transparencies not matching the screens created by them!?

By laser i'm assuming they used vellum??? I have heard with vellum it can shrink with heat. So i would guess that the heat from the bulb made the velum shrink and that's why it's different.

Hi Jeron,
No, it's just regular laser transparency film. I'm kind of baffled as to why, if the film warped because of the heat, the image on the screen didn't distort to match the film. The screens are good aluminum screens.

Maybe if you post a pic...

The only other thing I can think of is undercutting, but with the single light source I would doubt that.

Hi Jeron,
I scrubbed the screens, so I destroyed the evidence. I'm thinking it must be the film itself, since that's the only thing I changed. I'm kind of wondering if anyone else has experienced this, Being a relative newbie (I've been doing it for a couple years) I find there's still a lot of frustrating trial and error. Just when I think I've got it all figured out I find another way to put a wrench in the works! Anyway, once I get this figured out, it should be smooth sailing for a while, I've changed films, and am hoping that solves the problem. I really appreciate you taking the time to respond to my question.
Nick

Measure the film accurately. Then expose it on a screen as you normally would. Then measure again.

Then you know if the positive is changing size or if you have positive/screen contact issues

I suspect the film, as you inferred that it worked fine before with the inkjet.

However, you said everything has been fine before and worked well before, but you also said that you need more opacity. Either it was working well, or it wasn'? The positive films for screen printing are designed to hold lots of ink for opacity. You could try some of that on your inkjet and change settings to dump more ink into the film.

Check that the two transparencies still register with each other and if they do have another go.
Quite the opposite to undercutting, I suspect that one of the transparencies may not have been 100% flat to the screen, causing a slight shadow.
Try putting a foam pad or even some board inside the underneath of your screen to give a flat, firm area for the glass to press down onto the image.

thanks Pat, I will try that

Wouldn't the OP have had contact issues with the inkjet transparencies that worked great for them before? The only thing that we are told has changed here is the film itself....... Why would you suddenly get issues related to positive / screen contact when you didn't before? Unless the new positive was off a roll and the inkjet film laid flat? Doesn't add up to me.

Things change.
If Nick is using a 150w bulb I am assuming he isn't using a vacuum blanket.
I would assume that if the transparency was going to shrink it would have done so inside the laser printer, not under a 150w bulb.
Nick says that the image was off at one end- shrinkage would probably effect the entire image.
The thing with troubleshooting is to rule everything out one step at a time.

I agree - so why no contact issues with the inkjet film and only with the laser film?

I don't know. But Nick has already said that the problem is only at one end of one of the screens.
I had a similar problem about 6 years ago when one screen out of dozens was slightly warped and the glass wasn't sitting flat. I was using a single point light at the time and I had image problems where the glass didn't touch. It kept going back into the pile because I didn't realise the problem. Every time it was reused the problem reappeared.
More recently I was using a piece of picture frame glass very much larger than the screen, it wasn't centered on the screen and the weight at one end caused the glass to bow. There was enough loss of pressure at the other end for the transparency to lift fractionally.
I now use a piece of black foam on the underside of the screen. This raises it up slightly from the bench, giving upward pressure on the mesh/transparency when the glass is in place. This has the same effect as a vacuum blanket.

I had personal experience where Staples would print transparencies at different sizes for a large image that spanned two 8.5x11 pieces of transparency paper. Don't use them to print your transparencies. You can buy inkjet transparencies very cheaply on eBay if you don't have a laser printer yet.

Also, you need a lot of pressure on your screen mesh and your frame when exposing or the image can distort.

I just reexposed the screen using new 11x17 transparencies I bought from asc365. The screens came out fine. I did, however take Pat's advice and put some board under the screen to prevent bowing of the screen. I think I can rule bowing out though, because I've made many screens before and never encountered this problem. I have to conclude that there's something going on with the film Staples is using. In retrospect, I remember having some problems with a previous 3 colour separation I had them print out, but I corrected the discrepancies by hand. I think it's warping under the heat of the incandescent bulb. I will have to find better film though, the stuff I used jammed two copiers and had to be done on a large format machine. I think I burned my bridges with a couple printers with regards to the use of there regular machines. Cost me $28 CAD. Thanks for the advice bangtees, I will check ebay. Anyone else have problems jamming printers? Thans for everyone's input and interest.
Nick

Some printers need film with tape on the leading edge so the rollers can grip it. It comes like this out the box.

Try "waterproof" inkjet screen print film. You'll probably get much denser prints.

Look up which printers use which ink... You have dye or pigment. Find the right printer and then buy an all black system with dense or uv blocking ink. Your positives don't necessarily have to be totally black, they just need to block out the uv light spectrum for your emulsion.

Check out Ryonet for examples of printers that will work straight out the box. Epsom often come out strong. You'll save money, frustration and time.