Accurate Drilling - centering microscope, USB cam, optical punch?

Gallery, Projects and General > How do I??

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dvbydt:
Another vote for throwing out the centre punch. Edge find or centre find, use DRO or the dials and use a spotting drill. If the job is too big to fit on the table in one go then mark out only and use a sharp point in the chuck to find the intersection. Like these :-

I bought a box years ago, they are hardened and ground. Also useful for making scribers or very small spade or spotting drills. My version of DaveH's "pointy" bit.

Ian

Lew_Merrick_PE:
Bry,

1) If you have laid out your sheetmetal well, you will add "index edges" that allow you to establish a "zero" with an edge finder or some other reasonably accurate means. There are several ways to control your axis moves very accurately (dials and DRO's are fine, but they have errors associated with them that gauge blocks and stops overcome). You can also use the method known as "3 disk alignment" or "tool buttons" -- both of which are documented in Machinery's Handbook.

2) There used to be a type of drill specific to sheetmetal. They have disappeared from the commercial market over the past four decades or so, but they look like the drilling portion of a "UniBit" in that the flute is straight and leaves (about) 75% of the periphery in bearing as the drill cuts. They are much more rigid than a twist drill and will actually produce round holes in sheetmetal! Larger bits (say 3/16 or 4.5 mm) are fairly easy to make by turning a (say) 135° included point on a piece of properly sized drill rod (silver steel on your side of the pond), milling out a (just over center) 90° slot, hardening and tempering it (draw to straw), stoning it, and stoning a relief for the point. Smaller bits are easier to grind from pre-hardened and tempered stock. Grind the tip (relieve it later) and mount the "bit" in a block steel such that you can press it into a drilled & reamed hole located very near the corner of the block and grind out the very slightly over center 90° flute with a die grinder mounted to the spindle of your mill. That way you don't get your work ruined during quenching.

I bought a set of sheetmetal drill bits back in the late-1960's. In those days they were a common product in tool & die supply houses. They cost about the same as a set of twist drills in those days. I only have the odd sizes left and was quite surprised a few years ago when people in the tool & die supply business looked at me strangely when I tried to buy replacements. I guess this is what happens when you get old....

Jasonb:
Lew surely the whole problem that Chris has using a depthing gauge is that he does not know how far to wind in the dial or read off the DRO so there is little point in establishing a zero.

At best the hole will be located a set distance from one edge and at its intersection with an arc, at worse it will be at the intersection of two arcs so you can't use co-ordinates to position the hole.

As for round holes when clock making isn't that what they make broaches for, bit like a reamer but produces a round hole in sheet material.

J

Edit, is this the type of drill bit?

modeldozer:
Will get them together and maybe to a seperate post under tools. Plans in pdf OK?

Chris, Centrecam mostly and the video plugin for Mach3.

Abraham

picclock:
Hi craynerd

IMHO best way is to use DRO's. Its a low cost solution which will get you to within a thou. Just mount on the X and Y table axis and read off the display directly. To locate the work clamp to the table with mdf or similar underneath, and then use an edge finder. I use a starett one on everything except aluminium. The work should have 1 straight edge which you can pick up on with a dti to make it square to the table. Then just use the edgefinder and zero the dro's after taking off the edgefinder radius.

I use a cheepy 6" one for the y and a 300mm one for the X, overall cost <£40. Only thing is must be covered with acrylic/plastic or similar to stop swarf, lubricant etc. Works really well with amazing repeatability. My starett finder has a point the other end which you can use to centre on an existing hole within a thou or two.

This completely takes out the centre punch and manual alignment. I use a small BS1 centre on super accurate stuff to set the start position. Other thing is your eyes only have to be good enough to see the numbers :thumbup:

Best Regards

picclock

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