Machining times & Feed Rates are WAY off

Discussion/questions about software used with your CNC Shark and programming issues

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benaroh
Posts: 28
Joined: Thu Oct 10, 2013 1:57 pm

Machining times & Feed Rates are WAY off

Post by benaroh »

I've been having this problem for awhile, and still can't get to the root of it. And it's driving me crazy.

In V-Carve, I set the feed rate on my .25 upcut bit to 150 IPM. Then with an imported a vector (curve fit it to eliminate most of the nodes) I calculated the machining time. V-Carve calculated it as 1 minute, however when I cut the file it actually takes well over 2 minutes.

I know the Shark is a fairly slow machine, however I'm positive it is capable of machining twice as fast. When looking at the code- the F Code is set at 150, so it's correct.. But I know something is off. Perhaps post processor, or the laptop I'm using?

Any suggestions would be wonderful- I'm fairly inexperienced, but I feel like I've tried everything.

Ben

4DThinker
Posts: 951
Joined: Wed Jun 27, 2012 9:00 am

Re: Machining times & Feed Rates are WAY off

Post by 4DThinker »

VCarve has no way to know exactly how long any CNC will take to cut a file as the length of a vector and most CNC's need to speed up (accelerate) and then down (decelerate) before changing direction varies. If you are using the Shark 2.0 (or greater) control software then it does a great job of posting cut times once the file is loaded. Somewhere in VCarve you can set a scaling factor for the estimate but even then the number of curves vs straight lines can still make a great difference.

benaroh
Posts: 28
Joined: Thu Oct 10, 2013 1:57 pm

Re: Machining times & Feed Rates are WAY off

Post by benaroh »

Thanks for the reply! But here is the kicker - I once offset the vector .001 outward, I'm assuming this recalculated the vector to read the poper feed rates. After doing this, the profile cut out 3X faster than it had been.

I have been trying to repeat this with no luck. I'm positive the vector can be cut out substantially faster.. Just cant figure out what the problem is. No luck changing the bit feed rates, creating a new file, offsetting the vectors, etc.. it seems stuck at 50IPM.

rungemach
Posts: 460
Joined: Mon Aug 02, 2010 8:24 am
Location: Sarasota, Florida

Re: Machining times & Feed Rates are WAY off

Post by rungemach »

I know there have been a few issues if you are trying to cut something like a slot that is exactly the same size as the tool. If you made the slot .001 larger, the tool-path would generate correctly. Usually all cuts are somewhat larger than the tool, so it is is usually not an issue, and may have even been fixed in more recent versions of Vectric software.

On a shark, 150 ipm is a pretty fast speed if you are needing any accuracy in the cut. Vectric defaults their tool speeds for faster machines and most people assume that the Shark can just use those default speeds. The Vectric defaults are a bit aggressive for a Shark. I would suggest the 40 - 80 ipm range if you need good dimensional accuracy

You have seen that Vectric is generating the g-code that says 150 ipm. (The speed you would like to go). So the issue is most likely not Vectric, nor is it your Laptop.

When most machine controllers get that g-code, before they start they look ahead a bit "down the road" a several (or many) lines of code to see what is coming up. They continue to look ahead during the run. On some machines this "look ahead" amount is adjustable. The controller also knows what the machine is capable of doing, and will purposely slow down the feed rate based on the machines capabilities. So you may be able to hit 150 on longer straight sections, but any tight curves will run at a slower speed based on what parameters have been built into in the controller. Vcarve is not aware of what limitations your controller may need to impose to keep the Shark from damage, so Vectric would give you times based on what a machine that can cut at that full speed would do.

Just for fun, If you want to see this speed modulation in action, just draw out a little "race track" shape with a long straight section, a few curves , and a really tight slalom section. Try to cut it in air at 150 and then watch the controller modulate the speed as it tries to drive as fast as it can through the different sections ( given its factory programmed limitations). The speed modulation is often difficult to see easily on most things you would cut, but if you make a shape that contains long straights and tight turns , it is easier to see.

benaroh
Posts: 28
Joined: Thu Oct 10, 2013 1:57 pm

Re: Machining times & Feed Rates are WAY off

Post by benaroh »

Thanks for your help!

The good news is I have a CamMaster Stinger II on the way, so that should speed things up a bit!
Thanks yall!

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