Machining Inside Out of Part Without Causing it to Fold Up?

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SteveHGraham
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Machining Inside Out of Part Without Causing it to Fold Up?

Post by SteveHGraham »

Haven't been here in a while. Hope all are well, and that many fine new hats have been purchased.

I'm making a Telecaster-style guitar. I decided I want to use an ashtray-style bridge. Here is a link to an ad. The first link shows photos. The second, luckily, has technical drawings.

http://tinyurl.com/2v8oq66
http://tinyurl.com/377f28t

Problem: I want to expose the wood I'm using, and I'm using a different neck pickup, so the slanted slot where the neck pickup has to go, along with that half of the bridge. And I want to use brass, because the guitar's hardware will be brass and gold.

I have machined a bar of 360 brass, about 3.25" long (width of the bridge) and about 1.15" wide and around 3/8" high. I plan to mill the inside out of it to turn it into half of an ashtray bridge.

My concern is that as the metal gets thin, the workpiece will get so weak the vise won't hold it, and it will go flying out and kill someone. Me, for example.

Can anyone tell me if this is a real risk? Also, how do I avoid it? I'm willing to make the metal thicker than the factory bridge, but I don't know if that will save me.
Every hard-fried egg began life sunny-side up.
Russ Hanscom
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Re: Machining Inside Out of Part Without Causing it to Fold

Post by Russ Hanscom »

Several different options come to mind.

It may be easier to start over and cut out the inside first then whittle down the outside, or

Some people have great success by super gluing the part to something larger. Need to take small cuts and keep the temperature down. Solder has also been used in a similar manner.

Some times leaving the part attached to a the whole bar, or at least a larger part of it, until the very end provides useful ways to hold the part.

Cut a cavity in a block of something and imbed your part using one of the very low temperature alloys designed for just such a use.

Hope one of these will get you going.
hobgobbln
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Re: Machining Inside Out of Part Without Causing it to Fold

Post by hobgobbln »

Couldn't you use the screw holes to attach it to solid block, then clamp the vise down on that?

You could probably even use a block of wood to attach it to so you wouldn't have to worry about scrapping a piece of flat stock.

Griz
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SteveHGraham
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Re: Machining Inside Out of Part Without Causing it to Fold

Post by SteveHGraham »

Thanks for the help.

As it turns out, the brass was stiff enough to stand up to the mill, and no one was killed. Now I have to figure out how to get the machining marks out of it.
Every hard-fried egg began life sunny-side up.
whateg0
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Re: Machining Inside Out of Part Without Causing it to Fold

Post by whateg0 »

Glad that worked out for you. Not sure why something like that wasn't made from sheet stock, though.

Dave
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SteveHGraham
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Re: Machining Inside Out of Part Without Causing it to Fold

Post by SteveHGraham »

Used what I had.

Also, to make it out of sheet stock, I'd have to have some way to bend it, and it would be pretty ugly compared to a machined bridge.
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JackF
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Re: Machining Inside Out of Part Without Causing it to Fold

Post by JackF »

A trick I have heard of, but have not tried, is to use dull cutters on brass or at least reduce the positive rake so the cutter doesn't want to dig in too much while cutting. :shock:

Jack.
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Harold_V
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Re: Machining Inside Out of Part Without Causing it to Fold

Post by Harold_V »

JackF wrote:A trick I have heard of, but have not tried, is to use dull cutters on brass or at least reduce the positive rake so the cutter doesn't want to dig in too much while cutting. :shock:

Jack.
Dull cutters can yield some strange problems. Brass, acting very much like a bearing, will float cutters instead of machine. You are generally better served to reduce rake angle and front relief, to minimize a tool's ability to hog. Using a sharp cutter with the altered geometry tends to yield more precise cuts and leave a decent finish. Same principle applies to easy machining cast iron, too.

Harold
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JackF
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Re: Machining Inside Out of Part Without Causing it to Fold

Post by JackF »

Thanks Harold,

For the reply. Actually, the dull cutter remark came from a friend telling me that he dulls his drill bits when drilling brass to keep from hogging and I transposed that to milling cutters. I can see where re-profiling drill bits per your recommendations for brass would be a better choice. :D

Jack.
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Harold_V
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Re: Machining Inside Out of Part Without Causing it to Fold

Post by Harold_V »

Yep, that procedure is the one recommended for drills, too, where it's very easy to accomplish. You simply grind the face of the helix at the cutting edge. A slight flat is all that's required--even a few thou will do the trick, so the drill can be returned to normal use by sharpening when the job is finished.

If you choose to alter a drill by this method, care must be exercised to avoid grinding the flat beyond the margin of the drill. Otherwise the drill cuts undersized until the unground portion of the margin reaches the hole. Depending on the nature of the grind, it can cause the drill to seize in the undersized hole.

Harold
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steamin10
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Re: Machining Inside Out of Part Without Causing it to Fold

Post by steamin10 »

Drilling and lathe work, for me on most brass objects, are best done with a scraping effect from the tool. Unless dead sharp, most tools will try to slide over a light cut, and a small infeed will cause a jump into the work, taking much more than desired.

Milling I do with dead sharp new bits, for best dimension control. We tend to think of brass as a soft material, but it can be very tricky for small cuts and small parts.

Dead sharp cutting edge, or a scraping profile. The least bit dull and all bets come off.

Drills tend to hog and stick on breakthrough. This can be death in small ports and passages. A coupla passes with a stone, or jewelers file, can take the attack off a drill to prevent this.
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