Square Hole Production

      Woodworkers brainstorm about how to machine decorative square holes in a wood faceplate. May 8, 2012

Question
We are drilling (in production) an Arts & Craft design on a wood faceplate. It's a group of 4 square holes - the Frank L. Wright motif. Holes are 0.2 inches square. So:
1) Is a 7/32 bit the closest size available, and is that 5mm?
2) Where do you buy these?
3) If it's a motif of 4 holes, is there a way, using a drill press, to combine 4 bits to drill all at once? Sounds stupid, but maybe we can make a jig that holds the 4 bits.
4) How else to make production reasonably fast?

Forum Responses
(Architectural Woodworking Forum)
From contributor D:
Woodwork can be accomplished in two ways - additive or subtractive. Additive involves joining smaller pieces of wood into a larger whole; subtractive involves removing wood from a larger piece.

Your chisel method - subtractive - can be accomplished perhaps with a machine shop made punch after a smaller hole is drilled, depending upon material thickness, number of holes, etc. Forest City Tool makes excellent mortise chisels and they may make a custom size. The bit would have to be sized so as to not round the edges as seen in typical hollow chisel mortise tooling.

A subtractive solution would be to assemble smaller pieces of wood into the required shapes, with 0.20 square voids. This could even be set up so that the assembly could then be sliced, like bread, for many parts.

And the historical perspective: Arts and Crafts, FLW included, arose as a return to craft and featured details that could only be accomplished by skilled craftsmen - through tenons, square holes, inlay, etc.



From the original questioner:
This is in very thin wood - maple and walnut. The additive method combining multiple partial pieces is something worth exploring, but it seems more time consuming.


From contributor D:
Well, yes, more time consuming, but that is why it is what it is. And it ain't easy no matter how you go at it. This is a symbol of serious craft, and you are trying to mass produce it - the antithesis of what it is.

I think you will find your best track is to pursue custom tooling, with an undersize rotating bit, and very careful layout, with over-thick stock planed or sanded after the square holes are placed.

The additive solution is for small hands, labor intensive, and then can you grain match? Do you need to? Do you use import outsourcing?

I am surprised someone with CNC equipment has not added to the mix with their solution, which might include a smaller diameter bit to clean the corners at a 1/16" radius or so - if that would even be acceptable.



From the original questioner:
Well, that's a bit to digest. All is true, and well-articulated. As I'm thinking, the additive way uses only 2 parts, each with 2 notches. So 2 parts = 4 notches = 4 holes when combined. Not too bad.

Yes, I'd like to grain match, but as an ideal only. No one will shoot me otherwise.

The factory has a 3-axis CNC. I take it a 1/16 radius is practically indiscernible from 90-degree? So they'd make 2 passes with the CNC - 1st to drill round, then a 2nd to square off the round? Why can't the CNC just make one pass and make it square? Maybe it's an awfully small hole, even with backing?



From contributor L:
The reason the CNC doesn't work well to just use an 1/8" bit to make the square hole is the bit would most likely break. Seems like an old industrial quality hollow chisel mortising machine could do that. The cheapy hobby level mortising machines or drill presses probably won't work.


From contributor J:
Benz makes an aggregate for CNC machines for doing just this.


From contributor N:
This is not a solution I'm offering, just a nice conversation topic. Long ago someone actually invented a method to drill a square hole. Seems no one is marketing these special cutters anymore. Google Reuleaux Triangle if you find this as interesting as I do.


From the original questioner:
I don't have 5-$10,000 for an aggregate. We are talking about a head, not a bit, right?

So far the best idea is the manual, additive method. Next would be a punch used after a round hole bore. Adding material thickness before making the square cut, and planing afterwards.



From contributor G:
It seems to me that this can be done with a simple table saw setup similar to making box joints. I assume you are using 3/4 solid. My method would be to first grain match and glue up oversized door blanks. Second, rip it into 3 pieces, then take the two wider ones and machine them on the saw. Third, glue them back together.

It's a little labor intensive, but I'm sure you can find something to do while the glue is drying, like reading the forum posts here.



From the original questioner:
Yeah, we can keep an eye on these posts just to see what we missed, as we're halfway through production!

My recent thought is:
1. bore 4 round holes on the CNC
2. place on the drill press and clean 'em up with the hollow chisel.
What think?



From contributor N:
If you have a CNC, just use progressively tinier bits to clean up the corners. Do you have a tool changer? Load up 1/4, 1/8, 1/16, and 1/32 inch bits. A 1/32" bit leaves a 1/64" radius corner. Most eyes can't tell the difference. Cleaning up with a chisel mortiser or half ass drill press with mortise adapter takes a lot of time and jigging up, even if you have the throat clearance. A little buzz in each corner will take like a whole second with each bit. I say let the router do the work. Add twenty bucks for some tiny bits, twenty minutes labor, twenty minutes programming time, then sit back and watch.


From the original questioner:
Sounds ideal, but you have detractors, don't you? Someone says the smaller bit will break in the CNC. I will ask about the bit changers. It would be nice if your method worked because there's also 2 kerf lines (decorative) and 2 screw holes (for handle) that could be CNCed, and probably without moving the wood.

Also - they don't have a bit changer.



From contributor N:
No tool changer is a bummer. Breaking bits, though, is operator error. Trying to take off too much too fast. Thus the progression gradually to tinier bits. I'd still do it in batches if you had a lot though. Run 100 panels with a 1/4, change bit, rinse and repeat. This is basic stuff. An industry standard cam software, Alphacam, actually has an option to click on (take into account previous machining) which optimizes your paths so each small bit only goes into the very corner where the previous larger bit couldn't reach. Actually pretty easy to do this manually in your case, but the function is great when you have hundreds of radii on a sheet that need sharpening.


From the original questioner:
If the CNC doesn't work out, then what about:
1) Route out the back of the drawer faceplate the width of the 4-hole area, along the entire 6' length of board, leaving 1/8" board thickness at the 4-hole area.
2) Use drill press using a 4-hole punch die which I can buy somewhere. 1 shot, 1 kill. /it's only 1/8" through and no difficulty with alignment on the press.


From contributor D:
I know I sound like a pessimist here, butů There are 2 problems with the 1/8" thick routed area: The punch, especially a four hole gang punch, is going to take one heck of a lot of muscle to go through hardwood, even at 1/8", and then the plugs/waste will need to be cleared from the punches - how?

Also, the punches will want to tear out on exit, and/or distort the wood enough to split it, or the wood will jam between the punches and the weak short grain - at 1/8" thick - will crack and come apart. Then there is the 1/8" thick short grain in service - how durable is that?

I think the progressive routing is the best solution yet. From what I can tell, the end use is not so critical that people will be noticing a 1/64" radius.

As stated earlier, there is a reason this was a symbol of craft. It is surprisingly difficult to do, even with modern tech.



From the original questioner:
The tech issues of my routing idea, most I knew. My minimal woodworking product designer won't listen to me and thinks the 4-gang punch is a clean and easy way. Fact is you raised even more issues than I knew - it's even worse an idea. I like the CNC approach and will see how my factory likes it. Otherwise I think the cut and glue method will work since in standard American maple the grain is not dramatic and we're only removing 2 saw widths. If we control for color I think that's good enough. Lams happen to be the factory's strength.


From contributor O:
Okay, just a complete out of the box thought. What about 4 black vinyl stickers instead of 4 holes. It would look very similar.


From contributor R:
Metal workers use a square broaching tool to go from a round hole to a square. The tool has a round pilot to pick up off the hole, then the tool goes to a square cross section at the far end. You could probably drive it through with a mallet, and finish with an arbor press.


From contributor P:
Is the hole a through hole? If not how about subbing it out to someone with a laser and just cutting down .06 or so, then painting the background?


From the original questioner:
Using a CNC to make these square holes, how do I spec the bit?
-mortise bit (I think 3/64 is smallest available)
-round
-spiral
-2, 3 flute, etc.
-other ?

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