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Thin flat bar milling

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Munty Scruntfundle

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Hi there.

A small project I'm designing at the moment requires a flat aluminium bar, 22x8 x 300. I'll take this down to size from a length of 25x10. Or at least that's the idea.

The best order of machining will be to surface finish one of the top 300x22 faces. But. How the hell am I going to hold flat bar that thin on the bed? I don't really want to use multiple vices as I don't have multiple vices, and I don't want to move the part.

I've been looking around but I can't find any solutions for something this thin. If it were steel I could use a magnetic bed I suppose. Maybe I need to change to steel and spend a fortune on a magnetic bed! At least I'd have a magnetic bed!

Any ideas?

Many thanks. And merry festive stuff.
 

julianf

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The long way round -

Fit some sort of sacrificial surface.
Mill that surface flat.
Cut your stock oversize.
Bolt it to your prepared (flattened) surface.
Mill flat.
Cut to size.
 

TFrench

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How big is your current vice? Think my biggest one is 200 mm, with light cuts I think it would be fine with 50 mm overhang each end.

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julianf

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You can make hold downs easy enough if you have something suitable below the stock.

Eg cut another couple of 300mm strips of somthing and drill them periodically along their length. Then bolt this down to somthing underneath your work.

Eg you could stick a plank of wood in your main vice, screw a sheet of somthing sacrificial on top of it, that you then mill flat (relative to your cutter) then put your job on top of that, held down by the previously mentioned strips, that are then screwed down into the wood.

If your passes are considered, you're not going to be applying that much force to the work, so it's not like you need some massive hold down strength either.

You would need to trim your stock afterward, bit you could probably mill part way through on the same setup, and then finish up using a belt sander.
 

SteveW1000

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Piece of steel approx 300 x 25 and a least 12mm thick. Place in vice and mill tool side flat. Clean both steel and ali with meths or acetone and super glue ali to steel. Mill ali and then heat steel to release ali then mill edge.
 

CHJ

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Use a ply or similar substrate clamped to bed, use hot melt glue all round periphery to secure alloy strip.
 

MusicMan

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I would not use ply as a substrate as it is less stiff. At least for the surface, you could either use superglue, or (better I think) good double sided tape is strong enough. The narrow edge, I would hold in a vice and slide it along when necessary. And stick it straight on the miller bed after cleaning.
 

TheTiddles

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This is a fairly common problem which is best solved by designing some hold down points into the design (like holes for screws) or using tabs

Also, stress relieve your bar first or taking 2mm from one side will likely make it warp

Aidan
 

Munty Scruntfundle

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I can't buy the stock to size, it need machining. Hence the need to machine it!

I found some low butterfly kind of clamps, should do the job and as suggested I'll use some parallels underneath for clearance. It all became clear when I sat and actually thought it about properly.

Thanks for you replies.
 
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