Trace command is confused about top and bottom of model

[garywatson00]

I have a model of a tessellation lizard +10 mm thick, repeated 18 times in a tessellation pattern. I've selected the top outline of each lizard using the Trace command to cut the outlines of each one. I selected an Axial offset of -4 mm to cut 4 mm into the stock with a 20 degree V bit. The simulation looks correct but when I run the gcode, the cutter is positioned 6 mm above the stock top.

Fusion thinks the model top is the model bottom! I must  use an Axial offset of -14 mm to cut 4 mm into the material. Now, however, the simulation shows the tool cutting through the material completely by the extra 4 mm.

I have the same problem when I Engrave the lizard's backs. To correct, I probe the top of the model, then move the Z down 10 mm and rezero Z. The simulation looks correct but if I run the router with Z=0 at the top of the model, the cutter is only cutting air, well above the stock.

I don't know if this even makes sense as described but I have tried everything I can think of to correct the situation to no avail.

[daniel_lyall]

Can you post the model with this problem To attach a file Go to File -> Export and save as a .F3D Archive File and attach it to your next post, if you can not post the file you can PM it to me or say in your next post you can not post the file and one of the Guys that do NDA work will help.

[garywatson00]

Hi,

Attached is the F3D file of the Lizards. I added more since the last post. Examining the gcode will show that the machining is done in the air for the Trace command. To fix this issue, I edited the gcode to basically subtract 10 mm from the Z values.

I could not do this for the Engrave command so I had to tell Fusion to machine 10 mm lower than the model top so again, the machining is done in the air, just below the model bottom. The simulation shows properly for the Trace command but shows the Engrave command machining through the part.

While I used Inventor and Solidworks for years, I am a relatively new user of Fusion 360, especially the manufacturing part, where I struggle with all the height meanings, the offsets and the confusing error messages. 

Thank you for looking into this problem for me. 

[daniel_lyall]

The problem is that you changed the heights.

Clearances height is basically the height that the machine can move around the machine without crashing.

Retract height is the height to lift the cutter above any obstacles on the model.

Feed height is rapid from the retract height to feed height.

Top height top of the model or stock this can be where you want it to be as well.

Bottom height where you want the bottom to be for engraving its model top -##

Traces at its default settings the selected toolpath is the top and bottom height you move the bottom height with a - axial offset.

So basically if the clamps holding the material down are 5 mm high a clearances height of 6mm will be ok then if there is nothing to crash into inside the model the retract height and feed height could be 1mm.

There are times when the top height can be model top or stock top 0 offsets depending on what's there on the model and if the stock is thicker than the model and the model is below the stock top if they are the same ever is fine if all the stock has been removed model top will be fine.

Have a look at this video Kevin explains it quite well https://www.youtube.com/watch?v=Qmf44xm0P_o

Also, go through his other videos there is some good stuff in there and if you want to up your game his training is worth it.

[garywatson00]

I thought I replied to the above suggested help but I don't see the post so... I will try to reply again. I think I understand the definitions of the heights, it is the application that seems to be the struggle. I have viewed Kevin's video and watched either it or something similar some months ago. The problem I'm having is that the actual tool position is not the same as the simulation, no matter what I do.

With the Trace command, I select the contours to trace as the geometry and reference everything from there.  The only height commands are clearance and retract if I recall. I set the stock top as the model top, i.e. don't remove any stock. I tell the axial offset to be -4 mm, expecting the cutter to dive into the stock 4 mm and trace the pattern of the lizards. However, the cutter ends up 6 mm above the stock as if the thickness of the model (10 mm) is above the top of the model/stock. I want to cut 4 mm into the stock no matter how thick the stock is, that is why I probe the top of the stock. It's thickness should not matter. This is where the problem lies... the program thinks the 10 mm stock is on top of the model, even though the view and simulation show the model within the stock.

This was easy to fix in the gcode, I just replace Z6 wit Z-4 everywhere and it worked. But the simulation looked correct even though the Z height was wrong.

This was not possible for the Engrave command because the Z height varied as the cutting took place. So I had to select the bottom of the model as the top. This meant the simulation cut all the way through the stock but the gcode was correct.

That is the best I can do to explain the problem. If someone can fix the supplied file and resubmit it, I can look at what was done to correct the problem, but as of now, I can't find a solution.

Thanks again,

[Joshua.Aigen · Accepted solution]

@garywatson00 Looking at your file the WCS is located at the bottom of your part, this explains why probing the top of your stock would create a 10mm offset from the desired Z-0 you were looking for and maybe lead to a confusion around heights (I've been there). 

[daniel_lyall · Accepted solution]

As @Joshua.Aigen said, you do not have the WCS set so it is on the bottom in this model it is important for users to just set it every time you do a setup.

[garywatson00]

Late response but thanks again for the help. Yes, I see that the WCS location was the problem. This is the tie between my machine and the model that I was neglecting. I still feel the height tab is confusing but I guess I am learning to live with it.