I have a deceptively simple milling job I’m trying to do with LazyCAM for my Taig mill. 4 round holes and a square slot in a rectangular faceplate.

I have synchronised LazyCAM and Mach3 tooling (I’m using one 6mm end mill for everything).

What seems to be happing is that LazyCAM is generating spurious or incorrect G-Code for the leadin for the round holes. The tool plunges, shoots off at 90 degrees to the leading, then comes back and mills a nice circle as it should do.

Anyone know what is going on, is this a bug or some knid of noobish behaviour on my part? 

F1.0 is so i could watch whats going on. Its usually F625.0, im working in metric and milling plastic

What are your leadin settings ?
I used the following and it worked well on my home PC.
I used 3 units for the rectangular opening.
Good luck,
RC

6 mm tool and 4.75 mm leadins. However I don't have the Pro version and don't have a functioning offset tab. Is this necessary for this kind of milling operation?

I get error messages regarding tool and arc radius in Mach3 with such circular short leadins... "Tool radius not less that arc radius with compLine 13"

N70 G3  X24.6820  Y13.1205  I24.9989  J12.6407

Intriguingly if i add arc leadins of 1 mm to all layers with my 6mm tool i get the following image. As if the original straight leadin gets a leadin of its own... I think this is the problem.

Yes, I believe you need the lic.
I ran you file through mine and it seems to run fine.
Try the one I sent.
RC

Looks like now you are leading in with a circle to your original straight lead in. One or the other...not both.
You have to delete the straight one if you want to use the circular one.

Im getting the same behaviour with your file. Did your run it? Running it live or as a simulation creates those odd spikes.

What i get with Overlords tap file ....

Looks like now you are leading in with a circle to your original straight lead in. One or the other...not both.
You have to delete the straight one if you want to use the circular one.

Yeah managed to get rid of the second leadin but got back to the old problem i had with circular leadins on the small holes: "Tool radius not less that arc radius with compLine 13" line : N70 G3  X22.4029  Y11.6154  I22.8827  J11.9322

Your original file runs perfectly here.
OK  one more thing to check.

Exactly same setting for Motion Mode, Distance Mode and IJ Mode. I only get the radius problem when my Mach3 tool 1 is a 6mm end mill with a 4mm (and i presume smaller) it works (when the leadin radius is 4mm NOT with 1mm) but I'd like to use 6 mm tooling as I have a 6mm slot mill which is ideal for this job and I dont really want to use 4mm if i can help it.

Anyhow Id really like to understand what LazyCAM / Mach3 is doing here. Because it does not look right.

It could possibly be because you don't have the lic. file.
I remember when I did not have it, it would not post any code at all.
Not consistently anyway.