Gator foam clean edge cuts question

[jhicks]

We have done our share of gator foam with and without metal finishes but never are quite thrilled with the foam edge cuts. it seems there is always some material dragging and the edge has its own version of chatter. More like chunks being removed or being ripped from the low density foam rather than clean cuts.
We are now looking into painting the edges of a metal brushed chrome finish foam and have seen some competitive letters with very clean cut edges then probably painted with acrylic latex. They look very sharp with color contrast against the brushed metalic face.
My question is; Does anyone have a method, speed, feed, bit, or technique to get a smooth edge consistently?
Ours are OK but not as clean as what I've seen from others and we would like to overcome any questionable edge finish.
We've seen the best results with Super O cutters but with 2" thick stock the 1/4" diameter leaves large radius inside corners so just looking for tighter crisper inside corners and smoother edges with and without metal veneers.
Any input is appreciated.
Thanks

[Brady Watson]

Yes...Onsrud makes a 3-flute spiral-O. This works well...but suprisingly, a GOOD coated 4-flute end mill works well, also. Run between 15,000-19,000 from 4 IPS on up...the sky is the limit depending on the shape of your design. Try it with a 4-flute end mill and see how you do. Good vacuum is a must - I recommend the BradyVac II since I cut 225 sheets of Gator with that system using a single Fein & ran up to 8 IPS with perfect edge quality. You'll need to clean the bit with MEK every 5 sheets or so (and no it won't take off bit coating) because you will get some gator/clay build-up at the top & bottom of the bit. A few wipes & you're back in biz.

The problem that most people have when cutting any type of foam (even the pink) is that they don't run enough flutes and enough RPM. This is key to clean foam cutting.

-B

[jhicks]

Thanks Brady, I have a 4 flute end mill I'll try and see how things compare to my O flute.
As always, I appreciate the tips and experience

[paco]

Does that look good?


4793

This was cut with a 1/4" CED, 2" CEL, 2 flutes spiral up, solid carbide (Onsrud foam bit) at 1.5"/sec. and 17000 RPM. Vacuum hold down. More detailed pictures at my Picasa web album (http://picasaweb.google.com/the.real.paco/GatorFoamCut). Most pictures we're taken from 4-5" (macro).

Even though I can sometime be happy (or not), I often wonder how other perform.

[jhicks]

Thanks paco...Looking good. I have the Onsrud foamcutter O flute but will try 2 flute as well and crank up RPMs but run at same 90IPM.
Know of any smnaller diameter with long CEL
Single pass I assume?
I have a nice 3/16" 1" but would love an 1/8" with 2"+ CEL for foam letters for tight inside corners.

[jhicks]

Correction have nice 3/32" not 3/16"

[Brady Watson]

Jerry,
Did you try a sharp 4-flute end mill yet?

-B

[paco]

1/8"CED X 2"CEL; that doesn't make sense!? Longest 1/8"CED I have found is 1-1/8"CEL. Drill bit?

When I use the 1/8"CED in up to 1" thick foams, I now use 4 flutes 1"CEL coated end mill.

Yes, always single pass in styrene (insulation) foam.

[jhicks]

Been away a while. No Brady, not yet. Busy doing things that must be done but I will try soon.
Paco, what doesnt make sense? To cut 2" thick foam, one needs at least 2" cutting depth. The smaller the better for sharpest inside corners.
Did I say something incorrectly?
More to learn so thanks for the feedback and i'll try that 4 flute to see how it improves.

[wcsg]

You know what Jerry, Just go conventional instead of climb and you will get a finish just like Paco. I use a Belin single flute upcut spiral and the difference between climb and conventional is night & Day.

[jhicks]

Thanks Eric, I'll be reviewing and trying these suggestions. Still interested in longest smallest diameter bit I can find for foam so anyone who has a secret source, please let me know.
I may just have to try my long 3D 1/8" tapered ball nose to see what happens with it.
Paco, I was trying to say where can I find one? not that I had one.
For 2" stock the smallest I have found is 1/4" CED super O flute but its not as clean as your cuts and would love to have 2" or more CEL with smaller diameter.

[wcsg]

Belin makes a 1/4" CED 2-1/4" CEL Tool# 1365B

And 3/8" @ 3-3/16" CEL Tool# 13952A

Usually anything thicker I'll cut x2 and bond them together

[paco]

Jerry,

I knew you were trying to trick me!

[jhicks]

Thanks Eric, are you saying you would cut laminated metalic gator in 1" then glue them together with a metalic inner or use one layer metallic, one non metallic?
Guess some things aren't meant to be easy but it sure would be nice to find an 1/8" 2"+ bit wouldn't it?
Paco, wouldn't you like sharper corners than .125 R in thick letters? Foam should not be a problem with breakage but I guess the bit makers aren't thinking of foam as much as harder materials and chip loads.

[tgm]

I'll chime in here with a recent episode we have had.
We are cutting 2 1/4" high leteers out of 'Ultra Aluminum', which is .030 aluminum faced, expanded foam core and a rigid styrene back, all told 1/2" thick. This has been the most difficult material we have ever tried to cut in the last 5 years.

You have to have a good edge on the aluminum face when finished, you can't pack the aluminum chips into the foam core and you need a good finish on the foam core to paint.
We checked with the manufacturer and they recommended a 2 flute Onsrud upcut bit which just tears everything right up. Obviously they have never had any experience cutting their own material.
We have finally ended up using a low helix 3 flute to cut the aluminum only on the first pass and then we take a full depth cut thru everything else at the same time taking a clean pass on the aluminum edge to remove any burrs.
I am still not happy with the overall cut quality of the foam core. I have tried inquiring on some sign forums, figuring this is sign material and they would have the edge. No such luck. Guys tell me they cut this material all day in one pass with good results. I don't know what 'magic bullet' they have but I have yet to see a good letter that small done in one pass, aluminum and all.

If anyone does have or know of that 'magic bullet', please feel free to post it, as i am sure I am not the only one with this problem.

Thanks guys,

Tom in PA

[paco]

If you intend to cut foam core aluminum faced with a spiral up bit, spin it as fast as you can. This is just theory but I can't imagine cutting this stuff at low RPM. Speaking of high RPM with long thin bit, use solid carbide only as HSS will wobble just when you'll reach 12000-14000 RPM.

If I had to do this and the 2 flutes spiral up bit wouldn't work, I will try to cut the top AL layer with a straight edge O-flue then the foam core and the bottom AL layer (if there's any) with the spiral up bit. It may need a small (tiny - 0.005-0.010") allowance to not rub the cutting through spiral bit on the nicely cut top layer.

I'm not very surprised at your results. Thin unsupported AL need to be cut with straight edge bit (preferably O-flute). AL is better cut in climb fashion too. Foam (expanded styrene) need a fast RPM for a clean edge in a deep narrow kerf.

Hope some of that make sense. Whenever I'm ask to cut laminate stuff that I'm not familiar with I ask if the layers are holding together very strongly; I doubt the AL on foam is...

[Brady Watson]

TG,
Cut thru the AL face 1st, sucking up all AL chips as you go. Then come back, full depth and cut out the rest. I've cut a ton of this stuff. You can't do full depth passes and expect not to tear up the foam edges when you have an AL skin on it. The chips will completely tear up the edges.

1 pass @ .045" deep & clean all AL chips
1 pass @ full depth

Use a single spiral-O for the AL. You can use the same bit to cut the Gator, just realize that speeds are limited to about 1.5 IPS. The foam needs multiple flutes and high RPM to cut cleanly.

Good vacuum hold down is a must.

-B

[tgm]

Brady,

We are using two passes as I stated, with head 1 cutting the aluminum with a 3 flute. I'll try the next batch with an O flute in head 2 for the foam. It really gripes me that the manufacturer has no clue on such an expensive product.

Thnaks for the tips,

Tom in PA

[Brady Watson]

Tom,
I have found very few material producers and suprisingly, tooling companies that have any clue about real life feeds & speeds. So...I never listen to what they tell me because it is almost ALWAYS wrong! A little R&D with a keen eye will give you the best feedback and advice.

Since you have 2 heads - This would be the hot ticket:

1) Use single super or regular spiral-o for cutting the AL. Speeds will be under 2.5 IPS, with RPM in the 13,000 to 16,000 range.

2) Use a 3-flute Spiral-o or 4-flute end mill to cut the foam. You'll be getting nice clean cuts up to about 6 or 7 IPS if you have good hold down. They like about 18,000 RPM. Remember - foam is prone to tear out from the tool grabbing it and pulling out chunks...If you want clean cuts in any of the soft foams, use multiple flutes and high RPM. You will be hard pressed to melt it...unless you use a down-cutting tool, which I do NOT recommend. The 4-flute regular old endmill (got it with coating on it for $2 more) lasted about 100 sheets. You'll have to stop and clean the parts of the bit that contact the top and bottom skins of the Gator about every 5 sheets or so, as they all get buildup. Just take some MEK or acetone on a rag and pull down on the flutes to clean. Take care not to slice your finger open on the flutes like I did...a couple times...


-B

[tgm]

Brady,

Thanks for the tips. That is just about where we ended up on the last run. We tried to get the aluminum with even a cleaner edge by taking a final .010 on the final foam cut and it worked super on all but the smallest letters, the 2 1/4" ones.
On these letters the serif areas of the font are only .070 wide, so at this point you have this 1/2" wall of foam with only a .070 wide with a small chunk of aluminum floating on top that you are trying to cut the edge of. It's like putting it atop a bowl of Jell-o at that point.
I'll try exactly as you suggested for the next run and let you know how the small letters turn out.

Thanks again for the tips,

Tom in PA