You can use the Woodpecker jig, but I d do a few of other things, too. Note that hole patterns for the Woodpecker jig is 4×3. This is too small in my opinion - so we ll make a bigger jig, using the accuracy of the provided jig. The problem is that there could be a little bit of slop, and with many overlaps the jig method yields a larger error at the end (0.2 mm off and 10 spacings = 2 mm - just enough to be annoying). So the steps to counter this are to:
1. Make three long plates (1/2" of stable and flat plywood or MDF) that are at least 1 m long (11 holes and 10 hole spacings in a line = 960 mm o.c.+ extra space on each end - let s say 42"). Also, leave the width wider than 120 mm (approx. 4 3/4"). Take care to place 11 - 20 mm holes as straight as you can. Using the jig is a good way, but use clamps and give yourself some time to practice! If you get the first plate perfect, then make the other two off of the first one, using a pattern bit and double stick tape. Principle - If we can t make 11 holes in a straight line at 96 mm spacings, we shouldn t expect a square hole pattern with better accuracy. If you get it right on - proceed. Note - the long edges of these plates need to be smooth (de-nibebd) and straight, parallel to the hole pattern. You can use a spare piece of plywood that is reliably parallel - line it up with the dog holes on one side - and fix it to the 11-hole plate. Then, use a table saw (or track saw) to trim the edge parallel to the holes. This can be done for both long edges. Check with a caliper and adjust as needed.
2. Using the jig, create a 5×4 hole pattern plate using woodpeckers jig to a stable piece (1/2" plywood or MDF). First, cut all 12 holes using the 4×3 jig (follow woodpecker s manual). Then, place two of your 11-hole plates along the wide side of the jig. You should be able to line up the 20 mm holes on the bottom row (you just cut) and the plates, using 20 mm bench dogs. Once you have the long plates set and aligned, clamp these down, you can move the 4×3 jig up two holes to make the 4×5 hole pattern. You can now check the diagonals - 3×4 x 5 spacings, using your 11-hole plates. If you are good here - proceed. Otherwise practice until you get it right. This was just for practice, but you can also use it in the next step, as a spacer and clamp block for the template.
3. Next, you ll want to set your target piece - larger table for the full hole pattern. You could proceed a couple of different ways, but the key is to get a straight line of at least 9 holes on one edge (I d start along one long edge) and a perpendicular set of holes of at least 7 holes on a short edge. Use your 11-hole plates from step 1 to check 3-4-5 triangle spacing (in this case 6-8-10). That s a great way to check 90 and to place the templates. Once you have this set, I d lay out a 9-hole pattern parallel to your first row of holes - checking 90 degrees with the 3-4-5 technique. Now, you have a great place to start the larger hole pattern and to use parallels and your 11-hole plates to guide the jig. This also avoids the error propagation from one end to the other. This method is actually quite similar to the parf-system.
Note that your target piece needs to be flat as you work on the hole pattern. 1/4" out of flat and you ll be fighting the geometry. So, if you are concerned about getting a flat base, I d work on that first - using a torsion box method.
One advantage of the woodpecker s jig is that it allows thicker and harder bases (hardwood or thick plywood). You can also avoid cutting the tiny drill holes first. However, you ll probably want to use a drill to make the routing easier. For thicker materials, you might make smaller holes (say 1/2" or 5/8") with a drill bit, then remove the rest of the 20 mm waste with the plunge router and jig. Much nicer on your expensive router bit.
Another option (if you haven t realized it by now) - get a CNC shop to make a one plate of at least 11 20 mm holes in a straight line (aluminum or laminated mdf best) - then duplicate that for a nice set of straight-line hole plates. You can set up parallels and spacings that follow previously set holes (and your own guides) to make accurate hole patterns. Another option is the Part fence (
https://www.axminstertools.com/us/ujk-parf-system-fence-stop-kit-1-000mm-107462?glCountry=US&glCurrency=USD ). Leaves some money to buy a dog hole set and pattern bits. You can come up with quite accurate placement methods with uniform offsets that fall within the tolerance of the hole patters of the original plates.
Final tip - did you know that 3/4" PVC pipe ID is surprising close to 20 mm? You can ream out any slop with a 20 mm bit and you have some nice collars. Buy a 27 mm bit and you can epoxy the PVC into small plywood plates with a 27 mm hole in the middle. Sized small enough to be placed end to end with a bit of space between - you can use two dogs and one reference plate with 96 mm spacing (like a part fence) to position the plates. Trick - you don t worry about hole spacing, but you simply mount the plates with a spacing set by the dog holes and reference. Glue and pin nails onto another sheet of plywood. Just need a straight edge to align the other holes along one consistent line of 96 mm. Trim the edges paralel to the holes using a parallel spacer on the table saw (or track saw). Cover the whole thing with laminate - and then trim route and chamfer the holes. All things you already know how to do a low cost materials!
I ve spent way too much of my own time thinking about this, so I thought I d share these odd tips. One thing I realized was that I don t really trust all the hole patterns I ve made in the past for square, but it s so easy to use the hole patterns with a 1/2" bolt and a block (and a square) to get it right on. Woodpecker s goal was to offer a good way to make a reasonably accurate hole pattern - with the goal of setup and clamping options - not for CNC accuracy out of the table itself. I think that s reasonable - and you may simply want to get that jig and go to town.
- Jerroni