Sheet metal help!

[revwarguy]

Hello,

I am mostly over on the DIY CNC forum, where I built a router table. I am very happy with the table I built, and have made many things out of wood and plastic.

Now, I need to cut some sheet aluminum, from .032 to .125 kind of stuff. It will all be profile type operations, which necessitates the need for a spoiler board underneath. The work is some large (up to 24x36) instrument panel type cut-outs, so there are a lot pieces removed, which I believe kind of rules out a vacuum system. I have advice on a variety of cutters to use with my router and the speeds and feeds that other have found successful cutting aluminum of this kind.

I have tried double stick carpet tape, but it is very hard to get it up without putting a bend in the sheet. In fact, it is more likely to get bent than not, and it also leaves gunk on the back. If that is the only way, someone please tell me how to release it, and clean it, and what to use for a spoiler board.

Those are the only ways I know - if there is a better way, I would love to hear it!

How do you guys do it?

Thanks in advance,

[ImanCarrot]

weaken the tape by soaking it in meths.

Or you could try simple wax- het it on and heat it off?

[Shotout]

We use a 3M tape spec'ed out by the 3M adhesives rep rather than carpet tape, but MEK (methyl ethyl ketone) available through paint stores in bulk is a great solvent for adhesives. Read the safety information on this product. You'll have to ease your material up with multiple applications but we routinely make shims that taper from .032 to .006 (+/- .002) using this when they are to small for vacuum fixtures to hold well.

Originally Posted by revwarguy Hello, I mostly hang out over on the DIY CNC forum, where I built a router table. I am very happy with the table I built, and have made many things out of wood and plastic. Now, I need to cut some sheet aluminum, from .032 to .125 kind of stuff. It will all be profile type operations, which necessitates the need for a spoiler board underneath. The work is some large (up to 24x36) instrument panel type cut-outs, so there are a lot pieces removed, which I believe rules out a vacuum system. I have advice on a variety of cutters to use with my router and the speeds and feeds that other have found successful cutting aluminum of this kind. I have tried double stick carpet tape, but it is very hard to get it up without putting a bend in the sheet. In fact, it is more likely to get bent than not, and it also leaves gunk on the back. If that is the only way, someone please tell me how to release it, and clean it, and what to use for a spoiler board. Those are the only ways I know - if there is a better way, I would love to hear it! How do you guys do it? Thanks in advance,

[GeorgeRace]

I build aircraft parts out of .016 up through .125 aluminum.
The largest item that I build is 18 X 15 inches. I hold down everything that I cut with INCRA Clamps. Here is a link: http://www.incra.com/product_buildit_clamp.htm I do have a "T" slotted machine table. You can see the kind of stuff that I do at: http://www.mrrace.com/Products/

For cutters I mainly use 3/32 solid carbide 2 flute end cutter bits. I always use a spiral lead in and everything thicker than .032 I use multiple cuts of no more than .015 per pass. I use a cutting rate of no more then 15 IPM and a plunge rate of no more than 5 IPM. If working with .125 I usually do a "Climb Cut" for the finish pass. I am using a Bosch router and I usually run between 1500 and 2500 RPM, adjusted so it "sounds" good when cutting.

Hope this helps,
George

[Algirdas]

sheet work machines have special grips for sheet holding as usual. These work as pliers clamped the sheet edge.

[metalworkz]

Hello revwarguy,
As Algirdas has described the normal sheetmetal working method for both punching and laser cutting is a hydraulic or pneumatic set of clamps that will clamp onto the edge of the metal blank and the sheet can either be moved to the various X and Y positions with these clamps or in a gantry type Laser machine the table normally is stationary and the gantry performs all the X and Y movements. I have yet to see this type of sheet metal clamping employed on DIY routers etc., but you may be able to do something similar by merely clamping the perimeter of the material blank and using tabs extensively to hold the parts into the blank. Punched and lasered 2d parts are normally tabbed or wire jointed to the material blank and then shaken or broken out after the number of sheets has been punched/lasered. Perhaps the blank can have an addition mounting point near the center if a spoilboard is used and this will help avoid lifting of the material towards the center if needed. If you saw how a precision sheetmetal blank is punched it would be obvious that the material does not need to be held down flat as long as it is flat as it is being punched. A turret punch employs a stripper on each punch that will hold the material down flat as the punch begins to pierce the metal and if it moves around some it makes no difference as long as the parts remain tabbed into the sheet.
I normally clamp my aluminum blanks around the edges on both my DIY CNC router and my SX3 mill and this has always worked fine for me. The thinner gauge metal may require some additional clamping, but as long as the part stays tabbed into the material even if it lifts some it should not affect the 2d cutting if your safe Z is set high enough to clear any lifting.
I know a lot of this is completely different than what you are trying to do but offered it as a way to see alternative principles for holding sheetmetal parts as opposed to rigid clamping, vacuum and tapping the material down. The edge clamping method is an industry standard for sheetmetal turret punches and laser machines and many people might be shocked to watch a sheet of metal being punched at 1000 hits per second and the material being slid back and forth over the machine table, but this is something I do for an occupation and it is the norm for this type of high production punching and rapid prototyping of sheetmetal. If and how one can apply it to a DIY CNC router for sheetmetal work I have yet to see.

[Boltz]

You'll probably want to make a special spoilboard.

If there are bolt holes in the part, you can just program those first, and then put hold down screws into the spoilboard. This could be as simple as drywall screws into the MDF, or as elaborate as a special aluminum or plastic fixture with threaded holes.

If production needs were higher, you could build a special vacuum fixture with channels for gaskets cut inside the perimeter, and around all the holes and cutouts. This can work with a very small vacuum pump.

-Jim Hart

[Signmaker]

+1 for the screws.

Cheap, easy, fast and guaranteed to work... what's not to like

[malcf]

How about sandwiching it between two boards of 6mm mdf and cutting through into the lower board holding it all in place with clamps or screws?.

[revwarguy]

Thanks for the ideas and help guys. I will try some special clamping fixtures.

[revwarguy]

Hey George, thanks! I knew a fellow Tech Counselor would help! I got a lot from looking at your website pictures.