Jig Pin holes

[kilohotel]

Just how important is it to protect the drill holes in the form blocks with steel bushings. I bought 1/4" OD by 3/16" ID brake line tubing for this, but I don't like the fit and they are tough to cut to the right length. Is it OK to just be extra careful while drilling through the blocks? I am using 3/4 inch MDF and I plan to coat them with PC-Petrifier Wood Hardener...

[Chris In Milwaukee]

Just being careful should be fine. You’re really not drilling drilling enough parts that the holes will open up much. Just use a drill press if you can and the issues will be minimal.

[S Lathrop]

I used a transfer punch to locate the holes and then punched the holes. As a general practice, I avoid drilling holes in thin sheet metal. Drilled holes seldom end up as round holes.

[Chris In Milwaukee]

I used a transfer punch to locate the holes and then punched the holes. As a general practice, I avoid drilling holes in thin sheet metal. Drilled holes seldom end up as round holes.

I agree with this very much (although I drilled, not punched). When I drilled the holes in sheet, I also used a punch as a starter and then drilled them outside of the jig. You’ll likely see a tiny bit of misalignment when you sandwich pieces together in the routing jig (if that’s your preferred method). That’s when drilling through the stack while in the jig to cleanup the alignment holes for pinning that you may experience a bit of side load on the holes which can lead to their widening. But not enough to throw things off. Just be gentle and all will go fine.

[kilohotel]

Good plan! I'll use the transfer punch, drill press, and extreme care lining up the holes...

Does the punch tool allow you to line-up with the transfer punch mark?

[Chris In Milwaukee]

Good plan! I'll use the transfer punch, drill press, and extreme care lining up the holes...

Does the punch tool allow you to line-up with the transfer punch mark?

Depends on the punch. This one has center point in some of the dies. May not reach all the holes, but you may be able to find a tool with a longer reach.

https://www.northerntool.com/shop/tools/product_200635671_200635671

As it’s just jig holes we’re talking about here, roundness may be less of an issue. If it’s a rivet hole, a driven rivet will fill an odd-shaped hole. Pulled rivets will certainly benefit from round holes.

[fairchild]

KH---- I put those steel tubing bushings in my master rib and also in the cutting jig. But I think having them in the cutting jig is optional. Here is why----
I don't drill through any of them to start with. When I use the cutting jig-- I cut out my blank with the air body saw then trim it a little closer to the line with the band saw.
Then I lay the blank between the cutting jig halves. I line it up so there is a margin all way round. Then I have a sharp punch made from 3/16 Piano wire. Punch a dimple
using the first hole. Drill that hole 3/16 using only the punched dimple (not the jig) Put blank back into cutting jig and slip a 3/16 bolt or smooth pin through the first drilled hole.
Now punch the 2-nd hole and make a dimple. drill that hole. Now the sheet is locked into position in the jig.
If you want more accuracy for keeping it centered--- pilot drill the dimples with a tiny bit (like .040) --- then enlarge the hole to 3/16.

So if you don't have to use a drill bit in the MDF it may not need a bush. I like using the brake line bushes---- even though I may not need them 100%.
Tim

[Glenn Patterson]

We made a full sized MDF wing pattern that we glued a mylar copy of the mylar pattern. Drilled the master template for the jig pin holes. I used the master MDF template to spin off the router templates that were was held by screws & wing nuts. We used one side of the router form and used it as the drill guide in the drill press. Lower the bit and turn it backwards by so the template self aligns with the bit. Clamp the pieces then drill one side and put a screw in two maintain the hole position. then do the same with the second hole. This won't wear out the router form holes & is fine for constructing a pair of wings. We ran string ;lines through the ribs with a bead that just cleared the holes for perfect alignment. A person can look through all the jig pin holes from one end of the wing to the other. We ran a level across the flanges to check that the flanges were flat before putting the skins on. There was no issue with wandering jig pin holes. Just take your time and exercise care then you will be good. We started out with the brake line guides and after one decided it was a pain. I made the router templates in pairs that I held together with 3/16 screws with wing nuts. The screws were round head so I did a bit of a counter bore for the heads so that the screws did not ride on the router table.
Glenn
BH727

[Chewie]

I did almost exactly as Glenn described and fully agree with his tips.

My biggest advice is to make sure your drill press table is absolutely square. Use a coat hanger or circle cutter. MDF is thick and any error shows.

One trick I started doing late in the process was to use a jig like this. This eliminates the need to match drill through the form blocks, and you get exact hole spacing every time. Note the pin on the right side. The forms were drilled on the same jig.

[Chris In Milwaukee]

I did almost exactly as Glenn described and fully agree with his tips.

My biggest advice is to make sure your drill press table is absolutely square. Use a coat hanger or circle cutter. MDF is thick and any error shows.

One trick I started doing late in the process was to use a jig like this. This eliminates the need to match drill through the form blocks, and you get exact hole spacing every time. Note the pin on the right side. The forms were drilled on the same jig.

That's a really good idea. Very repeatable!

[fairchild]

Chris--- Im doing the same thing. Drill first hole. Put pin through it and drill 2-nd. Put pin through it--- drill 3-rd (on the big ribs---now)--- Then all the rest (6 total)
However---- I don't drill through the guide---- I PUNCH through it. Prick punch. Leaves a funnel shaped dent. Then I drill the hole with one of those wood bits (3/16)
that has a little spike point on the end. The sharp point on the bit "finds" the center of the dent and all ways drills (so far) exactly where you punched with no wandering.
so far my metal falls onto the 6 pins sticking out of the big main rib---- with no binding or slack. same on nose rib. PLUS---- if you don't drill through your templates---
(snug punch only) they never get bigger from wear.

Tim