Model Boat Mayhem
Technical, Techniques, Hints, and Tips => Engineering Techniques and Materials. => Topic started by: AlisterL on January 09, 2012, 12:31:19 am
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Not sure if this is a silly question or not, but I need to move the prop further in towards the fore end of a kort nozzle.
With the nut in the "normal" place the prop is too close to the end of the nozzle:
(http://s18.postimage.org/v174thgvp/P1010380.jpg) (http://postimage.org/image/v174thgvp/)
So will the alternative arrangement work ok?
(http://s18.postimage.org/mpfz5z8vp/P1010379.jpg) (http://postimage.org/image/mpfz5z8vp/)
I can't think why it would be a problem, but thought I'd check with the brains-trust...
And no the nozzle can't be made longer :)
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I do not think that would work as the prop and nut would unscrew its self, have you thought of shortening the shaft and tube, assuming you have access to a die of the correct thread it would e a relatively easy job to slip out the bush, shorten tube and extend the thread by the appropriate amount. You would then be able to fit a nut, the prop, and a locknut to hold it all together.
Regards,
Nick. :-)) :-)) :-))
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I new there was a reason... Thanks Nick. Unfortunately the problem is not with the length of the shaft, but the position of the prop relative to the end of the nozzle. The washer and the nut (mostly the nut) push the prop an un-scale distance away from the end of the shaft. I might try filing the nut down a bit.
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Guys.....just thinking.......the principal of using a lock nut is simple
1. a nut can be positioned at any given point on a threaded shaft
2. we introduce a second nut and apply a torsional moment between the two nuts [holding each nut with a close fitting spanner] and tightening toward each other
3. in effect we are stretching the threaded shaft....however we must not exceed the yield point value of the shaft material as if that happened the shaft would fracture & split
4. placing Loctite is a form of insurance, however it is the induced torque applied between the two components that locks them to the shaft
5. we can consider the propeller tapping to be one nut....the other component is the lock nut
6. the difference in the length between the propeller tapping to the nut length has no influence ...again it is the induced tension between the two components
7. in an extreme overkill...if each component were tightened against each other beyond the shaft materials yield point..........the component with the shortest thread form length [the nut] would have caused the yield failure
Now the alternate to this is locking the propeller against a shoulder on the prop shaft & installing a lock nut.........however the same principals apply.......stretch the shaft thread
As I am sure many would understand cylinder heads on large marine diesel engines are secured by hand and without a lock nut O0 as the cylinder head studs [160 diameter?] are hydraulically stretched....the nut engaged to seat & the hydraulic tension on the stud released :-)) ....same principal
For my money...........if you install the prop & locknut as per the points above ...they will never move........ :-X .....Derek
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And that, Derek, was what I based the original question on - if the prop and the lock-nut are tightened to each other then it should be secure. Maybe I should have said it that way to start with.
TYVM!
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For piece of mind could you fit a spring washer between the nut and prop, or is there enough thread to fit a nyloc nut?
Brian
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Brian & Alister....some of the principals applied to both small & large diameter screwed/bolted applications are... %)
1. having close toleranced male & female threadforms
2. having square shoulder faces of the components relative to their shaft axis
3. a spring washer when compressed is only a spacer........it does not contribute to shaft thread stretch & the induced torque applied between components
4. a spring washer [when tightened] will also attempt to alter the axial alignment of the components via the male to female thread tolerance
5. a result of this is out of balance alignment
6. a Nyloc nut when correctly torqued/tightened offers no greater resistance to loosening other than the friction offered by the nylon insert to the shaft thread within the nut
.....Derek :o
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could the torque on the prop eventually loosen them though. i know i have had the odd prop come off (usually only in the middle of the pond though :D ) and thats what i have put it down to. possibly going astern a bit quick.
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mmmmmm :D... this is an interesting subject {-)
1. the anti rotational torque [acting] on the propeller blade surface is the resultant of the applied input power - this applies equally to FWD or ASTERN rotation
2. these are complex calculations....... >>:-(
3. if the resultant applied power [torque] exceeds the induced mechanical tension [torque] applied between the two components .....then :embarrassed: yes something else will fail in the drive line
4. however this does not include the loss of induced tension/torque between the propeller & the lock nut
5. if you have experienced... 'the odd prop come off (usually only in the middle of the pond though)' <*< ...please re-read & consider the points offered %) ....Derek
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Not sure if this is a silly question or not, but I need to move the prop further in towards the fore end of a kort nozzle.
With the nut in the "normal" place the prop is too close to the end of the nozzle:
(http://s18.postimage.org/v174thgvp/P1010380.jpg) (http://postimage.org/image/v174thgvp/)
So will the alternative arrangement work ok?
(http://s18.postimage.org/mpfz5z8vp/P1010379.jpg) (http://postimage.org/image/mpfz5z8vp/)
I can't think why it would be a problem, but thought I'd check with the brains-trust...
And no the nozzle can't be made longer :)
Alister,
Put the thrust washer onto the shaft, smear the thread with Loctite 243 thread lock, screw on the prop, a little more thread lock onto the shaft and lock up your lock nut, leave to cure overnight and It will last for ever.
If you don't want it to come of again use Loctite 603.
I have been doing this for years and no mater what the rotation of the shaft or the speed (up to 15,000 rpm Flash Steam and on fast electric with brushless and Lipo's up to 30,000 rpm ) and I have never lost a prop yet.
I really don't know why all this technical book stuff on so simple a solution.
George.
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Thanks Derek, Brian and George for your comments. Two things I will do:
- File a flat on two side of the centre portion of the prop so I can torque it on properly and
- Get some Loctite
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ON the previous pics the prop will be fine either way.
the prop/locknut combination will provide the mechanical locking required as it is the reaction of the 2 nuts slightly stretching the threads on the nut(s) that lock the prop to the shaft.
My only concern was I thought in the written description you wanted to put the washer between the locknuts which would negate most of the locking properties.
Bob
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With Locktite,if locknut is used ive found it ok to undo. But stronger mixes sutch as studstick Bearingfit etc do require heat to break. They are made to hold and thats what they do. Actually oxcy act with the correct jet does give you a very accurate hot flame. At least my set does. I use it to silver soider. John.
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so do you use Loctite product's on your shafts when you sail ? and which side do you put your nuts on ? :D
Peter
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For what it's worth, what Derek wrote was of interest to me and I thank him for his contribution, as I do all the others who contributed.
Bob - no way will the washer be in-between the prop and the nut - but thanks for checking :)
Usually I tend not to get involved when threads get a little heated as this one seems to be - perhaps we should all call it quits on this one as I have the answer I needed.
Thanks again to all.
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Honestly ,,Being a retired Ship.s /Marine ,Engineer ,with a B O T Ticket ,what I myself does is ,get the prop lock nuts on a surface plate and put a good flat finnish to them ,so when you lock/up with the proper size spanner/s ,no need for big stuff they only wreck ,you just lock up as proper and them nuts /props will not come loose ,if you wish a drop of the pink loctite will give you a bit of peace of mind ,but this method does me ,pure engineering .learned over time and lots too.
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Hi all
Another alternative method of securing the propeller to a prop shaft without using the aid of a lock nut is by drilling say a 0.5mm hole through the boss of the prop and through the shaft. Then, with say a brass pin or a stainless steel pin which is a tight fit driven into the hole and therefore permanently locking the prop onto the propeller shaft, obviously the propeller would have to be located at the correct distance as once this has been pinned, it is fairly permanent. This will give something for the Ozzy engineers to think about, because they haven’t thought of this method yet %)
Aye
john
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Hi all
Another alternative method of securing the propeller to a prop shaft without using the aid of a lock nut is by drilling say a 0.5mm hole through the boss of the prop and through the shaft. Then, with say a brass pin or a stainless steel pin which is a tight fit driven into the hole and therefore permanently locking the prop onto the propeller shaft, obviously the propeller would have to be located at the correct distance as once this has been pinned, it is fairly permanent. This will give something for the Ozzy engineers to think about, because they haven’t thought of this method yet %)
Aye
john
Very clever John! And I like the idea with the pin too :)
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Honestly ,,Being a retired Ship.s /Marine ,Engineer ,with a B O T Ticket ,what I myself does is ,get the prop lock nuts on a surface plate and put a good flat finnish to them ,so when you lock/up with the proper size spanner/s ,no need for big stuff they only wreck ,you just lock up as proper and them nuts /props will not come loose ,if you wish a drop of the pink loctite will give you a bit of peace of mind ,but this method does me ,pure engineering .learned over time and lots too.
Good tip :-)) :-)) :-))
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Hi all
Another alternative method of securing the propeller to a prop shaft without using the aid of a lock nut is by drilling say a 0.5mm hole through the boss of the prop and through the shaft. Then, with say a brass pin or a stainless steel pin which is a tight fit driven into the hole and therefore permanently locking the prop onto the propeller shaft, obviously the propeller would have to be located at the correct distance as once this has been pinned, it is fairly permanent. This will give something for the Ozzy engineers to think about, because they haven’t thought of this method yet %)
Aye
john
John, Good idea, will now replace the split pins with brass as the split pins always rust off and unbalance the shaft, %) %) %) %)
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Not keen on the pin idea, if you want to remove the prop you would have to knock the pin out which could damage the boss and bend the shaft.
Just hold the prop with a thick glove or rag and tighten a stainless lock nut, I have always used this method on all
my sports boats with flexishafts and a shaft saver, never lost a prop in over 50 years.
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Not keen on the pin idea, if you want to remove the prop you would have to knock the pin out which could damage the boss and bend the shaft.
Hum %) A good engineer would have the sense to remove the prop and shaft from the model and secure the prop in a vice or on a V block so the hub of the prop was secure enough to knock the pin out without distorting the shaft :-)) %) {-) {-)
aye
john
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Not keen on the pin idea, if you want to remove the prop you would have to knock the pin out which could damage the boss and bend the shaft.
Hum %) A good engineer would have the sense to remove the prop and shaft from the model and secure the prop in a vice or on a V block so the hub of the prop was secure enough to knock the pin out without distorting the shaft :-)) %) {-) {-)
aye
john
Hum, A lot of models you can only remove the shaft from the inside, by removing the rudder and its linkages therefore having to remove the prop first, (example)
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Hum, A lot of models you can only remove the shaft from the inside, by removing the rudder and its linkages therefore having to remove the prop first, (example)
Hummmmmmm that indicates a lack of for-thought on behaif of the designer and modeller if you have to go to so much truble to remove all the rudder linkages to get the rudder off %) %) {-) {-) {-)
Looks a nice model mate :-))
aye
john
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I'm amazed at this thread!
Surely, just put the prop where you need it, screw up a locknut to lock it (use loctite if you want) and then a spacer plus a sealing washer between the locknut and the end of the tube to keep it in position. Then another washer and set of spacer, locknut and coupling at the inboard end to complete the installation. hardly rocket science!
Colin
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You obviously have no imagination Colin. {-) {-)
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Hummmmmmm that indicates a lack of for-thought on behaif of the designer and modeller if you have to go to so much truble to remove all the rudder linkages to get the rudder off %) %) {-) {-) {-)
Bluebird perhaps you could enlighten me how you would have fitted the rudder and its related components and still keep the models authenticity.
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I want to know how you change prop will you have to change shaft as well or do all your props have the hole in exactly the same place,
Peter
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Hi all
First of all I wish some people would read and understand the question and replies given properly before jumping in with both feet!!! I did say in my original reply to AlisterL that this is one method of doing the job and it will be more than likely a permanentfix .. not that it was the only way nor that it was the right way.
The next thing we should all remember is - that not all modellers have the same knowledge or a well equipped workshop with all the tools such as a surface plate and grinding compound as some of us ... May I suggest the next time you answer aquestion on a ‘How do I do this subject’ try and imagine yourself on a desert island with only the basic tools such as a file, hand drill and a pair of pliers to do the job with - then see what reply you come up with REMEMBER some of us on this forum may not know what tools or knowledge the person asking the question has at his disposal!
My replies to Patternmaker were meant to be a tongue in cheek and not taken to heart!
He has asked me how I would have gone about making a removable rudder. I have put a couple of scribbles / ideas on :
First one is the top half of the rudder post is permanently fixed to the hull with its related components and the bottom half blade is removable
The second idea is to use say a10 or 12 BA bolt through the tiller stock which locates into a tube which in turn is fixed to the servo linkage.
Aye
John
retired time served engineer
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My replies to Patternmaker were meant to be a tongue in cheek and not taken to heart!
He has asked me how I would have gone about making a removable rudder. I have put a couple of scribbles / ideas on :
First one is the top half of the rudder post is permanently fixed to the hull with its related components and the bottom half blade is removable
The second idea is to use say a10 or 12 BA bolt through the tiller stock which locates into a tube which in turn is fixed to the servo linkage.
Yes your ideas would work, as I can remove my propeller easily without disturbing the shaft or rudder with the tried and tested way a locknut, there is no need for the extra work on the rudder, your second idea which I considered when building would have meant a larger slot in the transom. I certainly would not use a 10 or 12BA screw to take the thrust of a 12 sq in Rudder blade with a high torque servo, 5BA minimum, the head would have shown on rudder, from the onset I have tried to keep this model as original as possible to the 25ft boat.
All I said was I am not keen on the idea of a pin which has how been changed to a taper pin.
If its tongue in cheek not to be taken to heart why say it.
Its not what you say it's the way you say it.
I like others I feel sorry for Alister who asked for advice on this subject to be caught up in all this sniping, end of
as far as I am concerned.
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Off topic posts removed, please play nicely!!
Bob
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Mark Mark Mark,
Are you trying to confuse us?.
Not wanting to get into a slanging match but,
Reread post 3 as you suggest and did not come to the same conclusions you did.
As a layman, may I suggest to all, KISS is always appropriate in any commentary, my understanding of what the enumerated points in post 3 are referring to is "Tension" namely stretching between the two points which will then try to regain their original positons by eliminating that tension by compressing back to normal. I don't read that as meaning the forces applied being torsional/rotational.
However to be fair, there is a comment much later, of "tension/torsion".
This as far as I see it doesn't alter the tension, stretching applied to the nut and propeller connection referred to by all.
So in KISS terms why is post three and similar statements wrong and to be ignored?????
Not trying to confuse anyone, (unfortunately it tends to come unasked for {:-{ )
I'm not interested in a slanging match, but I will try and explain my to reasoning.
My main argument against Derek's postings is with his incorrect use of terminology, confusing the different forces involved in the 'locking nut technique' to the extent he picks one 'out of the hat'.
Now the following may appear as picky/pedantic/whatever - but it can confuse those who don't fully understand the terminology and then start repeating the mistakes 'as gospel' to others >>:-(
While the forces "compression" and "tension" are not mutually exclusive, to describe the nut and prop, (I'm using the same 'components' as the thread), as being in tension is wrong. The nut and prop are in compression, so the shaft between the two parts must in tension.
The only 'torsional force' involved is, (basically), how hard you turn the nut against the prop to obtain the 'locking' effect.
Now take post #8 - I'll reply 'inline' in red as it's easier that trying to quote/reply every point
mmmmmm... this is an interesting subject
1. the anti rotational torque [acting] on the propeller blade surface is the resultant of the applied input power - this applies equally to FWD or ASTERN rotation Very confusing >>:-( torque can't apply to a blade surface - it applies to the prop-boss to shaft interface, but does apply to either rotation
2. these are complex calculations.......
3. if the resultant applied power [torque] exceeds the induced mechanical tension [torque] applied between the two components .....then yes something else will fail in the drive line Just a very confusing statement due to incorrect use of power/torque/tension.
4. however this does not include the loss of induced tension/torque between the propeller & the lock nut Again, incorrect use of the same terms - it's loss of 'compression' between the prop and nut
5. if you have experienced... 'the odd prop come off (usually only in the middle of the pond though)' ...please re-read & consider the points offered Easy to read and consider - not so easy to understand!
Please don't mistake me saying that Derek doesn't know what he's talking about - from 'reading between the lines' he knows exactly what he wants to say, but just tries too hard to use big and technical words and finally makes a right pig's ear out of it.
Mark.
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If you stand on your head Derek's posts make perfect sense {-)
keep it up, or is it down under, Derek. %%
Peter
PS Now this IS supposed to be a joke post in case anybody takes offence.
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Well, this topic certainly demonstrates just how many nuts there are on Mayhem.
Never have I seen something so simple made so complicated.
Colin
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When I fitted the prop to my first ever boat, using the thrust washer and lock nut principle, I had absolutely no idea of the physics involved. I just put it all together and tightened it up, and to this day, I have never had a problem. If I'd known the possible technical complications I may never have attempted it without first doing an engineering degree.
Having read some of the preceding posts with great interest, I now have a much better grasp of the underlying principles of the seemingly basic job of fitting a washer and lock nut. However, I can't help but wonder if my early successful effort was just sheer blind luck, or, as Colin suggests, it really is a very simple exercise after all. %)
Peter.
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Folks.......I must admit the following quotation from CF-FZG whilst a little simplified ...does seem to cover the answer to original question :P .......
"While the forces "compression" and "tension" are not mutually exclusive, to describe the nut and prop, (I'm using the same 'components' as the thread), as being in tension is wrong. The nut and prop are in compression, so the shaft between the two parts must in tension.
The only 'torsional force' involved is, (basically), how hard you turn the nut against the prop to obtain the 'locking' effect".
One point that we have not considered yet is the material selection between the three elements ..... :o & hence the relative material yield points...will a shaft fail by shear at the root diameter of the thread form or the nut thread start to strip as the compressive load applied to the shorter length as opposed the the longer threaded propeller hub?
I would be more than happy %% to make a few brief assumptions if the majority of members are interested >>:-( please don't hesitate to respond :kiss:
I also appreciate the concern displayed by HS93 in the difficuility of reading & understanding all of this cods wollop whilst standing on your head in OZ ...... {-) .....Derek
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Off topic posts removed, please play nicely!!
Bob
shipmate60, can I ask why MY post was removed I dont think it was of topic it was how we do it on a powerfull electric boat where we change props four or five times a day .?
Peter
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shipmate60, can I ask why MY post was removed I dont think it was of topic it was how we do it on a powerfull electric boat where we change props four or five times a day .?
Peter
Its called censorship, nice to see it doesn't just happen to me.
Send the PM Bob.
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I think I read it earlier in daylight hours in OZ HS93...... :o ....or before most of UK was awake {-)
From memory it related to shear pins in model outboard drives and also in Z drives ...I found it interesting O0 as I have ZERO experience in these drive formats.............thankyou.....Derek
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Thankyou Derek I'm glad my comments were not wasted, they were also not off topic. >>:-( Still got removed though.
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Yep that was one Of Dickeys, mine was about a high powered boat that has a out runner that will run at 2700 watts Continuous plus a Continuous 90 amps murders batteries, and how we Just silver solder the nuts on. some days testing we may have 5 prop changes and a few gear changes trying to get a bit more speed out of the boat , of and we haven't lost a prop through falling off.
Peter
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DickyD & HS93.....Gents...in OZ during my daily lunch break [30 minutes] I usually log on to both Mayhem & Paddleducks....... O0 to catch the latest postings from Europe ... %% from the previous evening
Today I read briefly about ......
"and how we Just silver solder the nuts on. some days testing we may have 5 prop changes and a few gear changes"....
.and
"shear pins in model outboard drives and also in Z drives"
This evening on return to home ....I find both communications deleted <*< ...by a Mayhem Administrator <:(
I may be 20,200 km from UK..........but do not remember reading any comment in the above two postings that warranted the RED pen of moderation...........Derek
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Guys,
That is interesting looks like mine was also removed but here is the strange bit, have a look at reply 31 where my post is quoted verbatim.
So it seems it is OK to use my post in reply 31 after the deletions but not stand alone?
Would appear mistakes have been made.
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Did we answer your questions AlisterL ?
What a wealth of information for such a simple question.
I think this subject has been thrashed to the ultimate end, considering all we want to do is make a model boat.
Thank you all for contributing
The end
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Hear Hear! :-)) :-))
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and the next topic to be flogged to deeth is...............................do we really need a fuse?
only joking mind ya {-) {-) {-) {-) {-)
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Guys,
That is interesting looks like mine was also removed but here is the strange bit, have a look at reply 31 where my post is quoted verbatim.
So it seems it is OK to use my post in reply 31 after the deletions but not stand alone?
Would appear mistakes have been made.
What's really strange is that I quoted your post after the 'thread cleaned up' post, methinks there's some very strange censorship moderation going on here <*<
Mark.
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Hi Kenny,
yes thank you I think the question is answered.
My thanks again, to all those who contributed potential solutions to the questions I posed - it is much appreciated.
I have not built many boats and those that I have have all been relatively simple, and this was something where I thought there was a good reason not to do it, but couldn't remember what it was (everything coming undone). However, as I expected, the experience of others on the forum shows that it is possible, by several means.
FWIW, I will be using loctite to make sure nothing comes off as I don't think I will be able to get the prop more than finger-tight, but I will be using the lock-nut too.
John (Bluebird) - thanks for the thought about the fuses, but I discounted them as not being useful in locking the prop on :) :) :)
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Hi there Alistair
To make tightening props a little easier for yourself you can make yourself a small prop spanner quiet easily from a piece of flat steel bar – say 1/8” thick by say 1” wide x 3” long and at one end drill a hole slightly larger than the boss of your propeller. Then, drill 3 equally spaced holes of roughly 1/8” diameter to take the dreaded steel 1/8” steel pins set into them. This makes up a form of ‘claw’ spanner. The pins locate over the blades of the prop and hold it securely thus enabling you to tighten the propeller and the lock nut fairly tight. I have attached a scribble to show you what I mean.
Aye
John
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That's a good idea John. :-))
ken
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Agreed :-))
One tip is to cover the pins with something like fuel tubing to protect the prop blades :-))
Mark
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Agreed :-))
One tip is to cover the pins with something like fuel tubing to protect the prop blades :-))
Mark
All in all some good tips here simple and practical.
:-)) :-)) :-))
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Yep, I liked that idea! TYVM!
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Hi there Alistair
To make tightening props a little easier for yourself you can make yourself a small prop spanner quiet easily from a piece of flat steel bar – say 1/8” thick by say 1” wide x 3” long and at one end drill a hole slightly larger than the boss of your propeller. Then, drill 3 equally spaced holes of roughly 1/8” diameter to take the dreaded steel 1/8” steel pins set into them. This makes up a form of ‘claw’ spanner. The pins locate over the blades of the prop and hold it securely thus enabling you to tighten the propeller and the lock nut fairly tight. I have attached a scribble to show you what I mean.
Aye
John
Have you got a picture of the one you use ?
Or you could use a thick glove or fat fingers as we do.
Peter