View Full Version : lens mounting question

Don Corbeil
04-05-2015, 6:09 PM
I recently picked up a 76.2 mm (3") fl lens from a third party source. Thought I'd give it a try.
Question: What type of glue do you use to mount the new lens into the holder? (Trotec mount)
For a reference I looked at the 2" trotec supplied lens, and it looks like they just applied a small drop at each of the three slots that surround the lens. Am I correct in that? I know that the convex side is up for the mount, but am not sure what other procedures to follow to do this correctly.
Also, for future reference, how do you go about removing the lens at the end of it's life? I read in another post something about soaking the lens & mount in acetone?

Thanks for any help

Scott Shepherd
04-05-2015, 7:34 PM
That's right Don, gel super glue holds it in, Acetone takes it out.

3" lens? Never seen one of those before. What are you going to use for a focus tool?

Don Corbeil
04-05-2015, 7:53 PM
Thanks Steve.
Yes, it' an odd size. I wanted to get something that was between the typical 2" and a 4" cutting lens.
I'm going to have to fashion a focus tool that is the correct distance. Interestingly, in the trotec job control they offer several 'odd' lens choices including a 3.2", so I'm not sure how that's going to work with the 3".


Scott Shepherd
04-05-2015, 8:41 PM
That function only matters when you're using the programmable autofocus. If you're not using that (by entering the material thicknesses in the material database), then that setting doesn't mean anything. There used to be a file on the discs that was the focus tool that you could cut out on your laser. I know Mike Null has mentioned it a number of times. You might try and track that file down and just modify the length and cut your own tool out of acrylic. Should be pretty simple.

I think Mike said that's what he uses or used for a long time, but I could be mistaken, it's been a couple of years since it was brought up. If he has the file, I'm sure he'll post it if you ask him.

Don Corbeil
04-05-2015, 8:52 PM
Oh I see, only for auto focus... OK - I only use manual, so no problem there.
I've got the SMC discs, so I'll search for that file. I also thought I saw a corel file somewhere in this forum with various focus tools already laid out.

Mike Null
04-06-2015, 8:49 AM
Here's the file in version 11.

I found the two inch to be almost a mm short.


Don Corbeil
04-06-2015, 11:24 AM
Thanks Mike, that's the exact file I saw awhile ago and could not locate again!
I'll use an inclined piece of wood/aluminum to get the right fl for the 3".

Here's the file in version 11.

I found the two inch to be almost a mm short.


Mike Null
04-06-2015, 11:45 AM

The 1 mm difference was between the aluminum piece that came with the machine and the cut acrylic piece from the file.

Don Corbeil
04-06-2015, 12:04 PM
OK, thanks Mike.

Kev Williams
04-06-2015, 6:47 PM
I quit using auto focus about 3 years ago- not because it doesn't work right, but because there's always something in the machine that the plunger runs into...

I cut 1/4" thick strips of Cintra to about 3/8" and cut them to length and uses as my focusers.

As for 3" lenses, I got one about 3 months ago, I use it in my Triumph probably more than the 2". Works great for doing big graphics on leather and wood, I can get away with dropping the resolution quite a bit and still get great results (in less time)

Scott Shepherd
04-06-2015, 7:03 PM
Kev, there's no plunger on the Trotec. It knows where the table is and it moves accordingly. There's nothing for it to hit. You just setup your materials to the right thickness, and it knows where the table is, so it'll just move to the right place. Or, if you don't want to go that route, it's shooting a beam across the bed and it'll stop when it detects the top of the surface. That's doing it the "semi-automatic" way. The automatic way just knows where the table is and how thick the work is and goes from there.

Don Corbeil
04-06-2015, 8:01 PM
I have to say I've never used the auto focus up to this point. I just got into the habit of using the manual tool, and haven't tried the AF yet.

The only time I got into trouble with manual focus was when I was using the rotary with the 2" lens & cone, and didn't check the nose cone clearance with the highest spot on the rotary. During the first pass the nose cone slammed into the end of the plastic rotary mount, enough to gouge it. Scared the heck out of me. I thought I might have done something to the drive mechanism, but it seemed OK. From then on I use the shorter cone or none at all on the rotary.

Don Corbeil
04-07-2015, 12:48 PM
Picked up some loctite gel superglue and glued the lens into place this morning (convex up!).
The glue ran a little into the lens area, but not by much. Hopefully this won't create a problem when in use. Does this look OK?


One thing I notice with the new 3" chinese lens is the clarity of this lens is nowhere near as clear as the trotec supplied lens. Perhaps this is in part due to the difference in focal length, but it just looks a bit more hazy.