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Milling slots in gelcoated solid panel


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6 hours ago, Sailabout said:

Has anyone milled slots in a gelcoated laminated panel 6mm thick, its for ventilation.
Any tips with what bits are happy in a router or use milling machine?
Thanks

I'd try a spiral bit, 1/4 inch. They make them either up-cut or down, can help with chipping the gelcoat.

 Practice on some scrap.

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It's been stated implicitly but I'll state it explicitly just in case: you want the cutter to pull the gelcoat into the glass. If you use a cutter that pulls the gelcoat away from the glass, it'll do exactly that. If you're cutting from the gelcoat side, use a down cutter. If you're cutting from the glass side, use an up cutter.

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On 12/19/2021 at 2:08 AM, Sailabout said:

Has anyone milled slots in a gelcoated laminated panel 6mm thick, its for ventilation.
Any tips with what bits are happy in a router or use milling machine?
Thanks

How big is the piece, how much access do you have, how much ventilation do you need?

I'd just buy a metal cutting circular saw blade(5" to 7-1/4"), they have a triple chip grind with a negative rake usually, so are much less grabby that the woodworkers ATB style in composite and leave a nice clean line.  Plunge cut from the back so the tooth is cutting into the gelcoat and then supported by the glass.  Clean up with a needle file or saw blade to give the ends of the cuts a little more support.

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1 hour ago, Startracker said:

How big is the piece, how much access do you have, how much ventilation do you need?

I'd just buy a metal cutting circular saw blade(5" to 7-1/4"), they have a triple chip grind with a negative rake usually, so are much less grabby that the woodworkers ATB style in composite and leave a nice clean line.  Plunge cut from the back so the tooth is cutting into the gelcoat and then supported by the glass.  Clean up with a needle file or saw blade to give the ends of the cuts a little more support.

about 600 x 600 and trying to put as many slots as possible but will experiment to see how it looks and how strong it ends up with what size slot and spacing.

If I used a saw I would use a diamond wheel.

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On 12/19/2021 at 11:23 AM, wick said:

If routing/milling with the finished face up, use a down spiral bit. If only a straight bit is available, apply masking tape firmly along the tool path and cut through that. 

Sounds good

also remember the the high speed router bit will instantly overheat and be destroyed….move slowly  and only remove a little with each pass to preserve the router bit 

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I once used a router to cut a large hole in a fiberglass panel about the same thickness. I used a template and a carbide tip bit. It worked, but the bit barely made it to the end. I've since used solid carbide burrs. The burrs are slower, but seem to hold up better. 

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@SailaboutI've found much faster, cleaner and better cuts with a proper toothed blade vs a grit or diamond like masonry or steel cutting disk especially on larger cuts or for ventilation slots, cutting from the back and controlling your depth you can even create the look of a round vent with a slotted seamless cover.  For stainless I do like the new diamond and metal Zip disk equivalents.  They're handy in awkward spots when doing fibreglass repairs too, as a kickback won't be as severe or as dangerous, slow and not as nice a cut in my experience as a proper blade.   

I have a full kerf version of the blade below but chrome plated, looks like they don't make them anymore which is a pity, I liked the chrome much better than paint and the wider blade as long as I could get enough horsepower to the saw.

the tooth pattern is the important part:

"A Triple Chip Grind (TCG) has a trapezoidal tip that cuts a groove with slanting sides.  This is followed up by a square top tip that makes the side of the groove square.  The first tooth, or lead tooth, has a double 45 degree angle corner bevel. This is followed by a flat topped raker tooth ground lower than the lead tooth. The raker tooth removes the corners left on both sides by the beveled lead tooth. Triple Chip Grinds combines a balanced cutting force, low tooth drag and free chip flow. This helps to eliminate chipping in brittle material such as chip board, and laminates.  This divides the chips to achieve smooth cuts in hard materials such as MDF, OSB, and plastics. This tooth design is also used on blades for cutting non-ferrous material.  Use TCG grind when cutting plastics, aluminum, and non ferrous metals.""

https://www.diablotools.com/products/D0748CFA

7-1/4" is specced for Plates & Bars (Thickness 1/8" (11 gauge) min 1/2" max) in steel.  

  • Cermet II (Ceramic and Metallic) teeth deliver a more efficient and productive metal cutting solution through high heat tolerance and increased hardness for superior wear, fewer blade changes and up to 25X longer life versus standard grinding discs
  • Up to 50X cooler cuts with a circular saw blade when compared to a grinding disc that increases temperature of steel by up to 500 degrees. Grinding discs increase the temperature enough to permanently discolor the steel.
  • Up to 10X faster cuts with a circular saw blade for maximum productivity and efficiency, resulting in up to 60 seconds faster cuts in both metals and stainless steels versus standard grinding discs
  • Triple Chip Cutting action reduces sparks and the possibility of needing “hot” permits
  • Optimized blade design reduces wandering and deflection of metal, creating precise cuts that require virtually no re-work

 

 

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20 hours ago, Sailabout said:

about 600 x 600 and trying to put as many slots as possible but will experiment to see how it looks and how strong it ends up with what size slot and spacing.

If I used a saw I would use a diamond wheel.

go with the diamond wheel

they cut really fast and leave a sharp edge

use a jig if it's a dress required finish, not so important if it's hidden or will be covered ( not stated in brief )

a brickwork pattern will be better than a tile pattern

 

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If this was built-in stuff with only one shot at not chipping out, or if I was doing a bunch of these I'd use a straight fluted tungsten bit.  Not cheap, but they cut composites like butter.  The sharpening place I used to use stocked/made them.  You might have one in your location. 

If you do go the router route, make your initial plunge as you move the router along your guide/template.  Going straight down might cause a wobble - especially with a longer, skinny bit.

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53 minutes ago, Leeroy Jenkins said:

If this was built-in stuff with only one shot at not chipping out, or if I was doing a bunch of these I'd use a straight fluted tungsten bit.  Not cheap, but they cut composites like butter.  The sharpening place I used to use stocked/made them.  You might have one in your location. 

If you do go the router route, make your initial plunge as you move the router along your guide/template.  Going straight down might cause a wobble - especially with a longer, skinny bit.

That will work.  If you're hell bent on router over saw, a double flute carbide tipped 1/2" inch shank bit will do the trick relatively cheaply, I wouldn't go straight carbide unless you are doing enough volume to justify the expense.   1/4" shanks just suck in glass.

https://www.dimarcanada.com/products/industrial-bits/straight-bits/with-plunge/1-16-dia-bottom-carbide-straight-bit-for-plunging-2-flute-1-4-shank-2-length-1

30$.  

 

These actually look quite interesting, a drill bit point that then doubles as a guide.  Neat piece of kit for not a bad price(50$).  According to the manufacturer they are often used in boats, I can see why but I haven't tried one yet.  

https://www.dimarcanada.com/products/industrial-bits/panel-pilot-with-drilling-point/115r8-12-sf

Although if you're cutting from the back side with a jig, the half inch triple flute spiral in solid carbide up cut will finish cleaner, often without much chipping of the gelcoat on the front side.  Set a shallow depth and make multiple passes increasing depth by 1/8" each pass, free handing the plunge depth with an up-cutting bit is asking for problems.  The 3 flute style always seemed less grabby to me but that might just be mental, in any case it's not noticeable enough for me to bother switching from 2-3 flutes in practice if the other bit is already in my router.

https://www.dimarcanada.com/products/solid-carbide-tools/3-flute-spiral-bits/3-flute-spiral-upcut/1-2-dia-solid-carbide-spiral-router-bit-upcut-3-flutes-1-2-shank-3-1-2-length

Downside is cost of course, so if it isn't something you're going to do often, I wouldn't spend that kind of money on it.  

I've tried all of the discussed methods, they all have pluses and minuses.  With the least pluses going to abrasive cutting wheels including diamond, it's a tool of last resort, and only when safety or access limits me to it.   For what you're doing, the steel triple chip blade in a circular saw still gets my vote.   I would estimate I got around 200 linear feet of cut between sharpening, I had it freshly sharpened before cutting out the deck on a 30' boat to replace core, and by the time it was finished I sent it in again, though mine was carbide not Cermet like the one I linked above, which is supposed to be much longer lasting, but after a decade of use, I see no need to upgrade yet.  

 

As a mostly unrelated side note, https://www.suncoasttools.com/crm/ItemPage.aspx?ItemNumber=410.50021885600235TM&VendorNumber=TOOMEX

are about the best damn things I've ever bought for dealing with fasteners in glass.  Once you try one you'll never go back to those horrid multi-toothed countersinks with a drill bit in the middle, and for rebedding deck hardware they create the perfect countersink for sealant under the hardware.  

 

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  • 2 weeks later...
On 12/23/2021 at 1:18 AM, Grande Mastere Dreade said:

how thick a slot?    how about an oscillating tool?

I need to do 8 600x600mm panels and they need to be the same as they are beside each other

Not sure about the slot width, want max vent but it has to stay rigid so a few tests need to be done.

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16 hours ago, Sailabout said:

How about water jet cut?

Anybody with any experience on fibreglass?

Actually I used to work in a water jet shop.  Cut piece finished side up, if there's any blowout, which was common when I was in it, it'll happen on the back side.  We cut everything from fiberglass to laminated tempered glass with the middle sheet being shattered after being laminated for artsy fartsy installations to structural steel parts for machine shops to a fuck ton of granite countertops.  

Also be aware, many shops including the one I worked for do not warranty your materials in use.  E.G they supply material after cutting = you pay the price for it one time no matter what.  

You supply the material and they blow it up = you eat the material cost and supply them another piece, and the labour to that point too if they can get away with it.  This happened fairly often where I was because the owner was too cheap to let me buy the needed parts for the machine.  Common failures were jet not shutting off when the machine goes home resulting in a ruined face, the carbide pickup tube below the ruby wearing so the jet lost focus resulting in blowouts and surface damage to the finished face.  The ruby with a hole in it that focused the water blowing out, same result.   You can imagine the screams when a 5-10k$ granite slab was scrapped at the clients cost when a 30$ relay would have prevented it.  I quit after that one.

 

Just the right pressure and media flow rate makes a huge difference in FG.  Too high = lots of wasted material.  Oddly to most people, too low would lead to more backside blowout, higher pressure I guess kept the stream more cohesive.  Back then we would take a test coupon of the same material and try different settings until we got a good one, supplying the shop with a small coupon and get them to test a cut length of 2" and give you a price per inch, then just add up the length of the paths you want.  Might be automatic and computerized these days in terms of pressure/abrasive flow for material.   From memory we reduced abrasive flow a lot VS granite, and as the abrasive use is one of the main cost drivers, it cost less.   

All that being said, I'm not sure why you're so against just cutting the stuff with a circular saw..  I spent 8 months arguing with my boss that he should buy a gantry saw for the straight cuts, before I gave up.  4 years later I heard he bought one, and was finally cost competitive with the guys who only had saws no water jet.     If you want to make cool patterns Waterjetting is slick as hell though.  

 

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  • 2 months later...

We all love updates..

Had a water jet cut, awesome cuts are perfect, very fast done while I waited.
If you can take the part out of your boat its the way to go.
Panel was gelcoat laminated with vinylester and bagged, cut like a hot knife in butter and very smooth finish

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14 hours ago, Kenny Dumas said:

Cool. I’m late to this thread but would suggest an array of holes (hole saw) on a hex pattern would yield best ventilation for stiffness ratio. Still true for water jet. 

Its forced ventilation, i guessed slots is best for that in a circle pattern matching the fan?
I made it about 5mm thick ( way heavy) so strong enough to experiment

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Hard to say. I did a study long ago that showed that fewer fins worked better on a heat sink because the air flow was stalling, which was counter intuitive. And I got lucky rescuing a horrible desktop supercomputer design by using the washout on muffin fans   The radial outflow worked really well even with a solid wall an inch directly in front of a 3” muffin fan. I think a series of slots with increasing area aligned in a spiral pattern coincident with the fan direction would be a good bet. The slots should continue well outside the fan diameter to maximize outflow efficiency. 

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