So much sanding after changing bits

This forum is for general discussion regarding VCarve Pro

So much sanding after changing bits

Postby rosielee » Tue Nov 06, 2018 8:32 pm

Hey

I'm a newbie (ish) to cnc and this forum so I hope I'm posting this in the right place!

I am using VCarve Pro. I'm doing a simple pocket tool path around some lettering on a 10 x 10" piece of pine. I'm using a large area clearance tool 1/4" bit and then a 1/8th inch bit for the detail.

I'm using a touch plate to zero my z axis each time.

The 1/4 does a great job, very clean. When the 1/8 goes round there is a indent line (not super deep but very noticeable) around every letter which will require a whole lot of sanding.

Is this something I should just accept? Or would you expect, given the touch plate and all, that the sanding would be minimal?

Jules
rosielee
 
Posts: 3
Joined: Thu Jan 11, 2018 7:40 pm
Model of CNC Machine: CNC Shark

Re: So much sanding after changing bits

Postby Rcnewcomb » Tue Nov 06, 2018 8:54 pm

Wood moves when it is cut. If the relative humidity in the shop is higher than the moisture content in the wood then the piece absorbs water. If the shop is drier than the wood then moisture flow out of the wood.

You may get better results by using the smaller bit and then the larger bit.

A better holddown method such as vacuum may help.

Sometimes it is faster to do the whole piece with a single bit rather than spend time sanding.
- Randall Newcomb
10 fingers in, 10 fingers out - another good day in the shop
User avatar
Rcnewcomb
Vectric Wizard
 
Posts: 3115
Joined: Fri Nov 04, 2005 5:54 am
Location: San Jose, California, USA
Model of CNC Machine: GCnC/WinCNC

Re: So much sanding after changing bits

Postby steve323 » Fri Nov 09, 2018 9:33 pm

Maybe the 1/8" bit has a bit more flex than the 1/4" bit. Would the lines go away if you raised the 1/8" bit a very small amount? My touchplate it handheld. I move it manually to the location where I want to reference. A sheet of paper or a playing card under the base would result in a small offset in height.

Steve
steve323
 
Posts: 6
Joined: Wed Dec 20, 2017 9:01 pm
Model of CNC Machine: Homebuilt kit

Re: So much sanding after changing bits

Postby martin54 » Fri Nov 09, 2018 10:34 pm

is it a fixed touch plate or one you place on top of the material? If it is the latter then are you placing it in exactly the same place & orientation after your bit change? Wood often isn't as flat as we think it is so even with a touch plate it is possible to get different z heights when changing bits :lol: :lol:

As Randall says changes in humidity can affect things as can tension within the wood that is released when a large amount is removed from one side. Have you experimented with different types of wood ?
User avatar
martin54
Vectric Wizard
 
Posts: 3986
Joined: Fri Nov 09, 2012 2:12 pm
Location: Crossgates, Scotland
Model of CNC Machine: Gerber System 48 (modified)

Re: So much sanding after changing bits

Postby rosielee » Sat Nov 10, 2018 4:24 pm

thank you for the replies!
I did the whole job with the 1/8th bit nudge a touch higher and the result was much better! I guess it's all about experimenting with different types of wood too.
Thank you
rosielee
 
Posts: 3
Joined: Thu Jan 11, 2018 7:40 pm
Model of CNC Machine: CNC Shark

Re: So much sanding after changing bits

Postby Heime » Fri Nov 16, 2018 10:08 am

Over on the Shopbot Forum they put up a good video on best practices for zeroing this week. It dealt exactly with your problem. Well worth a look.
Heime
Vectric Apprentice
 
Posts: 68
Joined: Mon Sep 19, 2011 10:54 pm
Location: Melbourne, Australia
Model of CNC Machine: Shopbot Buddy 48"

Re: So much sanding after changing bits

Postby scottp55 » Fri Nov 16, 2018 11:37 am

Here's yesterday's tutorial on Zeroing multiple bits;
https://www.youtube.com/watch?v=0sOTwmWmOq8&feature=youtu.be
scott
User avatar
scottp55
Vectric Wizard
 
Posts: 2351
Joined: Thu May 09, 2013 11:30 am
Location: Kennebunkport, Maine, US
Model of CNC Machine: Shopbot Desktop 5.5"Z/spindle/VCP9

Re: So much sanding after changing bits

Postby Adrian » Fri Nov 16, 2018 11:56 am

I thought that was everybody who zeroed to the material surface did anyway? :? Still doesn't account for the cut area expanding or the different vertical "pull" of the tools etc. Not a lot you can do to get around that though.
User avatar
Adrian
Vectric Archimage
 
Posts: 8526
Joined: Thu Nov 23, 2006 2:19 pm
Location: Surrey, UK
Model of CNC Machine: ShopBot PRS Alpha 96x48

Re: So much sanding after changing bits

Postby scottp55 » Fri Nov 16, 2018 12:05 pm

Agree Adrian.
Doesn't take into account a lot of things.
Just posted for the OP for basics.
scott
User avatar
scottp55
Vectric Wizard
 
Posts: 2351
Joined: Thu May 09, 2013 11:30 am
Location: Kennebunkport, Maine, US
Model of CNC Machine: Shopbot Desktop 5.5"Z/spindle/VCP9

Re: So much sanding after changing bits

Postby rosielee » Fri Nov 16, 2018 12:43 pm

Thank you, that was actually very helpful :lol:
rosielee
 
Posts: 3
Joined: Thu Jan 11, 2018 7:40 pm
Model of CNC Machine: CNC Shark


Return to VCarve - General

Who is online

Users browsing this forum: dgreen2, Google [Bot] and 30 guests