Hole layout 101

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Tin Falcon

Well-Known Member
Joined
Jul 9, 2007
Messages
7,207
Reaction score
787
many new folks struggle with accurate hole layout.

For those who have cnc or a Digital Read out DRO simply put in the numbers and check hole locations after a quick peck into the part. but even with dro or cnc a good layout can prevent errors.
there are varied ways to lay out parts the army TC 9-524 covers basic layout. as does the MIT video series. here is how I do a basic hole layout. start with a squared up piece . you NEED two finished edges that are perpendicular (square) to each other. use a poster marker to dye the part.

s0070857_sc7

scribe lines with one of these.
g9619.jpg

sitting on a granite surface plate and resting against
g9574.jpg


Once all lines are scribed use an optical center punch to punch centers of the holes.
h5781.jpg

Above photo grizzly tools
Then center punch with one of these:
image_18511.jpg


photo HF tools

Then drill with a thin drill bit like 1/16 this will follow the punch mark. then with a spot drill . the a pilot drill and finish drill .
Hope this helps.


for bolt circles I like a 6 hole cirlce it so happens that the radius of the circle and the cord distance between hols is the same.
or you can use the above method to lay out after converting from polar to rectangular coordinates. This can be done with math or consuting the machinery handbook.
Hope this helps
tin
And other fell free to add your favorite method .
 
I read a very good article many years ago that dealt with hole accuracy. In short, even if your marking out is very good and you drill carefully often the hole still ends up in the wrong place! Not so noticeable with small holes but large diameter holes, especially a line of them can look really bad. The authors answer was what he called "boxing". Basically he marked and centre punched where the hole needed to be then accurately scribed a box around it that should enclose it. If the hole started to wander as you go through with successive drills you could see it and take remedial action - worse case was to use a file!
If you are drilling by hand it's a technique worth considering.
 
The optical centre punch seems like a great idea. What is the best one to get please ?
 
The optical centre punch seems like a great idea. What is the best one to get please ?
The one pictured is from grizzly tools . I purchased one from enco Mark-on brand IIRC made under licence by pc tools. I laso made one. veritas tools (woodworking tools) in canada sells a nice one.
mine has only one punch and lens.
Tin
 
I read a very good article many years ago that dealt with hole accuracy. In short, even if your marking out is very good and you drill carefully often the hole still ends up in the wrong place! Not so noticeable with small holes but large diameter holes, especially a line of them can look really bad. The authors answer was what he called "boxing". Basically he marked and centre punched where the hole needed to be then accurately scribed a box around it that should enclose it. If the hole started to wander as you go through with successive drills you could see it and take remedial action - worse case was to use a file!
If you are drilling by hand it's a technique worth considering.

I'm suggesting that this was Tom Walshaw AKA Tubal Cain but George Thomas also went into this thoroughly.

One doesn't play with centre drills to start holes in the best circles:hDe:
 
That's how I was taught and I stick to it, because it works:

Scribe the crossing lines. With a sharp center punch*) make a light punch. Check and correct if necessary. Correcting should not be necessary, because you can feel where the two lines meet. But that requires a sharp punch.
Drill with say 2…3 mm (if that isn't to big a hole, dummy!). Measure. If need, correct with filing*)
Increase drills until you are at the desired size, maybe correcting in between.

While drilling, rotate work every once by about 90°. This reduces wandering of the drill.

If you need to make precise work, you have to start precisely. Lower the drill into the punched location and watch wether it bends left/right or back/forth. You'll have to rotate the drill to see that bending better (you'll learn when you try it). Align vise accordingly. You will never get straight bores if you ignore this initial step.


*) Center punch:
You only need one. The cone has at about 70°…80° included angle. Keep it sharp by grinding lengthwise (forget about oil stones).

*) Correcting
If the hole is off by say 0.05 mm in one direction, file the hole oval into this direction, making it bigger by twice the error (0.1 mm).

Center drills are for the lathe, spot drills for the mill. They have nothing to do with drilling to a scribed and punched location.


Nick
 
I'm suggesting that this was Tom Walshaw AKA Tubal Cain but George Thomas also went into this thoroughly.

One doesn't play with centre drills to start holes in the best circles:hDe:

Hi Big Brother,

Gus with you but may I add on.I have no DRO. I use a Japanese 150mm Steel Ruler and Starrett Scriber and a Cheapo Prick Punch and do it the TubalCain USA method,using clockmaker's finger drill from 1.5mm 2.5mm and 4mm if required to spot on starter holes so that drill will not wander off. Ever since all the holes been spot on.I use box when necessary with critical holes.
Looking for suppliers who will ship spotting drils to Singapore.

IMG_1252.jpg


IMG_1267.jpg


IMG_1352.jpg
 
Last edited:
The issue is really that you are not using an Archimedes pin drill in conjuction with a watchmakers loup.

OK it's old hat stuff but I have a set of loups of various powers, the perspex.plexiglass thing, the surgeon's binoculars and--- a couple of microscopes. One is a proper brass affair whilst the other is from a children's toy science set.
The best lathes should have a plsce for the microscope. I always use a surgeon's pair of binoculars for setting my verniers. Nice having a daughter who has a Masters in Dentistry and a son in law who is a senior consultant in heart surgery.

Cheers

Norm- the Happy Wanderer
 
I use a Japanese 150mm Steel Ruler [snip] Ever since all the holes been spot on.

I think, you do have a different definition of "spot on". With a ruler, I'd say you'll be always "quite off" (at least to my definition).
You need a height gauge (first post, first picture) to get precise work.

Why not use center drills or spot drills? They do not bend, they are designed to be rigid. When drilling to scribed lines, you want a flexible drill to see wether you are spot on or not.



Nick
 
I have a little trick I use if at the start of drilling the hole is not quite spot on or has started to wander i have some very small end mills and I take the closest to the size of the hole I am drilling and remove just enough material so that the hole acts as a guide for the drill, you can remove material from the edge of the mis drilled hole with the end mill to re align it and hopefully get a truer hole. I haven't tried this with anything over 4mm but I think anything larger is easy to spot and rectify before needing to use end mills
Doug.
 
I am wondering how many of us make models where hole location tolerance is less than .005". Using the basic scribing and punching techniques described here should result in at least that degree of accurancy, esp. as drills are not particularly precise instruments themselves.

I know that 99% of the holes I need to drill are either tapped holes or are clearance holes for screws, and a small deviation in a tapped hole's location can be accounted for by adjusting the clearance hole.
 
The issue is really that you are not using an Archimedes pin drill in conjuction with a watchmakers loup.

OK it's old hat stuff but I have a set of loups of various powers, the perspex.plexiglass thing, the surgeon's binoculars and--- a couple of microscopes. One is a proper brass affair whilst the other is from a children's toy science set.
The best lathes should have a plsce for the microscope. I always use a surgeon's pair of binoculars for setting my verniers. Nice having a daughter who has a Masters in Dentistry and a son in law who is a senior consultant in heart surgery.

Cheers

Norm- the Happy Wanderer


Hi Big Bro.Norman,

Where can I buy WatchMaker's Loup. Using my fingers to twirl 3mm drill is tedious.

Hole Drilling Topic getting hot.:):):):)

After finishing Trade School,went to Metal Box as a Trainee. Was surprised to see master fitters using "Box" to drill holes. We were taught using O and cross hair in Trade School.

Getting a bit hot today with my Made In China Ceiling Fan at full blast.:fan::fan::fan::fan:
 
Great info there Tin.
Thats how we learned it in "Tech School" also, never failed me, just my eyes.

Another great tool for aligning a machine spindle to a scribed
line is a ""Wiggler", it's kind of a "floating" scriber point chucked
in a machine spindle. You set it running "true" with your thumb nail, (with
the spindle turning) & position the X/Y location under the point.
Used pretty often in mill machine set ups, & actually pretty darn accurate.

John
 
Hi Gus!

First --'Metal Box' Long time ago, one of my mates was Chief Buyer in UK and went to India.
We used to go white water canoeing!
And to loups and things. I would be looking at some UK company like Proops Online. They sell nice little 'goodies' such as loups, archimedes drills and tool holding stuff. It isn't the best but it it is there-- and is cheap. We talk in big terms of about this and that when cheap little bits of tools are more than enough to have and use.

And so, my friend, to the Year of the Snake. Not long now.I was wanting to go out to HongKong again but my wife isn't fit enough. So I am off to Newcastle's Chinatown with 203 Masonic brothers to feed the dragon. Too much food, too much whisky!
Kng Hai Fat Chow in the Year of the Snake

Norman
 
Gus ENCO tools in the US IIRC has loupes the other hand tool is an optical comparitor . I used a hand held pocket one when I worked in the printing trade. handy for measuring layout errors small radii etc. Another tool on my buy someday list.

John good point on the wiggler.


Tin
 
Hi Tin Falcon,
Spotting Drill & Loupes.Enco does not ship to Singapore.Will try other sources.My eyesight is not best at 70.Only some days I am good at popping centres spot on cross hair. Will need to buy the optical aid to pop centres.Got profits coming in about a month to take care of new requisition.
Tried using the conventional Mag Glass which ended up needing three hands .Ha Ha.
One more week to go & hit TokyuHands,Osaka,Japan with my better half.

Will keep u posted in Osaka.Still trying to locate other machinist shops but no avail.There are some on the net but only in Nippon-Go,no English.Fishing Equipment Shops are aplenty.

Best Regards

Gus Teng.
 

Latest posts

Back
Top