Milling machine technique?

Milling machine technique?

Postby areibel » Sat Jul 20, 2013 9:24 pm

OK, this one is for all you guys with some milling experience. I have an idea that may be nuts but might work, you tell me!

I want to make several cabooses, but I keep having problems cutting out the scribed wood sides. I was wondering if you could use some two sided tape and fasten the scribed wood to a sacrificial piece (like foam sheet) and cut the sides out and the windows with a small end mill? I would get parallel sides, and I could use it to rough out the window openings so I'd just have to cut or file the openings to final shape. I'm just not sure if there would be any problems with tear out along the cut edges? Or any other problems I'm not seeing?
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Re: Milling machine technique?

Postby Rob M » Sat Jul 20, 2013 10:37 pm

Sounds to me like it would work. With my setup I can set the machining to do a "climb cut" which would eliminate tear out.
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Re: Milling machine technique?

Postby Rob M » Sun Jul 21, 2013 1:02 pm

Yep, works good. Still had the cad file from the brass caboose I etched a few years ago. Didn't have any scribed wood so I did the scribing as well. I think the scribing would have come out better with a V cutter though.

There is a little bit of fuzzies but no tear out. And the corners would need to be squared up a bit.

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Re: Milling machine technique?

Postby areibel » Sun Jul 21, 2013 1:43 pm

Cool Rob, Thanks!
Ask for an opinion, get a demonstration, can't do better than that!

I've tried to cut three or four by hand out of Northeastern Scale's scribed wood, but I can't get the side square without a lot of messing around. Granted, it's probably related to my OCD of wanting it "right", (I doubt any of the old time modelers would be checking them with a dial caliper) but if I can get a good one built I want to make molds and cast a couple. Plus getting all the windows all aligned and the same width seems much easier, I was dreading that part!

Can I ask what speed you cut at? I was thinking faster would be better, but I'm not that experienced at milling period.
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Re: Milling machine technique?

Postby Rob M » Sun Jul 21, 2013 1:56 pm

I have the speed set at 8 inches per minute but you should be able to go faster. Most everything I've done so far with this machine has been in plastic and if you go too fast it will gum up the bit. That shouldn't be a problem with wood.
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Re: Milling machine technique?

Postby ConnRiver » Sun Jul 21, 2013 8:57 pm

Al, Rob, hey,

Al, just a suggestion, since you're going to be cutting out windows, why not use plastic for your project and cut "wood joint lines," too? Plastic looks more like wood than wood does, state some modeling articles no doubt we've all read.

I use .060 styrene sheet (I bought a 4' x 8' sheet at a plastics warehouse here) base upon which to place the material to be cut. I tape the material to the base with Scotch #665 Permanent Double Sided tape. Boy, that stuff holds in place every material I have ever tried to cut. (I use an X-acto chisel blade to get under the tape after cutting is done. And, I use the same tape to affix the base sheet to the Sherline metal table.)

Here's a photo of TT scale NE-5 caboose sides I cut a few weeks ago:

NE-5.jpg


The plastic material is .125" thick; I pocketed to a thickness of .042"; The ribs are .002 thick after I using a .125" dia. end mill to cut them out (feed 16 ipm, spindle rpm 3k).

I drilled out the corners of the windows with a #87 (.010" dia.) drill bit then cut out the windows shapes with a .018" dia. end mill (feed 6 ipm, spindle 7k).

Pockets for the grab iron brackets (separate parts) were cut with a .006" dia. end mill (feed 4 ipm, spindle 8k, -.003" layer depths).

I cut a jig to hold the cutout side pieces, interior side up, precisely in place. I then pocketed the outside perimeter, at the bottom where the floor will fit, and along the edges where the ends will be located (the ends have male tabs, fitting into the female pockets visible. The windows are pocketed as well. Separately cut frames, which will also be pocketed on the back side to receive .005" clear plastic window "glass", will be cut when I get back to the project.

Since I'm self-taught in CNC machining, there might be faulty figures here. But, basically, I follow the feed and speed cutting formula given to me by Fred, a Sherline employee.

Maybe this helps?

-Brian Chapman
Evansdale, Iowa
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Re: Milling machine technique?

Postby areibel » Sun Jul 21, 2013 10:21 pm

Hi Brian,
One big reason- I already have the wood! I bought some already scribed so I wouldn't have to do runs .025-.030 apart. I've slowly been wasting it trying to get the nice square sides I want. I tried to cut the windows on one of the scrap ones for practice, it's a bugger trying to get them all right even using a scalpel blade to cut. And I managed to crack it on one, it might be fixable but it's scrap anyway. That's what gave me the idea to use the mill, a small cutter and a careful cut would just leave a small radius in the corners that I could clean up to add the window frames. The curved tops on the ends and cupola faces would have to be done by hand, but that's not too bad by comparison. I can cut it close to the template and sand it to match. I just had nightmares about the windows not being in line or crooked, or the sides having enough of a difference from end to end that it would be obvious.
My hat's off to the old timers that built everything like this by hand, the skill level must have been miles above mine!
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Re: Milling machine technique?

Postby ConnRiver » Mon Jul 22, 2013 12:52 pm

Yeah, the skilled scratchbuilders, they're something. I've got a book here written by Gerald Wingrove, a citizen of the U.K., and the photos of his classic automobile models are . . . unreal. I don't know words to describe just how gorgeous are his scratchbuilt models.

BTW, to anyone who has viewed my photo of the NE-5 caboose sides, the photo is distorted. All horizontal and vertical cuts are true, but in the photo they're a bit distorted. Damn that photographer! Although, the bottom piece is warped a bit. Will be fine when assembled.

-Brian Chapman
Evansdale, Iowa
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Re: Milling machine technique?

Postby ConducTTor » Mon Jul 22, 2013 7:17 pm

Brian, I'll take 3 when they're done :)
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Re: Milling machine technique?

Postby ConnRiver » Thu Jul 25, 2013 1:11 am

ConducTTor wrote:Brian, I'll take 3 when they're done :)


Hey, my first sale, ever! Thank you, Alex!

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