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Need Suggestions: Drilling holes in a plate to match existing platenut locations

Saville

Saville

Well Known Member
HI all:

I've run into a problem which I am willing to bet is a well-solved problem on the VAF. So I need some suggestions.

Short Version:

I have a set of 6 plate nuts in two rows of three already installed - 3 holes on each of two flanges (RV-8 battery support structure).. I need to figure out a way to drill holes in a piece of 2024T3, 0.63 aluminum to precisely match those holes so I can screw this plate down onto the plate nuts.

You cannot get a drill up from the platenut side. Here's a picture of the holes on the flanges:



I've labeled the holes 1,2,3,4,5 and 6. The green arrow points to the plate nut hole. The hole above that in the picture is a builder mistake.


Long Version:

I want to install an Odyssey PC-925 AGM battery in the battery compartment which is aft of the aft baggage compartment. Presently there's a Gill battery there.

The footprint of the AGM will not fit the battery tray as built. So I have to rotate the battery 90 degrees and also install larger right angles onto the tray. Here is the old battery tray as it's installed in the airplane:



Notice those two Tinnerman washers......problems......

Here is the new battery tray I built:



I lived under the delusion that as the holes for screwing the trays to the mounting flanges are pre-drilled, the new tray will fit right right where the old tray was and those 6 screw holes will line up perfectly.

Well guess what? No way. Holes 2,5 and 6 are where they should be but 1, 3 and 4 are no where near. What is worse: look the old tray just laying on the flanges with the screws out:



Lousy, appalling drilling. @#$%^%&*@#$

Ok after a session of swearing I tried to figure things out. First off, here is the new tray on the flanges. Note that holes 2,5 and 6 actually line up well:



So here is my plan but I'm open to better ideas:

1) Get a piece of 2024-T3 0.63 thick aluminum and bore holes in it where the plate nuts ARE on the flanges. Screw that plate to the flanges.

2) Install 6 plate nuts on this new piece of aluminum in such a way that I can fasten the battery tray to the new piece of aluminum.

3) Lay the new battery tray on the new aluminum plate and screw it to the new plate.


That's the plan. Comments criticism better ideas welcome.

Now it turns out that I can use the old tray as a template for 4 of the 6 holes (1,2,5 and 6). But I need to figure out a way to locate where to drill holes for #3 and #4.

Here is a close up of #3:



Here is a close up of #4:



Number three actually fits one of the holes the builder drilled in the tray at that location so I might be able site that hole.

Number 4? No idea.

Perhaps making a template out of a piece of plexiglass.
 
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Could you use a piece of thinner Al and a" hole finder" to make an accurate template of where the nut plate hole are? You can make several if needed until you get them to fit properly . Then transfer that accurate template to the battery tray and drill the new holes.
 
Just get a piece of paper or poster board and lay it over the holes. Punch the holes out wih clecos into the nut plates, remove the clecos and use the paper as a template to transfer the holes to your new piece
Works great
 
Maybe I'm missing something, but is there any reason you can't take a stiff piece of paper or posterboard, place it over the holes with the platenuts, fix the paper in place, shine a light from behind and mark the hole centers on the paper, and end up with an accurate paper template to work from?

EDIT: Dang it Steve, great minds... I like the cleco-punch idea too.
 
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sf3543 said:
Just get a piece of paper or poster board and lay it over the holes. Punch the holes out wih clecos into the nut plates, remove the clecos and use the paper as a template to transfer the holes to your new piece
Works great
Click to expand...

This works well. I just use a fingernail to outline the holes. A crowned hammer (small) or a flat squeezer die just moved around on the surface works too. No need for a hole. It will just be less accurate. Then, center punch through the center of the circle with the template reaped to the subject part. Be sure it is taped for making and using the template and know how you will align it with the part.
 
Can't you just use the old bracket and match drill the holes into the base of the new piece. You can mark them first as a guide to check the locations.
 
Less accuracy, but easier

Another option is to pretend it's a production aircraft with sloppy holes instead of exact match-drilled holes. :)

The precision you need is because you are using countersunk holes for flush screws. If you had holes with a bit more "slop" and used regular head screws and washers, a simple nylon plate shim - with lightening holes cut in it, of course - under the battery would prevent the screw heads wearing on the bottom of the battery.
 
Another option: Draw two center lines to each hole (at approximately 90 degrees) on the old battery tray while it is in the position you want. Overlay the old tray on the new one (trim the old tray if necessary) with bolts in the good holes, and transfer the lines to the new tray through the holes in the old tray.

Greg
 
rzbill said:
It won't help now that you have drilled holes in the wrong positions but if you were marking a fresh plate, a set of transfer screws would be my tool of choice.
Click to expand...

1) I haven't drilled any holes - the builder drilled these holes.

2) As I mentioned in the OP, I'm thinking if a plate sandwiched between the battery tray and the mounting flanges so I am, essentially, making a fresh plate.

3) I looked at your link - it's not obvious to me how these are screwed in to the plate nut....I cannot get a wrench underneath on the plate nut side...are these screwed in from the opposite side from the plate nut?

thanks
 
sf3543 said:
Just get a piece of paper or poster board and lay it over the holes. Punch the holes out wih clecos into the nut plates, remove the clecos and use the paper as a template to transfer the holes to your new piece
Works great
Click to expand...

I thought of something like that (or the pencil rubbing over the hole trick) but the problem I see with all of these is that while they perfectly locate the position of the circumference of the hole, they do not make it easy to pinpoint the exact center of the hole - the point at which you have to set the drill bit.

I'm not very good at placing a pencil mark or punch tip at the exact e=center of a 1/8" circle.
 
Saville said:
I thought of something like that (or the pencil rubbing over the hole trick) but the problem I see with all of these is that while they perfectly locate the position of the circumference of the hole, they do not make it easy to pinpoint the exact center of the hole - the point at which you have to set the drill bit.

I'm not very good at placing a pencil mark or punch tip at the exact e=center of a 1/8" circle.
Click to expand...

That's why slightly 'sloppier' holes might be appropriate in this case...:)

http://www.vansairforce.com/community/showpost.php?p=1130569&postcount=9
 
az_gila said:
That's why slightly 'sloppier' holes might be appropriate in this case...:)

http://www.vansairforce.com/community/showpost.php?p=1130569&postcount=9
Click to expand...

Hi Gil,

I read your post. Only problem I have with sloppy holes is that I fly acro with the plane. If the hole is sloppy then the shaft of the screw does not provide any resistance to the sideways sliding of the battery tray. At least not until the side of the metal plate slides over and contacts the shaft.

Perhaps I don't understand the mechanical operation of these screws - is it the downward force of the screw head that keeps things in place? Or the shaft of the screw?

Probably both...which is more important?

I do know that as the tray attempts to slide to the side, the countersunk head of the screw actually pushes the plate down on the flange harder (at least that's how screws keep planks on a boat tight as the boat works).

If I drill the hole slightly large, the action of the countersunk screw head is lessened.

But I'm not an expert so I'm willing - even eager - to be educated on this.
 
Saville said:
Hi Gil,

I read your post. Only problem I have with sloppy holes is that I fly acro with the plane. If the hole is sloppy then the shaft of the screw does not provide any resistance to the sideways sliding of the battery tray. At least not until the side of the metal plate slides over and contacts the shaft.

Perhaps I don't understand the mechanical operation of these screws - is it the downward force of the screw head that keeps things in place? Or the shaft of the screw?

Probably both...which is more important?

I do know that as the tray attempts to slide to the side, the countersunk head of the screw actually pushes the plate down on the flange harder (at least that's how screws keep planks on a boat tight as the boat works).

If I drill the hole slightly large, the action of the countersunk screw head is lessened.

But I'm not an expert so I'm willing - even eager - to be educated on this.
Click to expand...

I'm only suggesting "sloppy" in the order of thousands of inches - perhaps one or two drill sizes.

Vertical loads are no problem, it's simply the tensile strength, and sideways loads should be taken care of by friction under the washer heads if the screws are fully tightened.

There is also friction between the plate and the mounting angles when it's all tightened up.

If lateral shifting shows up in use, then adding two location pins in opposite corners would stop any movement. These could simply two short AN bolts with the threads cut off. Match drill the holes and use a friction fit in the plate - with the battery above the bolt heads the shortened bolts can't shake out.

Try it without the locating pins and drill the holes as accurately as you can, and then slowly enlarge them (only one of two sizes) until the screws fit. Don't worry about the locating pins until you actually see some movement while in use.

I would use a clear material for a marking template and like mylar drafting film, but no-one uses that material any more...:rolleyes:
 
I would agree with Gil and have done the paper transfer method for locating holes many many times. I have had marginal luck with the hole finders. Their thickness requires some careful positioning.

However, it is your airplane and if you want that accuracy, short of having transfer pins on hand, you can make your own if you have a small lathe. You don't need highly tempered material for one time use, just get some cheap #8 screws, chop the head off, and turn down a point. Hand thread them in and then a bit more with some pliers. That is just one of many ways to skin that cat.

Gil - I still remember drafting class and my instructor grading on the number of erasures you had which he could see through his light table! I just use whatever paper I have on hand these days but find thin cardboard stock to take a pencil well and hold up better. Whatever works.
 
JonJay said:
However, it is your airplane and if you want that accuracy, short of having transfer pins on hand, you can make your own if you have a small lathe. You don't need highly tempered material for one time use, just get some cheap #8 screws, chop the head off, and turn down a point. Hand thread them in and then a bit more with some pliers. That is just one of many ways to skin that cat.
Click to expand...

You don't even need a lathe. Cut the head off then stick the screw into a drill press. Turn the drill press on to make sure the headless screw spins straight. Then use a file to grind a sharp point while the drill press spins the screw. After this do the hand threading thing and mark the location(s).
:cool:
 
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GalinHdz said:
You don't even need a lathe. Cut the head off then stick the screw into a drill press. Turn the drill press on to make sure the headless screw spins straight. Then use a file to grind a sharp point while the drill press spins the screw. After this do the hand threading thing and mark the location(s).
:cool:
Click to expand...

That is too easy Galin, and now he doesn't have an excuse to buy a lathe. Shame!
 
Saville said:
1) I haven't drilled any holes - the builder drilled these holes.

2) As I mentioned in the OP, I'm thinking if a plate sandwiched between the battery tray and the mounting flanges so I am, essentially, making a fresh plate.

3) I looked at your link - it's not obvious to me how these are screwed in to the plate nut....I cannot get a wrench underneath on the plate nut side...are these screwed in from the opposite side from the plate nut?

thanks
Click to expand...


1) Ah, I missed that your new battery box was pre-drilled.

2) OK, transfer screws (or strap duplicators maybe) still apply.

3)The transfer screw is a basically a set screw with a sharp marking tip machined onto one end.
They are designed to go into a blind hole (in this case a nutplate) if necessary. The column of the sharp marking tip is machined in a male hex shape (smaller than the set screw body) that fits the female hex wrench end of the "container" they come in.

So..to use them. Remove them from container. Set one in the nutplate from the top surface shown in your images. Use the container to engage the hex and screw it into the nutplate leaving the marking tip slightly proud of the mounting surface. Repeat for all holes. Set part to be marked in position and whack it with something heavy to impress all six punch marks on the backside. Remove screws with container wrench. Drill marked part at punch marks. Open beer and relax.. :rolleyes:

yes you can make a semblance of a transfer screw at home but the utility is less because of the lack of the hex for installation and removal.
 
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Battery box

I had a similar problem where my new battery would not fit the stock battery tray. Thought I would have to build a new one. If the battery is same width as current tray(?) fits between fore and aft of current tray. Simply take the two end angles off and attach a new piece of aluminum with rivets to the bottom edge of original tray and you extend the trays width by whatever length you need and rue rivet angle to the edge.

Allan Stern
RV8A
 
Hardware store plastic-$2.00

Go to the hardware store and buy some thin clear solid plastic similar to cheap plexiglass. Mark your holes with a sharpy. Drill the marks for a pattern and transfer to your aluminum. Move on to the next task.
 
Why not just tape the proper size washers to the miss aligned plate? Position the washers over the large holes aligned with the nut plates and tape them on the plate and use the plate as a template. Larry
 
Allan Stern said:
I had a similar problem where my new battery would not fit the stock battery tray. Thought I would have to build a new one. If the battery is same width as current tray(?) fits between fore and aft of current tray.

Correct. The new battery fits the tray in the fore and aft direction, but the battery is narrower in the port to starboard direction.

Simply take the two end angles off and attach a new piece of aluminum with rivets to the bottom edge of original tray and you extend the trays width by whatever length you need and rue rivet angle to the edge.

Allan Stern
RV8A
Click to expand...


My original plan was going to be to simply transfer the bigger angles from the new tray to the operational old tray - until I removed the tinnerman washers from the screw holes and saw how badly those holes were drilled. I can't bring myself to permanently re-install that old battery tray all mis-drilled like that.

Ultimately I think my plan and your idea above is similar - although I don't have to extend the tray - I actually need wider angle ends for the narroer side-to-side battery footprint. I'm going to drill a new flat plate piece of 2024T3 so that it fits the existing plate nuts perfectly.

Then I'm going to add plate nuts to the new flat plate and drill holes in the new tray such that I can connect the new tray to the new flat plate.
 
LARCO said:
Why not just tape the proper size washers to the miss aligned plate? Position the washers over the large holes aligned with the nut plates and tape them on the plate and use the plate as a template. Larry
Click to expand...

BRILLIANT! I knew there was a simple yet foolproof way of doing this.

I will turn long screws into the over-wide holes with that washer on the screw. That way the washer hole lines up with the nut plate hole.
 
Something I have done a couple of times is to mount and shine a laser beam light on the hole then sit the new piece in place and the laser will be shining where you need to drill or mark for the new hole.
 
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