.049 Prop bush

pkrankow:  I have used silicone fuel hose with over sized slow run props quite successfully, so using a rigid tube is not specifically necessary.

 

Like Phil noted, using fuel tubing is a common and effective means to center a prop.  The tubing should not extend beyond the hub, since its only function is to keep the prop centered until the prop screw is tightened.  After that, the compression on the hub will hold it in place. 

1/2A APC props have a large hole in the hub and need either a turned bushing or tubing to help center it.

I had some bushings made for APC props that are very well engineered. Your problem however is with the Cox props themselves. My solution to your problem may or may not help but it's certainly worth trying. If your using a stock Cox screw, I would try another. Use a 5-40 Allen socket head which has a shoulder on the last remaining portion and not threaded the entire length of the shaft. This may just help your loose fit. In addition, many of the steel prop screws are just plain bad, they're not straight which can compound and telegraph bad vibes which can certainly rob performance. The socket head is much harder and not as susceptible to bending and it will square the spinner to the prop correctly vs the other way around. Ken

Just wrap a strip of paper around the shaft/screw until you get a good fit. Put a drop of glue on it to keep it from unwrapping.

In the meantime, why muck about?  Cox props from Bernie are $1.95 (http://coxengines.ca/propellers/) and whilst a little more expensive from Matt, he has a much wider selection (http://www.exmodelengines.com/propellers/?&sort=orderby&sort_direction=0&objects_per_page=50).

Ken Cook wrote:I had some bushings made for APC props that are very well engineered. ........ If your using a stock Cox screw, I would try another. Use a 5-40 Allen socket head which has a shoulder on the last remaining portion and not threaded the entire length of the shaft. This may just help your loose fit.

The holes in the smaller APC props are often drilled off center --- APC admits this.  However, the recess molded in the back of the hub is centered, but bushings have to have a shoulder that fits snugly and flush.  If you either have access to a lathe or someone who can turn these, this is the best approach for APC.

I do the same as Ken WTR COX prop screws.  The shorter socket screws are almost always fully threaded, but once you get to an inch in length, they will generally have a shoulder.  I buy this type, both for COX replacement and NORVEL replacement screws, then cut to length so that the screw tightens down just before it bottoms out in the shaft.  The additional length allows maximum thread contact and helps support the bored out section of the crank.

Just wrap the propscrew with a bit of tape is my easy solution. Use alum duct tape IF you feel the need to get fancy...
Cheers, Paul

Thanks for your replies, went with the fuel tube over the screw option. Also now using cox cap head screw and spinner. I will probably try everything in the end, I link to tinker!