How to mill incredibly small slots in a milling machine

[bbussey]

Max — I figured you were thinking of milling a mold for casting purposes.  Brass will work just fine, so that eliminates the need of a coolant system.  K&S McMaster-Carr has the most reasonable prices on brass bar stock.

Yes, you can do what you want regarding milling spoked hubs.  But start with larger diameter end mill bits to remove the bulk of the material, then follow with smaller diameter bits for the fine detail.  That saves time and materials (in the form of non-broken micro bits).

Also — if this is for a one-off (or two-off, etcetera) project, use wax block instead of brass.  That saves a ton of stress-wear on the mill bits, and the wax holds the detail perfectly as long as you don't leave it out in the sun on a hot day.











My RPO and Diner wax molds were milled with the following bits in this order:  .055 flat head, .040 flat, .020 flat, .010 flat, .005 flat, .008 round head (for rivets - dip the head ½ the diameter, raise, move, repeat).

If you're going to do injection-molded plastic, then brass is the way to go for runs that aren't going to be tens-of-thousands of copies.  All the American Limited core-kit tooling was milled into brass plates.

[robert3985]

Max — I figured you were thinking of milling a mold for casting purposes.  Brass will work just fine, so that eliminates the need of a coolant system.  K&S has the most reasonable prices on brass bar stock.

Yes, you can do what you want regarding milling spoked hubs.  But start with larger diameter end mill bits to remove the bulk of the material, then follow with smaller diameter bits for the fine detail.  That saves time and materials (in the form of non-broken micro bits).

Also — if this is for a one-off (or two-off, etcetera) project, use wax block instead of brass.  That saves a ton of stress-wear on the mill bits, and the wax holds the detail perfectly as long as you don't leave it out in the sun on a hot day.












If you're going to do injection-molded plastic, then brass is the way to go for runs that aren't going to be tens-of-thousands of copies.  All the American Limited core-kit tooling was milled into brass plates.

I was going to suggest this very thing, except I'd machine wax masters for investment casting the driver centers.  But, I have the casting equipment.  If you could get away from the idea of "completely building everything" yourself on this, oftimes jewelry shops or rock shops have casting facilities and people who will tree up your waxes, invest them and then cast them.  In my case, I have several projects in which I take my masters down to my local rock shop, along with pelletized brass that I use in my own castings, and these guys will do a single cannister of parts for me for $25...which is really cheaper than I can do it with my own burnout oven, crucible and caster.

[bbussey]

Also, why wax is better:  I had to redo both the RPO and diner at least three times each.  With a wax mold, it was a matter of milling .050" off the top surface with a .250" bit in under five minutes, then starting over.  Much easier to deal with than brass, or any other metal, and much less expensive.

Wax blocks are available from MachinableWax.com and also from McMaster-Carr.

[Andrew Hutchinson]

Very cool, I'd say go for it.

If you really want to go down the road of casting and a master it's not a bad path - you'll gain a lot of experience working with small slot drills! However, you might want to consider other ways of the skinning the driver cat. Myself, I'm not a fan of plastic in wheels except where necessary for isolation. More metal = more better... You might want to look at the work of Tom Mix ( P48 yahoo group/brass loco builders yahoo group) or Nick Baines ( http://www.nickbaines.me.uk/ ) for examples of nice metal wheels. There's a redux of an old Sid Stubbs article on CLAG ( http://www.clag.org.uk/bill-newton1.htmland )
originally published by the Manchester model railway club ( http://www.mmrs.co.uk/technical/wheels.htm ) that works on similar lines. Admittedly they're much larger models but the technique is similar in N scale and by building them up (soldered construction)you can get an easily tapered spoke with little tooling carnage. If you wanted to mill from the solid then a slitting saw (ganged if you don't need a tapered spoke) will get you where you need to be provided you have some rudimentary indexing facilities. The more organic features of the hub can be machined using coordinate drilling or by way of a profile milling set-up under microscope or by some deft work on a rotary table. I would imagine you'll be looking at a dozen wheels whatever way you go.

When you 're at the GEARS show look for books by Kozo Hiraoka on building live steamers.

There is a German fellow building a destroyer (going by memory here and my favorite/links are on a different machine) in 1:48 using something similar to the machinable material you mentioned earlier. I'll post the link when I find it.

Andrew Hutchinson

[Kisatchie]

Wax blocks are available from MachinableWax.com and also from McMaster-Carr.

Spoiler Alert: Topic drift


Hmm... I wonder if they
make wax lips...

[mmagliaro]

Wow... I was actually considering something like what that fellow, Nick Baines is doing,
but using something would require a bit more hand-work... but less machining skill, which I do not have.


EDIT...I found some thick-wall 3/8" tubing with a .065" wall thickness.
We have  .375" in diameter (outside), 0.245" inside
A 51" driver needs to be .3187".

In a lathe or mill, you chuck the brass tubing and mill off .022" (total diameter of .044" removed) for a nice NMRA flange depth, then you part the thing off the end of the tube, and you have a tire with a thickness of .021", a flange depth of .020", and a wheel diameter of 0.331".    That's 53", but we'll fix that later.

The eccentricity of the flange rim would only be as good as the tubing, but that tubing is pretty darn good,
and it would never show on a small blackened rim.  Plus, it would not affect the running at all if it wasn't perfect.  It's
the tread that matters.

As for the spoked center, I was going to make up a jig on a metal plate with some pins in it, so you could put a piece of
small brass tubing in the center that would eventually be the hub that goes on the axle, with the turned tire place around it,
and then take strips of brass and solder them in place. 

When it's all done, press a shaft through the center brass tube/hub, chuck that back in the mill, and machine off a little more of
the tread and flange to get it down to the final 51" diameter, and correct any slight error with respect to
the tire/hub.

It sounds very labor intensive, but it would be a great challenge to see if I could make it work.

[peteski]

Max, I can understand your quest for machining the wheel mold and casting the spokes drivers. However, I don't see a good reason not to use some more modern techniques now readily available to modelers who scratch build.  For example, if you could design the wheel centers in a CAD program (SketchUp is easy to learn and would be plenty capable of this type of a drawing), then have the design 3D printed on a high-res printer in wax. Then have it investment cast in brass.  According to Robert G. jewelers can do this for a nominal cost.

After all, this is how the real companies which make brass models "scratch build" their models.  Why not you?

[superturbine]

Yes that's a very tall order... especially when you consider shrinkage rates and accounting for them in a scratch built piece such as a driver and properly fitting them to a machined tire. And you will have to built at least 2 drivers for masters when you consider counterweights.  In addition, all of you spokes need to look exactly the same both drivers masters.   Or you will need to build one driver which can survive the casting process and modify the counterweight/ main rod connection point.  Speaking from experience, spoked drivers are not easy to cast in N scale.....But then again, you are a gluten for punishment!!

I say do it!!!!!


PS.....and while you are at it build me some 74" spoked and boxpok drivers 

[Sokramiketes]

Thanks Bryan.

And all...

This all started as I pondered a future loco project (which will probably be a small SP&S steam switcher, like an 0-6-0).
I have always wondered about making a 100% scratch-built N Scale steam engine, including the drivers

That means no wheels from somewhere else, and no "cheating" by casting wheels from another model, or drawing them
and sending the CAD file off to Shapeways.   I would want to make them myself.

So I wondered how feasible it would be to actually mill the hub and spoke pattern into a metal plate as a mold, and then use
some sort of casting plastic (urethane, whatever) to pour into it to make the wheel center. 

Sounds like it's a tall order.

Ah, that is much easier. Look up Freeman's machinable wax. You can mill the cavity and pour resin in directly.

EDIT- Bryan beat me to the punch way before... hazards of posting from my phone.

[Andrew Hutchinson]

Max,

I mentioned I'd seen a fellow using something similar to Renshape to make fixtures. Turns out it's something altogether different -rather my idea of what Renshape was turned out to be wrong. Whatever the material is (fiber impregnated resin of some sort that almost looks like tufnol) he seems to use it to hold parts in position while soldering. Some of the components are pretty wild but you can see how they'd work for simpler items just as well. Anyways, here is the fellow's build of a US destroyer:

http://www.ship-model-today.de/fotoreport.htm

Cheers,

Andrew Hutchinson

[mmagliaro]

After some more research, I do agree that a slitting saw arbor and blades would be a much easier way to do this.
I could mount a steel disk on a rotary table, set vertically on the mill, and then just rotate the piece and exact
number of degrees, cutting .010" or .015" (somewhere in there) slits at 17 perfectly-spaced locations around.

The same plate could then be put under the mill to machine out a center hole where the hub goes, and finally,
back on the rotary table, I could machine out a depression for the outside rim. 

Now, the "tire" can be placed into the jig, a piece of brass tube placed into the center depression, and then
the spokes can just be placed into the slits and soldered in place.

When the whole thing is done, tap a hole in the center, thread a screw into it, chuck it back in the mill and skim off just a
hair from the outside surface of the tire to make sure the whole thing is perfectly concentric around that center hole.

The counterweight does not concern me as much.  That can be cut from a sheet of brass, or heck, even a sheet of styrene,
and just glued onto the face.

I *think* this could work.

[victor miranda]

take my word for it, that plan will not work.

the spoke will either warp or get kicked off the hub.

If you are determined to make a spoked driver....
a drillpress and minimum of three holes per open area
are how to start. (one at the hub and the other at the roots of the spokes)
drill more holes or use a jewelers saw to cut out the pie shaped area.

small files will clean up the spokes.

luck.

victor

 

[Chris333]

Tom Knapp made Nn3 28" spoked wheels buy drilling and using small files 

Me I'd just used some Tomix 51" drivers:
https://picasaweb.google.com/ErieChris333/ErieRailroadB5060NScale#5191607752575294690

[mmagliaro]

take my word for it, that plan will not work.

the spoke will either warp or get kicked off the hub.
...snip...

victor

You mean you think that the solder joints will not be strong enough, and even if I managed to assemble and solder
up the whole thing, the spokes would twist off their soldered joints or just plain break off?

[Chris333]

Another thing, I forget where I saw it, but someone etched brass spoked wheels in many layers. Use the center hole to line them up and solder them together. Then chuck them into a lathe to better form the flanges. I guess if you used silver solder around the edge that could be your tread.