PDF changes size. WHY?

[cavx]

Hi guys,

Can anyone assist me with my scaling issue? I have created patterns for a project in Sketch-Up and I can export the files as a JPEG. The scaling does not change. The patterns are quite large, so I've been getting them printed on A2 paper at the local Office Works. They always open my JPEGs in Photoshop and today they even saved the file as a PDF for me. However, every time I get these printed, they are at least 10% over sized.

Tonight I saved all of my JPEGs as PDFs using Photoshop and I got the same thing. On screen using the "actual pixels" icon, the size is correct. Save as a PDF and open at 100% and I've suddenly gained about 10%. I always include a 25.4mm XY axis for checking scaling and the lines are about 28mm, not 25mm. If I view the image at 90%, it is pretty close to being correct. Yet when I asked OW for them to print them at 90%, they were too small - about 5mm too small on a straight edge.

Is there a setting I've missed or another way to do this? Any help would be appreciated.

[ashbash]

Are you using an offset printer?

[TheWolf]

Is their printer set to expand the picture to the page size?

[cavx]

Are you using an offset printer?

Not sure. I take the files into Office Works and they print on their gear. I can't print over A4, so use their large format printers to get A2. Originally I was printing multiple A4s and taping them together, but found the single page was better to work with. Apart from joins, I never had scaling issues when printing myself.

Is their printer set to expand the picture to the page size?

I got to see the screen and it shows no scaling.

The only thing I am thinking is that maybe I need to expand the original bitmaps to be the same size as an A2 sheet of paper. What I did notice but don't understand is there is larger scaling issues with smaller files sizes.

What I don't get is that X number of pixels to create a line 25.4mm should remain the same at 100%, yet for what ever reason (PDF conversion?) is altering that even though all settings are for 100% or 1:1 bit mapping.