Best way to scribe melamine without chipout?

[ryanjg117]

I'm soon to be installing some simple melamine shelves, two feet deep by about 8 feet long. I know the drywall isn't flat, so my plan is to cut the back perfectly straight, throw it up on the wall, and scribe with pencil along the back edge. Easy stuff.

But, knowing melamine is prone to chipout, what's the best way to make that undulating cut? I was thinking a compression spiral bit in a router, but visibility (following the line) is going to be tough. Belt sander would make a mess, and sadly it's the one sander style I don't own. Any other ideas?

 

[Packard]

I have not tried it on melamine but I think it will work.  I use my 4-1/2” angle grinder with a flap sanding wheel.  It makes fast work of stock removal.  I use it regularly to scribe crown molding.

The direction of the grinding is downward and it does not chip out the finish on pre-finished moldings.  I believe it will do the same on melamine. 

There are videos on line on how to do this with crown moldings.  It takes a few practice cuts to get the hang of it.  For me, it was just on how to hold the grinder. 

Wear glasses.  There is stuff in the air full time.  And a mask is not a bad idea either.  If you can, do this outdoors.  It does kick up a lot of dust.

This is the type of flap wheel you need:

 

[woodferret]

You don't explicitly mention blue tape for scribing (usually given), but worthwhile to mention it just in case . Knife cut is also useful for prefinish and likely here too.

Not sure why you'd go router first though.  You're back beveling, no?

 

[AstroKeith]

I'm soon to be installing some simple melamine shelves, two feet deep by about 8 feet long. I know the drywall isn't flat, so my plan is to cut the back perfectly straight, throw it up on the wall, and scribe with pencil along the back edge. Easy stuff.

But, knowing melamine is prone to chipout, what's the best way to make that undulating cut? I was thinking a compression spiral bit in a router, but visibility (following the line) is going to be tough. Belt sander would make a mess, and sadly it's the one sander style I don't own. Any other ideas?

If going the router method, perhaps get am 8ft length of 10mm thick plank. Scribe that and trim with a jigsaw or whatever. Then use the plant as a template, using a template profile cutter, or a following ring.

 

[Michael Kellough]

BOSCH T101BR jigsaw blades.

 

[Packard]

BOSCH T101BR jigsaw blades.

I assume these are the down cut blades.  I have one of those and they make very clean cuts on the top surface, but not so clean on the bottom. 

 

[Michael Kellough]

BOSCH T101BR jigsaw blades.

I assume these are the down cut blades.  I have one of those and they make very clean cuts on the top surface, but not so clean on the bottom.

Yes, I was assuming the op was only concerned about how the outside of the cabinet fits the wall. If I’m wrong the process will be a lot more elaborate, a scribed template and a pattern bit. And the unit will have to be unassembled to transfer the templates to all the parts.

 

[peter halle]

If you are using melamine from the big box stores you will have certainly have a harder time.  That stuff is notorious for its thin brittle coating.  Melamine from a cabinet material supplier is usually superior.

Jigsaw with down cutting blade as mentioned might be best choice.  If so, if possible experiment on a scrap to test how you saw reacts, speed setting, and oscillating setting if you have one.  I seem to recall that I didn't care for using the blades in my Carvex and that the best cut was with the oscillating off.

If your shelves were not to be adjustable, and the waviness was minor that you look at back beveling leaving a sharp point at the top and then doing the bump into the drywall.  That was a technique taught to me by a professional cabinet installer.

Peter

 

[Packard]

I would also mention, that once I got the hang of using the angle grinder with the flap disk, I had more control over the contour that I would have with a jig saw.

Unlike the jigsaw which requires that you commit to each change of direction, the angle grinder allows me to nudge gently towards the scribed line.  It allows me to do that while maintaining the undercut.

I’m certain that a skilled jigsaw user will get the job done faster, but I get better results by grinding away and slowly approaching the cut line.

 

[Lincoln]

Power plane, this is what they're made for. Finish off with a swipe with a 180grit sanding block. I use the EHL65, due to dust extraction, ergonomics and, most importantly, the spiral blade. A 'must have' tool for installation work, but one that doesn't seem to get much attention in the Festool world.

 

[xedos]

this will cut a scribe line that should help prevent chipout:
https://www.amazon.com/THINGAMEJIG-...t=&hvlocphy=9010956&hvtargid=pla-422560645138

 

[ryanjg117]

The Thingamajig looks great. I'm going to snap one up, along with a cheap Power Planer. The HL 850 would be amazing, but not in my budget right now (and this is a tool I probably won't be using very often).

I tried a few different techniques to cut the scribe line. The angle grinder with flap disk worked fast, but caused tearout on one end of the melamine. Jigsaw was the worst, even with the Bosch T101BR blades. But it was fast.

Even though it was a little more time consuming, I made a template out of a thinner scrap piece, scribed and cut it with the jigsaw. Since it was a scrap template tear-out really didn't matter. To transfer the scribe, I cut most of the material away with the track saw (where I could) and then used a Rockler pattern flush trim bit to transfer the edge to the finished piece.

(The real reason I went through all these hoops - this was a big shelf, 10x2 feet, 3/4" melamine. Too large for me to install myself, and I didn't want my friend to have to sit around while we install it multiple times to scribe both edges since it sits in a corner. But the template was light enough for me to install and remove multiple times.)

I discovered compression bits really aren't necessary for hand routing melamine. A straight cutting bit is fine, but spirals will cause chip-out.