Cutting path questions

[chris161190]

Hi all,

I'm pretty new to the world of cnc cutting. However am skilled with autocad and am a furniture maker so I'm not a complete novice to the industry.
Weve just bought a used clean example of an 8x4 pacer cnc and have just started to get it set up and running.

Im confident that the table is both perfectly flat and level we did it with engineers levels and lasers so I'm happy it's all set up correctly.

So where im at it this:

I've installed a cutter at diameter 15.8mm and selected the offset at 7.9mm and have successfully cut squares and rectangles manually using the keyboard manually moving the machine a given amount for example a 400mm square. This is all working great and cuts both square and accurately.

My problem is when it comes to cutting a basic 2D shape from a cad drawing.
Were using the pacer XMC-e software which I'm getting used to using however when I import a dwg of this basic rectangle the software is saying that it's an open path with the corners of the geometry overlapping eachother where they meet. This means when the machine is cutting you end up with a funny shape at the corners where the machine continues on its cutting path for an extra millimeter or so then lifts the cutting head repositions slightly before cutting in the next direction. also the dimensions are out if this makes sense where a 400mm side is coming out at around 428mm.

I did the basic shape on sketch up because I left my laptop at home with auto cad on it and had to convert the file to a dwg to import into the pacer software.

So im thinking it could be a few things wrong here?

1. Maybe sketch up simply isn't the programme to draw with
2. I need to group my geometry together in cad before importing it into the cutting software?
3. My tool setup isn't correct?
4. I've got the cutting path on the software set up incorrectly?

Any help would be great whilst I'm learning to use this.


Chris

[magicniner]

Geometry is the usual issue, translating between packages can result in the odd "Funny"
Check version compatibility - do you need to "save as" an earlier version of .dwg for the CAM package to corectly interpret the geometry?
Having the imported object as simple as possible will also improve your chances.
That's about all I've got ;-)

- Nick

[Ger21]

In AutoCAD, make sure it's a closed polyline.

I'm not a fan of Sketchup for CNC applications.

[chris161190]

Ok thanks that makes more sense, I'm not a massive fan of sketch up anyway but didn't have autocad with me at the time so tried it on that I think I'll try with a poly line on autocad and try again. Alternatively could I simply draw any geometry on autocad then group the geometry together to create the shape that way?

Chris

[Ger21]

That depends on what exactly their software expects. I'm not familiar with it.
Generally, closed polylines work best, but it varies with different CAM software.

[Boyan Silyavski]

A good drawing program like Coreldraw or Adobe Illustrator, or even better Aspire . Enter in node editing mode and make sure all lines a joined properly at the corners.

below is a sample when you magnify a problem. Third pictures looks ok but could be problematic if you have not joined the lines:

[chris161190]

Hi thanks for the picture, yes you're exactly right when I magnify the corner in the cam software I get a corner which is over shot on both lines like your first picture. The test shape I cut was done just using the basic line tool and not a polyline so I think this is the first thing to try.
im going to stick with autocad for now cos it's what I'm used to and cos I have it I obviously tried sketch up but I don't find it that good for drawing tbh we only use SketchUp to take a 2D autocad view and render it in 3D for clients approval.

Chris

[Boyan Silyavski]

No problem. When i see the toolpath simulation doing crazy stuff like digging a grave there, i know its some open line or edge left there

[Clive S]

I get a corner which is over shot on both lines like your first picture.

Chris Do you have "object snap" clicked ( F3 on mine) there are settings that you can snap to end of line or centre point etc.

[chris161190]

I do when I use autocad yes but am unsure on whether or not it is set to default on sketch up?