Drilling a square hole??

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Yikes Terry !!! Way too much maths for my dumb brain !!! Mortice for wood, broach for metal....and then you get nice sharp corners:biggrin:
 
Lol Skip, its not that bad....

I'm just wondering if rotary broaching wouldnt work for wood as well, as the angles are the same. Having two seperate systems just doesnt make sense?
 
Mmmmm, not that bad huh Terry????:mad:

Ok, Slim clever brooks, answer this.....:tongue:

When drilling through a thinnish metal plate with a drill that has only two flutes, why do we always get hole with FIVE sides????? :confused::confused::confused::confused::confused:


:biggrin:
 
skiprat said:
Mmmmm, not that bad huh Terry????:mad:

Ok, Slim clever brooks, answer this.....:tongue:

When drilling through a thinnish metal plate with a drill that has only two flutes, why do we always get hole with FIVE sides????? :confused::confused::confused::confused::confused:


:biggrin:
Click to expand...

The drill bit is probably warped due to excessive heating :befuddled:

I have no clue but why do you drill thinnish metal plate as opposed to using a punch?

If I had to guess I'd say its one of two things, wrong angle on the bit or speeds to high causing tearing/folding.
 
LOL Terry, you obviously are a better drill sharpener than I was.:biggrin:
It is a weird phenomenon that if a drill bit is sharpened with one edge slightly longer than the other and the workpiece is not securely held, then the result will be a 5 sided hole. I have no idea why

Now that I've left SA, we have machines to make holes. I don't have to 'punch' through steel anymore:tongue:
 
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Skip and others, the reason for the 5 sided hole in thin material, is that the cutting edge is going thru the bottom of the metal before the top edge starts to cut, leaving both top and bottom cutting edges unsupported. To get around this problem you need a drill bit that is a very shallow cutting angle ie; instead of 118* somewhere around 160*,(something like a brad point drillbit) so that both top and bottom cuttingedges are supported. The easier alternative is to CLAMP a piece of wood underneath and on top, drilling thru both.
The reason for the 5 sided hole with a drill with a slightly longer cutting edge is the same, if you were to clamp the metal under the drill press you would end up with a stepped hole, depending on the size of the drillbit it could be from a small fraction (hardly noticible) to a 1/4 of an inch.
That process is sometimes used in engineering to drill a particular sized hole when that size is not available or not worth buying for a short run process.
Regards
Kryn
(Over 40 years in the engineering game)
 
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If you have access to the book written by Alexander G Weygers, called The Complete Modern Blacksmith, or an electronic downloadable version, there is a small chapter 9, How to Drill Square Holes. Pages 219 thru 221.

A discussion in another forum.

http://bbs.homeshopmachinist.net/showthread.php?t=28214&page=2

Goggle rotary broaching and you can find videos of rotary broaching tools along with manufacturers. They can make internal and external square, hexagon and I believe splines in lathes and or milling machines. There was a series of articles in one of the metal working magazines a while back on making rotary broaches for the home shop. Can't remember which one.

So who is going to be the first to make a square pen?

Pete

 
I have a better way to make a round hole in thin material. Interpolation. A punch is fastest, but you have to have one the right size to begin with..Interpolation is whatever size you want and fun to watch in progress. Matter of fact..the machine should perform interpolation before and after every cut, regardless whether necessary or not..at least for grins and giggles!
 
Polygon dude!

While for all intents and purposes an interpolated hole functions as round, it isn't round due to the nature of the way a CNC milling machine makes the hole. It is a polygon with corners having the radius of the cutter you used. You use the same process to make any regular geometric shape.

The CNC makes the hole by moving in a straight line from point to point until the circle is made. The more moves the smoother the inside of the hole. When you don't have a lot of moves (by choice or machine limitations) you can see the facets in the hole. Make a 6" diameter hole with just 100 moves and the facets are about 3/16" long (point to point). Use a 1/4" cutter and it is pronounced. Do it with a 4" cutter and your neighbour will believe it's round.......but we both know it isn't. :wink:

Pete
 
Yesterday I went to ask the best programmer we have at work and asked about interpolating holes and found out that there are two kinds if machine programs. One uses the point to point language that I described and the other does cut as you described, round holes. The limitation on the roundness being with the design and condition of the machine. We have both types in the plant. I am an inspector, not a programer and learned something new.

I sit corrected. :-)
Pete
 
Back in the day before cnc's, (like mid 70's), we did a job that required a square hole, about 1" square. We made a hardened tool steel template to go onto the part, and used a trangle shaped cutter in a floating holder. It was pretty slick.
 
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