for all who drilled instruments holes one day... panel holes to big

Hi, i cutted 3 1/8-, 2 1/4- and 1 1/4-holes into my panel using hole saws from home depot. the holes look great but are slightly larger then the nessecary diameter for the instruments, 1/32...1/16 or so. when i test fit the instrument into the hole, it looks good as long as the instrument is really centered. is there any magic technique of match drilling or whatever to ensure a centered instrument?

thank you guys...

Kay

RV-7, sliding canopy almost done, next airplane will not have a canopy. just a hole to stretch the head out.

Fly-Cutter

Hi Kay,

I used a fly-cutter for my panel. It works pretty well as long as you have a backing board to keep the pilot drill centered when the hole is finishing. Its noisy and takes a while but you can cut decent holes with it. If I had to do it again, I would probably buy a instrument punch. I think Aircraft Spruce sells these as a combo 3.125 and 2.25 inch punch. My bigger problem was drilling the instrument screw holes. I think you can probably buy a jig for these as well.

Good Luck,
Tom RV-7A N175TJ Flying

KayS said:

Hi, i cutted 3 1/8-, 2 1/4- and 1 1/4-holes into my panel using hole saws from home depot. the holes look great but are slightly larger then the nessecary diameter for the instruments, 1/32...1/16 or so. when i test fit the instrument into the hole, it looks good as long as the instrument is really centered. is there any magic technique of match drilling or whatever to ensure a centered instrument?

thank you guys...

Kay

RV-7, sliding canopy almost done, next airplane will not have a canopy. just a hole to stretch the head out.

Click to expand...

The technique I used was to mark the hole center, center-punch it, then drill it to #30 so I could cleco the instrument screw hole jig to the panel. Then, I squared up the jig and drilled the holes. The #30 hole in the center of the instrument cut-out then became the pilot hole for the fly-cutter or hole saw.

It'll be tough centering up everything else after cutting the big holes.

kerf

The standard hole saws often have cutting teeth that project both ways, to produce a kerf or cut that is wide enough to clear wood chips when boring.

You may be able to lightly grind off the outside cutting edges so that the final hole diameter is correct for thin aluminum. A trial run on scrap will tell you what the result is.

Dave A.
6A build

I used holes saws once

Never again. What I did second time was to have one of my CAD buddies draw me a template full size with a hole center for the big hole and the 4 small holes. I had him make a six pack full size. When I was happy with the spacing I glued the drawing to the panel. Then I got the fly cutter in the drill press.. Go slow and you get perfect positioned and sized holes.

I even added instruments to the finished airplane using the flycutter in a battery drill and still got perfect holes.. Even on a painted panel.

KayS said:

.....is there any magic technique of match drilling or whatever to ensure a centered instrument?.....

Click to expand...

Magic technique is not required. It is easy to accurately lay out and drill standard instrument mounting holes using a jig. Works like a charm. See if you can borrow one from another builder. If not, the jig is widely available. Here's one source:

http://www.aircraftspruce.com/catalog/topages/instrumentmounting.php

since you have already cut the big holes, you will need a little patience to get the small holes in the correct position.

I would either:
1. make a AL template with a step to center it in the hole
or
2. clamp the panel down to table. Find the center of each hole. Use a compass to scribe the exact diameter of your bolt circle. This should center the instrument in the hole.

Step 1: Build CNC Router

Step 2: Cut Panel

Go with a Dynon, just one rectangular hole to cut. Don
On the Cub I am building my partner laid it all out on the computer and Backcountry Super Cubs CNCed it. Sent it ou to Texas and had it laser engraved.

KayS said:

Hi, i cut 3 1/8-, 2 1/4- and 1 1/4-holes into my panel using hole saws from home depot. the holes look great but are slightly larger then the nessecary diameter for the instruments, 1/32...1/16 or so. when i test fit the instrument into the hole, it looks good as long as the instrument is really centered. is there any magic technique of match drilling or whatever to ensure a centered instrument?

thank you guys...

Kay

Click to expand...

Kay, Just purchase this jig........ http://www.aircraftspruce.com/catalog/topages/instrumentmounting.php and wrap masking tape around it till it fits the hole the way that you want.

Aircraft Spruce sells a template

Aircraft Spruce sells a template for locating the mounting holes. Since you already cut the big hole getting concentricity is a little more tricky but not too bad. By the way, I cut my panel holes with hole saws, hack saws, fly cutters and punch tools. I like the hole saws best.

Bob Axsom

CNC is precision and hi-tech but is it really required? Not in my experience. In addition, after generating a few test holes with the brand new tool, I sold the high dollar instrument hole punch when I decided the holes it produced by shearing action could not match the quality I routinely produce using a flywheel cutter and a drill press. That is because there are slight differences in standard hole sizes between one instrument manufacturer and another. I can easily reset the flywheel cutter to compensate for that. The key to attaining that kind of accuracy lies in drilling a test hole or two on scrap before turning it loose on the instrument panel blank. An instrument hole punch is certainly acceptable but it is a one-size-fits-all deal. Add a layer of paint and suddenly an instrument might not fit into its assigned hole without rework. I haven't seen an instrument hole yet....and I've produced two instrument panels containing all manner of square and round holes....that I could not precisely fashion using a simple fly wheel cutter, cut off wheel, rotary tool, and assortment of files.

jig

Kay,
I have a instrument hole jig, that will let you drill the 4 corner holes (for both 3.125 and 2.25 instruments). Your welcome to borrow it. I'll try to bring it Thursday if you like.

@ Dave:

sounds cool. what would i do without you guys? i go to germany on wednesday so i can't be at Chris house on thursday. but i give you a call next week when i'm back.

Kay

KayS said:

..the holes look great but are slightly larger then the nessecary diameter for the instruments, 1/32...1/16.

Click to expand...

Have you measured the hole saws with a caliper? I also used Home Depot hole saws to fabricate a new panel for my Cessna 170 and they came out right on. A couple of things that might cause them to cut slightly larger would be a bent quill on your drill press, or the arbor hole in a cheap hole saw being slightly off center. You might want to check the runout with the saw chucked up.

... another trick

you can use, is to make a panel overlay the same size as the panel blank out of .016 aluminum, and be more careful when you drill, punch, poke, the holes through it. You can rivet the overlay to the base panel around the circumference of the orignal panel and across the bottom and it will look great.
Ask me how I know...

Another recovery idea

Kay,
If Dave Edgemon's jig has a center hole in it, you may be able to make an allignment plate to fit your sawn holes and work with his jig. This could be lathe turned of course with center hole and OD of proper size.

If lathe is not available, the minimum you need is a triangle with the tips at the right diameter and the center hole in the right spot and size to fit his jig. This could be made via accurate layout with a compass, drill press and hand tools.

You could opt for a square or a pointed cross. Any of the three shapes could be carefully worked to the right dimensions with hand files. Keep the 3 or 4 contact points small, like 1/8" wide or less so the panel hole curvature is less of an issue.

Given these ideas, you might use Dave's jigs to 100% fabricate jigs of your own by adding a larger plate with the 4 screw hole positions.

Good Luck, I hope this helps.

BTW, when I use hole saws on aluminum, I usually grind off the tooth "set" on the OD of the hole saw so the OD is completely smooth and closer to desired dimension. I get reasonable holes with a wobbly Harbor Freight saw set. I didn't use them for instruments though, I used a fly cutter and did test cuts to get the diameters spot on.

Here's a pic of the cub panel Yakdriver built recently. Nicely done

I plan on getting my panel cut by a CNC with a cheap test panel laser cut out of plastic. A friend (also a builder) of mine located at Spruce Creek, Florida (Laser-logic.com) has a small business doing panels for the local builders. He has both a CNC and a large bed laser. The typical process is to cut the first edition panel out of 1/8? plastic and let the builder do a test fit before cutting the final product on the CNC. For RV?s he has the blank templates so he only needs the instrument/switch locations and sizes (he also has templates for most commonly available avionics and instruments). The machines work with CAD drawing but if you have a dimensioned drawing he can create the CAD dwg. He practically insists on the test panel because he finds the builders 90% of the time find out they want to change something when they put the test panel in place, or a switch or other panel component does not exactly fit in the cutout. The cost is very reasonable, but if you want to spend more he can paint and engrave the panel markings, or add plastic panel overlays.