I'm never sure where to ask question like this.

I am just getting to terms (or not) with the CNC I have built and was doing some test cuts when I encountered this wonky cutting issue, see attached.

I drew a simple recess cut in Fusion 360 as per the attached photo & used the Pocket Cutting selection in their Cam which produced the attached code.

When I tried to cut the recess using a 1/4"cutter at a feedrate of approx 1500mm-min (60"Min) I ended up with the real wonky cut as per the attached image, as I lowered the Feedrate the cut improved.

Needless to say I was expecting the outside cut to have 1/4"diameter radiuses in all corners and a nice square block in the middle, even when I lowered the FR to 600 (24"Min) I still didnt get the 1/4"radius corners.

Does anyone know the most likely culprit causing this issue?

My first guess would be that you have your motor accelerations are set too low.

dq828,
You must set the CV.
I use mm on our Mill
If you use mm then make all the same CV on all angles = 100.
If inches then CV = 4.
You can test this on the simulation Toolpath, make a small square then run it, if the corners are square at your speed then you have the right number in the CV.
Regards,
Mauri.

My first guess would be that you have your motor accelerations are set too low.

That was my first guess but I haven't had a chance to test yet thanks for the input I'll report back.

dq828,
You must set the CV.
I use mm on our Mill
If you use mm then make all the same CV on all angles = 100.
If inches then CV = 4.
You can test this on the simulation Toolpath, make a small square then run it, if the corners are square at your speed then you have the right number in the CV.
Regards,
Mauri.

Whats CV & where does it live?

I dont have Mach Simulation

Well that definitely helped, whats a normal Acceleration rate, if there is such a thing?

dq828,
In the Mach4 Configuration page you will find CV Constant Velocity as well as Exact Stop, the CV need to be Ticked.
CV is an adjustable movement when approaching an 90Deg angle cut, for example say you are moving X axis at 1500 and are approaching a right angle going in the Y direction, then CV will slow the machine speed down to 100 cut the angle and then go back to 1500.
This is an alternative to doing a Exact Stop which means at the 90Deg angle it comes to a stop and the starts up again into the Y direction.

There are three ways of setting CV.
1) Using the CV Wizard as supplied by Mach4.
2) Edit machine.ini and replace all the =0 with your chosen CV Value on all 180 angles.
3) Write some code to automatically change all the 180 angles to the angle chosen.
I have used cutter TBN down to .05 Radius D-Bit on brass and the same cutter has been used for 6 days of cutting, so 100 on all angles was the best for us, it is always a compromise between speed and accuracy.

Every one has simulation, you need to select it in Config.

Regards,
Mauri.

dq828,
Each machine and motor combination will have a different acceleration set as not two machine are alike.
Many factors come into play, like on a Mill how tight your gibbs are set, the size of the motor (Torque) being two.
You need to read the information provided to understand how to set and test motors in Mach4.
If you are using a Router Table and machining timber then you will most likely have a higher acceleration than say a Mill cutting Brass or Steel.
Regards,
Mauri.

dq828,
Each machine and motor combination will have a different acceleration set as not two machine are alike.
Many factors come into play, like on a Mill how tight your gibbs are set, the size of the motor (Torque) being two.
You need to read the information provided to understand how to set and test motors in Mach4.
If you are using a Router Table and machining timber then you will most likely have a higher acceleration than say a Mill cutting Brass or Steel.
Regards,
Mauri.

Thats sort of what I expected thanks

dq828,
Each machine and motor combination will have a different acceleration set as not two machine are alike.
Many factors come into play, like on a Mill how tight your gibbs are set, the size of the motor (Torque) being two.
You need to read the information provided to understand how to set and test motors in Mach4.
If you are using a Router Table and machining timber then you will most likely have a higher acceleration than say a Mill cutting Brass or Steel.
Regards,
Mauri.

I broke the bank building the CNC and I only run the basic Hobby version, the simulation software is extra and I wasn't sure it was worth it given the free Fusion 360 has a simulator in it. I dont have enough knowledge at this stage to playwith the software so I'll see if I can get the CV Wizard to work for me.

thanks for all of the help