Cutting down for flush trimming?

[Michael Kellough]

With as much difficulty as has been involved so far, I wouldn't double the thickness, before getting it square.

My reference to gluing one oversized piece was "well over", like an inch, then trimming that off with the track saw after it's dry.

I think you should go ahead and see what happens. Especially while you in the mindset of improving your technique.

CRG is saying you’re more likely to get bad results if the toe adjustment is off. He’s right, especially with 1-1/2” of mdf. But you’ll find out pretty quickly this way (cutting thick MDF). In the worst case the saw will bog down and become difficult to advance, but before that you’ll smell burning as the side of the blade starts rubbing the stock. Looking at the cut you find it becomes progressively off 90* (the bevel) and it will be curved.

 

[makpacman]

And another thought, try to make sure you have solid material on both sides of the tracksaw blade, especially with the battery operated saws, because the ultra thin blades can deflect if you try to barely trim up a piece. This also helps dust collection.

I always try and leave at least 1/4" of material to waste side of my track saw cuts for these reasons.

Very good. I figured, but wanted to iterate that point in case it could be of help in determining a reason diagonals/dimensions on the first top were off.

Clamps fore and aft also help rail squares do their best work. Anyway, I'm convinced your next few long cuts come out more to your liking due to how you're considering all these guys' input. Once you know what to look for before putting saw to track, things go remarkably smooth.

 

[Packard]

Following on from CRG, you don’t even need a router.

Just laminate the sheets and when the glue is dry cut it with the tracksaw.

Use geometry to make it a square rectangle this time.
Sure it’ll be a little smaller than the first time but you adding edge banding right?

That’s what I did on my table saw. I used Woodworkers 3 (glue) for the longer open time.  Four 18 gage pins to keep it from sliding about.  And evenly displaced weight lifting plates for “clamping” (about 200 pounds total). 

If I wanted to trim after laminating, I would use the absolute minimum overhang that I felt comfortable with.  If you don’t pin the corners before clamping, it is going to slide around on you and you won’t maintain alignment.

The less overhang you leave, the easier it is on your router, and far less dust too.

Note:  80 pound sand bags work fine too and are very cheap.  Keep away from sharp objects or you will be doing a lot of sweeping up.  You want to spread the load over a wide area.  You can use a 3’ x 3’ piece of plywood between the sand bags and the laminating sheets.  80 pounds for 9 square feet is plenty of pressure for glue-ups. 

If you have a place to store the sand bags, they will last until the bag rips.  When that happens, I add it to my garden. 

And bring a helper when you go to buy the sand.  Even loading just 4 bags, and unloading 4 bags will test your willingness to do this type of work ing the future.

 

[sawdust-samurai]

Very good. I figured, but wanted to iterate that point in case it could be of help in determining a reason diagonals/dimensions on the first top were off.

Clamps fore and aft also help rail squares do their best work. Anyway, I'm convinced your next few long cuts come out more to your liking due to how you're considering all these guys' input. Once you know what to look for before putting saw to track, things go remarkably smooth.

I do have a pair of rail clamps that I recently bought, but I'm not in the habit of using them... and did not on cutting the first top.  I'll have to change that going forward.  I also appreciate all the tips that everyone has been giving, even if I happen to be using them already. 

That’s what I did on my table saw. I used Woodworkers 3 (glue) for the longer open time.  Four 18 gage pins to keep it from sliding about.  And evenly displaced weight lifting plates for “clamping” (about 200 pounds total). 

If I wanted to trim after laminating, I would use the absolute minimum overhang that I felt comfortable with.  If you don’t pin the corners before clamping, it is going to slide around on you and you won’t maintain alignment.

The less overhang you leave, the easier it is on your router, and far less dust too.

Note:  80 pound sand bags work fine too and are very cheap.  Keep away from sharp objects or you will be doing a lot of sweeping up.  You want to spread the load over a wide area.  You can use a 3’ x 3’ piece of plywood between the sand bags and the laminating sheets.  80 pounds for 9 square feet is plenty of pressure for glue-ups. 

If you have a place to store the sand bags, they will last until the bag rips.  When that happens, I add it to my garden. 

And bring a helper when you go to buy the sand.  Even loading just 4 bags, and unloading 4 bags will test your willingness to do this type of work ing the future.

Pinning the corners is a good tip, I had not thought about that.  For the clamping, I was thinking about using actual clamps alone the edges and then using screws in the center.  I'd remove the screws after it dries and since they would be on the bottom side, no issues with the holes showing.

 

[Michael Kellough]

Also, just in case…you need a strong flat surface to lay the stock on for lamination.
You don’t want to make a permanently twisted work surface.

Does not need to be a continuous surface, could be a grid, but does need to be strong enough to resist sagging when loaded. While you at it, make it level too.

 

[tsmi243]

This is actually a pretty good learning opportunity.  Do the track saw thing- but cut each edge to a different amount of overhang before flush trimming with the router.  Then you'll get to see 1st-hand what the difference is between a 1/16" flush cut and a 1/4" flush cut.  And also how much faster the saw is....

 

[Crazyraceguy]

So are you suggesting I cut the oversized sheet down to a 1" overhang with the track saw and glue that to the already sized sheet.  Once it is dry, take the track saw and trim that 1" overhang to be flush?  No use of the router or any attempt to try and square everything up?

No, get it square first, at the 3/4" thickness. This has been enough of a struggle, don't make it worse, with more thickness.
Get it square and glue on the oversized piece. You don't have to be so precise/careful with a larger piece. Then cut closer with the track saw, route last.
This is slower than it needs to be, but I'm trying to not waste your first piece. Once you get square cuts, straight from the saw, worked out, you can try doubling up first.

 

[sawdust-samurai]

So are you suggesting I cut the oversized sheet down to a 1" overhang with the track saw and glue that to the already sized sheet.  Once it is dry, take the track saw and trim that 1" overhang to be flush?  No use of the router or any attempt to try and square everything up?

No, get it square first, at the 3/4" thickness. This has been enough of a struggle, don't make it worse, with more thickness.
Get it square and glue on the oversized piece. You don't have to be so precise/careful with a larger piece. Then cut closer with the track saw, route last.
This is slower than it needs to be, but I'm trying to not waste your first piece. Once you get square cuts, straight from the saw, worked out, you can try doubling up first.

Thanks for clarifying.

 

[Packard]

A question, basically because I am nosy:

Why full lamination of the 3/4” MDF?

MDF is awfully heavy when you are building with it, but not so heavy when you are planning on building it.

If I want to give the appearance of a 1-1/2” thickness, I will glue strips around the perimeter and trim to flush.

If I need more strength, then I would rely on the structure underneath the tabletop.

I am under the impression that most MTF-type table accessories are designed to work with a single thickness of MDF.

I made a shelf once using two layers of 3/4” thick MDF.  It did not seem to be twice as strong.

So, why double up?

 

[Vondawg]

This is a very good point(s) weight, accessories…and the clearance needed with festool type clamps

 

[sawdust-samurai]

[member=74278]Packard[/member] and [member=41086]Vondawg[/member] It was not mentioned in this thread, but I'm not building an MTF style table.  This top is for my CNC workbench, so the extra weight in not a negative and I will not be clamping to it.