Help Please Flex shaft replacement.

[boatmanpete]

I lost the right hand flex shaft and prop on a very early outing (my own fault of course). Some time later and at huge freight expense a replacement arrived but it is 105 mm too long. I am a Newbie. Do I send it back or can it be cut and fitted. If it can be cut are there any tricks'n'tips

The boat is the Venom King of Shaves. I really loved the way it moved and I want to see it do that again.

[JIM MARCUM]

Use a dremel & a 1" 1/32 thick cut-off wheel. Don't get it too hot, quench as you go. JIM

[m4a1usr]

I lost the right hand flex shaft and prop on a very early outing (my own fault of course). Some time later and at huge freight expense a replacement arrived but it is 105 mm too long. I am a Newbie. Do I send it back or can it be cut and fitted. If it can be cut are there any tricks'n'tips

The boat is the Venom King of Shaves. I really loved the way it moved and I want to see it do that again.

Easy fix. Do you have any skills in shortening something like this? All you need is a cutting tool and some type of grinder. If you dont have a dremel tool with a cutoff wheel you can use something as crude as a pair of dykes. But your going to need to cut it long if using dykes so you can grind it down to the required length. Actually its a pretty simple in scope. What you need to end up with is the length long enough to slowly cut down in OAL with the grinder while not overheating the flex shaft and ensuring the outer sheath does not unravel as you reduce the OAL. Does that make sense? BTW. Welcome to OSE!

John

[SirBudman32]

A Dremel and a cut off wheel, no biggie. Cut a little at a time and cool between so not to weaken it.

[boatmanpete]

Jim that is a fabulous fast reply and I get your drift but as you might expect of a newbie I have a follow up question. The shaft seems to have some sort of stiffener at the core of the inboard end. When I make the cut 105 mm towards the prop end it seems as if I will have gone beyond that stiffener. Should I try to insert a new one or will I be able to retrieve the old one from the cut off piece?

Most appreciative of your input.

[boatmanpete]

John and Sir Budman, I am amazed at the way the responses are flowing in. I think I am just about on top of this already but if you think of anything which a mug might need to know please dont stop.

Best wishes to you all.

[m4a1usr]

Jim that is a fabulous fast reply and I get your drift but as you might expect of a newbie I have a follow up question. The shaft seems to have some sort of stiffener at the core of the inboard end. When I make the cut 105 mm towards the prop end it seems as if I will have gone beyond that stiffener. Should I try to insert a new one or will I be able to retrieve the old one from the cut off piece?

Most appreciative of your input.

Uh oh? A more basic question should be asked. Did you order the correct side flex? Twins typically run a left and a right hand lay flex. Dont butcher one up if its not meant for that side.

John

[dana]

If heating the cable weakens it, then how do you solder cables?

[m4a1usr]

If heating the cable weakens it, then how do you solder cables?

Cutting one usually involves some pretty concentrated amount of heat. Very localized. One would have to keep cutting for a relative long amount of time to effect a flex in some amount of strength but its sort of assumed with relative newbies that they may not know that right away. Most of us hate to see a new guy do something that they may not be well enough informed about. I guess you could call that second guessing on our part but its just a warning. Nothing more.


John

[JIM MARCUM]

Pete, the stiff section at the end of a flex drive is usually "stiffened" the last 1/2-3/4" with silver solder or epoxy to keep the strands from seperating when squezed by the collet and/or twisting between the collet & stuffing tube. On flex drives = to or larger than 3/16" I don't "stiffen" the end & I've not had a seperation problem, yet.

People who make flex drives with attached prop shaft usually use silver solder, occasionally brazing. Not sure how they do it with out de-tempering the flex shaft. But imagine they heat up the prop shaft only with a torch, let capillary attraction "suck" the solder into the shaft, while keeping the flex shaft cool by wraping it with wet cloth or water imersion.

There have been OSE threads on how do-it-yourself guys use everything from epoxy to blue locktite to attach the prop shaft to the flex shaft. I prefer a good quality epoxy for connecting prop shafts, and to stiffen the collet end of small flex drives.

Some people like using silver solder for both ends. But they must be a Hell of a lot better at soldering than me (I use a micro-torch even when soldering wiring larger than 12 gage) to not overheat the flex drive.

That's my opinion anyway. JIM

[martin]

Some of the best flexes around are brazed, if you want a .187" flex & 3/16" stub or 1/4" flex & 1/4" stub they must be brazed as the outer wind on both these type is removed & just the inner core of the flex goes into the stub hole. You put chopped up pieces of braze rod & flux into the hole then the flex goes in & the flame is concentrated on the stud & not direct on the flex, youll be suprised how hot the flex can go without affecting its temper. Re Loctite on joining you must use a retainer Loctite either 603, 638 or 648 which are all green at least they are in the UK.

[JIM MARCUM]

PS: The only times I've made 1/4" drive lines, I had a machinist friend make the SS prop shaft wiht a a .254" hole for the .250" flex shaft, turned down to .1875" at the prop end. With big boats, 5692 motors, and 70mm props I just don't trust the cut-down flex shafts. All that remains is a .1875 flex shaft where it really counts, not a full length .250". JIM

[martin]

Not so, yes you have the smaller inner core going down into the stub hole but you also have the outer wind brazed to the inner core + the braze extends along the outer wind of the flex at the butt of the stub & flex for around 1/4" - 5/16". These flexes hold up fine to gas motors turning 70mm 3 bladed props. Just about every 1/4" flex & stub is made this way.

[martin]

I should add that most of the fastest ic hydros that use .187" flex & 3/16" stub are also made this way.

[boatmanpete]

I am most grateful. I will do the deed on Saturday and let everyone know how it goes. Thanks so much.

[boatmanpete]

So sorry, I have thought of one more question. I have decided to use epoxy and I have jumped to the conclusion that you dip the end into the epoxy, wipe off the obvious excess and then leave it to cure before fitting. (rotating it slowly to retain an even cover. Then, I have guessed when it is rock solid you sand (wet and dry) off any spots which prevent an intimeate fit.

BUT BUT BUT Maybe you meant the fit to be done while the epoxy is still tacky.

Please advise. I am most grateful for all the advice you have provided thus far.

Best wishes

Peter

[Bug777]

Once you get it repaired & in the boat install a collet onto the flex shaft between the motor & stuffing tube. This will stop the shaft from falling out in the future. I learnt this after losing 2 flexshafts with alloy props in 4m of water.

[JIM MARCUM]

If going the epoxy route, I'd clean up the last 4" or so of the flex drive, collet end, with acetone & hang it collet end up till it's dry. Mix a small cup of good quality epoxy and, wearing gloves, work it into and rotate the last 3/4" of the shaft. Afer 24 hours the epoxy should be cured enough to remove any excess epoxy with a sanding block. Grease the drive up. Done. JIM

[JIM MARCUM]

Not so, yes you have the smaller inner core going down into the stub hole but you also have the outer wind brazed to the inner core + the braze extends along the outer wind of the flex at the butt of the stub & flex for around 1/4" - 5/16". These flexes hold up fine to gas motors turning 70mm 3 bladed props. Just about every 1/4" flex & stub is made this way.

Martin, I have twisted one out of the prop shaft last year running a Leopard 5692 1090kv motor & 68mm prop. It may have been my fault for not leaving enough room for shaft shrinkage.

That said, I'll stick to a 100% 1/4" flex drive & machined prop shaft. JIM

[martin]

Jim as with any flex they do break from time to time & all of the 1/4" gas flexes ive seen break has been at the front of the brazed joint, this is 1/4" - 5/16" in front of the butt between the outer wind & the stub. where they have broken their was no step down in the flex but full diameter that had broken, obviously a shear point going from a flex to a ridged part of the flex but it wasnt the step down that caused the break on the flex.

[JIM MARCUM]

Jim as with any flex they do break from time to time & all of the 1/4" gas flexes ive seen break has been at the front of the brazed joint, this is 1/4" - 5/16" in front of the butt between the outer wind & the stub. where they have broken their was no step down in the flex but full diameter that had broken, obviously a shear point going from a flex to a ridged part of the flex but it wasnt the step down that caused the break on the flex.

IMO, the brazing process weakens & de-tempers both the full 1/4" flex shaft & the cut down section. I've seen 1/4" brazed cut-down shafts fail on gassers too. I suppose you could re-temper a cut-down flex drive by heating the prop shaft/flex with a toarch & quenching in motor oil. But, there's no getting around the fact that a 1/4" flex shaft cut down to 3/16" is only as strong as the remaining 3/16" section. In fact it's weaker than standard 3/16" shaft.

Why? To build a step down flex shaft, the outer - first layer - of counter clockwise wire strands are removed, the second layer of clockwise strands is the new "outer" layer. After brazing the cut down flex into the prop shaft, the the torque generated in turning a 65-70mm LH prop will un-ravel/twist the outer flex strands and weaken the remaining inner strands. The pictures below are of my sheared FE 1/4" step down drive. NOTE: it failed in the 3/16" cut down section, and the Braized 1/4" section remains in tact.

On the other hand, I've never seen a full 1/4" diameter flex drive break/shear at the prop shaft connection, have you? JIMAttachment 75778Attachment 75779

[martin]

Jim i agree with you re full diam flex going into the stub being a much better way, but unless someone can have a custom shaft made in the way you discribe then their stuck with the way nearly all these flexes are made. Martin.

[Jeff Wohlt]

Nah...I braze them at 1100 degrees and so does Ed Hughey. No problems I know of. You also let them cool by air...no quenching them in cold water.

[Jeff Wohlt]

Some of mine have broken early on when beginning but learned they must be tinned all the way thru first then assembled. This puts the load on all wire. Not easy and Ed still makes one of the best I know of. Brazing these things really suck....I won't even do 1/4". Ed can do those! I use 55% silver...not cheap.

[JIM MARCUM]

Jeff, to braze or not to braze, and I still don't get it. But you showed me where I went wrong when I tried brazing - DON'T quench it! I did & it failed.

When I do solder, I use 60/40 (silver/lead rosin core silver solder. But it dosen't stick (NADA!) to my SS prop shafts. If you have a way to do that, I'd love to know how.

I know you guys know how to build great drives, you're pros.

Your cut down 1/4" drives are easier to remove, don't require a specially machined SS prop shaft, have slightly less drag, and are readily available. But, when it comes to absolute strength, my full 1/4" diameter drives will beat a cut down 1/4" drive every time. JIM

[Jeff Wohlt]

You need to use flux anyway.

[martin]

Flexes are made from spring steel wire & you deff dont quench, it makes the steel brittle & will snap like a carrot.

[tryinotocrash]

Hello , not sure if you got this all worked out but they sell replacements that fit right in with no mods. http://www.rchobbyexplosion.com/Elec...arts_s/585.htm that is just one place others on E-Bay.

[martin]

These are stock Venom flexes that arnt very good Quality, thats why most upgrade to better after market flexes with any rtr boats.

[tryinotocrash]

Yes I understand this however the OP seemed to have issues with modification of the aftermarket shafts so I thought maybe he would be better off with some that fit without mods.