Options that I know of:
· Cheapest (~$50):
o Buy a 7/8" keyed shaft coupler
o Buy or make a short tube that slips over the OD of the coupler
o Weld or JBWeld the tube to the coupler
o Make a a 1 1/8" spline fitting out of the inside part of the tube by "casting" a spline using JBWeld or titanium putty or other strong epoxy
§ Fill the spline part with wax
§ Lube your spline with WD40 or other lube to act as mold release
§ Mix appropriate amount of epoxy and pour into tube end
§ Smoosh the spline into the epoxy, keeping the spline shaft and the coupler coaxial (biggest problem)
§ After cured, use gear puller to remove the new coupler from the spline
§ Voila…coupler made for under $50
· Cheap (~200):
o Buy a 7/8" keyed shaft coupler
o Buy a 1 1/8" spline coupler (if available) or spline gear/pinion
o Bore one end of the spline coupler out to the outer diameter of key shaft coupler
o Connect, align and bond (JBWeld) or weld the 2 couplers together.
o Cost: $200 or less I'd guess (mine cost $100 total---(1) 7/8" keyway coupler ($15), (1) used pinion gear w/14-pt spline ($35), plus $50 to grind one end of pinion down to 7/8" to fit in the end of the keyway coupler.
· Expensive, but Best ($500+): Have a machinist make a coupler for you, boring for 7/8" w/keyway on one end and broaching 10-point spline at 1 1/8" on the other.
I used the first approach for my outboard motor (ETEK 7/8" keyway to 14-pt nom. ½" diameter spline coupler) conversion for about a year. In my case, the splines were too narrow and would only last for perhaps 20-hours before self-disintegrating and having to be replaced. After going thru about 3 coupler recasts, I made one out of titanium putty and used it until I discovered the 2nd method above. That new coupler cost me $100 total and has now lasted 5 years or so---I used a lower unit pinion gear for the spline fitting and the pinion gear teeth on the OD were never ground off since they don't interfere in my use as a coupler.
-Myles Twete, Portland, Or.
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of David Goldsmith
Sent: Tuesday, December 15, 2009 8:40 PM
To: electricboats@yahoogroups.com
Subject: [Electric Boats] MARS motor shaft to spline coupling?
I've been working on getting my gear box ready to mate up to a MARS
brushless motor set-up. The gear box and flywheel housing will make
mounting the motor through a 1/4" al plate easy enough. The problem
I'm running into is how to mate up the motor to the gearbox input. The
MARS motor has a 7/8 keyed shaft. The gearbox has a 1 1/8" spline
shaft (10 splines.) I've done some searching and can't find a coupling
that will accommodate that spline shaft. Is this something I'll have
to have made custom or what? Any ideas out there?
Thanks,
David
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