Rubber Belt Calibration Accuracy

[wacoustics]

I installed the rubber belts over the past few days and went through the belt calibration routines (firmware 1.153). Below are my results after calibration (fractions of an inch represented in decimal for easy comparison to CW values):

By tape measure:
Board1: 23.9375 L x 3.515625 W x 0.750 D
Board2: 48.03125 L x 3.50 W x 0.750 D
Board3: 35.00 L x 3.46875 W x 0.734 D

CW measurements:
Board1: 24.040 L x 3.521 W x 0.750 D
Board2: 48.045 L x 3.524 W x 0.755 D
Board3: 35.186 L x 3.497 W x 0.745 D


The width seems to be the most consistent measurement from run to run and the depth usually works pretty well too. The length will vary a bit (+/- 1/32 - 1/16") from run to run.

I calculate the length measurement error as:
Board1: 0.43%
Board2: 0.03%
Board3: 0.53%

Board2 was the calibration board, so no surprise it's the closest. I can't say I'm satisfied with the overall results though, particularly where Board3 is off in measurement by 1/8"+.

So I really have three questions:

1) Anyone with sandpaper belts out there which can do some similar tests on measurement to see how much it varies from the rubber belts.

2) Are these within the tolerances expected (i.e., should I be happy with the results)?

3) What's the overall impact of the length measurement being incorrect in this kind of an instance. Does one assume that it's off by a similarly small fraction across the entire board and distort the carving by extremely small amounts?


Thoughts on this and any similar data is much appreciated.

[wacoustics]

Does anybody have any insight to this at all. Part of what I'm asking here is an accuracy bs precision question. We all know that the machine is fairly precise (repeats values at very similar places), but how accurate should I expect this to be?

[fwharris]

Not sure if you have seen this or not..

http://carvebuddy.com/PDFs/CW_Tipsan...ks_Jan2010.pdf

Found on Carvebuddy.com learning center.
http://carvebuddy.com/learning_center.html

[liquidguitars]

Does anybody have any insight to this at all. Part of what I'm asking here is an accuracy bs precision question. We all know that the machine is fairly precise (repeats values at very similar places), but how accurate should I expect this to be?

my only insight at this time is somewhat radical.. cut a 1/2 off the keyboard side of the in-feed roller belt then check you measurements. The belts can hit the AUX roller screwing up the process..

3) What's the overall impact of the length measurement being incorrect in this kind of an instance. Does one assume that it's off by a similarly small fraction across the entire board and distort the carving by extremely small amounts?

This is less important if you build a sled and use " keep original size" and "place on corner" like i do, it will force the project to read from the front edge I run two sided project's this way.


from the tips and tricks:

3)The board length should be placed more-or-less
centered in the machine (i.e., the material length-center
should be approximately centered over the traction belt
gap).
Some users will instead, place a board with one of the
workpiece ends positioned nearest the center of the
machine to save a little time during the measuring
stage during a project run. Generally, this is not
recommended practice as it could invite a tracking
error, particularly if the board is over 3 feet long. The
longer the board, the greater chance for tracking issues.
It is usually prudent to center the workpiece length
when placing it into the machine for best results.

I think MT has missed the point on this one.. far better to load the sled or wood off center in the CW, where you place the wood has no impact on the measurements but has a inpact on how the board sensor reads y.
LG

[mtylerfl]

Does anybody have any insight to this at all. Part of what I'm asking here is an accuracy bs precision question. We all know that the machine is fairly precise (repeats values at very similar places), but how accurate should I expect this to be?

When I installed the rubber belts on one of my machines, the belt Cal came out extremely accurately (running 1.153). Here's what my results were...

My hand measured length was 40"...the machine said 40.029"

My hand measured width was 7.312"...the machine said 7.323"

That's pretty accurate, I'd say - I'm happy, to say the least!

[mtylerfl]

I think MT has missed the point on this one.. far better to load the sled or wood off center.

LG

Hi LG,

For what it's worth...

According to two of the engineers/programmers at LHR, the board placement centering as described in the Tips is very helpful in eliminating the possibility of board length tracking problems some customers have experienced. They specifically asked to have board length center placement emphasized in the article. (That's how I've always run my projects too - and - I don't have tracking problems)

[liquidguitars]

According to two of the engineers/programmers at LHR, the board placement centering as described in the Tips is very helpful in eliminating the possibility of board length tracking problems some customers have experienced.

Thats imposable just based on the math .. where you place the board has no influence on the x measurement as long as the wood is under the rollers. lets get real.

But, you missed the real advantage of loading off center.. it has little to due with the AUX roller.

LG

[mtylerfl]

thats imposable just based on the math .. where you place the board has no influence on the x measurement lets get real.

But you missed the real advantage of loading off center.. it has little to due with the AUX roller.

LG

Hi LG,

Perhaps the fellows who do the actual programming and designing of the board tracking sensor system can go over all the details and specific reasons for their recommendations. They are great guys and I'm sure you'll enjoy speaking with them. I think if you get the opportunity to talk to them it will help you gain some additional understanding of the issues they are concerned about along with their insight regarding the x-tracking encoder, the brass roller, the sensor assembly, the math interaction/calculations between the brass roller sensor and the x-drive encoder, etc. It is quite interesting.

David Jochim and Chris Rawls are the techs you'll want to contact (although I think they are kept locked up in their offices without phones most of the time!) Chris R and Dave are the ones who had primary oversight over the article, but I also received input from Joe L and Omar. Between the four of them, I think they did a great job specifying what needed to be pointed out for the benefit of users.

[liquidguitars]

If talking to them has anything to do with it.. yes I two talk to the "guys" at times, even sold them one of my guitars I made on the CW last year. However your sled is built wrong as is the location that you are telling us to load it so go figure.

MT, you did a fine job I just had some small points to make if ok with the masters.

LG

[mtylerfl]

MT you did a fine job I just has some points to make if ok with the masters.

yes I two talk to the "guys" at times, even sold them one of my guitars I made on the CW last year. However your sled is built wrong as the location that you are telling us to load it so go figure.

LG

Yes, your guitars (and violins) are legendary. We all love 'em!