# Centering a square cap jig



## safetysteve403 (Jul 12, 2011)

Hello all, may I pick your brains?

I work for a large stair manufacturer and we've been racking multiple brains to come up with a simple, efficient jig for the following:

A specific style of post we make requires that we pre-drill in the exact center of the underside of the post cap. They are always square, but come in varying sizes, and these sizes sometimes have a 16th variance due to shrinkage. What we're trying to come up with is a jig for use with a drill press that would center the drill bit on the cap regardless of differences in size, for rapid mass-production. If they were all identical all the time it would be no problem.

The ideas we've come up with so far have either been far too complicated, awkward to employ, or require advanced engineering techniques we're not sure exist...

Any ideas here?


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## CharleyL (Feb 28, 2009)

Carefully drawn lines from opposite corners will form an X in the exact center. Then drill your hole there. A jig isn't necessary. Another possibility is to use a lathe center marking jig like this one, but it won't work very well if the cap isn't perfectly square.


Amazon.com: Woodstock D3098 Center Finder: Home Improvement


Charley


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## samurai (Aug 14, 2011)

bridge city thet have drilling jig for this kind of task.expensive but very nice.have a look on video


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## Dmeadows (Jun 28, 2011)

A large version of this?


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## michmags (Nov 25, 2011)

How about this? Make a square box with no bottom or top that is ~1/2" larger than your largest cap. Make the sides tall enough to contact the flat edges of the cap. Center this under the drill bit on the drill press. When you insert the cap to be drilled, rotate it so all 4 corners are touching the sides of box and you will be centered.


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## andysden (Aug 9, 2011)

Try rilling the hole then squaring the top from a centre pin tahtshould be perfect
Andy


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## mgmine (Jan 16, 2012)

Instead of trying to center different size stock why not plan each post to a standard size and then go from there.


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## JOAT (Apr 9, 2010)

CharleyL said:


> Carefully drawn lines from opposite corners will form an X in the exact center. Then drill your hole there. A jig isn't necessary.


Yep, that's the way I'd go. You guys apparently forgot the acronym K.I.S.S. :haha:
Keep It Simple Stupid. :yes4:


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## rwl7532 (Sep 8, 2011)

safetysteve403 said:


> for rapid mass-production.


Looks to me that many replies have missed this phrase.

How many seconds each cycle? (Item into jig and desired adjustment time until drilling begins)


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## TomE (Dec 17, 2010)

michmags said:


> How about this? Make a square box with no bottom or top that is ~1/2" larger than your largest cap. Make the sides tall enough to contact the flat edges of the cap. Center this under the drill bit on the drill press. When you insert the cap to be drilled, rotate it so all 4 corners are touching the sides of box and you will be centered.


Think you're on to something but the box should probably have some sort of leveling "shelf" to allow a bore square to the plane of the cap. The jig can have a centered peg that aligns with the bit on the drill press. (think pin routing)

If the caps have a profile on top that hinders a flat just drop it in and turn motion then the boring might be better done from below.


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## bobj3 (Jan 17, 2006)

Hi Steve

I would suggest a ShopSmith they can drill that type of hole easy, once you have the top set it's duck soup to drill it over and over with some wood stop blocks clamped to the top, the size comes in little bit off you can just drop the table top down ..and keep on drilling ,you can find Used ShopSmith cheap now days days,you just need the head and the table saw top.

ShopSmith,,Great Horizontal drilling machine..

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safetysteve403 said:


> Hello all, may I pick your brains?
> 
> I work for a large stair manufacturer and we've been racking multiple brains to come up with a simple, efficient jig for the following:
> 
> ...


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## darrink (Sep 7, 2009)

Dmeadows said:


> A large version of this?


I think Duane has the right idea. Not knowing how your production line is set up leaves a lot of guessing. If the holes are drilled by a real person that actually handles the caps one by one, then I think a jig like this with a fulcrum handle that has a spring adjust tension, like a Visegrip, to accommodate the slight variance in size would be the way to go. To have a person stand there and screw and unscrew the knob each time would be time consuming. The jig would need to open up enough to make inserting and removing the cap quickly.

The jig should only need to be centered once if the caps are square.

I am a production manager, and I am constantly looking for ways to shave time off of jobs, especially on repetitive functions.


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## safetysteve403 (Jul 12, 2011)

michmags said:


> How about this? Make a square box with no bottom or top that is ~1/2" larger than your largest cap. Make the sides tall enough to contact the flat edges of the cap. Center this under the drill bit on the drill press. When you insert the cap to be drilled, rotate it so all 4 corners are touching the sides of box and you will be centered.


This...makes an awful lot of sense. I do believe we're going to try this with a toggle clamp or two for holding the piece in place.

Will post back on the results.

Thank you all for the input!


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## samurai (Aug 14, 2011)

hi steve!! just today i made a jig for this kind of task.it's so simple and easy to make.actually i have some extra steel parts for my hybrid pantorouter and idea come out from it.just have a look this video i just upload
i m sure you would like it.


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## Alan M (Mar 29, 2010)

i am not sure what kind of caps you are talking about but i am thinking the shallow angle pyramid type. 
if the caps are 4" for example then i would make a jig with a square hole in it mybe 3-3.5" . then when you drop in the cap upside down it will drop down but always stay centered in the hole. as long as everything is square then this should work. 
i would put some pieces around the edge of the cap that are roughly the same height asthe cap when it is in the hole. but keep them back a bit . 
when the cap is droped in the pieces willl help level the cap by eye . a toggle clamp should hold it there while you are drilling.


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## Clemo (Jun 9, 2012)

Mitchmags is right on the money. An onersized box clamped on the drill press platform with it's centre on the c/l of the drill. Stand your piece in the box and rotate so the the 4 corners all touch the inside of the box.

Without a drill press - an oversized square on a piece of flat. Put it on the end of the post and twist till all four corners engage the inside of the square, then just drill through the hole in the centre of the flat.

& Steve from Canada, yes mate.

Same tool in steel used in machine shops to centre pop square stock for mounting in the lathe.

Similar trick for centring short round sections. Carefully clamp a V-block on the bandsaw with the V in line with the blade. Rest the round piece in the V and touch the end on the blade. Back off and rotate the piece 90deg and touch again. You can acurately centre heaps in no time.

Tks
C ya.
Clemo.


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