Reaming a Kato Mikado worm adapter

[mike_lawyer]

I was very fortunate to track down a Faulhaber 1016 with a 4:1 gearhead from a forum member (thanks metalworkertom).  The output shaft of the gearhead is 1.9 mm, and the plastic cross piece for the Kato Mikado that goes into the shaft has a 1.5 mm hole.

Here is my question - what is the best way to ream the hole on the plastic piece?  I tried using a pair of needle nose pliers to hold it in place while reaming, but this allowed too much circular slippage, causing damage to the plastic cross piece.  I don't want to ruin another plastic adapter, so any thoughts on how to ream this piece without damaging it would be appreciated.  I have a few extra plastic pieces available, so I have more to ream.  Thanks!

[MK]

I'm assuming you are reaming this by hand.

Use a thin piece of rubber or grippy latex, e.g., a piece of inner bicycle tube or latex glove, and wrap the plastic piece.  Then use a vise that has a V grove and clamp the piece down with just enough pressure to not deform or break it.  With the V grove you now have 4 contact points instead of 2.

If that doesn't work, the ultimate would be to find a scrap piece of wood and drill a hole that is slightly less that the diameter of your piece.  Then cut the scrap piece down the middle of the hole you just drilled.  Now you have two "jaws" that will cover almost the entire circumference of your plastic piece.  This will give you the most surface contact.  Adding the rubber or grippy latex above would help but may not be necessary.  Clamp the jaws in a vise and adjust pressure.

[peteski]

Another alternative might be to use jeweler's ring clamp.  Those are hand-vises with leather jaws and with a tightening wedge to have excellent control of the gripping force.  I use one of those for workign on delicate parts.

[woodone]

Not sure how much room you have between the output shaft and the plastic gear.
I do not think you can ream the plastic gear and retain a good run out concentery. How about making a shaft adaptor.
The 1.9 MM shaft is more than likely a  2.0 MM shaft. I would try making a adaptor from 2.00 MM stepped down to 1.5 MM .

[narrowminded]

I was very fortunate to track down a Faulhaber 1016 with a 4:1 gearhead from a forum member (thanks metalworkertom).  The output shaft of the gearhead is 1.9 mm, and the plastic cross piece for the Kato Mikado that goes into the shaft has a 1.5 mm hole.

Here is my question - what is the best way to ream the hole on the plastic piece? 

USPS!    

Throw a couple in the box for those cars I bought.  Please include the shaft to assure a good fit.  They'll be back to you in whatever the ship time is, plus a day or two.   

[peteski]

Not sure how much room you have between the output shaft and the plastic gear.
I do not think you can ream the plastic gear and retain a good run out concentery. How about making a shaft adaptor.
The 1.9 MM shaft is more than likely a  2.0 MM shaft. I would try making a adaptor from 2.00 MM stepped down to 1.5 MM .

He is not reaming a plastic gear but a small universal coupling that gets installed on the motor shaft. At least that  is how I understand his description.
I agree that I have never heard of 1.9mm shafts, but 2mm is very popular.  But whatever it is, the goal is to ream the universal coupling which is  to be installed on that shaft.

[Chris333]

You could hold it in a drill chuck or pin vise if you had one big enough.

[mike_lawyer]

Thanks for all the responses.  Yes, I am talking about the plastic adapter piece that goes on the shaft of the motor.  I am hand reaming the part to make the hole bigger to fit on the motor shaft.

[peteski]

Thanks for all the responses.  Yes, I am talking about the plastic adapter piece that goes on the shaft of the motor.  I am hand reaming the part to make the hole bigger to fit on the motor shaft.

Remember that enlarging the hole will make the adapter (universal coupling) weaker, and it might split.

I woudl have ground the motor shaft down to around 1.5mm.

I do this by having the motor running, while grinding the shaft with a grinding wheel in a Dremel tool.  You just need to make sure that the motor spins its shaft in the opposite direction from the direction the grinding wheel spins.  I just did something like that last night.

[woodone]

Is this an N scale Kato Mikado locomotive?
If so, if I recall there are three parts to this coupling on the OEM parts. One part that is on the motor, a sleeve that connects the part on the motor to the worm shaft connection. I would worry about holding the motor shaft concentric so it would not vibrate.
There might be enough clearance in the coupling not to give any proplems?

[mike_lawyer]

Remember that enlarging the hole will make the adapter (universal coupling) weaker, and it might split.

I woudl have ground the motor shaft down to around 1.5mm.

I do this by having the motor running, while grinding the shaft with a grinding wheel in a Dremel tool.  You just need to make sure that the motor spins its shaft in the opposite direction from the direction the grinding wheel spins.  I just did something like that last night.

That's a good point... I was a bit hesitant to try that, thinking I might damage the output shaft.

[mmagliaro]

I'll say at the outset that I am spoiled by having a lathe now.

But...

I've done this sort of thing using a variety of the ways suggested in here, with varying degrees of success.  It's all a matter of how centered you can hold things and a little bit how lucky you are.

Chris333's idea of the drill chuck works well.  You can chuck that thing in a Dremel chuck or even a hand-held electric drill chuck, just so you can grip and hold it still.  This also keeps pressure around the outside of the part so that as you drill or ream it, the Delrin plastic doesn't have a tendency to try to just stretch out of the way, which leaves you with an undersized, irregular hole.

Ideally, yes, bore a hole slightly smaller than the part in a piece of metal or wood block and push the part into it.  That will keep it nice and round while you bore out the middle.   If you have a drill press, you can make a nice straight hole in a block, press the part in, and then bore out the center.  I though those Faulhaber shafts were 2mm also.  Are you measuring with a good caliper to get 1.9?  I'd really double check this first, but...  a 2mm would be .0787", so a 5/64" bit (.0781") will be close and will be a little undersized, and should do the trick.

I have also used the shaft grinding trick Peteski suggested.  It works well.   My experience with that approach is to run the motor and the Dremel at high speeds.  This minimizes the chances of getting an uneven or out-of-round shaft.

[mike_lawyer]

I just did the grinding on the shaft with my dremel, it worked well.  I just grinded off a little at a time and kept measuring until I got to 1.5 mm.  I put the plastic adapter on the shaft, and it appears to turn evenly and centered under power.

I have to grind some of the frame to fit the motor in the cavity, and my good Dremel cutting bit I broke last week.  So I will have to swing by Lowes and pick up a couple of new bits, grind the frame, and then test the motor in the loco.

Of the two options (grinding the shaft or trying to ream the plastic adapter), for me grinding the shaft was a lot easier to do.

[peteski]

I just did the grinding on the shaft with my dremel, it worked well. 
. . .
Of the two options (grinding the shaft or trying to ream the plastic adapter), for me grinding the shaft was a lot easier to do.

[metalworkertom]

USPS!    

Throw a couple in the box for those cars I bought.  Please include the shaft to assure a good fit.  They'll be back to you in whatever the ship time is, plus a day or two.   

Will do Mark