A How To operational question from Robert,

Robert’s Problem…

I just signed up for your videos, and I wonder if you could help me with a template problem I am having.

I need to cut 2 precision 4 inch holes in 3/4 inch MDF. Normally cutting holes is not a problem, but my smallest router is a Porter Cable Trim Router. Trying to cut a 4 inch circle is not possible because the diameter is too big when a circle cutting jig is attached.

So I cut out a 4 inch disk on my bandsaw and then filed it down to exactly 4 inches. My idea was I could use this positive disk with my router and a guide bushing to make a female template. However, I am unsure if this will work or not. In my research on router templates, I have found no instructions on how to make an accurate template from a positive object (the disk). There is plenty of information on using different guide bushings and bits, but I believe I should be able to cut out the template and then use it with the same guide bushing and bit to cut the 4 inch holes.

Is this correct Bob and Rick?

Thanks Robert
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How we would do it…

The fastest and most accurate way to cut 2 – 4 inch holes using your trim router is to use a home-made circle jig. To make this you need the following: double stick tape, 1/4″ piece of plywood, and a 5/8″ finish nail.

Step 1: Mount the desired straight router bit into the trim router and retract the bit so it’s behind the base surface.

Step 2: Then using double stick tape fasten the 1/4″ plywood to the base of the trim router. Make sure this is fastened well. Try not to use cheap carpet tape.

Step 3: Start the router and ease the moving router bit through the 1/4″ plywood. Now we have found the center of the home-made circle jig.

Step 4: Shut off the router and unplug it. Position the tip of the router bit even with the 1/4 plywood base. The router bit will show you the outside dimension of the desired radius, in your case 2″, which will make a 4″ hole.

Step 5: Mark the 2″ radius and position the 5/8 finish nail in the 1/4″ plywood. Create the position hole using the 5/8″ finish nail.  Try and set this position up in the 1/4″ plywood away from the trim router’s original base. Remember, you can locate this point anywhere you feel. Nothing needs to be straight with 1/4″ plywood or the base. The hole can be anywhere in the plywood plus the plywood can be any shape and/or size.

Step 6: locate and drive the 5/8″ finish nail into the MDF leaving just under 1/4″ exposed. Position the 1/4″ plywood with the hole over the 5/8″ finish nail and start the router bit and move it down at approx. 1/4″ at a time or to a depth that you feel comfortable cutting at a time.

That’s how we would do it….

Robert emailed me additional information so we added more information to compensate for the additional issues.

OK Robert,

So your trim router is 4″ square and putting the nail in position as described above doesn’t seam feasible.

How about this….

Let me revise the directions a bit:

1) And instead of putting the nail in the project piece lets put in the sub-base.

2 And instead of using 1/4″ plywood lets use 1/2″ plywood for the sub-base.

Then instead of putting the nail in the project piece we put the nail in the 1/2″ plywood sub-base and cut the head off so it’s under 1/4″.

Next using the same kind of nail mount it in a drill and use the nail as a drill bit to drill the correct size in the perfect position on the project piece.

Now we put the nail that is positioned at the 2″ radius in the router sub-base into the hole in the project piece and cut the perfect 4″ hole.

The only downside to the 1/2″ sub-base is the router bit needs to be a bit longer to cut right through the 3/4″ MDF. Might recommend a 1/2″ straight bit with a 1-1/2 to 2″ flute length.

Hey anyone else have an idea on how to cut the 4″ hole. Please add your ideas in the comments below.