[Scotten]

I have had mixed results with my step wedge tests. The equipment and process is as follows:

48" Blacklight Fluorescent Tubes (10) 7" from glass
180 amber mesh, Coated 1/1, Ulano QTX
8-30 second intervals (30 sec. to 6 min. exposure)
Rubylith to cover each step
SMT Step Wedge test printed on vellum from laser printer

So, using this test I figure I would have about a 90 second exposure using Ulano's Base Exposure Table + Variables. At washout I got mixed results. The screen started to wash out at the 30 second to about the 2 min exposure. It did have a bit of area that did not wash out. It did not wash out consistently over each step.

After this, I just went at burned another screen, using the same film, in just 2 steps: 30 secs. & 1 min. The 30 second side washed out faster than the 1 min. side but not completely. On the wedge test they go down to a .5 line and .5 mesh simulation. Some washed out, some did not. What bothers me is that the screen does not just wash out as easy as I thought. I have to use a pressure washer to get it to let loose. I did not get a step in either method to say I have the time dialed in for this set up.

Is QTX that fast that I could actually be getting a 45 sec. exposure with that light source?

Sorry this is so long. I was hoping for more clear results. I am ordering a Stouffer test strip today.

 

[CastandBlast]

How opaque is you vellum, that could be an issue too? Also once you burn your screen, spray it with water and let it soak for 30 seconds then hit it with medium pressure for most stuff. I use a ranar with the same set up as yours almost and qtx I burn fro 4:30 and rinse out with a garden hose with a spray nozzle with no prob, that said my bulbs could be a bit old I guess. It's not that complicated of a thing just play around with it till you get it right, don't stress! Could 45 sec be enough on a fast expose emulsion with your set up, sure, but I bet light is creeping through the positive.

I hope some of this helps.

 

[PositiveDave]

SMT Step Wedge test printed on vellum from laser printer

errr...no
do this:http://www.t-shirtforums.com/t-shirt-articles/t106506.html

 

[Scotten]

I do worry about my vellums. When I worked in a commercial shop years ago it was only film positives or Rubylith. I have a can of some stuff that you spray over your vellum after printing that says it will make it more opaque.

Dave, I will use the test you mentioned.

I am frustrated because even though I haven't been screen printing for over 20 years nothing has really changed in this area. I figured I would do a test or two and get it dialed in.

I'll keep chipping away.

 

[PositiveDave]

step wedges are calibrated, precision tools, you can't produce one from a $200 printer!

 

[Mike Caliper]

Stouffer 21 step sensitivity exposure guides and how to use them CLICK HERE
http://www.t-shirtforums.com/screen-printing/t116999.html
There are several good threads on how to get the proper exposure for your screen frame, your screen mesh, using your emulsion, your coating method, your exposure, etc, using your system and set up at your location. A search of this forum will lead you to that information.

The easy way is the Stouffer exposure guide which can be purchased from Stouffer Graphic Arts Equipment Co., Mishasaka, In, 46544, for less $9.00 Get one and be happy.

 

[Scotten]

Yes, I ordered one, Stouffer strip, today. I still thought with all of the tests I have done I would have come up with at least a time I was happy with. My tests are all over the place. I have years of experience, years ago (25 years ago) and know how to do it. i just can't figure out why I can't get consistent results. I am setting up a shop for my son to print shirts at home.

 

[Mike Caliper]

Strip testing or Stoffer step wedge testing depends on a repeatable emulsion. First be sure the application of the emulsion is consistent in every way, from preparation of the screen (reclaiming washing, retensioning), to even coatings using the same number and method of application, drying, storage, temperature, humidity, etc. The more consistent you can be the better the results will be.

With strip testing, you should have representative text, lines, or halftones to expose on the emulsion, and then apply the stepped exposure times. This should allow you to view the results of exposure on the text or lines and adjust for the best results.

With the Stoffers step wedge you only test the exposure time as it applies to wash out.

Use both methods at the same time to check one method against the other, and arrive at the proper exposure for your equipment and operation.

 

[Scotten]

To say it in a nutshell: POOR POSITIVES. I am using vellum on a laser printer and it just doesn't cut it. Not opaque by any means. I am sure my poor results were due to light burning through the image. If I apply some toner spray it makes it acceptable. I will have to work on that, but, that will have to wait a bit due to $$$. There are plenty of places that will do my output here in LA so I am not too worried.

Thanks again for letting me air this out. I know it has been asked and answered a number of times. I read every one of those posts before I posted my own question.

 

[Mike Caliper]

Try printing the same image on the same piece of vellum a 2nd or even a 3rd time to build up density. If you print the image in reverse, it will be in contact with the emulsion during exposure (not separated by the thickness of the vellum) and also give less undercutting and a sharper image.