Turning Clock or anti clock wise

What would you do, if you where in my shoes. I have to make a decision on how to mount the center part of the prop to the shaft.

a) I have a big table drill, up to 16 mm
b) I have a small lathe with milling capabilities
c) Am not afraid to file for extended period of time
d) I have restrictions; the shaft is too long for the lathe.
e) The shaft and all other parts of the prop are from SS 316
f) The shaft is 30 mm diameter

The prop will see an absolute maximum of 8 Horsepower.

Would you secure the prop to the prop shaft as per example 1,2, or 3
Is there any serious reason, should one be a very bad method. I like to know the reason
Many thanks
Bert

 

Here are two photo's to judge better.
Bert

 

Of the three options I like what's behind door number 2 the best. Here you have the securing mechanism inline with the shaft reducing the centrifugal forces on the bolts as opposed to the other versions. My prefered method might be to permanently affix a large threaded bolt into the end of the shaft and secure the prop with two locking nuts and a key.

MM

 

Thanks Mike, In principle you feel that no 1 would be the best. (Two locking nuts) . I am able to make a square hole in the prop bush and with the milling machine make a square on the prop shaft itself. The shaft is then mounted at 90 degrees with the lathe and it can be as long as I want, to mill the square. However I cannot regretfully have the shaft clamped into the lathe head. The shaft is too long for that. . The shaft square would be 2 cm by 2 cm and 18 mm deep. That should be able to withstand forces of up to 8 Hp. Thereafter to drill a hole in the shaft and make a 12 mm thread. Do you mean then, I should drill a vertical hole in the shaft? Let say 4 cm from the end and then place a pin or a screw thread to secure the 12 mm bolt. I should than be able to place two nuts at the front and even a split pen for security, like most propellors have. Thanks for the input.

If I am brave enough, I could mill an extra kind of round piece at the end of the shaft, after the square and than file it nice round and make thread on it. Let say 4 cm for the two nuts and the split-pen. But I don't know whether I am brave enough. If I make a mesh, I loose 4 cm shaft, while with your solution I should be able to drill reasonable straight a 10 mm hole for the 12 mm Bolt some 6 cm deep. Would it be better to place a 14 mm bolt in it? It means than only 3 mm on both side of the bolt "Meat" for the square, which has to transfer all the torque.

Did I understood you correctly? or do you feel solution no 2 WITH a 12 mm bolt in the center and two locking nuts?
Bert

 

Hi Mike,

I read your email again and you are right. Indeed the best would be to obtain a 14 mm stainless steel bolt with 2 locking nuts and drill 4 holes. I thought 3 holes with a bolt of M8 and I have the set of taps for 14 mm x 2.0 and they would do fine for the center bolt. It is also better, as I will be making my second prop after the first one is a success, because I will be running with 2 motors in the future after testing the first one. It will be easier to make a second one in this way. I am planning to drill a M5 through the 30 mm shaft to secure the M14 mm bolt. Would you agree with the sizes I have selected ? i.e. M5, M8 and M14 ?? Thanks for the help.

 

What power, speed and rpm (or torque, if you know it) do we talk about?

 

Hi BertKu,
I was thinking of a more conventional design using the material you have on hand. Drill and tap the shaft to accept your 14mm bolt...insert 14mm x 2.0 threaded section into shaft then secure prop using either a Nylok type nut or double lock nut arrangement or use a locking plate similar to that shown in figure 3. This would require either a key/keyway combination or shear pin which ever you prefer. Like the attached image only without the taper since you can't chuck the shaft in your lathe.

MM

 

The power is electrical power, i.e brushless motors. The power I aim for is 1 Hp - 1,5 Hp , with a speed of approx 4 knots. The full torque is as from the lowest revolution, the motor will run from 0 - 1600 revs, with a 4:1 gearing down to 400 revs at cruising speed. The maximum power I am able to deliver to the prop is 8 hp, but the motor has to be proper cooled and that I will only know, how good transformer oil is transferring the heat to the seawater cooled outside of the metal casing.
Bert

 

Hi Mike, Yes, I cannot place the shaft in the lathe, thus a conical shaft is out. I checked the forces on ONE bolt of 8 mm and 60 mm long, screwed into the shaft/propellor bush (on the edges) together with your 14 mm x 2.0 thread secured also for 60 mm in the center of the shaft, and then secured with a vertical M5 SS bolt some 40 mm from the end of the shaft. The bolt will not be able to disappear, due to the fact that the propbush will hold it in place. Hereby securing the Nylok type nut. Over and above I will place a split-pen at the end of the thread as 2nd security. The loss of very little material in the Metric 8 mm bolt should compensate for the mass of the head of the bolt, thus I should not have a balancing problem.
Thanks Mike for helping me clearing my mind.
Bert

 

I like what you've done...it looks to be easily repeatable such that your second or third prop will fit just like the original. Good work.

MM

 

Thank you. Without your input, it may have been different constructed and not as good, or easy reproductive. Thanks Bert

 

No reason why it won't work with low power. Propeller test models are generally made in a similar fashion. Why not put the pin at the front end of the hub? Simply cut a slot across the front of the hub and have a hole thru the shaft at the correct location. That is sort of the way that shear pins were used on old outboards.

 

Hi John, My apology for the late reply. I don't have a 4 jaw chuck for the metal lathe and had to make a tool (001.jpg) to allow me to make a 50 mm hole in a square SS plate. That took quite some time.

Photo 033.jpg shows you the result of the prop bush. I placed a M5 bolt 90 degrees into the shaft and large bolt to lock the bolt. In future I will not make a thread for locking the bush with the shaft, but will use instead a 8 mm bar. It was a nightmare to re-align the thread after removing the bush from the shaft and putting it back again. One can only learn from the mistakes one makes, never from the good things one does. The 8mm x 60 mm long bolt is locked by the large nut and the large nut is locked by the split-pen, to allow forward and reverse propulsion.

At the same time I made a seal bush (photo 002.jpg) Here is my questions
a) I have a seal which keeps the transformer oil from leaking into the water.
b) I have a 70 mm O ring to also to keep water out of the gearbox/motor casing. Should I still use " Glue Devil Gasket maker" of will that be an over kill.and a good O ring will do the job.
c) I have 2 extra seals with chamber opposite each other and should use "WHAT KIND OF GREASE" between it.
d) I have 3 x Metric M4 bolts with nuts which allows me to adjust the pressure against the seals and can compress the seals against the gearbox/motor casing. Any comment?

I was already puzzled by a reply by you, in one of the previous threads and then I clicked. When Daiquiri suggested to turn the blade 180 degree, I misunderstood him and not only I put the front of the blade in the right direction, also re-bend the blades. Thanks for picking it up, you weren't too sure. Yes, the forward propulsion is making the blades turn left. I have in the meantime made 2 more blades and have re-bend the blade back again.
This week I will attempt to weld the blades to the prop bush. Wish me luck.
Bert

 

Hi guys , why did you not tell me that if you use 2 stainless steel items together, like a SS screw in a SS shaft, the two metals may "weld" due to seawater with SS.
Lucky I had a good boat builder looking over my shoulder and he ticked me on my fingers , and told me, that I must use some copper grease between those two metals.
I forgive your guys, as you probable also did not know, you know it now. Here is the result of the Prop.

 

I like the props - slow rpm good thrust
nice