Using Plywood template and top bearing bit

[webbaldo]

Is there anything in theory stopping me from making a 3mm (1/8) plywood template for my sides then using a Top bearing flush cutting router bit?

I mean just pin the template (or d/s tape) to the top of some 3/4 ply, set the router depth, then just run round the top-mounted template?, thus cutting the 3/4 plywood below the template to perfect size?

Am I missing something or is there any pitfalls? As long as I take my time, set depth perfectly, im struggling to see any issues?

[shil]

That's how I did it. Make a rough cut with your jig saw first, outside the lines, then clean up with the router bit. Your router will thank you.

I cut both side walls at once. For the first pass the bearing rides on the template. Depending on your router bit you probably won't make it though the second layer. For the second pass extend the bit so the bearing rides on the cut you just made.

Good Luck!

[bobhenry]

Just a little F.Y.I.

I placed a sacraficial layer of blue foam underneath the work to protect the work bench surface.

[aggie79]

I used the same method. First, I drew a full size layout of the sidewall on 1/4" mdf and cut the mdf to make the template. (You mentioned 3mm template thickness. You may want to consider a little thicker material for the template for your router bit bearing to ride against.)


Then I overlaid the template onto the plywood and traced the cut off areas.



I rough cut the plywood with a jig saw (leaving 1/16-1/8" material to be removed by the router).



I then attached the template to the rough-cut plywood with screws and finished cutting with the router.

[KCStudly]

You may want to consider a little thicker material for the template for your router bit bearing to ride against.

+1. When I did my hatch ribs using 5 mm luan and a bottom bearing flush bit I found that the gap between the bearing and the end of the cutter forced me to run the bearing riding only about half way on the template in order for the end of the cutter to overlap the work. It worked okay, but I would have been more comfortable with 1/4 inch thk.

[CarlLaFong]

With a good router and templates you would be amazed at what can be done. Template routing is a fundamental skill that all woodworkers should learn and use. There's a program on some PBS and cable networks called "Router Workshop". They make all sorts of intricate projects using only routers

[jimqpublic]

From my limited experience making some plywood kayaks-

+1 on using stock thick enough to let the router bearing ride on the template. 1/8" doesn't work very well.

If you're using the router to "cut out" the parts, then a small diameter is best so you remove less total material- less time, less heat.
If you are using it to trim after rough cutting with a reciprocating saw, then larger diameter is best- higher blade speeds, less affected by uneven material.

Inside corners are limited to the radius of your bit- no sharp corners with a 1/2" bit!

[planovet]

I'm an Aggie so I tend to do things backwards. I used a bottom bearing bit and put the template on the bottom. I made my template out of 1/4" ply which allowed plenty of area for the bearing to roll on.

I also did both sides at once. I should have done one at a time (or used a jigsaw to cut out most of the excess) but I only burned up one bit

[webbaldo]

Thanks for the advice, ill use 5mm then (1/4?) for the template

[KCStudly]

No, 5 mm is only about .190 inch (3/16). Go with the full 1/4 inch (7/32 actual, about .22 inch). The templates that were CNC cut for me are that dark press board (melamine or OSB?) with one shiny smooth side in 1/4 inch. It's what Rover Mike (professional wood shop guy) uses for all of his templates.

[LDK]

Thats how I did mine also. I used 1/4" masonite for my pattern. Using a pattern is the best way hands down.

[webbaldo]

Ah right my mistake, 1/4 is basically 6mm ply here in the UK.

We are a funny bunch here in England with measurements, we use Miles for long distance, Grams/KG for weight of food, and MM/Metres for general DIY, but I still use FT and Inches as well!

We just cant let go of imperial lol!

[asianflava]

Thats how I did mine also. I used 1/4" masonite for my pattern. Using a pattern is the best way hands down.

I built my tear with sandwiched 1/8th luan, but I used 1/4 ply for my template. The extra height made the process more forgiving. I pieced the frame together and cut it with a top bearing bit using the template. I glued the luan to the frame and used the frame as the template, I cut the faces with a bottom bearing bit.