Sizing Error!

[Spooky]

In general everytime I've heard of accuracy errors they have been down to something being loose. Adjusting the servo offsets will cure the problem short term but long term it pays to find the cause as it may be something that will get worse.

I have to call Chris tomorrow anyways so I'll ask him what the problems were on the last job that had accuracy issues....I seem to remember there was a recent one that had X/Y errors... (hey I'm old and my memory isn't great)

best wishes

Dave

[PhillyDee]

Yep, it might just be a short term fix, but I have a couple of orders that I had to fulfil, so in this case unavoidable! There doesn't appear to be any backlash, the text lines up perfectly in both directions. I will get my clock on it and do a few checks at the weekend. See if when it moves 1mm, it moves 1mm. Both axis were out, and it may have been there from purchase, I never really checked any sizes when I did my first plays with it! It was just bog standard medallions, letters etc. This one has to be right, so its the first check its had!

[Bernie_of_CPE]

I wonder if something maybe lost in translation.

I use a MAC to produce my drawings, then output as .dxf, this format retains all the colour information and therefore the layering for engraving or cutting. Every part I have cut except for this last month where the machine suffered a mechanical error was perfect. One of the belt clamps came loose and is now fixed. I produce a slot and tab joint very often in prototyping work and use the 0.1 mm kerf as the only tolerance. I always set the software line to superfine. Because I use a MAC I have no choice but to convert with an extra step, this made me nervous at first as it's always a liability for error to occur. I haven't had a single translation error as yet.

Here are a few simple tests that might benefit other users too. You don't need any measuring tools to try this. In the laser software mine is V5.2 running on an ancient laptop bought for £25.00 (dead battery, old processor) draw a square and size to at least 50 mm. Engrave a dot or cut a small hole in one corner and also at one corner outside the shape so you can register it the way it's cut from the test piece. Go ahead and make the cut, minimally you will need 2 mm acrylic for this. Once complete take out the square from the surrounding material rotate 180 degrees and try to refit it. You will have doubled any error in the rotation so making it more obvious. If the part is not square (a trapezium) it won't fit, personally I would look for a mechanical reason in the belts and tracking.

Try again but with a 90 degree rotation, if all is well it should fit like a glove with the only clearance being the kerf (width) of the laser removed material itself.

Now the crunch, make a square of exactly the same proportions as you just made in the laser's software but with your normal drawing package. Import into the laser software, cut and try the test again but using the cut part in the first hole you made, if it fits you know everything is set up correctly. If it won't drop sweetly into the hole then you have found the problem is software and cut the trouble shooting in half. Just remember to keep the up sides up in both tests to prevent any issues with the sloping sides giving a false error.

Hope this helps.

[Pedro_Hernandez]

Hi Phill - pm me your email addy and I'll forward some info

Dave

Can you email me some info on this as well Dave, I'm also finding I'm having sizing errors. 235mm X 170mm cuts as 236mm x 171mm.

I've got a job that is pretty crucial as I'm being supplied printed card which I need to get my cut lines pretty damn good any help wouldbe much apreciated

Cheers

Peter

[Daven]

PM sent

Dave

[Pedro_Hernandez]

Ok, this has worked for me but is only a temporary fix until some one comes up with a solution,

I resized in Corel subtracting the diference, 235 becomes 233 and 170 becomes 169 and I get a perfect 235 by 170 rectangle in cut thin card !

If I'm missing anything here please let me know as this will frustrate me and bring me to the brink of throwing something across the room !, doesnt make any difference were on bed I cut sizing error is the same.

Regards

Peter

[Spooky]

Heya Pete,

I just drew a box in Corel X5 then exported as a DXF, opened the dxf in AutoCAD and there is a difference in size. The "why" I don't understand as yet but the difference is there. I'm thinking possibly a snap of some kind but I don't know very much about Corel to be honest.

I'll quickly draw the square your on about and post it here..

back in a bit

best wishes

Dave

[Spooky]

http://opticalpower.co.uk/files/test.zip

235 x 170mm rectangle created with AutoCAD 2012 and saved as AutoCAD 2000 format DXF

best wishes

Dave

[Pedro_Hernandez]

Thanks Dave

I run the file and it's cutting a rectangle 238 x 172, kinda of confused now !.

Regards

Peter

[Spooky]

I had the same problem Pete with another user, its the dpi settings in corel causing it,I'm not yet sure of the "why" but it's deffinatly the source of the problem.
As soon as i have an answer I'll post details

best wishes

Dave