# Cutting a large circle in melamine, with a jigsaw. Any other tricks to minimize chipping?



## derrick3636 (Apr 14, 2015)

Hello,

I'm not sure if this is the correct forum, but I'll try anyways.

I'm building a fire pit picnic table for my family. The base is just about complete:


















All in yellow cedar.

I'm doing the round tabletop out of concrete. I'm planning the form right now. I've located a 5×10 sheet of melamine. The top is going to be 55" in diameter, so I need something larger than the standard 4×8 sheet.

When I actually go to make the cut, is there anything else I can do to minimize chipping in the melamine? I plan on using painters tape and a 10-12 tpi jigsaw blade. I know I can sand out imperfections in the concrete. I'm just trying to do as little of that as possible.

Any help would be great!


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## bondogaposis (Dec 18, 2011)

Use a router instead of a jigsaw.


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## AndyJ1s (Jan 26, 2019)

Or use a jigsaw to saw a slightly larger circle, and then the router, on a circle cutter jig, to clean it up.


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## torus (Apr 8, 2017)

Try oscillating saw


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## derrick3636 (Apr 14, 2015)

I don't use my router much(still learning). I may try that.

Is it because of the direction of the router bit that it doesn't chip?

I'm also seeing that tape doesn't help as much as I thought. I did see that the underside of the piece looks a lot better with the correct blade on a jigsaw.

Now I've got options.


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## bondogaposis (Dec 18, 2011)

Is it because of the direction of the router bit that it doesn't chip?

Yes, A jig saw is pulling the chips upward where there is no support. A router on a tammel will get you a perfect circle without chips. There are many videos on you tube on how to make and use a router trammel. Very easy and a good skill to have.


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## squazo (Nov 23, 2013)

the side that the teeth enter the material will always be cleaner than the side they exit, this is true of all saws, think entry wound vs exit wound if your a hunter. You can get up cut and down cut blades for a jig saw. However you will get a much more accurate circle if you use a router. Personally I would rough cut with my jig saw and then make a very simple trammel.

What are you planning to use to make the edge of your mold? Also you can get some free plasticizer if you go to fritzpak.com and request a free sample. You were planning on using plasticiser weren't you?


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## derrick3636 (Apr 14, 2015)

> the side that the teeth enter the material will always be cleaner than the side they exit, this is true of all saws, think entry wound vs exit wound if your a hunter. You can get up cut and down cut blades for a jig saw. However you will get a much more accurate circle if you use a router. Personally I would rough cut with my jig saw and then make a very simple trammel.
> 
> What are you planning to use to make the edge of your mold? Also you can get some free plasticizer if you go to fritzpak.com and request a free sample. You were planning on using plasticiser weren t you?
> 
> - squazo


Well, I've gone back and forth a few times with the mold. That might be a game time decision. I was considering cutting the circle and attaching some kind of edging to it. Lowe's has some thick/smooth lawn edging. It's 4 inches tall, so I'd have to stack other pieces of plywood or something along this lines to fill the inner dimension to achieve a 1.5-2 inch desired thickness. As long as the melamine was the top layer, I'd still be able to get a smooth(ish) finish.

I've also considered using pvc trim pieces to wrap around the circle, but I cant find anything longer than 12'. I would just kerf cut that enough to where it would bend all the way around. 12' isn't going to do it though. I'd need 2 pieces, and at that point I'm at the same price as the lawn edging, which comes in a 29' roll. I've also seen 
Rolls of metal flashing used successfully, but that seems flimsy to me.

I do plan on using a plasticiser. I've been filling a couple channels on YouTube where they've been using Rapid Set Mortar mix from Home Depot to do countertops and tabletops. They both utilize plasticiser, so I'm just going to follow the directions that have already been laid out.


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## Unknowncraftsman (Jun 23, 2013)

How did you like working with Alaskan yellow cedar? 
Its one of my favorite woods.

Cool project Good Luck


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## rcs47 (Oct 31, 2009)

Cut from the bottom. That's the way we used to cut sink holes in formica tops without chipping using a jigsaw. The blade is pulling into the finished surface, not out.

Good luck.


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## derrick3636 (Apr 14, 2015)

> How did you like working with Alaskan yellow cedar?
> Its one of my favorite woods.
> 
> Cool project Good Luck
> ...


I love it! I have a mill close to me that has it at great prices. I built our pergola out of it as well. I plan on using it for some planters for my wife, but that is down the road a bit. Everything is in bloom right now, and she won't let me touch them. I'm zeroing in on the patio chairs that I want to build. I think I might frame them out in yellow, but then trim them in aromatic cedar. I've never seen any in person, but pics online lead me to believe it would be a great way to break up all the yellow. I'd like to do that and a lazy Susan in aromatic to cover the fire pit when not in use.



> Cut from the bottom. That s the way we used to cut sink holes in formica tops without chipping using a jigsaw. The blade is pulling into the finished surface, not out.
> 
> Good luck.
> 
> - rcs47


This is what I'm seeing. I need to go grab the piece of melamine and just give it a shot.


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## bigblockyeti (Sep 9, 2013)

I use a Bosch T101AO jigsaw blade for such materials, it cuts at a decent speed but leaves a very smooth cut surface with little to zero chipout on the top and bottom of the workpiece. Even when they start to dull, the cut quality is still excellent but the feed speed has to be adjusted.


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## derrick3636 (Apr 14, 2015)

> I use a Bosch T101AO jigsaw blade for such materials, it cuts at a decent speed but leaves a very smooth cut surface with little to zero chipout on the top and bottom of the workpiece. Even when they start to dull, the cut quality is still excellent but the feed speed has to be adjusted.
> 
> - bigblockyeti


I saw that one. I'm glad you commented on it. I saw that it had a high TPI count. That's what intrigued me the most.

Thanks for the tip!


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## John Smith_inFL (Dec 15, 2017)

I agree with the router:
for something that needs a true edge, a simple Circle Jig base plate
attached to the router will give you the most satisfactory results. 
first cut should be about 1/8" deep just to get through the melamine. (or any laminate).
then small increments deeper as you go. PRACTICE on similar material first.
hope you will start a new project thread when you start with the form and cement.


















just about any rigid material can be used for a jig base plate: I prefer PVC or Plexiglass.
drill the holes in the tail "as you need them". I am from the camp that drilling a hundred
holes that will never be used is strictly for looks. most will never be used.

.


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## Lazyman (Aug 8, 2014)

+1 on using a router with a trammel to cut the circle. The trammel doesn't have to be anything fancy. Attach the router to a strip of plywood with a hole cutout for the router bit and another hole for the a nail at the right radius. I would probably cut from the bottom with an upcut router bit.

Benda Board or some other flexible landscape edging would probably work for the edge form. The only problem with that is that you will get a sharp square corner which is not comfortable for a table top so you might want to put a bead of calk, wood putty, bondo or something around the inside corner of the form to give you a rounded edge profile. You can cut a profile on a piece of wood to the desired rounded shape to smooth what ever putty you use to get a consistent profile.


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## John Smith_inFL (Dec 15, 2017)

Nathan - I did not think about the hard square outer edge after the
top was poured (and put into use).

I would go to the Box Stores and look at the PVC Foam inside corner moldings.
they could be "modified" by removing the sharp corner with a sanding block
and sandpaper and easily glued & tacked in place. (just a thought).









I have always wanted to have an "insert" in my picnic table so that I could have 
hot coals in the middle of the table with a long KaBob rack so all the guests could
tend to their own KaBob sticks while "socializing".

.


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## theart (Nov 18, 2016)

> I'm doing the round tabletop out of concrete. I'm planning the form right now. I've located a 5×10 sheet of melamine. The top is going to be 55" in diameter, so I need something larger than the standard 4×8 sheet.
> 
> When I actually go to make the cut, is there anything else I can do to minimize chipping in the melamine? I plan on using painters tape and a 10-12 tpi jigsaw blade. I know I can sand out imperfections in the concrete. I'm just trying to do as little of that as possible.


I wouldn't even bother using melamine. Piece together whatever scraps of plywood (or even OSB) you have lying around for the bottom of the form. Two layers of luan ply wrapped around with staggered joints for the sides. Drywall joint compound to fill the seams and smooth out the surface. One or two coats of polyurethane, then wipe down with motor oil.

The only important considerations are:
1) Use a trammel, either with your jig saw or with a router, to get a perfect circle.
2) At least two layers of welded wire mesh for reinforcement, and figure out how you're going to get them to stay put before you start mixing up the concrete.
3) Use a random orbital sander (with no sandpaper) to buzz around the outside of the form as you're pouring to get the air bubbles out.


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## derrick3636 (Apr 14, 2015)

> I wouldn t even bother using melamine. Piece together whatever scraps of plywood (or even OSB) you have lying around for the bottom of the form. Two layers of luan ply wrapped around with staggered joints for the sides. Drywall joint compound to fill the seams and smooth out the surface. One or two coats of polyurethane, then wipe down with motor oil.
> 
> The only important considerations are:
> 1) Use a trammel, either with your jig saw or with a router, to get a perfect circle.
> ...


Yep. A trammel will get utilized regardless. I tried to freehand a circle a few years ago and learned my lesson.

Two layers of remesh? Can you elaborate if you have time? Everything I've seen, they just cut one sheet to size and call it a day. I've never thought twice about it. I want to have all these things ironed out beforehand.

The last example I watched, the person laid some simple framing to suspend the remesh in the concrete. That was the first time I'd seen something like that. Most examples, the just laid the mesh or rebar in and said something to the effect of "time it correctly, as to not have sink all the way to the other side". I like the simple frame solution.

Your alternative to melamine interests me. I planned piecing together the sheets below the melamine, because those don't contact the concrete, and don't need to be pretty. 
My thought for the melamine was that it would leave the smoothest surface for the top. If I go piecing things together, even if I use drywall compound, won't the seams still show up? I'm all for keeping it simple. I just don't want to get into a situation where saving a couple bucks(actually your description saves way more than a couple)only to make more work on the backend. Does that make sense?

Thank you for your response!


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## BurlyBob (Mar 13, 2012)

The only option besides the router would be a circle cutting jig on a bandsaw.


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## derrick3636 (Apr 14, 2015)

> The only option besides the router would be a circle cutting jig on a bandsaw.
> 
> - BurlyBob


I was think about something like that when I do the lazy Susan. I've seen different videos on those.


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## squazo (Nov 23, 2013)

I would use fiberglass or basalt rebar, it will never rust and is stronger than steel.


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## therealSteveN (Oct 29, 2016)

Wood magazine just had this in a recent issue, Saw it on the newsstand, and thought hmmmmmm.

https://www.woodmagazine.com/woodworking-how-to/wood-preparation/cutting-curves/how-do-i-make-a-perfect-circle-with-a-jigsaw

I'm with the router crew though, as I'm already set for that.


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## Lazyman (Aug 8, 2014)

I almost mentioned that you can get a better circle using a trammel with the jig saw than sawing by hand but the edge still won't be a nice as when using a router.


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## theart (Nov 18, 2016)

> Two layers of remesh? Can you elaborate if you have time? Everything I've seen, they just cut one sheet to size and call it a day. I've never thought twice about it. I want to have all these things ironed out beforehand.
> 
> The last example I watched, the person laid some simple framing to suspend the remesh in the concrete. That was the first time I'd seen something like that. Most examples, the just laid the mesh or rebar in and said something to the effect of "time it correctly, as to not have sink all the way to the other side". I like the simple frame solution.
> 
> ...


The purpose of the reinforcement is to add tensile strength. A table top like this gets loaded in bending, placing one side in tension and the other in compression. Mid-height is neutral. So a single layer of reinforcement in the middle of the slab will do nothing for bending strength. A single layer offset from the center will increase bending strength, but only in one direction. Two layers, each about a half inch in from the faces, will give you strength in both directions.

It might take a couple of coats, but you should have no trouble getting a perfectly smooth surface with joint compound. That is, after all, what it's made for.


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## derrick3636 (Apr 14, 2015)

> The purpose of the reinforcement is to add tensile strength. A table top like this gets loaded in bending, placing one side in tension and the other in compression. Mid-height is neutral. So a single layer of reinforcement in the middle of the slab will do nothing for bending strength. A single layer offset from the center will increase bending strength, but only in one direction. Two layers, each about a half inch in from the faces, will give you strength in both directions.
> 
> It might take a couple of coats, but you should have no trouble getting a perfectly smooth surface with joint compound. That is, after all, what it s made for.
> 
> - theart


That all makes sense. Thank you very much!


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