Focus Distance

[Mike Klafehn]

I have an Epilog Helix (about 2 weeks) and would like to know how to determine the distance the Z table travels with each press of the FOCUS button.

A tip for engraving acrylics says to lower the Z by .020" to achieve a better engraved image. It would be nice to accurately know the travel distance on the Z for this and other purposes.

Interestingly, Epilog tech support did not know the answer.

Thanks

[Rodne Gold]

I would try slip a shim or something under the focus gauge after you pressed and measure it.
If they use a stepper motor and a lead screw , they can easily work out the distance based on the amount of steps a press makes the motor turn.

[Tom Majewski]

I use a digital caliper mounted to a magnet. Extend it about an inch or so, then zero the gauge, then jog the z button.

I don't know about your laser, but the geomety of the Mercury makes it an easy mount.

[Rodne Gold]

The mercury should show the table distance above or below the AF point on the display , you can see exactly how far up or down you are (or maybe its only on the explorers and spirits?)

[Mike Klafehn]

Did some measurements using my digital dial indicator and here are some interesting results:

One press of the UP focus button moves the bed .020"
One press of the DOWN focus button moves it .015"

Don't know why the bed moves further when going up, but I took 15-20 measurments and that is how it read.

Also, when switching between the up and down buttons you have to press a button twice before the bed will move. So, lets say you are moving the bed down 2 button presses. When you switch to the up button, you must press it twice to get the first bed movement, then each press will continue to move the bed.

How accurate are these measurement? Well, since I don't have access to the actual servo or stepper motor specs, and I am only using an external measuring device which can induce some error, especially deflection error, I would estimate that the readings could be off by + or - .002.

Still its a fairly good measurment if you are looking for a slight out of focus beam. I am fairly certain, that even with the auto focus mechanism there is some deflection due to the substrate moving, the bed flexing, etc. that would as least produce an error of .002 in each direction.

Any other comments on this would be greatly appreciated.

[Abdul Baseer Hai]

Or else buy a GCC Explorer. It displays the Z axis movement on the control panel in .005 inch increments.

abdul

[Bruce Boone]

That is interesting to have different measurements for the different directions. I would expect numbers like those for the first press of the button due to backlash in the system and all the play forcing the table downward, but that should even back out after the first of the down pulses, and the rest should be the same .020".

For focus, what I did is made a series of very weak powered cuts into a fine grained wood and changed table height between them. I measured the distance from the bottom of the lens assembly to the top of the wood and wrote the measurement next to each test cut. I found the circle with the best focus and cut a popsicle stick of exactly that length with the laser. I included engraving of the focal length of the lens on the stick and a hole for mounting on a hook. The focus finder is pretty handy and works great. I switch back and forth between rotary and XY, so it saves time because autofocus needs to be turned off for rotary.

[Mike Hood]

On GCC Machines (I have an Explorer II), there is a function called "down table". Just set the distance down you want, and then select down table. It'll move to +/- distance you have set.

You can also adjust Z up or down and just watch the readout (+/- from zero)

Quite easy on our models.

[Mike Klafehn]

Selectable Z adjustment. Very nice feature to have. I have a similar arrangement on my CNC. It's too bad Epilog didn't engineer this into their models.

For now I will have to live with the up/down focus buttons and their strange function. I have mentioned to Epilog that it would be nice to have total control over the distance adjustment. They didn't see this as something they would do anytime soon. I guess alot of customers don't really care about this feature.

But then again, if GCC has it, there must have been at least a moderate number of requests for it.

[Mike Hood]

There are many things that would be nice features if they'd listen. There is a long lead on changes like this, but sure makes the difference between models.

I've built and installed a 2Ghz PC into my machine, as well as mounting a 17" LCD on a pivot mount to the back of the machine. With a cordless keyboard & mouse, the laser is totally self-sufficient and is a turn-key laser graphics station. All of my clipart, programs and job data are stored on the machine now in a 500GB hard drive, and the machine is wireless networked as well so I can manipulate jobs right here from the couch. :)

Next modification for mine will be a "Emergency" Stop button and a couple of keyed interlock overides for the front and rear doors. (I'm currently using magnets for pass-through work).

[Rodne Gold]

Mike , they do sort of listen , speak to Jason stone at GCC with wishlists.
I recon the best feature of the GCC machines is the ability to move the head freely and engraving from the centre of an object , finding centres is REAL easy.
There was some talk of an improved rotary and some talk of an add on optical registration mark reader (I would LOVE that) or processing labels and the like.
I dunno about the add on puter tho , vapours and smoke and fumes might be an issue , however you can buy non volatile ram for the machine and load the files onto that RAM and have a stand alone engraver without being connected to a puter - we have never considered it , but if i were doing the same few things again and again , would get it if i had multiple machinies doing the same jobs - we have multiple machines and run 6 lasers off 2 puters but most jobs are different.
Another thing you could consider is making your table a vaccum table , all it requires is removal and drilling of the top sheet and making a port to connect vaccum to and using some silicon to "seal" the tables edges. In fact you can take a feed off your blower or make a venturi tube for the vacuum. We use sheets of newsroll type paper on the vacuum tables as its porous and saves the table itself from laser damage when cutting.

[Mike Hood]

Interesting you mention the vacuum table. I was thinking of doing that with my vector table (pin type). By drilling the holes, and then setting the table on a 2x2 frame, I'd be able to pull a vaccum using my exhuast fan. I cut a lot of balsa and depron foam so sheets floating around the table is an issue. I also thought of building a new table using 1/4 tubing instead of pins. Then, the pins themselves would hold down the lighter foams.

I should probably clarify my statement though. I wasn't trying to imply they don't listen, but I know there a LOT of things I like about the GCC units over the competitors (front / rear doors, standard autofocus, standard air assist, larger bed size, free movement head, centering, table down settings, etc). Any manufacturer (not just lasers) should work hard to monitor and listen to groups such as this.

Also... the PC on mine is mounted in the "clean" section with the tube & power supplies. Staying cleaner there than in my shop :)