marking out steel for drilling query

[smokeyone]

Hello from a newbie

I know this is a really simple question but ....
for example steel bar 1 inch wide say 1/8 thick
need to drill a quarter inch hole on the centre line

lay a ruler/set square across the width, centre punch the half way mark or half an inch in ....

fix the steel bar down on the drill press, line up say a 1/8" drill on the centre punch dot and drill through followed by the quarter inch drill ....

double check afterwards and my hole is just a fraction out from the centre .... never spot on, so where am I going wrong please
Thanks

[steam4ian]

G'day Smokey

I have found using a centre drill for starting helps as it is more rigid than the 1/8 drill. To line up I have rod with one end turned to a point which I use for spotting the work to the drill centre line in the first place. Put it in the chuck and lower down to your centre pop mark and locate the work accordingly.

Bib question, how true is your drill press?

I never had any success until I got mill/drill. The quill on my drill press moves off centre with pressure.

BTW, in theory you can walk holes back to centre by using a chisel to move some material off the side of the hole as you start with the larger drill.

Regards,
Ian

[smokeyone]

Thanks for the info.
Centre drill bits.. are these the ones that sometimes come double ended, maybe the other end is a countersink !

Rod turned to a point, clever idea & will check if my drill press is true.

Any thoughts about my marking out - how "do you" mark a point on steel bar for drilling, something better than a ruler/set square !

[abby]

Drilling accurately positioned holes is one of those things that even accomplished model makers sometimes have problems with , and centre punching scribed lines is often the root cause of inaccuracy, there are aids for this but a good magnifying glass is useful.
When drilling holes through the sides of bars I - when ever possible - I mount the bar in my lathe tool-post or on the cross-slide , use a dti to set it square and centred , and drill in the lathe. Once centred further holes can be picked up using the dti and you should easily get to a couple of thou or even better.

[russell]

Depends how accurate you need it.
Surface plate, angle plate, and height gauge will give the best result but odd leg calipers from each edge will find the centre quickly and easily.

Russell.

[dickdastardly40]

Smokey,

Is your bar exactly 1" wide, when you scribe your centre line are you 'offsetting' the tip slightly from the rule? Did you measure your line from either side after scribing, are you fairly sure your pop mark was on the line?

As per Russell, try an odd leg caliper to ensure you are exactly bisecting the bar.

Al

[ilvaporista]

Check as well that your drill really is square to the table. It took me a while to spot that the column was not perpendicular to the table. Don't immediately think that because there is a dowel pin that all is OK. Some drill presses compensate for table flex but that should be in microns not mm's.

Like Russell I use Jenny's to find a centre of the bar and then an optical centre punch to pick up the line (eye sight probably failing due to earlier excesses ).

A centre drill is good for keeping things on track.

[smokeyone]

Thanks all for the tips, I do appreciate it.
Purchasing an optical centre punch should improve things no end.

So, just as an example for a different set of measurements,
how would you mark out across the width of the 1" steel bar,
say two different spots.
eg 15/64 & 33/64

I just used these to be difficult rather than use round figures.
Thanks again

[Smifffy]

.....I would use a height gauge/scribing block with an angle plate on a flat surface (I managed to pick up an old surface table for a tenner). Check out wikipedia for more background:

en.wikipedia.org/wiki/Marking_out

I would also go metric too, cos I can't be doing with all these silly (dated) fractions :-)

[dickdastardly40]

Smokey,

For that sort of malarkey, I'd personally do it on a surface plate with a surface gauge, angle plate and rule or if feeling posh a vernier height gauge. If you have no other equipment than a rule and scriber would make this particular example more difficult.

I'm sure others will chime in with their preferred way.

Al

(cross posted with Smiffy, sorry for duplication)

[smokeyone]

Thanks for the advice.
By a height gauge I assume you mean one of these
s166.photobucket.com/albums/u113/smokeyone2007/?action=tageditmany

Please explain a little more, surface plate okay,
angle plate to make certain our steel bar is 90 degrees to
surface plate table but how would you use the height gauge.
You would know the width of steel bar.......

[cotswold]

russell said:

Depends how accurate you need it.
Surface plate, angle plate, and height gauge will give the best result but odd leg calipers from each edge will find the centre quickly and easily.

Russell.

Odd-legs are a simple to use and surprisingly consistent (I say consistent because you are 'gauging' not 'measuring'). By using both edges you can expect a pair of lines - and if you think you have only one line, take a look under a magnifying glass. Now split the distance between those lines, preferably with an optical centre punch.

[chris vine]

Just a thought,

Make sure your centre punch is making a big enough dint and also that the point is not too narrow an angle.

A deep wide punch mark on the surface makes a lot of difference to how the drill stays where it is meant to be. Always assuming that the punch mark was in the right place anyway!

It is not easy to get right....

Chris.

[smokeyone]

Cheers for the advice. will look into odd legs but I have been usuing a centre punch with a very narrow point. Had not realised that a wide point is needed.
On with the small shopping list.
Thanks

[Tel]

you should make the initial mark with a fine centre punch - which is easier to 'click' into the scribed lines, then enlarge it with one of 60° or so included angle.

The trick is to drop the point into one line a bit away from the crossing point, and then drag it along the line until the point 'clicks' into the intersection

[paul]

I'd use a centre drill or at the very least a 1.5mm (1/16") to start the hole then switch to the 1/8" (3mm).

Alternatively, and this depends upon circumstance and is a long way round, you could use a slightly oversize piece of metal, make your hole then turn/file/mill whichever edge to make the hole central.

But what do I know!

[Shawki Shlemon]

In a situation like this one ,a line in the centre I mark the line from both sides and they should co-inside if marking is correct , the rest has been said above .

[Lurkio]

Smokey,

Reading through your posts you don't actually mention that you are scribing the position of the hole onto the work before centre-punching.....are you? Or are you just positioning the centre punch at the side of the rule?

Lurkio.

[smokeyone]

I am scribing the steel first although I will admit for some jobs I have just marked the steel from the edge of the ruler in which case the hole is even further out from true. Back to only scribing
then, I think invest in two new punches and a centre drill.
My vertical drill seems true but as other members have advised they can be out a shade and a vertical mill could be the answer.
The centre line of a steel bar was just an easy example, odds on for a new project the hole will be needed elsewhere.
One forum member pointed out about sticking to metric rather than imperial.....cuts down on the measuring......

[Lurkio]

Smokey,

OK, with practice you should be able to get your holes to drill in the correct place - to within a few thou hopefully. For many purposes as a newcomer to the hobby, using a rule, square and scriber will be sufficient to do that...it's how thousands of engineers began their training.
The other stuff can come as you progress and as the projects get bigger.
In the advice already given, Tel in particular points out the way to do it in my view. Make sure your scriber is nice and sharp.
For larger holes, I would use a small drill as a pilot before finishing the hole to size.

Lurkio.