Foam core pilot holes

A while back I posted a question, asking for advice on how to best construct a fixture for dropping pilot holes through foam wing cores. Responses ranges from ugly (Dan), to KISS (Ron) to industrial strength (Bob). Thanks, everyone, for your help. http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=251798&mesg_id=251798&listing_type=search#251814

I distilled the collective wisdom, filtered it through my experience and integrated it with materials I had on hand. Pictured below is the result.
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The upright is a 48x10x5/8 inch cheap-o, but flat, melamine shelf. A permanent centerline was struck along its full length. I added a bracket to the foot to act as a platform for the foam core and two more brackets to guide the pilot wire.

The foot bracket is an 18 inch length of 2x2x1/8 angle aluminum. It is attached as square as possible to the centerline of the shelf with #8 sheet metal screws.

The guides are also made from the angle aluminum and attached with the same type screws. The guides are drilled .157 (#22 drill) diameter and chamfered slightly on both sides to accept the 5/32 music wire pilot.

The entire assembly was clamped in my 6 year old daughter's new Workmate (she likes to help me in the garage, so Santa brought her the bench and some basic tools). The foot bracket acts to keep the shelf perpendicular to the bench top. The Workmate was leveled and the guides adjusted so the pilot wire was plumb.

The next picture shows the fixture with a core in place, ready to have the pilot dropped. Notice the paint sticks- they act as clamps to keep the core in position. The pilot wire is held in position with a clothespin.
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In operation, the end of the pilot wire is heated cherry-red with a propane torch, the clothespin is released and the wire drops through the core. The tip of the wire is so hot that the resulting hole is larger than the wire itself. It tapers from 9/32 diameter at the top to 3/16 at the bottom. Consequently, the wire does not get stuck on the hole.

One last detail- I fashioned a heat shield from aluminum foil to prevent damage to the core and the shelf while heating the wire. This seemed prudent. . .
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Derek Moran

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Derek,

Once again, a great idea comes from the mind of MPA. Simple, effective with all the details thought out. Awesome!

DEREK,
Where do you live? I'm thinking of moving into your neighborhood.

Greg L. Bahrman

That's about the right rod diameter. 1/16" tends to wander.

One can either poke the rod in and immediately withdraw it or let the rod fall through. I used to let mine fall through into a bucket of water. It's better to have something soft like a towel in the bottom of the bucket.

I was impressed that you had sufficient confidence to drill a wing that was already sheeted. I'd poke the holes in the blank first, then cut the outside of the wing, then sheet it, then hollow it.

Here's why you need the heat shield: http://clcombat.info/sosleadouts.html

Howard Rush

>I was impressed that you had sufficient confidence to drill a
>wing that was already sheeted. I'd poke the holes in the
>blank first, then cut the outside of the wing, then sheet it,
>then hollow it.

>Howard Rush


DOH! The reason I spent so much time worrying about the fixture is precisely because of the risk of putting those holes in the sheeted cores. It took me 4 sets of cores to learn the proper sheeting technique- a considerable expense of time and materials. On the bright side, I'm well practiced and very good at sheeting around leading edges now (and I kept good notes).

This apparatus is similar to my Slot Machine Fixture in that it eliminates as many process variables as possible. It worked perfectly from the very first hole- zero learning curve. I can hang the fixture on the wall and 3 years from now, after I've finished this plane, I'll be able to set it up and confidently pilot bore new cores.

Thanks again to everyone for their advice and suggestions.

Derek

I am angry,jealous and totally overcome with a deep sense of insuffiency!!! Thanks for that one.

I have a very similar set up for my foam cores. It worked the very first time and have never made a bad hole. ART

Kool..

That is EXACTLY how I do mine.

I have the brackets clamped to a door to the shop.

I routinely core after sheeting--haven't missed yet. The beaty of the fixture (I used standard hardware store angle brackets) is it is very repeatable.

I let the rod drop by gravity alone. And immediately retract it. Using 3/16" 4130 rod, it yields a hole about 5/16 diameter. I can hit the center on the bottom of a 30" panel within a 1/8 of TP.

I hold the core against the door with a piece of 1/4" aluminum plate just leaning on it.

Thanks for the validation of concept Derek!

You're gonna like it.

Curt

Be certain to put an accurate, symmetrical point on the rod--failure in symmetry can cause the rod to wander.

Paul Smith (ama21835) tells me this same design was published in Aeromodeler in 1971 by Richard Wilkins. Paul actually owns one that he purchased on one of his several trips to England in the early/mid 70's.

Paul, it would be neat to see a picture of your fixture or a scan of the Aeromodeler article. It's amazing how similar design solutions to the same problem occur.

Thanks, Paul. Needless to say, I'll be assigning all royalties to Richard Wilkins.

Derek

It's actually shown on my Superstar II plans, which I got from Richard.

You should see Phil's. He wanted to poke holes through by the hundred (it ain't called the Core House for nothing!), so the rod he drops is a car brake line. You know, with the flared ends. The brass compression ferrules got glued into the guides so the tube slides up and down smoothly. He cannibalized a 12V soldering iron element and tip, the wires go through the tube. 3V, and it's hot enough to melt the hole through the foam. He's got a sliding guide for the core blank, first poke one hole, then the other after sliding the blank over.

But now he just uses his CNC cutter to cut the insides out, starting through the leading and trailing edges. No need for pilot holes any more, ever again!

>Paul Smith (ama21835) tells me this same design was published
>in Aeromodeler in 1971 by Richard Wilkins. Paul actually owns
>one that he purchased on one of his several trips to England
>in the early/mid 70's.
>
>Paul, it would be neat to see a picture of your fixture or a
>scan of the Aeromodeler article. It's amazing how similar
>design solutions to the same problem occur.
>
>Thanks, Paul. Needless to say, I'll be assigning all
>royalties to Richard Wilkins.
>
>Derek

I still send him 3 pence a core. Otherwise some of his henchmen will call.

Nice work, Derek!

My cutter is mounted on 1x2 strip wood built out in a layer or two to allow coring on the rib centerline.

Bottom of the fixture is open, no contact with a table or other...

Hot rod travel is limited by a wheel collar at the top, cool, end to stop the drop when it hits the top guide.

Core clamping is between a fixed upper block and guide, and a slotted lower guide. 1/4" iron rod, running in small screw eyes turned enough from horizontal that they guide without wobble, yet freely.

Things are squared up and locked in place before the cutting rod is heated. Remember ventilation! This gives more smoke than wire cutting the airfoil...

Somebody almost impled that I couldn't produce the documetation. It took a while, but I found it before Morris was captured by the terrorists. This stuff dates back to the day of B&W photos (on film) and Ozlid copies.

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I went over to England and Holland to study the trade. Bought these from Richard himself. No need to travel so far now, world's best d-dojo is on the Bruce.

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Fire extinguisher. What a wimp, setup for a mag submission. The Outlaws didn't even imagine building fixtures with NEW materials.
Note: the design has been enhanced by a genuine titanium heat shield, not the drawing.

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My new home, foam cutting expelled to the carriage house. See the "filler block" off to the side. It sets the offset between the two holes.

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Fleet photos shows some productivity, and loyalty to Richard's method (but not the life style). No e-orders to Czecho in '79.

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Cool. Thanks for taking the trouble to dig up the pictures and post them.
I'd say we have covered the subject pretty thoroughly. Anyone who wants to make such a device has all the information they need.
Does Richard accept Paypal?
Derek

Gold, gov'nor, gold.

Paul,

Looks good, and mine is quite similar. I forgot to mention that my guide setup includes a 1/4" ID brass tube, which is what the screw eyes bear on to line things up. Aims the hot 1/4" iron rod better... The slot I put in is just to allow for different 'span' panels...

That's been considered to a great extent.

The over-riding issue was the 36" standard length of piano wire. Now, no doubt, somebody knows an industrial suppler who can get it 5 metres long, but we set up for the 36" rods from the LHS.

So, with about 24 " of it in the core, there wasn't much left to align.

The solution was to use a lot of care to align the fixture true with the world and Mother Nature takes the rod straight toward Middle Earth.