Sacrificial backing material

Get a piece of 3/4" MDF - medium density fibercore - looks like brown paper bags pressed together because that's basically what it is . But it's cheap , it's rigid , and it won't hurt your cutters . And you can buy less than a full sheet at ho-de-po or Blowes .

I thought that it actually is abrasive and also clogs the coolant pump.

It's not a good idea to use coolant when using a wood / wood product backer. This is one of the many times that it's best to machine aluminum dry and just vacuum up the chips and backer dust when it's done.

Ignoramus30138 fired this volley in news:k8Odnc0qg5DvTJbQnZ2dnUVZ snipped-for-privacy@giganews.com:

both.

And the statement earlier that "most" woods don't contain much silica is rife with problems. As wood selections get cheaper, and more and more of the scrap is salvaged, more bark, root, and knot sections get included in plywood and press-board products, raising the silica content beyond what you want on your nice tools.

LLoyd

Lloyd, do you think that I could use 2x4 and 2x6's for this sort of purpose, as a backer on my mill, and with coolant?

The wood "chips" would not be so fine as with MDF or some such.

Right?

Ignoramus30138 fired this volley in news:OYWdnSON94nlfJbQnZ2dnUVZ snipped-for-privacy@giganews.com:

Right, and you can, but you have all sorts of "prep" work to do to the backing that will generate lots of shavings and dust.

Go to a local plastics supply and ask them for some cut-offs and scraps. Just avoid insolubles like PE,PP,Delrin, or Nylon, because you cannot glue effectively to them (well, to nylon you can), and you can't dissolve them off the work if you want to.

The more I think about it, the more PVC and styrene have their attractions. For small work, you could even "convert" flat-bottomed pipe caps to work backers.

LLoyd

Well, it can be. Finely powdered wood can make a big mess in your coolant system. What I would have done is use a boring process with an end mill. I have a program that writes the G-code to bore out holes like that. depending on the size and thickness, I have versions to either obliterate the entire hole or to just trim around the edge and then let the slug drop out, then finish the OD. I use this technique for almost everything. This is not quite as fast as a twist drill, but if you have to go very easy due to workpiece deflection, then the boring approach may end up almost as fast.

Jon

Go down to your local Mal-Wart and get a cheap poly cutting board as your sacrificial backer.

And remember, you *do not* need coolant for most machining operations in aluminum.

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But you need _lubrication_, or you get false edges built up on the tooling.

All the more reason to use a polymer for the backer instead of wood.

LLoyd

FWIW, I use AL plate. Used stuff taken off a scrap machine. One plate will last for hundreds of parts.

Karl

I've had pretty good luck epoxying (5 minute variety) aluminum to MDF then applying heat when finished to soften the epoxy and release the aluminum.

I'll clamp up the MDF, and mill it flat, then mill alignment ridges or pockets if needed before gluing the aluminum in place.

Not if you are using sharp tools and the correct speeds and feeds. You can also use compressed air to blow the chips out of the way further reducing the risk of chip welding.

Either will work, the MDF will be cheaper, though likely to get reused less before being tossed, so probably a wash price wise.

Cheap dollar store cutting boards provide some useful material too. It machines quite nicely.

Best regards, Spehro Pefhany

I have never succeeded machining aluminum without coolant. Broke a few endmills.

I've never machined aluminum with coolant, and I've machined a lot of aluminum and never had a problem. If I recall you were running with way too low a feed rate at the time causing more rubbing than cutting, chip welding, etc. I use high feed rates and moderately heavy cuts so I get decent sized chips flying away.

Coolant, or lubricant? They're not necessarily the same, although I'd assume your coolant has some lubricity.

I've used plain, ol' ordinary lard (Crisco will also work) on aluminum; it works good and smells good too! ;-)

Cheers! Rich