CRAP... Did I screw up my mast tube?

[KDOG]

All that work, down the drain. I was rechecking the measurements of some holes and discovered that one of the 1/4" mast holes is a 1/16th of an inch off. I think that may be a little too much. The bolt wouldn't go thru unless I drilled the hole out, but I'm not sure about that considering the load on these particular bolts. Crap, crap, crap. Take a look at the picture and tell me what you think...

Also, I rechecked all the other holes in the mast, and the holes in the keel and tailboom, amazingly, they are all perfect...it has to be ONE hole... :mad: :(

I guess Starbee will be getting another order from me, DRILLED this time...

[Chaff]

I'm no Gyrobee expert, but...

Could you make one or both a larger caliber bolt? Take up the difference by using a wider bolt? Stress analysis expert, please comment.

[KDOG]

I would have to go 5/16ths. But I'm afraid of scoring the inside wall....

[Brent_Brown]

How much tube do you have from the hole and the end of the tube? it looks thin to me. I drill all my holes 3/16 put the gyro together and drill to 1/4. Drill to fit paint to match.

[KDOG]

Its one of the bottom rotorhead cheek plate holes....

[scottessex]

Sorry to say, but it looks like srcap to me.

I've been there, done that. I have been an aircraft mechanic for 19 years, It sucks when you drill a hole wrong in a 60 million dollar 767! :)

As a rule I don't like to have the edge of a hole closer than 1/2 a diameter to the edge of the piece. That way you will maintain your structural integrity. Especially on a rotorhead cheek plate, or other critical area, leave as much meat as possible.

I know it stinks, but just remember, it's your butt hanging from that mast! so don't comprimise there!

[Alan Coats]

Kevin,

At first it looked like the holes pictured were in the bottom of the tube, right at the end. After looking closer, though, I realized that that is a ruler you are holding against the mast to show how far out of alignment the one hole is. You said that the holes were the bottom cheek plate holes, I believe, so they are a long ways from any tubing ends.

Have you drilled the holes in your cheek plates yet? If not, can't you just adust the position of appropriate hole in the cheek plate to match the errant hole in the mast?

I am assuming that you didn't score the inside of the mast when you drilled the hole, and that the hole is out of postion vertically, not horizontally.

Alan

[Brian Jackson]

Sorry man, but it's scrap. Had the holes been on the end of the tube I'd say just cut off that last half-inch, but as it is now I'd feel better if you'd simply replace the tube. It's not that much money, and you'll be safer in the long run. Like Scott said, it's your butt hanging from that mast!

Brian

[KDOG]

ITs scrap, I didn't score the inside wall, but thats not the point. Can't risk my life over something so simple to replace. Its only money -$115 at that. Just sucks thats all. Now I'm considering waiting to see if I get a year end bonus from work and just getting the complete single mast rolling airframe kit from Starbee.... we'll see. Like I said, the keel and mast seem to be ok, but now the confidence in my work is shaken and I'm paranoid that there is something wrong with them too.

[GyroRon]

K dog if it is the bottom cheek plate bolt holes you are showing there is no reason to scrap it unless you scored the inside wall. Just drill the holes in the cheek plates to match, and all is fine. Everyone here telling you to scrap it is missing the fact that there is a tinted transparent ruler on the piece and they think the holes are drilled right at the tip of the piece which WOULD be grounds for scraping the piece - or doing as someone else here suggested and cutting off the end and re drilling below. Anyway save yourself the money and use that piece, there is nothing wrong with that piece. And be careful from now on!!! :)

[Brent_Brown]

I did miss the tinted transparent ruler and asked if it was that close to the end. I would drill the plate fit that hole and drive on. I I like to bolt the sub parts together as I go before drilling other part. I like to drill the holes in the tubes then transfer the hole to the plate one hole at a time. Your 1/16 off would just be transfered to the plate. Drill bit walking is going to get you off some. That is why 3/16 fit the parts then drill it out a step drill is good for this.

[Brent_Brown]

If you go to the affordaplane web site and see how they make it. you will see they jig it down and drill in place

[KDOG]

Yeah, I actually have the plans to the affordaplane. I see how they clamp the tubes and plates together and just drill thru both of them. Hmmmm, maybe you are right....the hole in question is the bottom rear cheek plate hole. Its not closer to the edge, its just a 16th closer to the top end. Hmmm now you got me thinking.....

[scottessex]

Hey I missed the ruler also! after a closer look, I thought the edge of the ruler was the edge of the mast.

Do what Brent said, just transfer the holes in the plate to match the holes in the mast and you should be good.

Also small deviations like this can be caused by the drill bit walking. that is why I only use the center drills on critical parts. But drilling them 3/16 then opening them up to 1/4 after you bolt them together takes more assembly/disassembly time it will work.

Good luck, and welcome to the wonderfull world of homebuilding!

[KDOG]

Speaking of the cheek plates, I was just looking at the plans and I see that they are made of 1/8th" 6061 - thats it? Shouldn't they be made of the 1/8th" steel or the 3/16th aluminum?
Maybe I can get StarBee gyros to cut the shape of the cheek plates and not the holes...

[KDOG]

Thanks guys, WHEW that was close, wasn't it?

CANCEL RED ALERT!!! :)

[scottessex]

1/8 th is plenty strong, I had a hard landing and bent my rotor blades, mast and keel, the 1/8th cheek plates are still flat! If you beef it up too much you will start adding more weight.

[KDOG]

Wow, I remember when you first posted about your hard landing. Is that a bee? Thanks for the info!!!

[scottessex]

No, it is a Bensen/KB3 not too much different than a bee. It will be much better this time.

[KDOG]

Was that your only aircraft? Maybe you should build a bee, too! ;)

[scottessex]

That was the only one! :mad: it sure was FUN! but it will be much better this time around. see progress under the bensen section, bensen rebuild part2.
http://www.rotaryforum.com/forum/attachment.php?attachmentid=4511&stc=1&thumb=1

[KDOG]

Nice!!! Did you have to by a new engine or did the other one survive? Also, are you gonna put a nice big HS on the tail this time? ;)

[scottessex]

yes- no- yes

the engine blew a head gasket on takeoff--very bad.

The engine is no longer made, and no parts are available.

I am going to a tall tail with HS in the center.

The old version had a small stab on it. you can see all the progress in the bensen section, pics, and engine info, all the good stuff.

[rfi]

I have built a dozen gyros and I learned a long time ago that the way to get perfectly matched holes is to drill everything undersize (3/16 for 1/4 inch diameter bolts) and Cleco the tubing and plates together and then ream the holes out to 1/4 inch. That way you will have perfectly matched holes.

You can purchase a set of Cleco pliars and a couple od dozen clecos for around $25.

[Brian Jackson]

I have built a dozen gyros and I learned a long time ago that the way to get perfectly matched holes is to drill everything undersize (3/16 for 1/4 inch diameter bolts) and Cleco the tubing and plates together and then ream the holes out to 1/4 inch. That way you will have perfectly matched holes.

You can purchase a set of Cleco pliars and a couple od dozen clecos for around $25.

What tool exactly do you use to ream the holes with? I just purchased a set of 3/16" & 1/4" centering bits today. I'm assuming the reaming is done on a drill press rather than by handheld drill for perpendicularity. I would greatly appreciate a detailed write-up of the drilling sequence, and any tips for using layout fluid (scribing dye) and transfer punches. Thanks.

Brian Jackson

[Dean_Dolph]

I have built a dozen gyros and I learned a long time ago that the way to get perfectly matched holes is to drill everything undersize (3/16 for 1/4 inch diameter bolts) and Cleco the tubing and plates together and then ream the holes out to 1/4 inch. That way you will have perfectly matched holes.

You can purchase a set of Cleco pliars and a couple od dozen clecos for around $25.Don, I haven't built a dozen gyros but I have managed to drill a few holes for Boeing in Wichita. Also beat a few rivets in to submission there and on boat and race cars projects while in Calif. It has been awhile. Actually it has been many, many years!

I agree that Clecos are a valuable to have around and using a reamer to finish a hole is the proper way. The reamers I use are the straight sided with straight flutes. A reamer should not be used to remove a lot of metal and is usually limited to 0.003 - 0.007. This means that the final drilled hole size should be this much undersize. Trying to remove more than 0.007 can mean big problems in that it can overload a reamer and you definitely don't want to have one break down in the hole. I suspect there is a magic way to determine the size of the pilot hole vs. the final drilled hole but I don’t know what it is.

I would use the following procedure to sort of match drill my holes.

1. Lay out the hole locations on the outer piece. DO NOT use a scribe to do this!

Using a lead pencil is also not a good practice. People have suggested that a fine point felt pen be used but I have found them awkward to use and I don't get the hole center placed where it is supposed to be. So, I end up using the forbidden hard lead pencil. If possible I use thin masking tape on the aluminum to do the layout. My only concern in doing this is the adhesive.

2. Verify the hole locations. Remember ye ole carpenter rule of measuring twice before cutting once? This ain't carpentry but the rule applies!

3. Next use an automatic center punch (use a low spring setting for aluminum) and make a small dimple at each hole location.

4. Then use a drill press with a properly squared table and the pilot hole size self-centering drill bit (Scott mentioned using self-centering bits to keep the bit from walking in another thread) to drill a pilot hole in each of the hole locations.

The idea behind using a drill press is to assure yourself that the holes are perpendicular to the surface. But if you are forced to use a hand drill then try to keep the bit perpendicular. There are hardened drill guides to help with this but I've found them awkward to use. There is a proper way to hold the drill motor to help keep the bit perpendicular but it is almost impossible to describe without a picture or diagram which I don't have. Some times, if the light is right, you can see the reflection of the bit in the aluminum and by moving the drill motor you will see it line up 90 degrees to the surface.

5. Then clamp the pieces, you want to fasten together, in the proper relationship. Verify that the relationship is right because there aren't any second chances once you start the next drilling procedure

6. Using the proper size transfer punch, in the pilot holes of the top piece, make a small dimple in the second piece. When I say a small dimple I mean don't hit the transfer punch with a ten pound sledge!

You can see transfer punches at this link http://www.thetoolwarehouse.net/shop/FOW-72-482-028.html

7. Now pick the prime hole (your choice!) and using the top piece as drill guide, drill a pilot hole in the second piece. Place a Cleco in the prime hole.

Then proceed to pilot drill each of the hole locations in the second piece using the top piece as a drill guide but place a Cleco in the first hole next to the prime hole and then as often as needed to assure yourself that the relationship between the pieces won't change.

If you are drilling a round tube then you must use a Vee block.

8. Once all the pilot holes are drilled then change to the final drilled hole size self-centering bit and drill the final hole at your prime hole location.

It slows down the process some but I would now swap the bit for the reamer and ream the prime hole to the final finished size. Place a Cleco or even better a bolt in the hole. This will lock in that first hole. As before, place a Cleco in the hole next to the prime hole and then as often as needed to assure yourself that the relationship between the pieces won't change.

You can get an explanation of reamers here http://www.unionbutterfield.com/UB/technical/reamers/nomenclature.htm

And while the ones shown are not exactly like those I have used it will give you and idea of what a reamer is and the hole sizes and precision they can provide.
http://www.discount-tools.com/creamersindexmain1.htm

9. Proceed with drilling the rest of the hole locations to the final drilled hole size. Again, placing a Cleco (or bolt) in the second hole and as often as necessary to maintain relationship between the parts.

10. When all the holes have been drilled to the final drilled size then ream them one by one but always keep enough Clecos, or bolts, in place to maintain the parts relationship..

11. When all of the holes have been drilled and reamed then pull the Clecoes and/or bolts from the parts.

12. Deburr the holes in the outer part and carefully remove all metal shaving from all pieces.

If for some reason you can't separate the parts to remove the metal shaving that are in between then you can use a chip chaser. No one ever has these so the next best thing to use is a hack saw blade that has had the 'set' ground away so it doesn't scratch the metal. You slide the saw blade between the parts, usually two sheets, and 'hook the metal shavings and pull them to the outside.

13. Do not remove excess metal from the edge of the holes when deburring. The idea is to break the sharp edge to eliminate a stress riser and not to chamfer it. There are fancy deburring tools to deburr the inside of tubes if you feel it is necessary.

I may have gone over the top somewhat with this drilling procedure but unfortunately I am cursed with being a perfectionist. But, my manual dexterity is so poor that I need all the assistance I can get so need to follow such a procedure in order to turn out half way decent results.

[Brian Jackson]

Dean,
Many thanks for that detailed and insightful writeup. That's precisely the great info I needed. I also appreciate the links to various reamers, etc. I have learned a lot this morning! I can see now that perhaps I should have purchased, say, 15/64" centering bits instead of 1/4" such that the hole would be undersized (~ .007 R) for the reamer.

For the blue layout fluid, the only areas I would consider "scribing" would be 1/8" cross hairs from within the approximate hole location... meaning I'd have to get pretty close with a fine-tip Sharpie, but I'd like to use the dye to scribe the ultra-precise micro-lines, but only within the hole circle, not over the remaining tube or plate material. On past (non-aircraft) projects I used to use a dial caliper micrometer to locate hole locations in relation to an edge or physical feature. The sharp-point jaw blades were excellent at scribing tick marks, while one jaw blade slightly overhung the edge of the material. I don't trust tape measures with hole clusters.

Thanks,
Brian Jackson

[Dean_Dolph]

Brian, I'll have to admit that I don't always use the drilling procedure I posted. It depends on how critical I think the job is. Also it sounds like you have had experience in layout so the caution about scribing, which if done within the limits of the hole as you have described, isn't a problem.

I don't know if this will be of help to anyone but amongst my assortment of books I have a few that I recommend people take a look at to see if they have any value. Since I have them, obviously I think they do! All of them have something to offer with books #6 & 7 being my favorites. They deal with modern race car construction which uses aircraft construction techniques and materials. Number 7 is the more useful of the two but #6 answers a lot of 'Why' & 'How' questions. The rest of the books are strictly for aircraft and present accepted procedures.

1. "Acceptable methods, techniques and practices - Aircraft Inspection and Repair "
FAA AC 43.13-1B with Change 1 AC 43.13-2A Combined
2. "The Sportplane Builder" by Tony Bingelis - Available thru the EAA & at various bookstores.
(I buy mine on line!)
3. "Sportplane Construction Techniques" by Tony Bingelis
4. "Firewall Forward" by Tony Bingelis
5. "Standard Aircraft Handbook" (The latest edition, I think, is the 6th)
6. "Engineer to Win" by Carroll Smith
7. "Nuts, Bolts, Fasteners and Plumbing Handbook by Carroll Smith