Reasonable expectation of flatness

Talk about all things CNC
Post Reply
aarvidsson
Posts: 150
Joined: Sat Aug 03, 2013 4:46 pm
Location: Frosty Sweden

Reasonable expectation of flatness

Post by aarvidsson » Wed Jan 18, 2017 9:00 pm

I'm just about to tram the spoilboard of my newly rebuilt Shapeoko, and it occurred to me: how flat can I reasonably expect this board to stay? It's an 16mm MDF that i'll remove 0,3mm from - how flat will it stay with changes in temperature, humidity and such?

For you guys that want a very high consistency in the Z axis (0.1mm and such) - how do you do it? Metal bed? Tram whatever piece of sacrificial material before running every job?
ShapeOko 2 #4143

CastIrony
Posts: 650
Joined: Mon Jul 21, 2014 10:21 pm
Location: Portland, OR

Re: Reasonable expectation of flatness

Post by CastIrony » Wed Jan 18, 2017 9:42 pm

Yeah, I've noticed some significant swelling from the piece of thick MDF I use as a spoilboard/mounting board. In the short term I'm probably going tram it, but eventually I would like to replace it with a material that won't warp or swell with changes in humidity, like HDPE.
Shapeoko 3 #192 - Complete! Needs limit switches.

WillAdams
Posts: 8542
Joined: Mon Apr 09, 2012 6:11 pm
Location: Pennsylvania --- south of the Turnpike, East of US-15
Contact:

Re: Reasonable expectation of flatness

Post by WillAdams » Wed Jan 18, 2017 11:33 pm

If you spray it w/ spar urethane or some other sealant before (top, bottom, sides and into all the holes) and after tramming (touch up where you cut), it should stay reasonably flat.
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets
Nomad 883 Pro #596 (bamboo)

DanMc
Posts: 257
Joined: Fri Apr 13, 2012 3:34 am

Re: Reasonable expectation of flatness

Post by DanMc » Thu Jan 19, 2017 4:31 am

I use mdf. If I'm working on something critical I'll tram a second sacrificial board specific to that job, but then I usually mill a jig specific to each project or series anyway with holddowns where I need them. Even with something that won't swell is the table the machine is resting on stable to <0.1mm? There's too many variables and it takes no time to skim the surface before a project.

aarvidsson
Posts: 150
Joined: Sat Aug 03, 2013 4:46 pm
Location: Frosty Sweden

Re: Reasonable expectation of flatness

Post by aarvidsson » Thu Jan 19, 2017 7:26 am

Good points from all of you, thank you very much!
ShapeOko 2 #4143

WillAdams
Posts: 8542
Joined: Mon Apr 09, 2012 6:11 pm
Location: Pennsylvania --- south of the Turnpike, East of US-15
Contact:

Re: Reasonable expectation of flatness

Post by WillAdams » Thu Jan 19, 2017 2:27 pm

For an example of such jigs, see the calipers which I made: http://www.shapeoko.com/projects/project.php?id=154 --- they also made use of sacrificial aluminum and nylon screws.
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets
Nomad 883 Pro #596 (bamboo)

Post Reply