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Magnetic Polishing for titanium?


#1

Would a magnetic tumbler work well on 6-4 titanium? I use 3
different grades of sandpaper and 4000 grit micromesh, and it takes a
lot of time to get a nice finish.

Wes


#2

Dear Wes,

Polishing titanium with small pins works very well. I use round 0,6
mm x 8 mm pins You only need to sand up to 400 However it takes half an
hour to get a nice shine on the titanium.

Martin Niemeijer

Ndesign
Cultuurwerkplaats R10
Rieteweg 10
8041 AK, Zwolle
The Netherlands
info@ndesign.nl ;www.ndesign.nl
Phone +31 (0)38 7501258
Mobile phone +31 (0)651831576


#3

Hi Wes,

Are you using a CNC lathe or starting by hand? The trick in the
finishing is eliminating the high and low spots. I haven’t had as
good success with tumbling because it tends to just amplify the
lines instead of taking only the high points off. On my new Mazak,
I’ve found that I can get a pretty good finish right off the lathe.
I use a 1/64 radius 55 degree diamond tool and push high rpms and
low feed (~.001"/rev) on the finish pass. I just touch it with a 1"
sanding disk on a Foredom by hand with around 1000 grit where it can
go perpendicular to the machining marks and I can go straight to
absolute mirror polish from there. The grit is fine enough to just
take off the small machining marks left, but not aggressive enough
to gouge. It saves tons of hand working time over my other machine
I used where the surface finish was not as good off the machine.
Having short stock and a nicely balanced spindle helps on the high
rpms.

Bruce Boone
Boone Titanium Rings
www.boonerings.com
770-645-6488


#4

My lathe is a fairly small hand lathe
http://www.titaniumconcepts.com/images/lathe.jpg I’ve tried different
speeds and feeds but I think it’s just not rigid enough to get a
really nice finish. Right now I use a .007 radius coated insert and
.0015" per rev, and 600 rpm. I’ve used .015 rad and there really
wasn’t much difference.

I do all sanding on the lathe, starting with 220 grit to get out the
machining marks, then 400, 1000, and finally 4000 micromesh which
puts a polished finish. I then buff with a small felt buffer and some
chinese (or japanese, i forget) white rouge, it’s pretty good stuff
but cost $25 for a bar.

I’m just looking for easier ways to polish, it wears my fingers out
(and burns!) if I have to do a lot of rings. I guess I’ll experiment
more with speeds/feeds, I think I need some better sand paper too -
I’m using automotive stuff and it breaks down quickly.

“I use a 1/64 radius 55 degree diamond tool” One question, do you
mean diamond shaped or diamond tipped?

Thanks
Wes
www.titaniumconcepts.com


#5

Hi Wes,

Yes, it looks like it will be a machine stiffness issue when trying
to get a super finish off the lathe, although doing them by hand,
you will need a lot of filing and hand sanding to get your
curvatures anyway. The tooling I was referring to is carbide insert
tooling. I haven’t used diamond as of yet. I understand that a
diamond burnishing tool is capable of 4 micro inch finish, which is
essentially mirror finish right off the lathe. It takes surface
speeds in the hundreds or thousands of feet per minute, so you
really can’t run it too fast. It may not do as well on a hand lathe
since they can’t be run as fast. I’ve used CBN, and it did fine,
and could be run very fast, but when it decides to die it fails in a
spectacular manner, taking out your toolholders and any tool that
will follow. I found that since cycle time is not my critical path
(finishing is), that I would just slow things down and let the tools
live. I get cheap carbide inserts, and I now get several hundreds of
rings from each side of the insert. I’ve run my original 1/2"
carbide drill since I’ve had the lathe, which has been a couple
thousand rings by now. I used to go through them about once a week.

I essentially was forced to dial in my finish turning on the CNC
lathe because it’s a 7000 rpm machine (scary fast), and it won’t let
me open the door for sanding when it’s running. It also blasts 50
psi coolant like Niagara Falls, so I’m not sure I’d want to open the
door anyway. :o)

I’ve found that for hand finishing on my manual lathe, using those
one finger leather gloves you get from a jeweler’s supply help with
the heat. They still allow you to have good control, yet will save
some blisters. I usually use around a 250 grit and wet sand with
WD-40, and scrub sideways to erase the machining marks. I can
usually polish to mirror finish from there if I’ve done it right. I
used to have to do it with 400, but the 250 can work if you get the
technique down. I have a huge polishing wheel and use the $7/lb
white polishing compound. I use an aluminum mandrel grip to hold
the ring and use heavy pressure on 45 degree angles. I made a clear
plexiglas box that the polishing wheel is in, and that’s attached to
a woodworkers vacuum system. The box keeps things from flying out
of there and does a pretty fair job of vacuuming the dust.

Bruce Boone
Boone Titanium Rings
www.boonerings.com
770-645-6488