Marking out / drilling holes in precisley the correct place !

Hi John, couldn't agree with more.

Thanks for the link on spot drills, may just invest in a few.

Regards Nick.

I'm surprised that the method of "boxing in " the hole positions with a height gauge hasn't been mentioned. This entails the marking out with a height gauge ( with a sharp scriber) on a surface plate. The hole position is marked out with a square "box" around the central position . A plate with the required hole size is then positioned over the "box" so that that the mid point of each "box" sides can just be seen and the hole plate adjusted so that the hole plate hole is accurately positioned over the "box" and clamped into position with toolmakers clamps. The hole may then be drilled thro' the hole . The hole plate should be of sufficient thickness to guide the drill before the drill point contacts the plate to be drilled and ideally should have the hole reamed. Also the hole plate should have burrs ( no chamfers) removed on it's underside and may be hardened ( & ground on underside) if it likely to be used a large number of times. This was a common method of marking out holes used in the days of "yore" when access to milling machines/jig borers/ lathe was limited (and before DROs were invented !) & only drilling M/Cs were available. Most of the old toolmakers had a number of hardened drill plates for this purpose & in addition a set of toolmakers "buttons" for use in the lathe or drill press. With practice "hole boxing" would give hole positions within 0.003" & was quicker than the more accurate use of toolmakers buttons.

Edited By Dinosaur Engineer on 17/02/2016 22:37:56

what you need sir, is an automatic center punch, use a standard punch to deepen them if you wish.

Michael W

for the OP i would suggest Commander W.T. Barker's article in ME 9th april 1953 if available. well worth close study!

for those of us of the 'old school'!

cheers,

julian

Having marked the job out. On a drill or mill you can line up the lines using a sticky pin running true in the drill chuck then center drill etc On the drill when lined up clamp in place then center drill On the mill job should already clamped down as you can move the tables and use the micrometer dials . this is for home shop not in the tool room
Regards Nobby

I usually dial in my hole locations using the DRO. I spot drill, then drill an undersized hole. I use an endmill like a jig bore reamer to correct any drift of the hole, then drill to the finished size. If I am using a boring head to finish the hole, I skip the end mill.

in miniature loco work, the only time i clamp the vice on the pillar drill is when drilling big holes in steel which is the coupling and big end conn rod holes. in every other case i let the vice float and the drill find the centre popped hole.

this was what i was taught many moons ago by a toolmaker.

cheers,

julian

Here is a good book that covers the topic. Holes, Contours and Surfaces Richard F. Moore, 1955 Predates DROs etc. The second book at the link is also highly recommended.

**LINK**

How is that going to make the hole location more accurate?

The method taught to me was to lightly slide a prick punch along one line until the intersection was reached (it will 'click' into position) and then gently tap the head of the punch. Inspect the depression and slip the tip of a sharp 90° punch into the hole (if all is square) and give it a tap to deepen the hole enough to give a drill bit a decent start.

Actually, for really precise location over marked lines I sometimes use my "CentreCam' which was manufactured about 8 years ago from the MEW article - It's accurate to about 1 thou (pixel) and great for centering over pre-existing holes.

* Danny M *

Years ago, in toolmaking, we had a bunch of drill and reamer guides. These took drill bushes and reamer bushes and were made to a nominal outside diameter. There centre spacing was set with length rods and trig. These were clamped into place and used on the drill press or mill, these were quite large for the clamp to be secured. We also used buttons, also spaced with length rods and trig. But a smaller hole was drilled and tapped, a small screw to hold in place, then an indicator to indicate the position. Lock the machine in place, then removed the button, and used a milling cutter as a drill/boring bar to remove the thread. Then drill to the size, another milling cutter used as a boring bar, then the reamer. We used this method until we had mills with digi readouts and of course a lot better quality mill.

At home here I made some small buttons with a hole in them. I then made a tool to go into the drill chuck that sits over the button. I then clamp after the tool locates the part for me. Remove the button and drill ream etc

Neil

Hi Danny M

Can you please post a picture of the "Centre Cam" tool ?

Emgee

Well, i found at college, that it was actually alot harder than you think to hit a small punch in an accurate manner using a hammer, so it would make it more accurate if you found that this was your problem too.

Btw, if you're worried about using a camera to find the position of scribed lines, more than likely marked out using a ruler, then maybe you shouldnt be scribing your lines at all.

Michael W

Tubal Cain recommended using a little archimedes drill to find the intersection of the scribed lines and start the indent.

Rod

Here is a photo of my minilathe tailstock centre taken when I was calibrating my CentreCam a few years ago.

One had to rotate the spindle 180° and count the pixels to offset the centre of the webcam software.

Webcam distance was tweaked such that scribed lines 0.640" apart on a test piece were 640 pixels wide. I then made a block to set the height.

I shall set it up tomorrow and take a few more photos, it was a brilliant article.

Well, i found at college, that it was actually alot harder than you think to hit a small punch in an accurate manner using a hammer, so it would make it more accurate if you found that this was your problem too.

Michael, my reference lines were marked out using a Mitutoyo height gauge on a surface plate. One of the first projects that I made as a student was a small brass headed hammer to tap small punches and stuff so no problemo.

Btw, if you're worried about using a camera to find the position of scribed lines, more than likely marked out using a ruler, then maybe you shouldnt be scribing your lines at all.

'Scribe a Line' is actually one of my favourite topics in MEW and it is quite presumptious to assume that everybody uses a ruler, despite what you learned in college.

* Danny M *

Edited By Danny M2Z on 18/02/2016 11:24:29

have we all gone 'soft' ? As already mentioned, mark the holes out using rule, height gauge etc, dot or centre punch and if you want, scribe a square box around the outline of each hole, then use a sharp spot or centre drill before opening up progressively with sharp quality drills etc. The hole should fit inside the scribed square box. If your drills are not accurately sharpened, they will drill off centre and unfortunately some new drills are not accurately ground. There should be no need to resort to using the mill for co-ordinates. 20 or more years ago, many MEs didn't even possess a mill. This sort of stuff is the sort of thing apprentices had to learn before being released onto the shop floor, and for newcomers to our hobby, it is just something you have to learn and get better at. There is no substitute for practice before you have a go at an important and expensive piece of metal etc.

No, I don't think so, we've just moved into the 21st century where marking out and centre popping is no longer a necessity.

Andrew

Believe the OP stated used centre punch or the like and drilling off. Will have to settle for the bodgers way reliant on a ruler, centre punch with mark 1 eye ball.

Usually centre punching raises the edge often a burr. If holding freehand or even in a vice your limited to getting the angle right and hope it starts cutting where desired and correcting.

Mill and a dro straight in no centre drills etc just the drill used, get a feel for whats happening and look for deflection. Accurate to size drill undersize then open up, drill or reamer will self centre.

I'm surprised no-one has mentioned about the light.

My workshop is by no means bad for light, but I still find that the act of making an accurate centre punch to a scribed line depends greatly on the quality of the light.

By the time you have your hand over the top of the punch, it blocks the light and you can't see properly.

I simply have an automatic punch set to the weakest setting, with a sharp pointy end. I also have one of those cheap pencil style LED torches. I just use one in each hand, and it eliminates any doubt. The torch lives in the drawer with the punch.

Once you have the dot in the right place, as long as the point cone on your ordinary punch is nice and round, getting a big welt with the hammer on target will be no problem at all.

HTH

Edited By Andy Ash on 20/02/2016 10:28:51