Is there a feature to slow down on the last part of a cut?

This forum is for general discussion regarding VCarve Pro
Post Reply
User avatar
hack613
Vectric Apprentice
Posts: 56
Joined: Mon Nov 27, 2017 9:06 pm
Model of CNC Machine: Various 6040, 3020, 2020
Location: Ottawa, Canada
Contact:

Is there a feature to slow down on the last part of a cut?

Post by hack613 »

I often cut stuff out from sheet material with one pass.

Just before the cut is finished the force of the cutter causes the very last part of the cut to snap. It leaves a tiny bit of flash that needs to be trimmed.

Is there a way to slow down the feed rate just as its finishing a cut?

Perhaps some sort of lead out or just cut the feed rate right down for like the last 2mm.

Thoughts?

mark-s
Vectric Craftsman
Posts: 217
Joined: Sat Feb 03, 2018 2:03 am
Model of CNC Machine: diy 4 X 4 CNC Router
Location: So. Cal.

Re: Is there a feature to slow down on the last part of a cu

Post by mark-s »

Mach3 feed over ride, second window lower right corner.
mark-s

User avatar
Rcnewcomb
Vectric Archimage
Posts: 5864
Joined: Fri Nov 04, 2005 5:54 am
Model of CNC Machine: 24x36 GCnC/WinCNC with ATC
Location: San Jose, California, USA
Contact:

Re: Is there a feature to slow down on the last part of a cu

Post by Rcnewcomb »

use lead-in and lead-out
- Randall Newcomb
10 fingers in, 10 fingers out, another good day in the shop

User avatar
hack613
Vectric Apprentice
Posts: 56
Joined: Mon Nov 27, 2017 9:06 pm
Model of CNC Machine: Various 6040, 3020, 2020
Location: Ottawa, Canada
Contact:

Re: Is there a feature to slow down on the last part of a cu

Post by hack613 »

mark-s wrote:Mach3 feed over ride, second window lower right corner.
mark-s

I'm aware I can change the feed rate in mach3 (which I happen to use).

But if I'm cutting a bunch of parts out, it's not very easy to change the feed rate just for 2mm.

Thanks for the thought though...

User avatar
hack613
Vectric Apprentice
Posts: 56
Joined: Mon Nov 27, 2017 9:06 pm
Model of CNC Machine: Various 6040, 3020, 2020
Location: Ottawa, Canada
Contact:

Re: Is there a feature to slow down on the last part of a cu

Post by hack613 »

Rcnewcomb wrote:use lead-in and lead-out
Okay thanks for this. I will try and see if this can reduce the feedrate for the last 2mm of a cut...

User avatar
hack613
Vectric Apprentice
Posts: 56
Joined: Mon Nov 27, 2017 9:06 pm
Model of CNC Machine: Various 6040, 3020, 2020
Location: Ottawa, Canada
Contact:

Re: Is there a feature to slow down on the last part of a cu

Post by hack613 »

Rcnewcomb wrote:use lead-in and lead-out
So I tried this.

I don't see any features in the lead screen that might affect the feed rate.

Also I noticed that the lead out happens after the cut is complete.

The idea is to reduce the feed rate while cutting the last 2mm of an outside profile cut.

Is there something in the lead screen that I'm missing?

User avatar
FixitMike
Vectric Wizard
Posts: 2173
Joined: Sun Apr 17, 2011 5:21 am
Model of CNC Machine: Shark Pro Plus (retired)
Location: Burien, WA USA

Re: Is there a feature to slow down on the last part of a cu

Post by FixitMike »

You can use a text editor to edit the toolpath by adding a line specifying a slower feed rate just before the final cut.
Here's the end of a toolpath that cuts on the line of a 4" wide x 3" high rectangle, centered at 0,0. The text defining the cut around the rectangle is in blue.

F80.0
G01 X-2.0000 Y1.5000 Z-0.7500
G01 X2.0000 Y1.5000 Z-0.7500
G01 X2.0000 Y-1.5000 Z-0.7500
G01 X-2.0000 Y-1.5000 Z-0.7500

F80.0
G00 X-2.0000 Y-1.5000 Z0.1000
G00 Z0.5000
G00 X0.0000 Y0.0000

And here is where I have modified it to cut the last inch of the last side at a feed rate of 20 inches/min. Added lines are in blue, my comments in red.

F80.0
G01 X-2.0000 Y1.5000 Z-0.7500
G01 X2.0000 Y1.5000 Z-0.7500
G01 X2.0000 Y-1.5000 Z-0.7500
G01 X-1.0000 Y-1.5000 Z-0.7500 Cut at the high speed to this point.
F20.0 Change the feed speed
G01 X-2.0000 Y-1.5000 Z-0.7500 Continue the cut to the original end point at the lower speed.
F80.0
G00 X-2.0000 Y-1.5000 Z0.1000
G00 Z0.5000
G00 X0.0000 Y0.0000

Note: Your toolpath may be formated differently to include line numbers.
Good judgement comes from experience.
Experience comes from bad judgement.

User avatar
Rcnewcomb
Vectric Archimage
Posts: 5864
Joined: Fri Nov 04, 2005 5:54 am
Model of CNC Machine: 24x36 GCnC/WinCNC with ATC
Location: San Jose, California, USA
Contact:

Re: Is there a feature to slow down on the last part of a cu

Post by Rcnewcomb »

Just before the cut is finished the force of the cutter causes the very last part of the cut to snap. It leaves a tiny bit of flash that needs to be trimmed.
Using lead-in and lead-out will solve this. You don't have to change the feed rate.
- Randall Newcomb
10 fingers in, 10 fingers out, another good day in the shop

User avatar
hack613
Vectric Apprentice
Posts: 56
Joined: Mon Nov 27, 2017 9:06 pm
Model of CNC Machine: Various 6040, 3020, 2020
Location: Ottawa, Canada
Contact:

Re: Is there a feature to slow down on the last part of a cu

Post by hack613 »

Thanks for the responses..

Yeah, I was thinking of changing the feed rate in g-code. I guess if it works it will be faster than trimming the flash by hand.

One difficulty I was thinking is if the piece I'm cutting has straight lines, I will need to add nodes into the g-code. For instance if I'm running a straight line for one inch, I would need to run high speed for .95 inches, then change the feed to slow and then go to the final coordinate. I wonder if adding nodes in my CAD drawing will cause the g-code generator to add nodes in...

I still don't understand the lead-out method. The lead out would happen after the piece separated and already has the flash on it.

User avatar
Adrian
Vectric Archimage
Posts: 14503
Joined: Thu Nov 23, 2006 2:19 pm
Model of CNC Machine: ShopBot PRS Alpha 96x48
Location: Surrey, UK

Re: Is there a feature to slow down on the last part of a cu

Post by Adrian »

How are you holding the material down? Without tabs you really need a vacuum table or you're always going to have issues like this. The part needs to be supported.

The other thing you could try is to cut in the opposite direction. The lead-in, lead-out may well work as well as has been suggested due to the direction of forces as it moves to the out.

Will Williamson
Vectric Craftsman
Posts: 210
Joined: Sat Apr 26, 2008 2:45 pm
Model of CNC Machine: Thermwood CS-45 5 x 10
Location: Capac, Michigan
Contact:

Re: Is there a feature to slow down on the last part of a cu

Post by Will Williamson »

Slowing down the feed rate, on the last line, is an advanced feature, used by Thermwood Control Nesting.
if the part is, under a certain size, in square inches, the software, slows down the fed rate, to a preset feed rate.
This is mostly, used in the production, of cabinet parts. This has been a thermwood, feature for over 10 years.
In Aspire when I need to hold, small, hard to hold parts, I use a, down spiral tool and let it pack the kerf, with sawdust.
works great.
Yes, a vacuum table is necessary.
Some one with code writing experience, could possible create a gadget,
Paul Roundtree if you see this, give us a shout.
Will Williamson willmade.com
Williamson Lumber & Millwork Inc.
Capac, Michigan

Post Reply