Drag-Knife Plugin

[Tool-n-Around]

However, I have made clean, unburred holes in gasket material with my CNC.  You do 'drill' them, at a very low rpm, using a hollow hole punch, not a drill or a mill. 

They come out perfectly smooth and sharp-edged, if you use the sort of punch tapered on the inside, rather than on the outside. (In other words, a "hole" punch, not a "disc" punch.) Lloyd

Good suggestion Lloyd. I do have the outside tapered disc punches, but as you say, they will break out an ear if not punched before the profile is cut. I could easily make myself some hole punches/cutters in several sizes, but I dont have a low spindle speed option. Still, they might come in handy as a manual punch. They are surprisingly hard to find.

Small holes do cut very well with spiral flute router bits with a spiral lead in, and also the type of drill bit similar to a brad point with the raised outer cutting edge. If the need arises for small holes in thicker stock, those may be the my only options. They all do create vacuum leaks in the hold down table. The knifed hole interiors stay put (most of the time).

For now, I'm trying to get by without tool change so I can cut many (nested) features in an unattended fashion and without secondary OPs.

The old school production method was steel rule dies and presses. Remember those?

Best,
Kelly

[dh42]

Hello kelly

Look at the picture ; is this what you want ?

To get this result ; for each polyline circle, I rotate them 180° around Z, so the first point of the polyline is at is left side instead right side. (a circle always has it start point at 3h00)

for the external shape, I add a new point to the polyline, at the right, them I define this point as the polyline start point.

the pink points show where the polyline start points are.

use Eddy's Cbbule plugin to check where is the start point.

http://www.atelier-des-fougeres.fr/Cambam/Aide/Plugins/CBubble.html

Seems that the positioning arc is always done at the right side of the polyline start point.

++
David

[Tool-n-Around]

Hello kelly, Look at the picture ; is this what you want ?

Yes!!

To get this result ; for each polyline circle, I rotate them 180° around Z, so the first point of the polyline is at is left side instead right side. (a circle always has it start point at 3h00)

Ah-hah! Very clever. Also I didnt know that circles always start at 3 O'Clock. Thank you.

for the external shape, I add a new point to the polyline, at the right, them I define this point as the polyline start point. the pink points show where the polyline start points are.

use Eddy's Cbbule plugin to check where is the start point.

http://www.atelier-des-fougeres.fr/Cambam/Aide/Plugins/CBubble.html

I'll go away and play with this a bit to make sure I understand it.

Seems that the positioning arc is always done at the right side of the polyline start point.

This along with the rest of your reply should give me what I need. Still trying to get my head around if that preserves the proper starting position of the blade but looks like indeed it does.

Thank you,

Best,
Kelly

[dh42]

I forgot to say that I use Eddy's "polyline add points" to add the point at the right side of the external shape.

Polyline start point can only be set on an exiting node of the polyline, so if there is no node where you want, you can add one with this plugin.

http://www.atelier-des-fougeres.fr/Cambam/Aide/Plugins/polyaddpoints.html

of course, to rotate the circles all at the same time, I select all circles and I use the nummove plugin with rotation center set to "Objects"

++
David

[EddyCurrent]

David,

That's a good trick to rotate the circles, maybe this could be added to the plugin.

Please note that the code changes all polylines to CW direction so changing polyline direction in CamBam has no effect for this plugin.

[Tool-n-Around]

I was also wondering about this observation commented in my post.

As aside, on the attached file, if I examine the DK profile polylines, I expected to see a different Z-heights at the lead out moves driven by the retract depth and angles selected, and the engrave MOP would follow accordingly, but all Z coordinates are at the depth of cut. Why?

I noticed the same was true in the amended file.

Maybe I'm misinterpreting the meaning of the drag knife settings in the documentation for retract height and angle, but isn't the retract height supposed to establish the depth at which the knife point is initially engaged in the stock and the angle dictates the ramp at which it climbs out through the (re)positioning curl? If so, shouldn't that portion of the drag knife paths have changing z height for the engrave MOP to follow?

I suppose being able to place these knife positioning moves in the waste stock makes this less important since it is inconsequential if the waste stock is scarred by the move.

Best,
Kelly

[dh42]

Hello

Please note that the code changes all polylines to CW direction so changing polyline direction in CamBam has no effect for this plugin.

Yes, and changing the CW/CCW do not change the position of the polyline start point.

That's a good trick to rotate the circles, maybe this could be added to the plugin.

The problem of the start point is the same for any shape, not only circle, I think it is the job of the user to set it at the right place so the arc start in the waste stock ... with only a polyline and no internal/external info as on a profile mop, the plugin can't know if you want to cut a hole or a disk and where is the waste.

++
David