Fine Milling with an old T-Tech 7000S Mill

[G0HZU]

On this thread here:
https://www.eevblog.com/forum/eda/isn't-it-strange-that-you-can-make-better-pcbs-at-home-than-factories-make/175/

Several paranoid experts and non believers said that milling fine traces isn't possible on a PCB mill.

I don't mill PCBs for digital stuff very often but here's part of a board I've just milled.  The gaps between the IC pads should be approx 10mil. OK, I haven't milled 8 mil traces as such but you can see that this would be possible. The specs for my machine say it can be used for 4mil traces although this is going to be the limit I think.

Sadly, I don't have a very good camera here. This image was taken with an old Panasonic camcorder but it is good enough to see that the milling can be done this fine. Under a microscope it looks a lot nicer than this and the trace edges are good. But this is straight off the machine after a quick wipe. I'm going to tin and build this PCB shortly.

Note also that I've used old tools here from work that have reached the end of their life according to the software used on the LPKF machine at work. This board was not milled with new tools! So this shows that you can still get decent results with fairly worn tools.

See the original artwork and the milled PCB below. Note also that my T-Tech 7000S milling machine is well over 20 years old and is running the original motor and bearings, everything is original in the milling machine. So the machine has 20 years' of wear and tear on it. However, I have looked after it and serviced it regularly.

[G0HZU]

The results using exotic laminates from Rogers Corporation look much nicer than this. FR4 material is fibrous and it can look a bit rough under closeup inspection. The Rogers material looks smoother when milled.

The next time I mill some fine traces on an RF PCB using Rogers 4003C or 4350 I'll post up the results here. Maybe with a better camera and with new tools. Under a microscope it can look really good with very clean edge definition.

[awallin]

looks nice! much better than with a 0.2mm V-cutter on 1990s LPKF protomat that I've been using 
What tools/diameters did you use for the board in the picture?

[G0HZU]

I used an old 8mil V cutter (with a very pointy tip) and a 16mil end mill. I think both tools are LPKF but I'm not sure. I collect up the old tools at work once they get past their milling limit and they are usually a collection of routers, end mills and V cutters but they aren't labelled in any way.

I had a quick go at milling an 8mil trace using the 8 mil cutter and I also did an 8 mil trace with a 15mil end mill and I also had a go at a 4 mil trace. All came out very well although I don't have a decent camera that can capture the trace edges. But they look great under a microscope. However, 4 mil is going to be the limit and I usually stick to a >=10mil trace width on this old T-Tech machine.

[G0HZU]

See below for an image of the 4 mil test cut.

The 8mil trace made with the V cutter looks slightly thinner because the V cutter cuts at an angle and it's hard to get an accurate cutting width down at this trace width. Also, there will be tolerance issues at play here. But if this old T-Tech machine can cut this fine then so should the newer machines that have better foot technology, better mechanicals and they haven't got 20 years' wear and tear.

The picture below doesn't really do it justice. There's small hair over the 4 mil trace which spoils the image but I wish I could show the microscope image. It looks very good. I'll see if I can take an image of the 4 mil trace at work using some modern tools. It might not be for several days though.

[DerekG]

How much would is likely cost for a currently available milling machine to be able to mill tracks/pads down to 6 mil do you think?

Any ideas on a specific model?

[james_s]

That does look like good output, although the layout itself could use some refinement. Try to avoid sharp 90 degree bends, and traces at angles other than 0, 45 and 90 degrees.

I considered getting a PCB mill at one point but I can consistently do 10 mil traces with laser printer toner transfer and these days it's so cheap to send out for professionally made boards that I only etch my own for one-off's when I'm in a hurry.

[G0HZU]

The layout looks a bit sloppy but it's just a small lashup test jig for an 8 channel ADC driven by a fairly slow AVR chip on another PCB. So it all runs in the kHz region.

The tool used to draw the PCB artwork was Eagleware Genesys and it can be used as a freehand layout tool with no schematic (let alone a schematic capture) and no design rules for angles. So it's a bit like drawing a PCB with Paint or Visio but with a library of component types like 0805 or various IC chips. It works for me because it is a fast way to produce a small and simple PCB like this. Just draw it with draggy shapes and then mill it

Not sure if this makes things look better or worse, but see below for the XRAY view of the top metal in Genesys. This shows how the PCB was done using draggy shapes and a few library cells for the components. Quick and dirty because there is no schematic and it is all freehand but it is very efficient

[G0HZU]

How much would is likely cost for a currently available milling machine to be able to mill tracks/pads down to 6 mil do you think?

Any ideas on a specific model?

6mil is very fine. Despite what you see from my old T-Tech machine I think 8 or 10mil is a realistic trace width if you want to mill fairly large boards. For simple and small boards it is possible to go below 8mil with some operator skill and sympathy for the amount of care required to set this stuff up.

I don't know how much they cost nowadays. This one was over £10k when new in the 1990s but I bought it used for about £800 back around 2001/2. Unless you are doing lots of RF stuff on exotic laminates (like I usually do) then these things probably aren't the best solution for you.

I would not recommend one of these if you want to produce lots of complex digital boards because the machine will be very slow to mill stuff like this. It could take several hours to mill a complex digital board. It's at its best when milling small and simple RF boards for rapid dev work.

You also have to be prepared to service it regularly and get used to its various niggles. T-Tech and LPKF seem to be the main manufacturers of these things. You won't hear a lot of good things about LPKF here on Eevblog because most people seem to have had bad luck with them. But our LPKF machine at work is an old C30S model I think and it is much easier to use than my machine and it always seems to produce decent boards even though it has seen an awful lot of use over the years. It must have milled thousands of PCBs and panels and laminated tools etc and it is still going strong after about 14 years. However, it has needed a few repairs along the way.

[123jerryboat]

I know this is an older thread but I was wondering, what you are using for a desktop to control the 7000s? I recently dug one out of the storage room, complete with original documents and purchase costs ($13k new). It is old but hasn't been used much. I was told the PC that used to run it may be around somewhere but have not been able to find it.

I am considering buying a modern open source controller, something like the TinyG, so that I can get this thing running again. I have done a fair bit of CNC work but am new to PCB milling.

[G0HZU]

I'm using an old Dell Inspiron P3700 laptop. It's a P3, probably about 450MHz and it runs Windows 98SE.

I use a 16 year old version of the Isopro 2 software to control the mill. However, I had to hack the Isopro software about a bit to make it compatible with my older 7000S model as it didn't support my (fixed speed) spindle motor controller. The original software that came with it was called Isolator and it was a horrible DOS program. Isopro is much nicer to use and you don't need the dongle to control the mill with Isopro. The dongle is needed for isolation and rubout generation. If your machine supports variable spindle speed then the old Isopro SW can control it directly.

You will also need to find the 'home' XY calibration data for your machine. You might be able to get this from T-Tech if you give them your model S/N. Otherwise, try and find this info on the old PC or it may be written somewhere in the documentation. The alternative is to try and reverse engineer this data yourself. This data sets the home position correctly for both sides of the PCB material meaning it can align double sided boards correctly.

[G0HZU]

A few tips...

Be careful with this machine in terms of personal safety. It has a panic STOP button on the controller box but I'm not sure this button is fast or reliable. If you get your fingers or your hair or your clothes caught in this machine it will keep moving and chew through them. My advice would be to have a reliable mains AC cutout button right within easy reach at all times. Also, it needs regular maintenance to keep things moving freely. You are realistically going to have to clean the old dry grease off the lead screws and oil the linear ways before using it.

But when you add fresh grease to the lead screws you can expect the machine to gum up and freeze if it generates a hydraulic lock due to too much grease in the twirly parts. Most of the reasons these things stop working is because the mechanicals are gummed up or because the electrical screw terminals have worked loose over time.

Keep the PC keyboard up and away from the general busy area. I keep my laptop on a shelf. If you drop or nudge something onto the keyboard and hit the wrong key you could start the machine running by accident. Not a good idea if you are changing a tool in the chuck at the same time...

Don't do service work on it when it has power. Always unplug properly from the mains AC.

Also, don't use it for real with new/expensive tools until you have practised a few dummy runs with no tools  in the chuck (or you can practise with old and worn tools). Part of the learning curve with this thing is breaking lots of tools and saying d'oh! lots of times.

[Shiv]

G0HZU do you know a way to get the software of this milling machine?

I get a QC 7000 last week, with lost software, only the control unit and the milling table.

I will try to make it work if it´s possible.

Thank you in advice