

But, I may drill/tap in one setting. Depends on my mood.

 

[Lew Hartswick]

IF and that is a BIG IF, you have an Albrecht chuck it's easier to do everything for
one hole at a time. I just today did 4 pieces (1 1/2 dia ) with 3 holes taped for
10-32 on a 9/16 r bolt circle 120 deg. Centre drill, drill through, power tap, move to
next spot, repeat. Can't beat that rotab with a 3 jaw chuck mounted, and an Albrecht
drill chuck. Then I did 4 four inch aluminum discs with matching set of countersunk
clearance holes, again : center drill, clearance hole drill, countersink. repeat etc.
Piece of cake.
...Lew...

 

[jgarrett]

Ken, I like your idea of printing a marking label. I have always used a combo countersk/drill to spot my holes. Guess I got some misinformation along the way somewhere.. I will invest in some center/spotting drills.
Lew. no Albrecht chuck.
Thanks for the replies.
Julian

 

[jgarrett]

After a quick look I do not see any spotting drills smaller than 1/8".
What is the correct way to spot and drill holes in the #44 size in material thicker than say 1/8"?

Julian

 

[Ken I]

The size of your spotting drill is not that important - what is important is that you don't spot larger than the hole you are going to drill otherwise you will be left with a 118° depression around your hole.

I just eyeball it.

Ken

 

[kvom]

I spot them all, then drill. The drill is going to go into the spot drill hole even if it's off by a thou or two.

 

[MachineTom]

Recently I had to put 50+ tapped holes in a block. Using a spotting drill adjusted to slightly deeper than the finished tapped diameter, all holes were spotted, then drilled then tapped, this left each tapped hole with the correct countersink, all the same.

If you spent a bunch of time you could make up spacers for the depth stop for each bit as you changed from spotting to drilling when doing a bunch of holes. I would think it would take much more time to change bits than to make two passes around the 50 holes.

Also put in dowel pins in that same block, did the same way, spot each hole, then drill, then ream. Depth control is often as important as location, if you can hit the location once, you can hit it three times.

 

[DICKEYBIRD]

Just finished drilling/tapping countersinking 16, 10-32 holes in a steel housing. My mind numbs & wanders on repetitive jobs so I complete all ops at 1 location before moving on to the next.

This particular job justified the time I spent building a pair of very solid table stops and a good vise stop back when I 1st got my mill. The job had a pair of countersunk tapped holes on each face of both ends of a piece of rectangular stock. Once I had it set up for the 1st pair and all the stops in place, no more dials or measuring were needed!

I used to use a keyless chuck (not Albrecht though) but kept having trouble with the tap slipping, especially when backing out. I switched over to ER-16 and ER-32 collets and love 'em! A little slower to switch tools but they're so secure!

 

[Lew Hartswick]

I used to use a keyless chuck (not Albrecht though) but kept having trouble with the tap slipping, especially when backing out.

Ah that is your trouble, (using the tap directly in the chuck) make a set of the tap
holders that hold the tap by the square end and have a round end for the chuck.
I believe Marv has pix of his somewhere, I made a set of them a few years ago.
...lew...

 

[jpeter]

I've had pretty bad luck spotting with a center drill. I make spotting drill using 1/4 drill rod. Lathe it to a point, I like 60 degrees, then harden it. Next, grind the sides away so it looks like a spade bit; pretty thin center section. Don't grind too far up the shank cuz you never spot drill to deep anyway. I grind it with a Dremel cut off wheel. Don't pass judgement until you try it. I keep them short, maybe 1 to 1-1/2 long. Cost about a dime to try one. Its a fun project and besides you get to use your lathe making it.

 

[ShopShoe]

jpeter,

I think I understand how you make your spotting drills, but could you illuminate with a drawing?

Thank You

 

[jpeter]

How about a picture?

I was careless about the discription. Notice I grind away half the side trying to get as close to half way through as I can. Its not hard to determine how deep cuz you grind to the point.

 

[ShopShoe]

jpeter,

Thank you so much! I was imagining something shaped like a spade bit for woodworking with some extra grinding. It looks like it is easy to do. Making and modifying tooling greatly adds to the enjoyment of this hobby. Gotta try it.

--ShopShoe

 

[Blogwitch]

To me, making a spotting drill by hand, OK, it shows you can do it, but you are introducing possible error where there should not be any at all.

They are so cheap nowadays, everyone should be using spot drills and NOT using centre drills, they are designed for another purpose, and are not very accurate.

I kitted myself out with cobalt spot drills from 3mm to 8mm, in both 90° and 120°, in the 3mm ones, I also bought a pair of tungsten as those are the ones that I use the most. If looked after and used correctly they should last a lifetime.

I think they cost me just over 20 UK pounds for the whole lot, somewhere around 25 to 30 bucks US.

http://www.engineeringsupplies.co.uk/drilling-c-160.html?9=172&10=&11=192&12=&13=


Bogs

 

[jpeter]

Yeah well when you need one and you don't have one... I find a lot of satisfaction in making my own tools, especially the ones that work. I make lots of my own tools. I just made 2 heads for my second v8. The head has holes for 18 head bolts and they all have to be dead nuts on to match with the block. Pictured is the spotting drill I used. I also made the counterbore I used on each head bolt. I also did the CNC conversion on the Bridgeport mill I used for drilling the holes and surfacing the combustion chambers.

Check it out

 

[Blogwitch]

Touchy!!

Please read and UNDERSTAND the second half of the first line.

Pi**ing contest on lads.

A couple of years ago, in my home shop, I drilled 5,000 holes, in 1000 components, over the space of four days, every was one spot on, and I didn't need the help of CNC. It's easy when you know how.



P-l-e-a-s-e, no need to ruffle your feathers.

 

[wareagle]

Gentlemen, this thread is now locked. No need for a brawl.