Protecting prop bolts with a wooden propeller.

Rob Swain · Post by **Rob Swain** » Wed Feb 11, 2015 5:31 am

I have a wooden prop on my RV6.
The an6 bolts that hold it on are a close fit in the prop.
This causes the cad plating on the bolts to wear off and the bolts to rust.
I'm about to buy my third set of bolts: £75 - ouch!
Anybody have any ideas how to stop this happenning again - short of drilling the bolt holes bigger which is obviously a no-no?
I also consider oiling the bolts is not a good idea with a laminated wood prop (staining, glue damage).
I did think about waxing the bolts, but I think the wax will just scrape off when the bolts are inserted.

Ian Law · Post by **Ian Law** » Wed Feb 11, 2015 9:43 am

Can't offer any reliable suggestions as to how to deal with this problem.

I have to find the best solution to protecting the bolts and fittings on the wings I am assembling; the drawings require the bolts to be a hand push fit, which they are, but I suspect that if the fit is tight enough most of any protective paste, such as Duralac, will be scraped off. JC5A is not supposed to go hard over time, but it might be cheaper to gold plate everything?

The holes have been treated with a couple of coats of a thin solvent based epoxy varnish ( Eposeal) and sized as directed in my plans. The bolts are a smooth push fit but I notice that they only have to be removed a couple of times for some of the plating to have been compromised.

Dipping all bolts in hot beeswax is the quaint and appealing recommendation in the plans, but I haven't tried this yet!

Ian

Chris Martyr · Post by **Chris Martyr** » Wed Feb 11, 2015 12:42 pm

Zinc Chromate paste [JC-5] is indeed the best solution. It retains a grease-like consistency and doesn't turn into yellow paint like Duralac does.
Ian's right, it is quite expensive but I have used it for lots of different applications when assembling metal/metal or wood/metal joints.
Personally I don't think that there is enough awareness about the use of jointing compounds, as Malcolm McBride's column too often bears witness to.

G.Dawes · Post by **G.Dawes** » Wed Feb 11, 2015 10:19 pm

No hole should be that tight on a bolt. it needs to redrilled with the correct drill in a pillar drill.
If it is that tight there is a danger that the tightening down might be to loose because the torque is being absorbed by the wood grabbing the bolt. If the bolts have been overtightened in the past then the wood fibres have been crushed and the hole made smaller/tighter. No Prop ever came out from a reputable maker that was too tight on the bolts.

Rob Swain · Post by **Rob Swain** » Wed Feb 11, 2015 11:29 pm

G.Dawes wrote: No Prop ever came out from a reputable maker that was too tight on the bolts.

Very interesting, but how tight is too tight? Or, of more use, what would be the correct clearance size for a 3/8 bolt? 25/64? 13/32?

The bolts push in and out just with hand pressure or a very light tap. Your torque comments are irrelevant in this case as the bolts don't have to turn, indeed the crush plate locks them, and they are fastened with nuts on the back of the prop extension.

Rob Swain · Post by **Rob Swain** » Wed Feb 11, 2015 11:51 pm

Ian Law wrote:Dipping all bolts in hot beeswax is the quaint and appealing recommendation in the plans, but I haven't tried this yet!

I have to admit I considered candle wax!

G.Dawes · Post by **G.Dawes** » Sat Feb 14, 2015 12:32 am

I would redrill with a 3/8 drill as I still think the wood has been squeezed too tight.

Light Aircraft Association

Protecting prop bolts with a wooden propeller.

Protecting prop bolts with a wooden propeller.

Re: Protecting prop bolts with a wooden propeller.

Re: Protecting prop bolts with a wooden propeller.

Re: Protecting prop bolts with a wooden propeller.

Re: Protecting prop bolts with a wooden propeller.

Re: Protecting prop bolts with a wooden propeller.

Re: Protecting prop bolts with a wooden propeller.