Milling a loco chassis

[Lemosteam]

Question for the chassis millers out there.

I assume you disassemble the chassis prior to milling.

When you mill the chassis do you reassemble them beforehand without the plastic spacers and accomodate thier flange thickness in your dimensions or do you mill each half separately to avoid heating up the plastic nuts?

What depths of cuts do you use and how many passes does it take sometimes?

Thanks in advance for any help. 

[woodone]

I don’t use the plastic bushings. I use some 4-40 screws, I have metal nuts that I modified to fit the frame. I then align the frame halves so all edges are flush. Then tighten the screws. I also have steel spacers to fit the frames so when I tighten the vice on them I don’t crush the frame. I use wood router bits for mill bits. I don’t take a very deep cut, 0.020 is about the max. And I use a high speed on the RPM of the mill. My mill is manual ,so feed rates are pretty slow.

[wvgca]

I use a  modified metal drill stand [benchtop] with a wood router bit .. cuts are maybe 0.025 thou, so it's pretty slow going, feed is manual with  a small milling metal holder vise .. all cuts are pretty well visual, I don't have a DRO on that one ..
I save the actual mill for harder metal, or something needing more precision, it takes longer to set up ..
I also do it very seldom as I'm into HO, not N

[Steveruger45]

I don’t have a milling machine.  So I take the chassis halves individually and screw them to a 1 by wood block that I shaped/recessed the side of to fit the outer frame half profile and screw the frame to the wood block with some No.4 pan head screws through the frame assembly holes.  This is so I can see what I’m taking off with my file and hacksaw so I don’t go too deep and into all those frame recesses for the motor and bearings and flywheels etc etc.  after I’ve done one half I use that to transfer reference scribes to the other half and “rinse and repeat”.   It’s slow going but very controllable and uses the tools I have.

I would invest in a milling machine if I were doing a lot all together though.  The proxon Miller gets good reviews and a few have that one on TRW.   Also the miller will let you do what my manual approach won’t and that’s nice neat recessed cuts.   I have used a dremel for that but it’s nowhere near as neat as what a milling machine can do.

[nightmare0331]

strip the mechanism down to bare frames/frame halves

clamp both halves together ensuring they are properly supported and shimmed.  (I don't bother screwing the halves back together for machining...milling vise and parallels make quick work of this)

If you've never done a specific model before, light passes.  It's a bit hard to explain, but you get a feel for what you can machine away with whatever setup you are using at the time.

As for how much to remove, depends on the specific decoder install needed.

remove from the clamps, debur the sharp edges with a file and blow off the chips.

If you scroll through my fakebook business page there are plenty of in process machining shots to look at that may help.

https://www.facebook.com/dufordmodelworks/

Hope this helps!

Kelley.
www.dufordmodelworks.com

[jdcolombo]

What Kelley said.  Clamp the frames together in a milling vise with appropriate shims, etc.  No plastic spacers, no screws.

I have a Proxxon MF70 micro-mill, which I find is perfect for N-scale work (you really need something bigger for HO, although I've used the Proxxon for HO projects - it just takes a LOT longer).  I typically use a 1/8" dual-flute coated end mill (I get my mills from McMaster-Carr), and typically don't try to take off more than 1/2mm per pass (that's pretty close to the .020" Woodone mentions). 

John C.

[peteski]

Same here: clamp the halves with no spacers.