Prevent tearout in hardwood?

This forum is for general discussion regarding VCarve Pro
Post Reply
Natenator76
Posts: 48
Joined: Mon May 30, 2022 12:31 pm
Model of CNC Machine: AXYZ

Prevent tearout in hardwood?

Post by Natenator76 »

Getting some tearout in 3/4" cherry and wondering ways I can mitigate this issue?

1/4" Amana compression bit
19000 RPM
350 feedrate
Climb milling

Example of the tearout in the image below...
20221128_150725.jpg
Thank you

User avatar
Rcnewcomb
Vectric Archimage
Posts: 5887
Joined: Fri Nov 04, 2005 5:54 am
Model of CNC Machine: 24x36 GCnC/WinCNC with ATC
Location: San Jose, California, USA
Contact:

Re: Prevent tearout in hardwood?

Post by Rcnewcomb »

Generally I would not use a compression bit for pocketing in hardwood. A downcut bit would be a better choice.

Unfortunately the camera focused on the floor rather than the wood so it is difficult to see the issue.
Attachments
Tearout.JPG
- Randall Newcomb
10 fingers in, 10 fingers out, another good day in the shop

ken.gentry
Vectric Apprentice
Posts: 91
Joined: Sat Aug 19, 2017 1:35 am
Model of CNC Machine: Joe's CNC 4x4
Location: Greensboro, NC

Re: Prevent tearout in hardwood?

Post by ken.gentry »

Also, is 19000 RPM the right speed for hardwood? Seems high. I cut red oak at 12000 RPM.

User avatar
adze_cnc
Vectric Wizard
Posts: 4329
Joined: Sat Jul 27, 2013 10:08 pm
Model of CNC Machine: AXYZ 4008
Location: Vancouver, BC, Canada

Re: Prevent tearout in hardwood?

Post by adze_cnc »

19000 rpm @ 350 ipm presuming a two-flute bit at 1/4" diameter gives 0.009 inch chip-load. Most charts will tell you that a chip-load of 0.009 to 0.011 for a 1/4" bit in hardwood. A decent place to start.

User avatar
adze_cnc
Vectric Wizard
Posts: 4329
Joined: Sat Jul 27, 2013 10:08 pm
Model of CNC Machine: AXYZ 4008
Location: Vancouver, BC, Canada

Re: Prevent tearout in hardwood?

Post by adze_cnc »

One way to get around tear-out is to prevent the bit from going around a corner but have approach the corner straight on.

One way to do that is to offset the border outwards by the radius of the end mill keeping sharp corners:
 
offset for cut.png
 
Then use the fillet tool to add "plasma loops":
 
plasma loops.png
 
Now create a "Profile Toolpath" using the plasma loop vector and cutting "on the line". The bit will cut past into the waste then loop around and re-engage the material:
 
maori shape.jpg
 
This was done in 1.625 inch really tightly grained Western Red Cedar with no chip-out even on the pointiest corner.

Natenator76
Posts: 48
Joined: Mon May 30, 2022 12:31 pm
Model of CNC Machine: AXYZ

Re: Prevent tearout in hardwood?

Post by Natenator76 »

adze_cnc wrote:
Tue Nov 29, 2022 12:22 am
One way to get around tear-out is to prevent the bit from going around a corner but have approach the corner straight on.

One way to do that is to offset the border outwards by the radius of the end mill keeping sharp corners:
 
offset for cut.png
 
Then use the fillet tool to add "plasma loops":
 
plasma loops.png
 
Now create a "Profile Toolpath" using the plasma loop vector and cutting "on the line". The bit will cut past into the waste then loop around and re-engage the material:
 
maori shape.jpg
 
This was done in 1.625 inch really tightly grained Western Red Cedar with no chip-out even on the pointiest corner.

Very interesting approach! Will give this a try. Thank you.

tomgardiner
Vectric Wizard
Posts: 447
Joined: Thu Oct 02, 2014 1:49 pm
Model of CNC Machine: FMT Patriot 4 x8

Re: Prevent tearout in hardwood?

Post by tomgardiner »

Take note of the up flute length on your compression bits. I suspect that your first pass depth is less than the up spiral section. Go for a deeper cut or go to a down shear spiral. I have had good luck with solid carbide straight flutes in hardwood. I get thousands of feet out of a two flute straight bit in ash with no tear-out.

Natenator76
Posts: 48
Joined: Mon May 30, 2022 12:31 pm
Model of CNC Machine: AXYZ

Re: Prevent tearout in hardwood?

Post by Natenator76 »

tomgardiner wrote:
Tue Nov 29, 2022 1:06 am
Take note of the up flute length on your compression bits. I suspect that your first pass depth is less than the up spiral section. Go for a deeper cut or go to a down shear spiral. I have had good luck with solid carbide straight flutes in hardwood. I get thousands of feet out of a two flute straight bit in ash with no tear-out.
Can you link me to what you'd recommend?

Thank you.

User avatar
Burnside
Posts: 44
Joined: Wed Sep 07, 2022 10:39 pm
Model of CNC Machine: ShopSabre

Re: Prevent tearout in hardwood?

Post by Burnside »

tomgardiner wrote:
Tue Nov 29, 2022 1:06 am
Take note of the up flute length on your compression bits. I suspect that your first pass depth is less than the up spiral section. Go for a deeper cut or go to a down shear spiral. I have had good luck with solid carbide straight flutes in hardwood. I get thousands of feet out of a two flute straight bit in ash with no tear-out.
This was my first thought as well. I wish Vectric had a special setting for compression bits that would allow you to force minimum pass depths. I always have to go in and remember to edit the pass depths to the spiral change depth.

Also the 19000 may seem a reasonable chip load but I’d say that’s true for a good, sharp bit. First thing I’d change is that after to check that the first pass is at least (or maybe a few thou more) the spiral change depth.

User avatar
Burnside
Posts: 44
Joined: Wed Sep 07, 2022 10:39 pm
Model of CNC Machine: ShopSabre

Re: Prevent tearout in hardwood?

Post by Burnside »

Natenator76 wrote:
Tue Nov 29, 2022 2:27 am

Can you link me to what you'd recommend?

Thank you.
It will depend on your bit. It should be documented. Usually it is called the “spiral change” depth. Just measure it and add a little bit. Whatever number you end up with make that your first pass depth. My 3/8 is .35 so I set my pass depth to .375. My 1/4 is .20 so I set that first pass to .25.

User avatar
martin54
Vectric Archimage
Posts: 7339
Joined: Fri Nov 09, 2012 2:12 pm
Model of CNC Machine: Gerber 48, Triac PC, Isel fixed gantry
Location: Kirkcaldy, Scotland

Re: Prevent tearout in hardwood?

Post by martin54 »

I don't run a production shop so my speed & feed settings are a bit more conservative & I haven't cut the same volumes of wood as some of the others.
Have you tried switching your cutting direction? I have read a lot of different opinions on cutting direction, some say conventional for softwood & climb for hardwoods, for hardwoods some will say climb with a conventional last pass & some will say it depends on the grain direction :lol: :lol:
If it were me then I would probably experiment a little with different cutting strategies :lol: :lol:

As someone else has said I don't tend to use compression bits for hardwoods although I can't say I never have :lol: :lol:

User avatar
Leo
Vectric Wizard
Posts: 4082
Joined: Sat Jul 14, 2007 3:02 am
Model of CNC Machine: 1300 x 1300 x 254 Chinese Made
Location: East Freetown, Ma.
Contact:

Re: Prevent tearout in hardwood?

Post by Leo »

Here is a pretty good explanation of how a compression bit works.

https://www.stepcraft.us/blog/stepcraft ... end-mill-8
Imagine the Possibilities of a Creative mind, combined with the functionality of CNC

User avatar
Burnside
Posts: 44
Joined: Wed Sep 07, 2022 10:39 pm
Model of CNC Machine: ShopSabre

Re: Prevent tearout in hardwood?

Post by Burnside »

Great article for review. Thanks for sharing. I usually don’t ramp them either. Compressions (well good ones) are ground so they can plunge right in without ramping.

One trick is that I set my pass depth for compression bits to slightly more than the spiral transition within my tool library. I don’t have to remember each bit’s override. Then all I have to do is check the box “Maintain exact tool path depth” and I’m done. Works great. I just wish Vectric did this automatically for compression bits.

Just yesterday I forgot to do that and sure enough I had some tearing in my Baltic birch ply. Luckily it was just a shop project.

Natenator76
Posts: 48
Joined: Mon May 30, 2022 12:31 pm
Model of CNC Machine: AXYZ

Re: Prevent tearout in hardwood?

Post by Natenator76 »

Want to post a follow up and say thank you to those that replied. I purchased a cheap spiral downcut bit, changed the feedrate and RPMs AND switched from climb to conventional and had no corner tear out on the main part that I was machining.

Soon thank you again to those that provided help!

Post Reply