Problem with Tolerance

Questions/answers/discussion about initial setup of your CNC Shark

Moderators: al wolford, sbk, Bob, Kayvon, al wolford, sbk, Bob, Kayvon

Post Reply
User avatar
mcsteve
Posts: 49
Joined: Sat Dec 20, 2014 10:03 pm

Problem with Tolerance

Post by mcsteve »

Hello all. Recently I've been experiencing some errors in dimension. Normally I am doing projects that I just rough dimension on the CNC and then finish with other processes. Projects like crib boards and such I typically use the sander to bring caps to the correct radius dimensions.

A most recent project is to place a small watch face in a cell phone stand to act as a desk clock when the cell phone is in use. The hole dimension was to be 1.275" but the actual pocket created was 1.222". This has caused me to create a tolerance test for my machine that I could check with a miter gage. The machine appears to be under sizing almost every entity in the project. Before I start messing with things I thought it best to check with those who have experience to gain your thoughts. My system is a Shark Pro Plus using the latest version of V Carve (10.514) for code creation.

I have attached the CNC files as well as representation of what was actually cut.

Any thoughts on where to start with trying to correct my issue?

Thanks in advance.
Attachments
Tolerance Test - Pockets with .25 EM.tap
(10.26 KiB) Downloaded 10 times
Tolerance Test - Scribe with 60 Deg.tap
(117.09 KiB) Downloaded 12 times
Tolerance Test Results.pdf
(94.81 KiB) Downloaded 14 times
CNC Shark Pro Plus - 12/2014
VCarve Pro, PhotoVCarve, Cut3D
ViaCAD 3D, AutoCAD, Sketchup
BobCAD V28

User avatar
Kayvon
Posts: 511
Joined: Tue Oct 21, 2014 11:46 pm

Re: Problem with Tolerance

Post by Kayvon »

I've experienced the same issue when cutting gears for clocks. The arbor holes don't precisely match what I expect, so I go back and use a drill press to get the precise hole size I want.

I've never investigated it closely enough to fix it, but I suspect the problem lies between bit sizes not perfectly matching and some small amount of flex in the plastic gantry.

User avatar
mcsteve
Posts: 49
Joined: Sat Dec 20, 2014 10:03 pm

Re: Problem with Tolerance

Post by mcsteve »

My first thought has been that it was flex in the gantry as well, but this would not explain why I am getting differences in the horizontal and vertical line distances as well.

I try to keep an eye on my bits as well considering that many are not "top of the line" brands. In this case I was using a Frued 2 flute spiral .25 bit with an actual of .244 so I had actually oversized the hole but that didn't help as the size difference was significant. My current thinking this may be an encoder issue. Do you know if there is a way to see the encoder settings in the Shark control panel so I can match those against the actual specs for steppers installed?

Steve
CNC Shark Pro Plus - 12/2014
VCarve Pro, PhotoVCarve, Cut3D
ViaCAD 3D, AutoCAD, Sketchup
BobCAD V28

User avatar
Kayvon
Posts: 511
Joined: Tue Oct 21, 2014 11:46 pm

Re: Problem with Tolerance

Post by Kayvon »

Try CTRL+E or CTRL+G in the Control Panel.

User avatar
mcsteve
Posts: 49
Joined: Sat Dec 20, 2014 10:03 pm

Re: Problem with Tolerance

Post by mcsteve »

I’ll give that a try. Thx.
CNC Shark Pro Plus - 12/2014
VCarve Pro, PhotoVCarve, Cut3D
ViaCAD 3D, AutoCAD, Sketchup
BobCAD V28

Post Reply