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A few years ago, when I had a bit more space, I had a Haas VF2 which produced excellent results, the first CNC we had was a Bridgeport Interact 2, which we retrofitted with a more modern control, that worked "OK", and after that a pair of Beaver NC35 mills, which produced very clean cuts ... they were just a bit big to have lying around. They had absolutely HUGE DC spindles and incredible torque at low RPM, well worth keeping an eye out for one if you see one and have space, right up there with Deckel/Maho in terms of rigidity in my opinion. An old Interact 2 with Linux EMC as the controller would be a great option too.
These days, I just have a CNC router, Linux EMC for control with a 9hp/24,000 rpm spindle on ISO toolholders, it is certainly not a milling machine, but it can do a passable imitation under some circumstances. It does a great job drilling aerial booms on occasion, the 8 foot bed is a useful feature, but it certainly can't produce the accuracy or surface finish you achieve. At the end of the day, there is no replacement for several hundred kilos of cast iron. Speaking of which I have a CNC punch that need to go ...
On Thu, 10 Sep 2020 at 09:18, Neil Smith G4DBN <neil@...
I can't get a traditional flycutter to produce a really good
mirror finish though. What happens is that when the cutter hits
the edge of the workpiece, even with the table locked, there is an
audible thump and some signs of resonance, so the surface has some
weird waves from the harmonics created. You can just about feel
them with a finger, but they are down at the 1 to 4 micrometre
level when measured with a Mahr Millimess on my big granite
surface plate. More cosmetic than anything, but annoying.
I found that laying some 2mm thick lead sheets on either side of
the vice and putting big lumps of iron and/or buckets of sand on
top really kills vibration. Also I cast and turned up a 2 kg lead
flywheel collar to fit the flycutter spindle, and that helped by
increasing the inertia of the tool. However, I had a cheap and
rather nasty Chinese 80mm mill and arbour, which was almost
unusable because the insert pockets were at varying heights, with
up to 15 micrometres of variation. After seeing some advice on a
machinists' forum, I tried removing all but one insert and runing
a slower traverse speed and it was a revelation. The mass of the
head gives a reasonable flywheel effect to reduce the harmonics
and wibble in the Bridgeport spindle and drive (Mostly in the
varispeed drive I am guessing). I might try try making a lead
collar for the arbour, but I think the real answer is to make a
copy of the Suburban Tool flycutters with a heavier head, maybe
even machining pockets on the back of it to fill with lead, and
using a 25mm lathe tool with a large radius insert. The 2HP motor
might struggle with really wide cuts, but the biggest things I
need to flycut are heatsink faces, and 70mm radius should be
sufficient for those. I would need to find a way to counterbalance
the off-centre mass of the cutter though, as there is a limit to
how long a 25mm insert tool can be, and I'm NOT getting into
machining insert pockets, for there lies madness.
I am limited by the spindle speed of the BP, so I have made up a
bracket to fit a 14,000 RPM spindle motor to the quill for doing
really tiny milling with end mills of 0.5 to 1.5 mm, but even that
isn't really fast enough. What I should do is make a coaxial
spindle with offset motor so the single bearings are in-line with
the BP quill, but finding precision bearings rated to 35k rpm that
would fit inside an R8 collet is pretty much impossible. The
bearings I used for the toolpost spindle on my lathe to cut the
0.5 mm (or less) choke grooves on the ends of the 122 GHz horns
were 35 mm OD and cost around £90 a pair, but have sub-micron
runout and can go to 48,000 rpm, which is almost fast enough for
the 0.5 mm end mills. Almost.
I'd certainly trade surface finish for the capability to do
complex curves and 3D tapering forms. Next move though is to get
one of the new large Anycubic Photon Mono X 3D UV resin printers
to make pattern pieces for sandcasting. The I'll be able make
arbitrary shapes for brackets, mounts, feedhorns, enclosures and
suchlike in aluminium or bronze without being dependent on my
On 10/09/2020 07:59, Robin Szemeti -
Thanks for the detailed info, I am a big fan of WD40 for
aluminium. It is useless as a lubricant in most situations,
but as a cutting fluid for aluminium, it works quite well!
You clearly have the old Bridgeport running well. My CNC
router does not have the stability to achieve anything like
that sort of surface finish, sadly, even though it cuts
aluminium quite nicely otherwise.
On Thu, 10 Sep 2020 at 07:54,
Neil Smith G4DBN <neil@...
I ran a load of
simulations in OpenEMS, but I’ll file the probe to length
and measure the actual length, then see how repeatable it
is. Without a trimming screw, I’ll have to file them all to
get them on frequency I’m sure.
I’ll publish the OpenEMS model when I publish the
On 10 Sep 2020, at 06:27, Alex May M1BSX <alexmay@...
A thing of beauty! :-)
Very intrigued as to how it was
milled and whether you're using an empirical
approach to determine the length of the
73s Alex (M1BSX)
On Thu, 10
Sep 2020, 00:01 Neil Smith G4DBN, <neil@...
This pic is my first try at machining
an SMA coax to WR90 waveguide
transition. Milled it from a lump of 1
3/4 inch aluminium square bar on my
ancient Bridgeport. It needs a bit of
trimming to get it bang on frequency as
I left the pin a little long. Now I'm
waiting for a load of Radiall SMAs to
arrive from Mouser.
I modelled it in OpenEMS with a
three-inch length of WR90 mated with the
oval cavity. Return loss (black) and
through loss (red) look promising, I
need to check the real thing once I have
the probe filed to resonance.
Fusion 360 CAD image
Robin Szemeti - G1YFG
Robin Szemeti - G1YFG