1/8 to 4mm Prop Adapter

[Tollytime]

When it came to stretching my Dumas Osprey, I have made a horrible mistake.
I never considered changing the drive shaft and stuffing box. I chose to use the original 1/4" inch stuffing box with a 1/8 shaft. I need a 4 blade prop about 50mm to create the proper appearance. So I ordered some 4mm threaded props thinking it was the metric equal to 1/8". I'm not really stupid, just ignorant. I assumed it was one of these 9/16" equals 15mm type of things. Don't even ask why I forgot metric threads are different than standard threads. I don't know why I didn't even consider what I was doing. It's too late to remove the 1/4" stuffing box and I know I can use an adapter from the Prop Shop to make it 3/16. But I would really like to use some 4mm threaded props from Graupner and Robbe. Is there an adapter to make a 1/8" shaft 4mm? I've never been good with understanding thread sizes and measuring bolt sizes. Oh god, I need help!

[Kmot]

Can't you return the 4mm threaded props? And get 1/8" props instead?

Or, you can buy a thread making "tap" and re-cut the 4mm threads inside your props to match the threads on your 1/8" driveshaft.

[Tug Guy]

Have you asked Simon if he could supply a 1/8 " threaded prop? His props are much better than any the other two suppliers make.

Don

[Tollytime]

Can't you return the 4mm threaded props? And get 1/8" props instead?

Or, you can buy a thread making "tap" and re-cut the 4mm threads inside your props to match the threads on your 1/8" driveshaft.
I didn't pay much for those (plastic)props, so no problem. I'll keep them for my next project or if I happen to change the shaft altogether. The props I mentioned are cheap and that's what I like about the 4mm prop range. I really don't want to get into buying $30+ dollar brass props until I really know what size I want to stay with. Dumas and Prop Shop offer (50mm or 1 3/4") 3/16 props but there kind of pricey for someone who doesn't know what they want. An adapter would just simplify it.

[Tollytime]

Have you asked Simon if he could supply a 1/8 " threaded prop? His props are much better than any the other two suppliers make.

Don
Is Simon the guy at Prop Shop? Remember, I'm a NOOB.

[patmat2350]

You may have some options here. Exactly what's your stuffing box like? Depending on size, you may be able to use sintered bronze flanged bushings sized for 5/32" shaft.
A 5/32" shaft is almost exactly 4mm, and can have 4mm threads put on... or you can use a pre-threaded 4mm shaft and put it into the 5/32" bushings.
It may be necessary to ream out a 1/8" bushing for this job.
Other alternative- use other brass tubes glued/ soldered into the stuffing tube to reduce to 5/32" ID.
Raboesch has a nice line of soldered brass props at reasonable price, but I don't see any 50mm props with their occaisonally available 1/8" thread (#5 English thread). Try Don at www.loyalhannadockyard.com if you want to pursue these.

Having a lathe, I have also silver-soldered a nub onto a smaller shaft, turned it true, and then threaded for the larger prop size.

If you use English sized couplings (like my fav, the Dumas dogbone), you can ream the 1/8" cup to 5/32" or 4mm. A lathe is great here too... free-hand drilling will definitely wander off-center.
Else, look for Graupner couplings, for example at www.hobby-lobby.com under "universals"... numerous metric and English sizes that can be mixed/matched.

Pat M

[Tug Guy]

Yes Simon use to own the prop shop until the recent sale of the company, He now manages it.
simon@prop-shop.co.uk
Don





Is Simon the guy at Prop Shop? Remember, I'm a NOOB.

[CG Bob]

Or, you can buy a thread making "tap" and re-cut the 4mm threads inside your props to match the threads on your 1/8" driveshaft.That would require filling in the 4mm threaded hole on the props. 1/8" = 3.2mm. Another option is to look for some threaded inserts (http://www.ezlok.com/InsertsMetal/SSthreads-unc.html), which might require drilling the 4mm hole to a slightly larger size. Some of the smaller ones are sized for 4-40 threaded shaft.

[Tollytime]

You may have some options here. Exactly what's your stuffing box like? Depending on size, you may be able to use sintered bronze flanged bushings sized for 5/32" shaft.
A 5/32" shaft is almost exactly 4mm, and can have 4mm threads put on... or you can use a pre-threaded 4mm shaft and put it into the 5/32" bushings.
It may be necessary to ream out a 1/8" bushing for this job.
Other alternative- use other brass tubes glued/ soldered into the stuffing tube to reduce to 5/32" ID.
Raboesch has a nice line of soldered brass props at reasonable price, but I don't see any 50mm props with their occaisonally available 1/8" thread (#5 English thread). Try Don at www.loyalhannadockyard.com if you want to pursue these.

Having a lathe, I have also silver-soldered a nub onto a smaller shaft, turned it true, and then threaded for the larger prop size.

If you use English sized couplings (like my fav, the Dumas dogbone), you can ream the 1/8" cup to 5/32" or 4mm. A lathe is great here too... free-hand drilling will definitely wander off-center.
Else, look for Graupner couplings, for example at www.hobby-lobby.com under "universals"... numerous metric and English sizes that can be mixed/matched.

Pat M
These ideas sound good, but I don't have a lathe. I have thought about replacing the shaft but not today. You have more talent than I do, so my options are limited. I did remove the 4mm brass insert from one of the plastic Robbe props to experiment. I bought a 3/16 brass insert at Lowes and screwed it in place. It's a tight fit with very little wobble when I chucked it in my hand drill. I think these plastic props wobble a little bit anyway. I might just try that 1/8" to 3/16" adapter with that setup. I do have a drill press and I'm going to try a 1/4" set screw and drill and tap the hex entrance. I could also solder a 5/32 tube over the 1/8" shaft and re-thread that as well, but I would like to know if you think that will work before I ruin the stock shaft. If all else fails, I could whack off the cone on the end of the prop and use a nut to tighten it on against a collar or washer. I can't believe someone doesn't make an adapter to at least go 3/16" to 4mm, even if it meant adding a 1/2" to the length of the shaft, I could rig it somehow. Thanks.

[Tollytime]

That would require filling in the 4mm threaded hole on the props. 1/8" = 3.2mm. Another option is to look for some threaded inserts (http://www.ezlok.com/InsertsMetal/SSthreads-unc.html), which might require drilling the 4mm hole to a slightly larger size. Some of the smaller ones are sized for 4-40 threaded shaft.
That looks good too!

[n.h.schmidt]

Hi
I have been reading of your difficulties in finding a way to make this work. I have done this conversion many times. There are two ways to do this. Both ways involve changing your existing prop shaft or getting a different one to use in its place. I can make a adapter that simply glues onto the end of the 1/8" shaft.It will make everything longer and you would need to cut the prop shaft shorter. The other way , is more difficult . The 1/8" shaft needs to be reduced to .109 on the output end. Then a 4mm threaded adapter can be glued onto the reduced end of the 1/8" prop shaft. Either way works well and holds up to some heavy use. I have had some 12 cell hydro boats run up to 35mph with these converted shafts. No problem ,so far. I do custom work for electric racers. Prop shafts are a everyday thing for me. n.h.schmidt