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Re: dermel'ing
On Sunday, July 9, 2017 at 11:10:10 PM UTC-4, Steve Wilson wrote:
  
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Fixed by using adjustable feet.  Machine tools do that.

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Cheers,
James Arthur

Re: dermel'ing
snipped-for-privacy@yahoo.com wrote:

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I find adjustable feet don't work. You have to put the machine in exactly  
the same spot every time. If you move it a slight amount, the feet are no  
longer touching and the machine wobbles. If it moves itself due to slew  
rates, you are in trouble.

The alternative is to bolt or clamp the machine to the table. That is a  
possible solution, and I use it with my grinder that vibrates horribly as  
it hits resonance. But it is a bit of a pain when you have limited space  
and need to move machines to and from the work area.

Three point solves the problem, except in the worst case of massive  
resonance. I hope a PCB CNC won't hit that.

Re: dermel'ing
On Sunday, July 9, 2017 at 2:32:08 PM UTC-7, Steve Wilson wrote:

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Easy; bevel or birds-mouth the pipe and weld.
When the weld cools, it's a fixture.

Re: dermel'ing

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Yes, you have to cut the pipe. My idea was to cut one of the legs in half,  
assemble, then weld the pieces back together.

Then I remembered an old fixture I made from 1/2 inch copper pipe, and how  
strong and rigid it was. I looked up the prices, and found a 1 inch copper  
pipe with the needed plumbing fixtures would be economical and probably  
more than strong and rigid enough for the frame.  


Re: dermel'ing
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use a pipe union for the last junction, after which it won't sit well
on a level surface. (wrong question)

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Put elbows on the ends with pipe stubs that go half way, and fit channel
or angle around the stubs and fix with screws.

--  
This email has not been checked by half-arsed antivirus software  

Re: dermel'ing
On Sun, 9 Jul 2017 05:06:05 -0700 (PDT), snipped-for-privacy@yahoo.com
wrote:

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I use regular steel drills to make holes in FR4. Carbide drills are
good if you want 20K holes per drill, and can spin them at 60K RPM in
an air-bearing Excelon drill.  

Actually, if I don't feel like trooping downstairs to the machine
shop, I just punch holes with my usual dental burr in the Dremel. A
little wiggling adjusts the diameter.



--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: dermel'ing
On Sunday, July 9, 2017 at 5:11:55 PM UTC-4, John Larkin wrote:
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60k?  I think PCB houses spin bits a lot faster than 60k these days.  No
need for all that though, a Dremel @ 30k RPM is good enough for a hole
or two in the lab.
  
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The carbide dental burrs look fine, but you won't be able to carve details
as fine as you can with the broken-drill-trick.  Carving with a broken
carbide drill is almost like writing with a pencil.

Cheers,
James Arthur

Re: dermel'ing
On 10/07/17 09:49, snipped-for-privacy@yahoo.com wrote:
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You need to try a modern dental air turbine drill. 500,000+ RPM
makes engraving more like sweeping away talc with a tiny paintbrush.

Re: dermel'ing
On Sun, 9 Jul 2017 16:49:24 -0700 (PDT), snipped-for-privacy@yahoo.com
wrote:

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I guess I could get some smaller cutters, but I can do 0603s and
SOT23s now. And I'll never be able to do MSOP10 or US8 type
packages... I use adapters for those.

https://www.dropbox.com/s/yd19osiwz1z74s4/HV_Proto_2.JPG?raw=1

https://www.dropbox.com/s/48c8qh80yhbehj6/Z356_Top.JPG?raw=1



--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: dermel'ing
snipped-for-privacy@yahoo.com wrote:
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   Like i said,use broken sewing machine needles.


Re: dermel'ing
On Saturday, July 8, 2017 at 3:24:01 AM UTC-4, Robert Baer wrote:
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Too soft.  Glass-epoxy chews them up instantly.

Cheers,
James Arthur

Re: dermel'ing
On Fri, 07 Jul 2017 19:08:03 -0700, John Larkin

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Here's how I used to do it in the stone age, before I could get
reasonably priced 2-5 day PCB deliveries or was spoiled by an in-house
PCB shop.

I just hacked this out:
<
http://802.11junk.com/jeffl/crud/PCB-cut.jpg

The "cut" is about 0.010" wide.  The way I made it was to put TWO
blades in a Stanley utility knife like these:
http://www.stanleytools.com/en-us/products/hand-tools/knives-blades/multi-tool/538-in-classic-199-fixed-blade-utility-knife/10-209
<http://www.stanleytools.com/en-us/products/hand-tools/knives-blades/multi-tool/512-in-299-fixed-blade-interlock-utility-knife/10-299
It has to be a non-retractable clam shell type because I'm counting on
pressure from the single screw holding it all together to keep the
blades rigid and aligned.

Insert TWO blades into the knife, with a piece of paper or tape
between them as a spacing adjustment.  Adjust the blade spacing for
the desired span.  The paper or tape works fine for 0.020" spacing but
no more because support by the aluminum handles is lost.  I milled my
own handpiece for wider spacing.

The way it's used it to scribe the copper that I want to remove using
the dual blade knife, preferably in one pass.  I could go over the cut
grooves more than once, but then I risk going astray, as I did trying
to make something worthy of a photograph.  Don't do that and try it my
way first.  The initial dual blade cut is only a cutting guide.  Also,
I usually use a steel rule to keep the knife going in a stright line.
Curves are more difficult.

Ideally, I would cut all the way through the copper and into the
fiberglass.  That's not necessary.  Instead, grab a second Stanley
utility knife, of any type, which has only a single blade.  I use it
to follow the grooves cut in the first pass with the dual blade, to
deepen both knife gooves until it looks like I'm through the copper.

Next, find a #1 slotted jewelers screwdriver or sharp pointed knife
and pry the copper off the PCB starting at one end of the cut.  This
takes practice and a sharp screwdriver, but can be done.  Don't use an
Xacto blade because they're rather weak and don't like being used as a
pry bar.  

Once I have a small amount of copper peeled upwards, I grab it with a
pair of pliers and SLOWLY pull the copper away from the PCB.  If I've
cut all the way through the copper, it will peel away smoothly.  If I
missed, it will tear and I get to start prying again.

At one time, I had a 2 blade contraption made specifically to lay
0.100" wide traces for 50 ohm lines.  I would scribe the 50 ohm trace
first, and then go over it with another 2 blade utility knife to
provide the necessary spacing to the ground plane.

Good luck, be careful, and don't cut yourself.

--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: dermel'ing

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Way too complicated. Get an X-Acto or Ace hobby blade:

http://www.acehardware.com/product/index.jsp?productId52%841656

Grind the cutting edge flat so you don't cut yourself later, and grind  
the end to a 120 degree angle. Grind the straight edge to a bevel so you  
can set the knife to the proper angle to cut the copper.

Use the blade upside down to cut a thin slot in the copper. Sharpen as  
needed.

I don't think you are going to have much luck cutting 50 ohm traces on 30  
or 60 mil copperclad. You need much thinner material and a different  
approach.

Now we need a cheap CNC router with 0.1 mil repeatability. The cheap  
Chinese units won't do the job. The best they can do is around 1.98 mil.  
Commercial US units are way too expensive. A DIY using copper plumbing  
frame might do the job.

The next problem is FR4 is going to be too lossy at microwave  
frequencies. Rogers is extremely expensive. We need to find a thin  
double-sided copperclad material that works into the tens or hundreds of  
GHz. Ceramic is interesting but might be difficult to use.

Any ideas?


Re: dermel'ing

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Neither is hard freehand with a Dremel. Draw lines with a fine-point
Sharpie first.

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An inch or two of FR4 is OK at 10 or 20 GHz.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: dermel'ing

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I was talking about the pcb thickness.  

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I need to go much higher.  
  


Re: dermel'ing
On Mon, 10 Jul 2017 07:27:22 -0700, John Larkin

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I've used FR-4 at 1.9GHz and somewhat regretted it.  The problem is
the dielectric constant Er which varies from 4.3 to 4.8.   There are
also variation is material and plating thickness.  Er and coef of
thermal expansion are also sensitive to the direction of the
fiberglass weave (anisotropic) in all 3 dimensions.

Eventually, I got things to work, but ended up with only one PCB
vendor willing to make them to the tighter Er tolerances required, for
an outrageous price, of course.  If it's only one short run, I suggest
you consider using semi-rigid coax and connectors instead running RF
traces on or inside FR-4.

--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
We've slightly trimmed the long signature. Click to see the full one.
Re: dermel'ing
wrote:

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This board makes clean 100 ps or so pulses with 45 ps rise/fall times.
That's roughly a 7 GHz bandwidth.

https://www.dropbox.com/s/qqwe00qt1lx6630/T240_First_Board.JPG?raw=1

It's a conventional FR4 board. The tricky part was fanning out to the
SMA connectors from the tiny pads on the chip-scale output driver.

We did a bunch of ATLC simulations to get the edge-launch SMA
footprint and stackup right.

https://www.dropbox.com/s/1zb71vy9g576c6y/E-field.jpg?raw=1

https://www.dropbox.com/s/3r297w59kp5wrek/Rob_51_ohms.jpg?raw=1



--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: dermel'ing
On Mon, 10 Jul 2017 20:47:21 -0700, John Larkin

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Very nice looking PCB, but you don't have any one or two inch RF
traces between the drive and the connector.  More like 1/8" trace.  If
you look at 12GHz satellite TV front ends, most use some kind of PTFE
laminated PCB.  I don't know what to suggest for a better PCB as I'm
not up to date on the available technology.  Here's an article by
Rogers that explains some of the problems:
<https://www.rogerscorp.com/documents/2244/acm/articles/Circuit-Materials-and-High-Frequency-Losses-of-PCBs.pdf
See Fig 4 for a loss vs freq graph for various PCB materials.

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Looks like ATLC2
<http://www.hdtvprimer.com/KQ6QV/atlc2.html
<http://www.hdtvprimer.com/KQ6QV/HomePage.html
not the original ATLC
<https://sourceforge.net/projects/atlc/>
I didn't know it had been ported.  I'll probably ruin my evening
playing with it.  Thanks.


--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
We've slightly trimmed the long signature. Click to see the full one.
Re: dermel'ing
wrote:

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Well, maybe a half inch. Conventional FR4 boards get ugly with long
traces; like the doctor said, don't do that.

Part of the problem is dielectric loss, but the bigger problem is
usually the skin loss in the copper. Standard boards have a black
oxide treatment on the copper, to make it stick to the epoxy better,
and that's horrible lossy crud. Just peel up a trace and see.

Shiny-bottom copper over teflon laminate is great for high
frequencies, but adhesion is terrible. You can cut fancy patterns
easily with an x-acto and then peel the copper off easily.

We recently did a tester board that wound up having about a foot of
trace end-to-end, with four switching relays in the path. The relays
are fine, but trace loss is pretty bad. A fast step comes out as a
70%-high fast step, and the rest is a slow drool. We'll be doing
risetime measurements, so that's bad. We should have done a thicker
board, so the layer1 to ground dielectric could be thicker and the
topside microstrip traces wider, which would have helped. We teepied
an inductor in series with the end terminator, which peaked things up
and made the step response better.




  If
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I used ATLC and Rob used ATLC2, and they agreed pretty well.  

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ATLC2 is even more fun than ATLC.

We have Sonnet Lite too... one of my kids learned how to drive it, and
it's occasionally useful.



--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: dermel'ing

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The Si-List has long discussions on the problems of FR4 at microwave  
frequencies, including most of the things you mentioned:

http://www.freelists.org/archives/si-list/

On the other extreme, the TI AWR1243 76- to 81-GHz FMCW Transceiver is  
meant for inexpensive automotive applications such as emergency braking  
and highway driving. The pcb stackup shown on page 39 uses Rogers 4835 on  
the top signal layer, and FR4 for the rest.  

http://www.ti.com/lit/ds/swrs188/swrs188.pdf

I suppose if you are going to make tens of millions, you might be able to  
get a reasonable price for the pcb. But if you only need 10, forget it!  

So I need to find a different way to make microwave pcbs for development  
work. I'm thinking of copperclad polyimide glued to a plain FR4  
substrate. Then I need to make the traces on the top layer, and connect  
to the ground plane on the top layer of the FR4. Making the traces and  
drilling the holes is not so bad, but electroless copper plating is a  
real bear.

I keep looking...

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