I managed to botch up one of the six bolts that fix the propeller to the flange on the reduction gear. Now these are a bit out of the usual, I cannot imagine they’d be available ready made so I’d either have to order from the factory (which generally works well) or have them made to order. Would this be an option?
Quality: 8.8
Diameter: 8 mm (which seems to exclude AN quality)
Head: hex, sw 13mm
Shaft, unthreaded: 115 mm
Thread: M8, another 15 mm
The present bolts, fitted ex-factory, have a 120 mm shaft, reduced with some washers; and the thread part must have been longer too, originally, I see signs of machining at the end.
I could machine up bolts on my lathe, out of some hex stock, but yours must be high spec high tensile steel bolts which can’t be just machined up casually. I would expect them to be forged and rolled. Rolled threads are also much stronger. Machining high tensile steel is a pig of a job, too.
There should be markings on the head, and if you do a google on bolt markings etc you should be able to narrow it down.
Presumably you can buy these from the aircraft manufacturer, at some silly price?
Peter, the investigation into quality indications had been duly done – Wikipedia says “High-strength steel bolts usually have a hexagonal head with an ISO strength rating (called property class) stamped on the head. ( … ) The property classes most often used are 5.8, 8.8, and 10.9.”
The bolts that I have mention 8.8 – as do those sold by my trusty hardware store. So while this stuff is hard I think it will be far less hard than aviation grade AN bolts.
As for buying from the manufacturer, I hope and trust their price will be less than astronomical; they have been quite moderate on previous occasions. All options are open, as yet.
8.8 quality is standard high tensile steel and I would use just this type as it is a bit tougher and less brittle than 10.9 or 12.9. You will find them easily in stores. Ideal length may be a little problem but cutting with a hacksaw is no problem.
Vicmmm, sounds like a tiresome venture with a manual hacksaw… Still, my main reason for asking was the ideal shaft length of 115 mm which is rather non-standard. 120 mm will be found, yes.
8.8 is the same standard as AN bolts roughfly, or just about exact? But 8 mm is very close to AN5 size bolt, within 0.08 mm hole size. If non-standard metric bolts are used, this indicates that it could originally be made for AN5 bolts and reamed up with a 8 mm reamer? or is it a Rotax?
AN bolts are not precision bots (not shear bolts), so if your application needs precision bolts then AN is not an option in any case.
half a minute in Ebay produced this :
http://www.ebay.de/itm/Sechskantschraube-M8x130-8-8-A4K-DIN-931-/261448801480?pt=Motorrad_Kraftradteile&hash=item3cdf901cc8
http://www.ebay.de/itm/M8-Sechskantschraube-mit-Schaft-Gute-8-8-DIN-931-Maschinenschrauben-verzinkt-/281365314983?pt=DE_Haus_Garten_Heimwerker_Eisenwaren&var=&hash=item4182adfda7
I guess it is not crtitical where the threaded portion ends.
VicI’d be wary of buying anything “important” on Ebay since almost anything on there which can be a fake probably is…
Well, yes and no. We are used to it being a channel for cheapo offers from cheapo manufacturers, mostly from certain cheapo countries. I must admit I avoid the place for that reason. But this here schraubenhermann even publishes a list of DIN-norms so he must obviously rock solid reliable. And the stuff offered is DIN 8.8, so just as good as what I have now. Only he does not offer anything more than my local trusted hardware store.
I will now first wait for reply from the factory, which will be Monday at the earliest – they need to get their interpreter up, first of all.
Well, I recently made bolted holes for my shoulder belts. The bolt size is AN5. I could have used a 8mm reamer from work, but being way too accurate I guess, I bought a reamer from ACS, 5/16 inch or 0.3125 inc (7.94 mm). I don’t know what the max hole size for an AN5 bolt is, but I would believe it is larger than 8 mm. Anyway, bolts and hole sizes are worth a study all by itself.
An AN5 bolt has a diameter anywhere between 0.309 and 0.312 inches (7.85 to 7.92 mm). The hole is usually drilled with a drill size equal or less than 0.309 and then reamed up to 5/16 (7.94 mm), but this is no spec, just common practice. So an AN bolt is not very accurate, it is not meant to be used as a shear bolt for instance (yet an AN5 bolt in a 5/16 hole feels very tight). Drilling the hole with a 5/16 drill bit will also make a perfectly good hole even though it may be oval and ugly. NAS bolts are close tolerance bolts. A NAS464-5 have a shank size of 0.3117 inch and a tolerance of 0.000 inch up and 0.0009 down (7.9172 mm – 0.0229 mm). To achieve such accuracy by hand when drilling a hole is almost impossible, even with a reamer. I know of no homebuilt aircraft that use NAS bolts, and certainly no NAS shear bolts. It would be incredibly stupid to design a homebuilt that no one could build at home, so AN bolts it is.
But here is the interesting part. An M8 bolt has according to DIN 931 a diameter from 7.78 to 8.00 mm. The hole is typically 8.2-8.4 mm where 8.2 is considered a close fit. This means an AN5 bolt is well within the specs of an M8 bolt, and AN material spec is the same as 8.8 spec, except AN bolts are plated not galvanized. So unless your holes are ridiculously large, an AN5-33 or -34 bolt would fit just perfectly.
This is something I have wondered about for some time. Is there a metric equivalent to AN bolts and fittings?
