7j43kPlastics just DON'T like being stretched. At least OUR kind of plastics.
Point well taken!
Here's a follow-up after "cooler heads" prevailed and I took my time and thought this through.
Below is a view of the patient, an Overland Cleveland Union Terminal P-1a. circa 1996.
The original 1.5mm shaft with the split horned balls is on the left and my first successful 2mm shaft that I made last week is on the right. I had to go with 2mm in order to get the correct O.D. on the horned ball.
Above is a close-up of the split ball still on the sprue. The one opposite is likewise split. In the center of the photo is the 1.5mm original Overland shaft showing the splits. At the bottom is my new shaft. You can see the finish on the NWSL shafting is just a bit rougher however it does measure 1.98mm.
As it turns out, I believe I was just too hasty in approaching this project. There IS considerable flash on the horned ball which I cleaned up but did not exersize enough care in preparing the bore. If the shaft were a little larger I would have done the freezer method but I thought softening the plastic was a more practical measure so I had a coffee mug of hot water handy and I could take the horned ball right out of the hot water and begin to press.
I polished the shafting in a drill press using some 40 micron finishing paper.
Tonight I'll assemble everything and make a test run before installing a DCC sound decoder.
Thanks for everyone's help and support! Ed
"put the shaft in Your freezer, for a couple of hours.." It will only take a few minutes to freeze a 3/16" diameter shaft. Hours won't hurt, but its not necessary to wait that long. Do be sure to handle the frozen shaft with a cloth or a cotton glove. The heat from your fingers will warm the metal in a matter of seconds.
RR_Mel ...I always score the shaft with a file and use super glue to prevent slippage.
If I could pull it off, I'd use a very gentle press fit combine with the knurling shown at the top of this photo:
Plastics just DON'T like being stretched. At least OUR kind of plastics.
Ed
zstripe gmpullman SO... I cut the new 2mm shafting to the proper length and carefully chamfered and cleaned the cut end of the shaft and proceeded to press the shaft into the ball. Ed, Off the top of My head.....put the shaft in Your freezer, for a couple of hours.....that's how You put new wrist pins on connecting rods to aluminum pistons. Just thinking out loud..... Good Luck! Frank
gmpullman SO... I cut the new 2mm shafting to the proper length and carefully chamfered and cleaned the cut end of the shaft and proceeded to press the shaft into the ball.
Ed,
Off the top of My head.....put the shaft in Your freezer, for a couple of hours.....that's how You put new wrist pins on connecting rods to aluminum pistons. Just thinking out loud.....
Good Luck!
Frank
Exactly right. The cold will shrink the shaft a few thousands of a inch and along with warming up the ball as mentioned it will slide right on.
Jim
LION has replaced motors on subway cars of him. Him removes the entire motor, (well duh, him *IS* replacing the motors). Him use a puller to remove the fly wheels form the old motor. Him put the wheels on the new motor, and in case of LION him not remove the plactic drive from the fly wheels, so not to break the universals, him protected them with a washer. The delicate parts were inside of the hole of the washer, and the force of the operation would be applied to the shoulder of the plastic part. LION put the entire assembly in a large vice (LIONS have access to LARGE vices in the power house, otherwise vices would be hard to come by in a monastery--not). Him slowly close vice. If one side comes togethere more quickly than the other, LION would put a hard tool in the finished gap and continue to apply pressure to the assembly to close up the recalcitrant gap.
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
hon30critter If anyone knows how to do it properly, they will.
Thanks for the link, Dave! It took me a little more "surfing" around their site but I came across this introduction that was very helpful. (last 2 pages)
http://www.nwsl.com/uploads/cat_INTRO_WEB_ONLY_04-15.pdf
My replacements came today so I'll make another go at it.
Usually I'll order enough supplies to cover any "oops" and to have plenty of stock on hand for future repairs but in this case by having to increase the shaft size to 2mm I was only left with exactly four of the Horned Balls that I needed, of which I broke two
(Other Ed) Quote: Plastic parts pressed on shafts appear to crack too frequently--I'm think of certain axle gears.
Yep, I've changed out about four-dozen Life-Like axle gears
I think there is so much variability in the molding process and the quality of the raw plastic that getting a plastic part to grip a metal shaft with any reliability is a hit or miss proposition. I noticed that the two horned balls that I split cracked in the same place, on the far side of the mold cavity where the plastic has to force around the shaft hole then meet again on the far side. If the mold is slightly cool or the plastic doesn't form a good bond you have an inherent weakness then the hard steel shafy pushes in and stresses the weak part and — pow!
Close examination of the shafting shows that it is ground to finished OD but, to my feel, it is a fairly rough finish. I may polish the ends with a little crocus cloth before attempting another pressing. I'm using a precision drill press as an arbor press and I'm leaving the ball on the sprue so I can control the position and orientation as I bring the shaft into the bore.
Ed, I'll measure the parts to be sure. Some of the NWSL bores are D shaped so a flat has to be made on the shaft but these are bored round.
Thanks for the suggestions, everyone. I'll report back soon, Ed
First thing I'd do is measure the shaft and hole diameters. Someone might have pulled the wrong size. The easiest way to check the hole size is with a drill bit.
I think warming the ball would only help.
I would call NWSL and discuss the matter. The one time I did call, I had a long and productive talk about my subject.
As you know, you need just the right fit. Plastic parts pressed on shafts appear to crack too frequently--I'm think of certain axle gears. Yours chose to do it immediately. In a way, that's a good thing--you don't have to disassemble the loco to find the problem and fix it.
Hi Ed:
I'd give NWSL a call or send them an e-mail. If anyone knows how to do it properly, they will.
http://www.nwsl.com/
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
gmpullmanSO... I cut the new 2mm shafting to the proper length and carefully chamfered and cleaned the cut end of the shaft and proceeded to press the shaft into the ball.
I recently purchased an Overland HO locomotive from someone who could not confirm weather the engine ran or not. Upon delivery, it didn't take me long to discover that the drive shafts connecting the gear towers were not spinning but the flywheels on the motor were.
Closer examination showed that all four of the "horned balls" as NWSL calls them were split and not gripping the shaft. Further measuring showed that the shaft was 1.5mm and the OD of the ball was 1/8" Turns out this is not a common combination.
After a little calculating I decided to get new shafting at 2mm dia. and a NWSL 482-6 2.0mm universal coupler kit as this would provide the proper size "horned ball" that I would need to engage the coupler mounted in the flywheel.
SO... I cut the new 2mm shafting to the proper length and carefully chamfered and cleaned the cut end of the shaft and proceeded to press the shaft into the ball.
Right away the ball split as I was pressing the shaft in! Ouch, I only ordered enough to make the two shafts I needed so I'm presently waiting for a replacement kit.
In the meantime I wondered if anyone has any insight on pressing these little buggers onto the shafting? Does it help to soak them in warm water beforehand? The parts are made of POM (polyoxymethylene), or Delrin or "slippery engineering plastic" as M-R calls it in model reviews.
Any hints would be appreciated. Thanks, Ed