Dimension error with screw holes on my Lightburn components

[rich1uk (Richard Taylor)]

Hi all,

I wonder if anyone can help me please?

I am having a strange issue with my screw holes on my parts in Lightburn. The round holes should be exactly 5mm diameter and the square holes should be 5.2mm x 5.2mm however I have noticed that the dimensions have changed by themselves slightly on some of the parts e.g., some of the screw hole circles are slightly oval e.g. 5.011 x 5mm and some of the squares are 5.408 x 5.408. It is like a rounding issue with the number after the decimal. It should be .000 not a fraction of a number. The overall part itself seems to have the correct dimensions so it is unlikely I have accidentally changed the dimensions by mistake as they are normally grouped together. My theory is the whole part would be slightly the wrong shape if I had accidentally knocked the dimensions out but it is only the screw holes are slightly inaccurate.

As you can see from the screenshots the dimensions of the screw holes are not locked.

It is strange that the issue only affects some of the holes on some of the parts. If I change them back to the correct value, some update correctly but some do not. I have attached a Lightburn file to show you what I mean. On the bottom part the software will not let me change the screw holes to the correct 5mm x 5mm size. Instead, I get a decimal/fraction each time I try to input 5.0.

I know the dimension error for the screw holes does not matter too much as my laser cutter will not have that level of accuracy anyway, it just seems a bit strange that I am getting this decimal error.

It could be something I have done wrong so sorry if I have made a mistake and caused this myself. I need to upgrade my Lightburn too so maybe it is an error with v0.9.24?

Thank you very much for your help and time.

It is much appreciated.

Rich

LED A2 L5 Frame Parts.lbrn (24.1 KB)

[cggorman (Chris)]

Do you ever switch the display units back and forth between metric/imperial?

I have noticed I get that (rounding error?) on my arrow nudge distances (arrow, Ctrl+arrow, shift+arrow) when I toggle back and forth. It may also happen on feature sizes but I haven’t noticed. Most of what I do in LB isn’t that dimensionally critical, so may well have overlooked it.

[rich1uk (Richard Taylor)]

Thanks Chris,

I do not normally switch between metric and imperial to be honest unless I have done it at some point in the past by mistake. I always work in metric.

Thank you for the suggestion though.

The size errors are not critical, it’s more for my OCD I think!

It’s just strange that I keep getting fractional errors on these holes when they should be whole numbers. It made me worry I had knocked the dimensions out of shape by mistake but the dimensions of the actual components are whole numbers so I do not believe this has happened.

It’s also odd that when changing the hole dimensions back to whole numbers e.g., entering 5.0, Lightburn sometimes changes this to 5 with a random decimal e.g., 5.11. This happens for me on some of the holes on the bottom component of Lightburn file attached.

You would expect this behaviour with locked dimensions where the height is proportional to the width but the dimensions are unlocked so independent of each other. Very strange!

It’s probably something I am doing wrong

[MikeyH (Mike Hembrey)]

@rich1uk

5.011 x 5mm

If the drawing dimensions are exactly 5mm, this could be either the laser beam shape, or backlash in one axis.

@rich1uk

squares are 5.408 x 5.408

5.2 to 5.408 is unlikely a rounding error. That might be a kerf offset applied to some sqiares. Although you might have backlash, I do not think the extra amount is that because the circles are less.

@rich1uk

should be .000 not a fraction of a number.

This contradicts what you said earlier, with “should be 5.2mm”.

@rich1uk

they are normally grouped together.

“Normally” is the key word here. Did you ungroup everything and retest? I group inside items first, then work out. Preview shows me where I missed one or more, and that happens a lot.

@rich1uk

theory is the whole part would be slightly the wrong shape

This is only true if everything is grouped in an orderly manner. I have learned to slow down and recheck everything before that first burn, and even then i sometimes screw up.

At this point, I will examine your file and come back with more comments.

[MikeyH (Mike Hembrey)]

I have confirmed what you say about the not exactly 5mm part. Nothing I did to it would tell me why. I suspect it is in how it was constructed. Maybe @JohnJohn has a clue.

I created a 5mm circle, Test Cir, beside it and that one sized to 5mm exactly. Feel free to CTRL-D that one and place it as needed.

@rich1uk

need to upgrade my Lightburn

I would say yes, not to fix this problem maybe, but to get all the nice features it has now. You will be amazed at what has been added.

LED A2 L5 Frame Parts-v2.lbrn (28.7 KB)

[rich1uk (Richard Taylor)]

Thanks very much Mike, I appreciate your response.

The strange decimal number which is appearing on some of my square or round holes is just what is appearing in Lightburn, I have not actually measured the final laser cut component.

Sorry, yes, you’re right, the circles should be a whole number 5mm x 5mm exactly and the squares 5.2mm x 5.2mm. What I am seeing is some of the squares are 5.408 x 5.408 or another unexpected decimal.

Yes, it could be a grouping error I have made somewhere along the way and carried the same error on later components which are based on previous ones. The strange thing is that some of the holes have a different decimal number so unless I have messed up several times (which is unlikely, but you never know!) I would expect exactly the same decimal error on the later parts, following the error I made based on the previous ones but this does not seem to always be the case. Hence why I wondered if it was a software/rounding glitch.

I was hoping to just correct the dimension error by entering the correct size e.g., 5.0. It works for some of the holes but not others (like some of the holes in my example file). I will have to replace them with new holes which seems to work as you suggested. The problem is, there are a lot of holes!

I was just wondering if it was worth the hassle if I correct all the holes to exactly the intended dimensions but the next time I open the file, the same phenomenon occurs. This post was mainly to see if it was a known issue or basically something I have done wrong to see if it was worth fixing all the components I have made.

Thank you very much for looking at the file – I am pleased it is not just me who cannot correct the holes to 5mm x 5mm (by just entering the correct size). I cannot understand why it is not possible. Regarding the construction of the circle, I originally just used the circle tool and entered 5 x 5 mm. Not sure if something I did later affected it. I have rotated the component to optimise material cutting, I did not change the dimensions (unless I did accidentally).

Yes, I will definitely upgrade my version of Lightburn, I have been looking at some of the improvements, they look very useful.

Thank you.

[MikeyH (Mike Hembrey)]

@rich1uk

wondering if it was worth the hassle

That is your call, but if it does not affect the assembly process, I ask why bother?

Yes, this is the age of computers and they are supposed to be predictable, and they are. Unfortunately, the people making, programming, and using them are not.