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Old 01-22-2015, 04:20 PM
moell54 moell54 is offline
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Default AiRTx Cold Gun

When I get the Cobra and after the initial learning period (#months to be determined), I have a pending request for an aluminum material project.

As an alternate to a mist system, I am wondering what the subject "cold gun" approach experience with you guys has been? Although this requires a steady stream of air to cool the plate and the bit, it also reduces moisture impact to spoil boards.

Aub
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Old 01-22-2015, 05:39 PM
BradyWatson BradyWatson is offline
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I've cut my share of AL. For most things within the reasonable scope of CNC routing, you really don't need coolant. With the proper tooling (single spiral-O flute) nothing is needed.

When you get into thicker materials (>3/8") then you will benefit from compressed air blowing on the bit. You can cobble together something pretty cheap using a Husky blow gun kit with football inflator & a few brass fittings to adapt to compressed air. Set it to 15-25 psi and cut.

Certain alloys cut better than others, so do your research before you buy anything. McMaster.com is a great reference for this.

Solid hold-down is essential & DS tape fails when the AL gets heat soaked...and if it's thick enough and machined long enough, it most certainly will fail.

-B
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Old 01-22-2015, 06:01 PM
moell54 moell54 is offline
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Great response Brady, thanks. Do you find that a good vacuum set up holds the aluminum pretty well during machining (adequately offsets lateral movement stresses), at least until the remaining surface area of the aluminum is enough? I know that's a pretty subjective question?

Aub
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Old 01-22-2015, 07:34 PM
moell54 moell54 is offline
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Brady - I found the "Black Box Vac Source" thread on the other forum that Gary Campbell started and that you participated in. Great discussion for anyone interested in vacuum system mechanics/theory. Very exhaustive treatment of subject, or is that "evacuative"?

Good job fellas.

Aubrey
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Old 01-22-2015, 09:55 PM
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Gary Campbell Gary Campbell is offline
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Aubrey...
Just to be clear... I started that thread, AFTER I learned what I could from one that Brady started: http://www.talkshopbot.com/forum/showthread.php?t=545

As you can see, we all learn from someone. He, (Brady) is the one you want to learn from.
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Old 01-22-2015, 10:51 PM
BradyWatson BradyWatson is offline
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Thanks for the kudos, gents.

To answer your question, yes - vacuum works well holding down AL, but it depends...

If you are holding down 4x8 sheets of AL - cutting things like channel letter backs, faces etc - then a universal type bleeder board vacuum works well.

However, if you get into 'billet' AL and want to cut things from AL bar etc, then that will not work for you. You will want to have the vacuum right up against the back of the material to maximize suction & minimize leakage. This is typically done with gasketing material (AllStar Adhesives 'spoilboard cover' is one option) and a low CFM, High suction vacuum source, such as a Gast, Welch etc. You can just make yourself an 'accessory' vacuum board or jig that mounts to your existing setup. No need to completely re-engineer your table.

In either case, surface area makes a big difference. The more surface area, the more 'weight' is pushing down on the part. Vacuum is by definition 'nothingness' or a percentage of nothingness, and what is actually holding your part down is the weight of the atmospheric column of gas from the top of your workpiece all the way up to space...

Since AL is so dense, cutting harmonics get transferred to the AL and this can cause the material to do the jitterbug...so some parts - typically billet parts - need to be clamped, screwed or bolted down in one form or another. Vacuum is the most elegant. Don't use screws to hold down sheet AL because you will dink the sheet and cause it to lift.

Oh...and one of my sayings is, "Drywall screws are bad news". You should never use them on your CNC. They break off and are meant for drywall. Instead, use something like Kreg pockethole screws or similar, which are strong enough to handle the torque needed to fasten most things without breaking off just below the top of your spoilboard. Been there, done that...not fun!

-B
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