Milling thin materials

In a separate thread, Turning Small Diameters, I asked about the capabilities and characteristics of lathes for small scale (2mm railway)
model making, and received excellent guidance. At the end of that thread the topic got on to milling machines, and as it was already quite large, I have started a new one to ask similar questions.
So, materials at small scale will often be quite thin. 5 thou to 40 thou (0.12mm to 1mm) brass would be quite common. There's probably little need for a milling machine for very thin material, and if I get a mill it would most probably really be for thicker stuff, but anyway I am intrigued to understand what is realistic on the sort of mill that I might get - around 50Kg weight or less (important to me), and probably 500 or less. I wonder if I would ever use the mill on these sort of materials.
What is the thinnest material I can realistically expect to mill?
It may seem impossible, but I know even less about milling than about turning. But I suppose the operations to consider are edge-milling a shape on thin sheet, and surface milling thinner areas. I guess there may be techniques for handling thinner materials like laminating with something thicker?
To get slightly off topic before we've even started, Dave Littlewood, in the Turning Small Diameters thread, said:

Mills in my size range seem not to have a knee at all - which I assume is the component that moves vertically on the column and supports the milling table. The table just rests on the base, and all the Z-axis movement is achieved from the milling head movement. Any mill I would consider would have a square column. The mill I have looked at most is the Sieg X2, basically because that's the one covered in depth on the excellent mini lathe site that is my main source of info (minilathe.com).
But I don't really understand your point. I assume you are talking about maintaining X-Y position after Z-axis head movements - unclamping a head on a round column would allow the head to rotate and lose position? But even the little Sieg X0 type micro mills, with a round column, use some sort of racked arrangement for Z-axis movement that I assume retains X-Y position? I must be getting the wrong end of the stick, as usual.
Chas
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I don't know the answer to this. I don't think I have ever gone below about 1/16". If I had to profile something thinner I would fix it to a sacrificial block (probably with screws and glue) or (for really thin stuff) clamp between two blocks. There must be some kind of limit beyond which the material will bend or tear without such measures. Probably for very thin material, etching is more suitable, especially for fluting rods etc. Hand filing is also an option...

This is pretty well universal for small mills; the knee type is found on larger machines, I only mentioned them for completeness (not always the best thing for clarity!).

Yes.
The racks are not always fixed in position or precise enough for the job. A square/rectangular column is best, though a dedicated keystrip on a round column is OK. My Emco FB2 uses one of these and holds position very well.
The Sieg X0 is arguably not a real mill, it's a little drill with very limited milling facilities. A useful mill should have (1) a fine down feed by leadscrew as well as a handle-fed quill, (2) some kind of taper in the spindle for holding tooling (a drill chuck will emphatically not do for milling), (3) a decent X-Y table with good graduated handwheels, (4) a decent speed range (some don't go low enough - something like 50 - 2000 rpm would be ideal).
A mill with a quill downfeed is ideal for precision drilling and tapping as well as milling. In fact, with DRO and stub drills, it is probably the best thing you could reasonable have for putting holes in *exactly* the right place. I have a drilling machine, but since I acquired the mill, the drill only gets used for woodwork.
I would guess my mill gets used more than either of my 2 lathes, probably about as much as the two added together. This obviously depends on the type of work you do.
Where are you based?
David
--
David Littlewood

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Unfortunately no. The X0 head swivels the column round as soon as the tool encounters a significant side load, no matter how tightly the column nut is done up. The head will also rotate about the column if you loosen the clamp bolt to raise it.
Cliff Coggin.
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wrote:

IMHO the simplest way to create "thin bits" is to start off with thicker bits and stick (cyanoacrylate) or solder them to a much thicker block to hold them for machining. The "Thick" block is sacrificial but reusable after removing the part and skimming. The odd hole here and there is no problem. The odd block of brass bought from your local scrapyard is perfect for this. Square up first to ensure all faces true.
With regard to machinery based on your size requirements I would suggest an X1 or X2. I have an X2 but am looking to change to a bigger machine, however for your requirements it would suffice IMHO. The size of the machine makes it simple and cheap to add a DRO. I have a YADRO with chinese scales and it really works very well. The main problem with the X2 is the crappy Z axis control, however with a DRO it is simple to drive low then raise to the required position thus ensuring that the head is "sitting" on the rack. This and ALWAYS clamping the Z make the unit well capable of your requirements. The use of the YADRO or any DRO means that you are not bothered if the base machine is "Metric" or "Imperial" either are now available with the DRO. A belt drive is definitely preferable to the standard gear drive. (Noise)
Richard
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Richard Thanks

Right, I figured maybe something like this. So this might be a way of milling thin areas (say 20 thou) into, say, a 40 thou sheet?
How about edge milling? This may be a daft way to do it, but would it be possible to layer 2 sheets of say 40 thou, and mill e.g. loco frames? I guess with something sacrificial under them, drilling wouldn't be a problem, but I really have no idea about the edges. Which raises a specific question which doesn't really matter - do you think a mill could edge mill PCB?
Obviously it isn't essential to use a mill for these things - I'm just trying to gauge what use a mill might be for actual model components.

OK, thats taken on board. There are so many accessories and conversions, that it's hard to know which are really worth while. I have read up wherever I can on the web about the Z-axis backlash and the consensus there seems to be what you say - it cannot be eliminated but working in one direction only allows repeatably precise work.
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Chas, I have been away for a while, so just chatching up.
Edge milling thin sheet is easy. I do 25mm sq 0.05mm thick aluminium foil with 1.6mm holes 3mm in from each corner on a regular basis, 50 at a time. You need a 30mm sq mild steel plate about 6mm thick, 0.05mm brass sheet on that then the 0.05m foil, brass again, then foil and so on. Top that off with another 30mm sq mild steel plate. Clamp that lot on the milling table, mill two edges to size, clamp over those two edges, then remove the original two clamps. Mill the second edges to size then drill the holes as far and into the bottom plate without hitting the machine table.
--
mick



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