Engine mount screws

Hi

I'm trying to decide the best tread standard for mounting .15s
in Australia. UNC are very difficult to obtain in Australia outside hobby shops and there are none in my town. I have had a few incidence where UNC screws shook loose both in engine and muffler mounting. Recently this happened on holidays, I had no spars and could not get to a hobby shop until the trip home. That killed flying for the rest of the holiday.

I have used metric and BSW which are a finer thread pitch than UNC and never hade one shake loose. Seems thread lock is essential on UNC. Both metric and BSW are commonly available in Australia though not so easy to find 3mm 1/8 inch and smaller. Electronic stores stock small sizes though. I would prefere to use metric because of simple availability and the finner pitch thread seems to hold better than UNC.

However UNCs from hobby shops come in neat varieties like socket heads and blind nuts are available for them. I have yet to find a source of metric or BSW socket heads and blind nuts in 2 - 3 mm sizes in Australia.

So any Aussies out there know of sources?

What are other aussies standardising on?

What is the easiest standard to find replacement for in Australia?

>http://www.microfasteners.com/

Ron B.
F4Fguy

Couldn't have said it better myself!

Hi Ken
I'm in Sydney and have found that you can get UNC socket head cap screws at decent engineers supplies, I go to Coventry Fasteners here in Sydney but you may have to buy in bigger quantities than at the hobby shops.
About the only BSW socket head caps that are available are 1/8 BSW, but this size is pretty much a non preffered size these days and you may have problems finding a stockist.
You may find 1/8 BSW in electrical stores such as Tandies or Dick Smiths, but the quality of the steel is very cheesey and if you're using these it may be the threads are actually stripping. I avoid the "Zenith" brand at hardware stores like the plague.
You can substitute 5-40 UNC for the 1/8 BSW, the only difference between these two is the thread form angle, 60 for UNC and 55 for BSW and you wouldn't be able to tell the difference!
But again 5-40 isn't widely used here in Oz either so you may have problems finding blind nuts for this or 1/8 BSW and you are unlikely to find any 5-40 fasteners in a hobby shop.
I use 4-40 and 6-32 for just about all my engine mounting. I don't usually use 6-32's untill I get to 45 - 60 size motors so I'd recomend 4-40's on your 15's. Next time you're in you local hobby shop buy a few extras screws and nuts to keep in your flight box. If you stay with the DuBro or Sig brands you'll at least be getting higher quality steels.
You really shouldn't have any problems with UNC as opposed to any other thread forms from coming loose UNC, BSW, BSF or metric for that matter.
If your mounts are coming loose I'd look at making sure that the the bearers aren't compressing, use the correct washers and invest in the slighly more expensive nylock nuts.
Cheers John

Ken,

In Newcastle, NSW we use Newcastle High Tensile Bolt Company. They have a web page at: http://www.hi-tensilebolt.com.au/

We've been able to get Unbreako brand socket headed h/t screws in 2 mm metric threads for OS headscrews, 3mm for Norvel etc and 1/8 Whitworth and 6 BA engine in engine mount sizes, in small quanities, in recent years.

We also have a Model Engineering supplier up here at Medowie,
Where I have been able to buy good quality taps (including 4-40) much cheaper than the hobby shop prices. He also sells the smaller BA, BSW, BSF and metric size machine screws. I was able to get some 6BA hex headed (not socket) bolts a while ago. They use them on the steam locos. Worth a phone call!

Winter E & J
..Model Engineerng Supplies
18 Kirrang Drv Medowie 2318
(02) 4981 7999
He does telephone orders and services much of the local Model Engineering demand.