Major surgery on an existing model and further progress
|Colin Bishop||11/04/2015 18:21:58|
4522 forum posts
Usually once you have built a boat that is it but I am currently resorting to major surgery on an unfinished project. I have four of these on the go at the moment and having put the new Special issue of Model Boats to bed thought I would actually do some modelling at last. One long standing project is a 1:48 scale model of the fishery cruiser Brenda. I originally started this back in 1992 just before I got involved in full sized sailing so the model has sort of been on the shelf ever since although it has the motors and R/C installed and kept in working order. It has been sitting on my work bench ever since so I thought I would make an effort to complete it.
The prop shafts and tubes were made for me by my late, very good friend Ronnie Lawson and somewhere along the way I managed to bend the port side tube while installing it so while the starboard one purrs away very nicely the port one screeched for no obvious reason. Something would have to be done! Unfortunately the tube was deeply buried in the model hull and only partially accessible at the inboard end .My initial efforts concentrated on exposing the tube within the model with some brutal applications from a power drill and attempting to adjust it to allow the shaft to run with less friction. This was unsuccessful as only the newly exposed part of the tube could be bent and it was of thin wall brass so eventually I managed to tear holes in it with the Dremel and totally ruined it. So what to do?
Obviously, like an impacted wisdom tooth, the defective tube would have to come out but not easy without damaging the model as it was very firmly epoxied in. I dug out as much as I could from the inside and then applied the traumatic effect of a hammer to the outside. Eventually the tube moved whereupon I applied a pair of pliers to the outside crushed and twisted and pulled it free. It eventually gave up the struggle and came loose without too much external damage to the hull, much to my surprise. The next step has been to clean up and slightly enlarge the hole ready for a replacement. I have ordered an 11 inch tube and shaft from Cornwall Model Boats which should be a straight swap for the tube although I will use the existing shaft as it is much longer and supported by an A frame at the stern of the model.
So, now awaiting the replacement tube and relieved that more damage wasn’t done in extracting the old one which is not something you would expect to do in a scale model!
Wait for the next thrilling instalment.
Edited By Colin Bishop, Website Editor on 11/04/2015 18:24:01
|David Wooley||11/04/2015 21:03:03|
599 forum posts
Hi Colin that's a rather smart model but as you succinctly say removing a prop tube is akin to a dental job especially when it is firmly bonded into place .
|Andy C||11/04/2015 21:15:52|
472 forum posts
Very good looking lady. Does she have more deck detail to go on, as she looks a little bare?
|Colin Bishop||11/04/2015 21:43:43|
4522 forum posts
Yes, plenty of detail to add although the basic essentials are there.
|Charles Oates||11/04/2015 23:12:37|
566 forum posts
|Hi Colin, I had to do a similar job recently. I heated the exposed tube with a micro blow torch, stopped, coughed, swore and went outside to try again. The tube came out in a couple of minutes, but the stink from hot araldite and a molten plastic bush was awful.|
|Gareth Jones||12/04/2015 08:55:50|
791 forum posts
I have found the best way to remove an epoxy glued propsahft is to stick a soldering iron bit in one end or the other and leave it for a few minutes to heat up. The brass tube conducts the heat quite well to the glued areas. The heat softens the Araldite and you can usually remove the tube by twisting it with a pair of pliers to break the bond. Don't try it with your fingers as the tube will be very hot!
|Colin Bishop||12/04/2015 12:02:14|
4522 forum posts
Yes, I did consider the heat method but it is a long tube (11 inches) and at least half of it was buried in the hull. I thought it might need rather a lot of heat and could damage the adjoining paintwork so I thought I'd try the moderate brute force first, luckily it worked!
One of my other projects, an even older liner model has home made tubes and shafts and I might consider replacing those using the heat treatment method but we'll see how this one goes first. It's always relatively easy to take things to bits but unfortunately they then often stay in that condition!
|Colin Bishop||19/04/2015 18:52:48|
4522 forum posts
Making some progress now. The 11 inch Caldercraft thin (6mm) tube arrived the other day and was duly inserted into the hole in the hull and tacked into place with epoxy. Still quite a bit of noise though so I enlarged the hole to let the tube lie where it wanted to and re glued it. Still some noise! Getting a bit frustrated now! However I found that inserting a wood wedge where the shaft exits the hull quietened things down quite a bit for no apparent reason. I also found that the motor was bit noisy too which was remedied with a bit of oil on the bearings.
At this point I decided to introduce some water resistant grease into the tube and this did make things slightly quieter but the drag of the grease added almost 1 amp to the free running power consumption out of the water (doubling it) which is pretty conclusive - don't stuff your tube with grease! It was possible to feel the extra resistance when turning the shaft by hand.
So I cleared out the grease with washing up liquid and then flushed the tube out with WD40 which brought the consumption right down again so I guess that ordinary lube oil is the way forward.
There is still some noise but I think that will be muffled by the water when the boat is afloat. I suspect the reason is down to the overall 15 inch length of the shaft using an 11 inch tube and an A bracket at the stern, there is just a certain amount of unavoidable whip.
Anyway, filler has now been applied to the hole in the hull and will be smoothed over in the the next few days, Hopefully the outcome will be acceptable!
|Tony Hadley||19/04/2015 19:45:29|
897 forum posts
The noise from the motor bearings was remedied with oil. Was this a temporary measure and part of this re-furbishment could involve the replacement of the motors with a modern brushless installation?
|Colin Bishop||19/04/2015 20:33:05|
4522 forum posts
The motors have been in there for 20 years or so and probably needed a bit of oil. I don't see any real need to replace them at the moment as it isn't a high power model.
Might change the batteries though. At present there are 4 x 4.5 Ah Cyclon lead acid cells. These days you can get up to 10 Ah in a D NiMH cell although I would need more of them for a similar voltage.
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Colin Bishop - Website Editor