How to machine hole on top edge of workpiece

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rronald

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I bought a kit for Hemingway's Sensitive Knurler. Thought it would do me good to machine some parts to a specification.

Nice drawings. But no tolerances on dimensions which seems like a really poor idea.

I'm making some progress, but I was surprised how complex the build is (at least to me). A couple of things jump out as "difficult":
  1. There's a pin that needs three sections turned. The outer parts are easy, just turn to the right diameter. But the inner section is not concentric with the outer sections (i.e., the inner section is eccentric). I've purchased twoER40 collet blocks (one square, one hex) and I think I can chuck the hex block in a 3-jaw chuck with a spacer.....or the square block in a 4-jaw for the eccentric machining.
  2. There's a hole drilled down thru a flat piece that is only about 60% over the work piece. The other ~40% extends beyond the edge. The diameter of the hole is 5/8" (15.9mm). In the picture, it's the hole at the top that is only center drilled.
    HoleOnEdge.jpg
I'm relatively sure that if I try to run a 5/8 drill down, it will attempt to break out and that bad things will happen to the part or the drill. Or both.

I have a CNC mill. It prefers to only cut aluminum, but I can probably make it work. However, I'd like to learn how to do this on a manual mill (or on the lathe).

I could cut out most of the material with the bandsaw. Once the material is removed in the center of the diameter, I could then bore it on the lathe? Or on the mill? I don't have a boring head for the mill yet, but I think could adapt a lathe boring bar with a HSS bit.

Any suggestions?
 
drill a small hole, then finish with a two flute end mill. run slow. On a knee mill use table to feed, not quill.

can finish with boring bar if needed.
 
I think I'd use a rotary table or a boring head. You could also hold it on the lathe with a faceplate or maybe 4 jaw. Though it would be rather off balance, so perhaps only for a larger lathe. Go slow.

You might be able to plunge a 5/8" endmill through if you have one, but I wouldn't hold it in the vise like that.

If I were starting at the beginning, I would probably move the part down a little and drill/bore a complete hole, then cut the top off close with a bandsaw and finish up with an endmill. But you already have the outside contour.
 
I would do this hole on the manual mill by first drilling a small hole and than use an end mill to increase the diameter step by step ( 2 mm step size) until at spec.

If the hole diameter is critical and there is not a suitable end mill, I would drill a small hole at the center to align the part in the 4 jaw chuck. Then turn the hole on spec with modest feed and speed.

Making the whole part is a CNC job. I would use quit a thicker piece to hold the part securely in the vice. Then mill it to dimension slightly deeper. Turn the part upside down and face mill it to the right thickness.
 
I agree that it would be easier if the stock was large enough to allow drilling the full hole and subsequently milling the edge that intersects it. But, the stock included with the kit is already the finish width, so that was not an option.

I did just drill a "small hole" thru. 5.5mm did not break thru the edge. In theory, a 6mm drill might also leave a remaining sliver.

About 90% of my mills are very small and for aluminum only (DLC coated). For my (new) manual mill, I bought a number of 12mm mills. Plus a face mill (1.25") and a fly cutter. Bottom line is that I only have 6mm and 12mm mills are suitable for steel. 6mm is too small for use on the manual mill w/o a rotary table. The 12mm is both too small for a 5/8" hole and also too big for comfortably enlarging a 6mm hole. At least I now have a good excuse to buy many new mills in various sizes.

I wonder if I positioned another piece of material along that edge that could be used to prevent a drill from wandering outside of the proper path?
 
Another approach, don't know if it would work here but I've done similar and been happy with the result.

You could clamp the part tightly to another piece of similar metal and drill through both.

Just a thought.

John
 
Inheritance Machine also did a video on the Hemmingway knurler that might give you some ideas on how to do it. He has a well outfitted shop, so his techniques would likely require tooling you don’t have.

 
The sandwich method will work. Sacrificial piece top an bottom, bolted together using the two holes already in place, will control the bit from wobbling.
Pierre
 
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