Engraving metal

[ffaelan]

SO here is my problem in a nutshell. I resurfaced my table this morning as we are starting an engraving project and needed super flat surface. testing engraving using scrap Chemetal that we will be using and a test image. the problem is that we seem to still uneven on the table. I'm uploading four images that show the issue. sorry for the poor quality, the surface is mirrored and really doesn't like to be photographed. As you can see it digs to the proper depth in the lower left which is the zero corner on this table but starts to lose depth as we move diagonally. any ideas.
4907
4908
4909
4910

[tparr]

How are you holding this material? Did you dial in the spindle before you surfaced the table? or inbetween surfacings? This type of thin material needs perfect support everywhere.

[Gary Campbell]

Ffaelan...
When surfaced, a spoilboard that is not completely adhered down can lift a few thousandths. Whan the part is placed on the spoilboard and masked, the additional vacuum sucks the spoilboard, and the part, down tight. Thats my guess. The pictures showing good depth at the corner and what appears to be lower away from the corner, bears this out.
Gary

[ffaelan]

For this test piece, it's a hunk of 3/4" MDF screwed to the spoil board in two corners and the Chemetal is adhered using a contact glue. I pulled the protective plastic and shot this new image. There was not a screw in the corner that the drifting seems to have happened. But would not the material lift into the cutter and make a deeper cut rather than shallow.


4911

The Zooms also show the drift. it is a gradual drift though, the picture is misleading in that, but you can feel it.

I'm not sure about dialing in my spindle. I'm new to the machine and just surface according to the book. I did zero the X,Y,& Z axis' before though.

[terryd]

Unless you surfaced the MDF don't ever consider it to be uniform in thickness. Might want to make that the first check.

[khaos]

Surface the MDF of the table. AND if you are using a second piece of MDF as a work area as it seems be sure to surface that as well. I have had a similar issue with plexi because my second waste board was not uniform.
Just my 2¢

[loriny]

I got better results when I inserted small pieces of gasketting onder my spoilboard (1-2"long) to support the spoil board. Lots should be good as the vacuum can go around the square if just blocking one line

[ffaelan]

I surfaced the table and my mounting surface. Still no good. I am only trying to engrave .002". Losing surface contact two inches from start. I also used spray 77 adhesive to adhear to my mounting surface so it's a clean contact.

[Brady Watson]

Try going deeper. You may have enough backlash in your Z axis to not be able to resolve a distance that small. Also, be sure that the thickess value for your Zzero plate is correct. Compare actual thickenss with digital calipers to the value for the plate thickness in C:/SBParts/Custom/my_variables.sbc

-B

[ffaelan]

Brady
This file indicates 0.121
the calipers 0.1215
that seems fine right?
I tried going deeper started at .006 and by the time it was 19" diagonally away from the start point it was floating above the work and not doing anything.


4912

[Brady Watson]

If this is the case, then your machining surface is STILL not flat. Keep in mind that temperature & humidity changes will move that MDF all over the place. Surface the 'accessory table' you have there, clean it, and immediately start egraving. See how that works.

-B

[rb99]

Could it be the old Z problems again?
Some sort of a glitch in the software or the actual steppers that causes the Z to screw up randomly?

RB

[Brady Watson]

The only time I've had the Z 'screw up randomly' is after executing a spacebar or 'S' stop, and it returned to a lower Z value than it should have. This was in older versions of the software. Aside from this, the only variations in Z came from worn out pinion on the Z or pinion to rack clearance was too high - or variations in the table surface (most prevalent). If you use screws to hold down either the spoilboard or jigs (unless they are pre-drilled and deburred) you're going to have variations in the Z. Drywall screws are a no-no when you need things ultra flat.

-B

[ffaelan]

So I used carpet tape to adhere my work surface to the table. then surfaced it taking off almost 1/8".
used spray adhesive to mount the Chemetal to the work surface. It all should now be flat to the world right.
I checked the thickness of the Chematal and got a consistent .026. I ran the engraver at a depth of .01 this time and still floated. Am I missing something. is the carpet tape causing variations? It seems to me that even if it does, they should be wiped off in the surfacing of the work surface over the already surfaced table. any idea? I'm stumped. thankfully the date on the project has been push two weeks, it was due today.

here is the latest batch



4913

[Brady Watson]

Try machining at mid-X (say 48" on a 96" tool) on the table instead of all the way on the left corner, which is cantilevered off of the table. See if this helps.

-B

[oddcoach]

I tried doing what you are trying several years
ago. It might seem strange but I got good results by putting a thin sheet of foam under the aluminum. It allowed the sheet to float. set the depth lower than the surface. It kind of works like the drag knife for vinyl in reverse. Home Despot sells rolls of the stuff for underlayment for laminate flooring. Just my 2 cents

[rb99]

When in the center, make the majority of the work direction in the Y axis.

RB

[ffaelan]

Richard
Are you saying to turn the toolpaths 90 degrees form what they presently are. if so, what would this accomplish? I ask as I was about to start the run in the center but running the same way it has been.

[rb99]

Khalid Khattak had a post on the efficiencies of making the Y axis do more work than the X.

I thought this might help sort out the problem.

(I personally think it is the Z screwing up. This is from my experiences years ago with the same problems.) I had many Z related problems years ago and if you read the forums there are still many problems like this. I lost a giant contract over SB related issues. These same issues seem to still be prevalent- and the reason I have not invested in the newer controls and Z's. I paid a ton of money and now I am supposed to smile and pay more! Once bitten twice shy.

RB

[Brady Watson]

Richard,
A Standard PRT (back in the day) was only good for .005 - .015" accuracy. ShopBot advertised accuracy at .015". So, I can clearly see why you would have problems resolving small moves in the Z. I had similar issues, and it wasn't until I learned how to adjust my Z axis backlash correctly, that I was able to get things dialed in for delicate work. The PRS Alpha is night and day to the PRT 3G that I ran previously.

Let's keep in mind that certain provisions need to be made - like adjusting backlash, keeping the tool clean & lubricated, and replacing pinions when it is time - whenever you do work outside of what the tool was primarily designed for. The ShopBot is not a metal engraver. It's primary use is for machining wood. A metal engraver is much more precise, has a much smaller working envelope and is setup for doing exactly one task - engraving metal. Can you engrave on a ShopBot? - Absolutely - but you need to prepare the machine for the demands of engraving.

What Kahid mentioned was geared towards 3D raster cutting, which is not applicable to Ffaelan's problem. 'Lop-sided' ramping is not recomended for the SB3 controller, which handles ramping differently than Mach2/3, which is what he was referring to.

If this is a newer tool, then there are only 2 things that could possibly be preventing good resolution in the Z - 1) Poor pinion to rack adjustment (backlash) or a worn out pinion, or 2) untrue spoilboard. Let's assume the spoilboard is good & flat. One thing I've learned in my travels to SB shops is that not everyone has the same mechnical ability - and in turn the finesse or knowhow to properly adjust a machine. The machine is only as good as the abilites of the person maintaining - and there is only so much one can offer over the internet. It's not the same as actually seeing the tool in person.

Ffaelan,
If you grab the body of the router/spindle and shake it up & down in the Z direction, can you hear any 'ticking' or feel any slop? Have you tried using a dial indicator on the Z and testing repeatability?


-B

[rb99]

I wish back then they would have told me the truth about the machine.

Instead they kept telling me to try this and that. I even changed the rails and they came into my shop and changed them back. A few years later they sold all the machines with rails they rejected on my machine.

I lost a very large contract and it contributed to the closing of my business.

Thanks again.

[ljdm]

Richard - venting your bitterness about your experience won't help solve the problem this post is about, and won't change the problems you had in the past. If you are that unhappy with Shopbot, buy a different machine, and post on their forum. Ooop... that's right, they probably don't have a forum where people can help each other, like this one, huh?

[rb99]

We all now know the American way...

[ljdm]

Hopefully the last post on the subject - I would never deny the freedom of speech, just this particular topic on the forum isn't the place for your gripe, since it serves no purpose in solving his problem. If you feel the need to bash SB, it is your right as an American, or non-American, no doubt.

"We all now know the American way..."

Would you like to elaborate on this? In the proper section of the forum, of course.

[ffaelan]

Brady
Well I moved to the center of a larger piece of material and it fail in a similar fashion. I tried jiggling the spindle, no clicking only slight play. I think it might be my adhesion. yesterday I got a full run complete but one corner had come up from the substrate and cut to deep. going to try a smaller piece again but with a better adhesive.

Anyone heard of Westech Aerosol, their rep came by my shop yesterday with a great newish product. Its a propane-like tank setup, but with no propellant in the tank. You supply the air pressure from a compressor and off you go. nice clean spray and a five our working time, but once you connect the two surfaces you can start working them. we sampled in on two surfaces and left them overnight.
pretty strong bond and I like that its a green product.
Has anyone heard anything bad about their stuff, I'd like to know before I plunk down the coin for a tank of it.

Will be making another run this afternoon.
will post the results later or tomorrow.
thanks everyone

[Brady Watson]

Ffaelan,
Thanks for the update. Yanno...a shopvac and a BradyVac II (http://www.shopbottools.com/BradysTricks.htm) would be ideal for engraving. No need for adhesive, no cleanup & quick swap-out of parts. You can machine a grid into ANY material and then puncure through the front side to allow vacuum to get under the part. Something to consider.

-B

[ffaelan]

Brady
I have actually be considering that option. If this becomes more common place for us I will probably go that direction. This company has had this shopbot since june 08 and I, being the new guy, just hooked up a dust collection system for it Monday.

[Brady Watson]

That's not usually an easy spot to be in...Kudos for your efforts (since your employer probably has no idea how hard you've been working)

-B

[majohnson]

You might look into the spring loaded engravers that Steve Knight uses or sells. What are using as a spindle? While I'm not engraving metal. I can run a engraving bit at .002 doing letter out lining and it's even all the way through the lettering.

[ffaelan]

Hey Everyone
Thanks for all the advice and suggestions over the course of this project. In the end we ditched the engraving and the Chemetal and went with 3/4" black acrylic. which turned out nice. Funny thing in the end as I made what I thought was the final piece, my boss/designer, came to me and said that the drawings he had given me from the beginning were wrong.
So he forwarded me the final version today and I spun it and polished it up for delivery. Just the nature of this biz I guess.

We want to look more into engraving though and will probably invest in the floating engraving drag knife since it seems to be a good solution to what we were trying to achieve.

Thanks Again.
ff

[curtiss]

Any special information to measuring backlash
expecially in the z axis?

thanx