Model Boat Mayhem

Technical, Techniques, Hints, and Tips => Other Technical Questions... => Topic started by: brisoreturns on January 21, 2019, 10:24:05 am

Title: Getting a damaged prop tube out of an old model
Post by: brisoreturns on January 21, 2019, 10:24:05 am
Hi, I was hoping for some wonderful how to from the learned people here on getting an old proptube out of a model without destroying the back end entirely!

This is an old Boston Blenheim model, wooden hull, very nicely done indeed, but the propshaft was seized solid. I managed to eventually get the shaft out (steel running in a brass tube). The shaft/tube looks home made and did not have bearings/seals at either end, the shaft was just running inside a fractionally bigger tube the whole length, not the usual end caps and larger diameter tube with the shaft well clear inside.

I started to get the proptube moving but it has fractured at both ends now and is 'inside' the keel for a length of about 8"... I have no drill bit long enough, and don't want to use excessive force in case the hull is damaged...help? anyone? I'd even entertain putting  it in coke for 3 weeks at this point! 
Title: Re: Getting a damaged prop tube out of an old model
Post by: Martin (Admin) on January 21, 2019, 10:34:28 am
 
Soldering Iron or small blow lamp, heat until you can twist / break it free with a pair or pliers.
Title: Re: Getting a damaged prop tube out of an old model
Post by: Martin (Admin) on January 21, 2019, 10:37:38 am
 
Also see: https://www.modelboatmayhem.co.uk/forum/index.php/topic,55895.msg579935.html#msg579935
Title: Re: Getting a damaged prop tube out of an old model
Post by: John W E on January 21, 2019, 10:57:37 am
hi there just been looking at the plan - if the model is built to the plan there should only be about 4 1/2 to 5 1/2 inches of prop tube actually glued into the hull.   As Martin has already suggested applying heat by a soldering iron may work - but - I do have a feeling you may end up drilling the 'old' prop tube out with an extended drill.
Title: Re: Getting a damaged prop tube out of an old model
Post by: Buccaneer on January 21, 2019, 11:18:58 am
I have removed a couple of old prop shafts by drilling. I was able to get the drill to 'bite' into the end of the prop shaft and then the torque of the drill was enough to break the seal of whatever glue was used. A bit of heat and a good welly with a hammer probably helped as well.

John
Title: Re: Getting a damaged prop tube out of an old model
Post by: tigertiger on January 21, 2019, 02:58:30 pm
If the ideas above don't work, you could try something based on a bearing puller.
If at first you tighten it and nothing happens, if you leave it under tension the glue may break with a little time.
It think you may be able to get threaded rod this fine.
Title: Re: Getting a damaged prop tube out of an old model
Post by: brisoreturns on January 21, 2019, 03:30:02 pm
Oh my giddy aunt, the place is full of geniuses! :-))

Many thanks for all the suggestions, I like the bearing puller style, I can use the old shaft as the rod.

Drill, heat then puller, in that order, it is.

And many thanks to Buccaneer for the plan extract, I had thought about buying it just to see this exact area.

Outstanding stuff all! And apologies for not searching first, these forum things are all new to me!

Title: Re: Getting a damaged prop tube out of an old model
Post by: CGAux26 on January 21, 2019, 04:28:26 pm
Please report back how it goes.  I have not had this problem (yet-knocking on wood) but live in fear of it.   <:(
Title: Re: Getting a damaged prop tube out of an old model
Post by: John W E on January 21, 2019, 04:48:03 pm

One more thought for the prop shaft removal -


- if the old shaft is redundant and no longer going to be used,


- it could be cleaned up so it’s a sliding fit to the old tube - heat the pre-cleaned shaft up on a gas ring, or with a blow torch so that it isn't bright red on its full length but you see the colour blue run from one end of the shaft to the other (as in tempering steel) and then when its still hot, place it back into the 'old' tube in the hull and leave there for a few minutes so that the heat is transferred from the shaft to the tube and therefore starting hopefully to soften the adhesive. You may need to do this once or twice or more, so that the adhesive is really soft.


 Doing it this way should ensure that you get a full heat transfer from the shaft to the tube along the full length - it should then be easier to extract the tube with a pair of pliers


John
Title: Re: Getting a damaged prop tube out of an old model
Post by: Klunk on January 22, 2019, 05:45:40 am
I  just did a prop shaft replacement last Thursday, first i removed the motor and coupling and removed the rudder and inner shaft. second had a quick wiggle of the outer shaft in the hull, then took a small hammer and a flat head screw driver and gave a quick tap from the rudder side, and behold it popped straight out!
Title: Re: Getting a damaged prop tube out of an old model
Post by: roycv on January 22, 2019, 09:19:51 am
i I have taken out a few in the past, usually a pair of mole grips clamped on and a sharp twist loosens most.  Perhaps a hammer blow from the inside straight along shaft centre would shatter the old adhesive?
Regards
Roy
Title: Re: Getting a damaged prop tube out of an old model
Post by: chas on January 22, 2019, 12:04:03 pm
Me too, I've had to remove tubes in the past. I also heat the tube, grip with pliers and twist. It's simple, easy, safe and only takes 5 mins. Never failed yet.
Chas

Title: Re: Getting a damaged prop tube out of an old model
Post by: bj on January 22, 2019, 12:21:19 pm
Purchase a length of K&B brass tube one size larger than the damaged outer tube. 
Cut atleast one shallow V in one end and place other end into an electric drill. Working from the stern carefully drill the damaged tube out. Clear the wood/adhesive swarf frequently. This hollow "drill" will cut grp resin/fibreglass and epoxy glue quite well.
Title: Re: Getting a damaged prop tube out of an old model
Post by: John W E on January 22, 2019, 02:14:47 pm

hi there, just a thought - we are all suggesting various ways but, has the model been built as plan?



The reason I ask is the rudder may be built into the model as mine is - and it would be a major job to remove the rudder, this is because the top end of the rudder where the rudder linkage is should be underneath the sloping aft deck, which would make it extremely difficult to locate and remove the top linkage. 


Therefore, the only way the shaft tube may come out is in towards the hull -  drilling from the outside or any other operation from the outside of the hull would be difficult because the rudder will possibly be obstructing.


Food for thought.
Title: Re: Getting a damaged prop tube out of an old model
Post by: brisoreturns on January 22, 2019, 04:08:14 pm
Hi All,

done! and undamaged hull more to the point. The rudder is as per the photo above from John WE, but luckily the bottom pintle plate was a short brass bar that had been screwed into the keel and came off easily, along with the rudder tiller screw being accessible.

I ran a drill bit up the tube from the stern end and out came a load of brass swarf but no rotating tube at the other end...bit worried at that point... so went all the way to the drill chuck then decided this was it and took the old shaft, rammed it up the tube hole until it hit a ridge, which must be what  was left of the brass tube inside, and battered the life out of it...out she came into the inside of the hull.

You can see where the drill chewed away the back end of the tube if I can get a photo to upload (new to all this forum stuff).

I did find the most unusual gearbox in her, it seems to have some sort of planetary arrangement and mounts straight onto a 540 style motor can (a toothed gear goes on the motor shaft and ends up in the middle of the 3 'planets'). I can't see a name on the gearbox but expect you will all have seen this type a thousand times before! I've only ever used direct drive to this point. I imagine the noise must be quite something.

I'll use bj's suggestion to open the shaft hole up to take a 4BA and fit a 4 blader.

Many thanks to all.

Title: Re: Getting a damaged prop tube out of an old model
Post by: Netleyned on January 22, 2019, 05:21:00 pm
Sounds about right :-))
The RN Artificer Apprentice
School had a ships crest of an arm
holding a hammer.
If it don't work hit it with a hammer.  {-)
Ned
Title: Re: Getting a damaged prop tube out of an old model
Post by: hopeitfloats on January 23, 2019, 09:27:38 am
Quote from: brisoreturns on January 22, 2019, 04:08:14 pm
Hi All,

done! and undamaged hull more to the point. The rudder is as per the photo above from John WE, but luckily the bottom pintle plate was a short brass bar that had been screwed into the keel and came off easily, along with the rudder tiller screw being accessible.

I ran a drill bit up the tube from the stern end and out came a load of brass swarf but no rotating tube at the other end...bit worried at that point... so went all the way to the drill chuck then decided this was it and took the old shaft, rammed it up the tube hole until it hit a ridge, which must be what  was left of the brass tube inside, and battered the life out of it...out she came into the inside of the hull.

You can see where the drill chewed away the back end of the tube if I can get a photo to upload (new to all this forum stuff).

I did find the most unusual gearbox in her, it seems to have some sort of planetary arrangement and mounts straight onto a 540 style motor can (a toothed gear goes on the motor shaft and ends up in the middle of the 3 'planets'). I can't see a name on the gearbox but expect you will all have seen this type a thousand times before! I've only ever used direct drive to this point. I imagine the noise must be quite something.

I'll use bj's suggestion to open the shaft hole up to take a 4BA and fit a 4 blader.

Many thanks to all.

many years ago I owned an electric screwdriver. it had a gearbox remarkably similar to your gearbox.
Title: Re: Getting a damaged prop tube out of an old model
Post by: JimG on January 23, 2019, 01:57:25 pm
Having used a monoperm motor with the Pile gearbox in the past I have found that planetary gearing is not as noisy as the more normal type. Especially as the enclosed planetary gearbox can be packed with grease for improved lubrication.
Jim