How to mill incredibly small slots in a milling machine

[mmagliaro]

Hoo boy.... This is a toughie.
I think I see what Victor is saying.

I can see how to turn a nice tire with a flange on it off a piece of thick-walled brass tubing.
Making a wheel center by scribing the spoke lines and then just hand-drilling and filing out
all the metal is a lot of work, and I would do it... but I don't see how on Earth I could ever make
the spokes uniform, not to mention uniform across 3 drivers on the side of an 0-6-0.   I think I'd end up with
3 drivers what were concentric and rolled perfectly, but still looked weird.

As I understand it, in real life, they make them by first creating a wooden form and then sand-casting the
molten iron.

 So I suppose the prototype way is to make a mold and pour it.
... mill out the cavities in something not-too-hard to mill with a tiny bit, and then
pour it.

[peteski]

Hoo boy.... This is a toughie.
I think I see what Victor is saying.

I can see how to turn a nice tire with a flange on it off a piece of thick-walled brass tubing.

Sounds like a good time to pick up a mini-lathe.    That way you could just turn your tire from a piece of round stock.  Or turn the entire wheel blank, then mill the spokes into the center.

[mmagliaro]

Sounds like a good time to pick up a mini-lathe.    That way you could just turn your tire from a piece of round stock.  Or turn the entire wheel blank, then mill the spokes into the center.

That's exactly what I'm thinking.  Although for something as thin as a driver tire, I could do it in the mill.
Just chuck the tubing into a collet, choose a tubing size that's a little bigger than the flange diameter I want,
and then turn it down with a tool held against the spinning end of the tube.  It only has to stick out, like, 1/4" or even 1/8",
so that thing is going to turn darn true.  Then, let it out of the collet a little, use another tool bit to turn a bit of a tapered
rounded edge on the flange part, and then part the whole thing off.

The tires, although they would take a little work, are the easy part.

[victor miranda]

I need to be in bed.

Max, what material are you wanting for the driver?

If casting resins are good, it is easier to mill a mold.
casting is a trick.  I think pressure when molding is required.

next hardest,
If you insist on brass....
think lost wax.

next and can get pricey...
If you have a milling machine
with rotary table  and a lot of patience.
a 1/16 inch end mill can get you surprisingly close.

I made a mistake in the both of the two I tried...
I'll try to locate them.

BUY DRIVERS!!!!

If you can.  It is WAY easier.
close is a good compromise.

victor

[victor miranda]

a long long long time ago...
I made these

one was free hand and one was using a milling machine and rotary table.
I think I used a 1/16 inch mill and I went as deep as the tool allowed.

[mmagliaro]

Very impressive (and tedious!)  work, Victor.  Thank you for digging them up.
I was wondering about doing that with a rotary table.
But I am going to go another way, be it a mold, wax, a jig, I am not sure yet.
One thing I am shooting for is trying to actually make 17-spoke drivers
(yes, I counted them on the prototype), rather than 10 or 12.

That raises the difficulty, I realize.   I used to have a 1/32" end mill.  It didn't last long
before I broke it.  But that was a few years ago when I was very stupid about using
the mill (as opposed to now, where I would call myself only inexperienced and foolhardy).

I do wonder about doing what you did, but instead milling the wheel center from a block of Delrin or other
plastic.  It is not hard to find blocks or plates of that stuff.  I looked. That would make life
on the tiny end mill much easier.  I would still turn the tire from brass tube, and put the wheel center into it.
If I could mount the whole thing on a sturdy axle, chucked in the mill at the end, the tire could be turned
a little to correct for any centering error.... maybe.

[Chris333]

Any links to the prototype? 

[victor miranda]

Chris333,
I am thinking a pacific....

Max,

options do include; buy something close.
I have a few brass drivers that I got off the bay.

again.... I'll hunt them, pictures etc.

if you are very determined to make your own...

you will want a way to lathe the tires if nothing else.
I strongly recommend making a set of drivers without the spokes
to see if you can get your drivers straight and concentric and the same size.
It is a task that is simple and has some surprises in it.
Consider how you want to insulate them.

Once you get that done, you can work on how to make them pretty.

plastic....
please consider installing a brass center to hold the axle
plastic does not easily have the strength to hold an axle.
MP Pacific drivers are an example of this.
the extra surface of a brass center has a better chance of
not cracking and letting go.

from all I have read, you may want to consider using ABS.
I have tried gluing spokes into an open center.
... a straight walled dish with
a center post cut from one piece of plastic.
I suspect this is the easiest way.
I could not get the spokes to look look right.

you may have better luck.

that done....  casting copies is a whole nuther art.

victor

[victor miranda]

oooof,
Been re-reading.
couple of things....
I suspect you are doing 50 inch drivers...
you are sure you want 17 spokes?

 find out if anyone can do lostwax casting for you.
I am just about certain you will want that.

make a mold for the wax...
it is far easier to cut a block of  aluminum
into spokes and rim and hub than to machine
out the open areas.

from there, wax is easier to cleanup
and then get them cast ...

btw I have not been able to find a lostwax caster here...

ah well.

[Chris333]

Is this it?
http://www.brasstrains.com/classic/Product/Detail/049562/HO-Brass-Model-Train-W-R-SP-S-A-1-0-6-0-4-Factory-Painted

Looks like 12 spokes?

[victor miranda]

I can find 0-6-0's with 15 spoke drivers....  not 17.
and most are looking like 12.

[PGE_Modeller]

The HO model in Chris' post (above) has 13 spokes (every 27.69 degrees).

Cheers,

[mmagliaro]

Chris's pic is close.  It will be that one, or an A-3.  Looking at photos I have in a book, I thought there were a lot more.
But now that I look closer, I think it is 14.
And yes, they will be 51" drivers.

I am currently thinking plastic spokes with a plastic center with a brass hub inserted in it to grab the axle better.

The first thing I will do is see how good I am trueing up heavy-wall brass tubing and turning it down to get 51" with
a nice flange on it, and then parting it off.  I do not have a lathe, only the mill.  But with stock this small, where it
only has to protrude from the collet 1/4", it really ought to mill down nicely.  I can't imagine there would be enough deflection
on such a small, short piece of brass.  The real trick, of course, is turning them so they all come out the same.  But that's what
measuring and centering tools are for (some Starrett tools are en route as we speak, so I can make sure
I have things straight and centered).
Unless the run-out on that mini-mill is awful, it should work, and I don't think it's awful.
There's even a guy on YouTube with a video of that Micromark mill and a runout gauge on it showing that the spindle
is true to under .001" and I doubt I'm any better than that with my newbie milling skills.

No matter what happens, I will learn a lot about milling.  That's for sure.

[PGE_Modeller]

Max (and others),

You might find this blog at http://modelopolis.blogspot.ca/2012/06/3d-printed-wheels-first-attempt.html by Julia Adams of the 2mm Scale Association's Oxford Area Group to be of interest as it shows her efforts in using wheel centres that she had printed by Shapeways combined with the 2 mm Scale Association's wheel rims (tires) and axles to convert a Graham Farish N gauge (UK) locomotive to 2mm Fine Scale wheels.  It is an interesting approach.

Cheers,

[Chris333]

Max (and others),

You might find this blog at http://modelopolis.blogspot.ca/2012/06/3d-printed-wheels-first-attempt.html by Julia Adams of the 2mm Scale Association's Oxford Area Group to be of interest as it shows her efforts in using wheel centres that she had printed by Shapeways combined with the 2 mm Scale Association's wheel rims (tires) and axles to convert a Graham Farish N gauge (UK) locomotive to 2mm Fine Scale wheels.  It is an interesting approach.

Cheers,

Nice blog. check out his latest. Trying to mill a small gear:
http://modelopolis.blogspot.ca/2014/09/cncing-about-part-2.html