Gallery, Projects and General > How do I??

Cutting a concave hole

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Bernd:
Ray,

Thanks for the link to that web site. I ran across that quite a while ago but never saved it. I see the translator takes literal translations. I think the pics and vids explain a lot. Don't need to know French.

Bernd

Jonny:
If you havent a rotary table, could you drill through or deeper than necessary with say a 1/4" to alleviate centre cutting aspect?
Still preferable to remove as much metal as poss before using a bull nose cutter. If you are careful, lock the beds and tension up the spindle you can get away with a router cutter but think it will cut larger or chaff which will show the flexing of the machines castings and any play.

Regularly use router cutters on aluminium, no problem. Made a fair few as well.

Mike K:
I haven't made any progress on the concave hole.  I'm looking for a ~1" plastic ball, making sure I have one before machining the recess to the wrong size.  The $1 store is my next shot.

I did, however, try out the "stepped cut" method on a couple of parts.  Works pretty well.




I modified the cutting method just a bit.  I think the Lautard book showed using a constant increment for one axis, and calculating the other axis values.

The problem is that the slope of the curve changes drastically, from very steep to very low (unsteep?):



So I used a constant increment for one axis for half of the coordinates (up to 45 deg) and then flipped the numbers:



I figured setting up the little brass crossfeed nut on the rotary table might be a chore.  But the table part could probably be setup on the RT with stops to place the part against to enable running through the corners quickly?

Mike

mklotz:
When doing incremental contours like this, you'll be well advised to use a constant angular step size rather than a constant step of the X or Y value.  For example...

N = number of increments
ang = total included angle of cut / N

x = R*cos(k*ang)
y = R*sin(k*ang)

where k varies from zero to N-1 in steps of one.

Mike K:
Oh, yes, that's even better!  Thanks, Marv.

Mike

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