Newbie- Q: Holddowns and how the machine knows where not to cut.

[Deviant]

I was curious if there are any examples of how you modify your program to not cut your fixture clamps etc...

Up until now, almost all of my machining has been on a vise with me operating the g codes with plenty of clearance to ignore the attachment method.

So how does this work? Do you have to model your clamps in cad and generate that way or?

I realize that half the battle is to hold the material in a way that the hold downs will never be in the way.

Unfortunately, I really haven't seen any training material on this.

I.e.

Step1, Cut softjaws for stock material.

Step2, Cut reverse mold into soft jaws.

Step3, load and offset material.

Step4, cut 3d profile x-amount deep.

Step5, flip part and cut profile from reverse axis x-amount deep.

Am I confused on how this works? Or is there a level of assumption that cam programs don't cover this?

This isn't specific to any particular software. I'd just yo see more examples of how this is handled.

Thanks for the help,
-Deviant

[hilnem]

Hi Deviant,

I started out using regular box tape (2 inch shipping tape). The material that I have been machining is 3/4 inch oak.
I would vacuum any dust off of the surfaces and then use a plastic card to squeegee the tape tight competley on all 4 sides. This has been working very well although I knew that I would want to put a better system in place at some point.
I was surprised that I was not able to not find more posts about holddown options. There does seem to be many people using vacuum systems.

Here's a solution that I came up with recently thats working great for me. It works great for wood or a material that can be nailed into fairly easily.

-I made 2 side rails out of oak about a foot long ,3/4 inch high, and 1 1/4 inch wide.
- I then drilled pilot holes and inserted some decking screws long enough to leave the screw tips exposed on the other side (I used 1.5 inch screws and had quarter inch exposed tips). I also used a dremel to sharpen the screw tips very well after installing.
-The end bolts on the rails are counter sunk and attach to nuts in the slotted channels of the table.

I keep the left rail locked and then tap my work piece into the screw tips with a tack hammer. I then tap the second rail into the workpiece and tighten its end bolts.

I keep my router away from the screw tips by homing my x half an inch from the left rail and also make sure that the object I'm going to cut (its dimensions in my gcode file) do not come closer than a half an inch to my right rail.
Here are a couple pics:

[dblox]

Well I use Dolphin CAM, and in that particular package, any drawn contour can be partially machined, so I just measure where my clamps are and break up the toolpath to suit. Then I program an optional stop to reposition the clamps, then generate the toolpaths required to machine the material previously under those clamps.
Quite straightforward, but not "automatic".