Re-power

[PaulP]

Helping a friend with repowering his Z8 project. I machined out his chassis and that went well.
He proceeded to try to remove the gears and adapters from his old motor and that’s where the project didn’t go well.
He destroyed one gear and adapter and scared up the other gear before giving up!
He was ready to shelve the project but agreed to see if I could help.


I decided to try to turn him some new one piece gear/adapters. I proceeded to turn a blank and then ground a bit as close to the stock gear profile as I could.



So far so good. I am looking for some advise on the bore. I have no way to bore or measure a 1.5mm hole. So seems it will have to be a drilled hole. Reamer appears to cost in the $30.00 range with shipping so that seems out for one time use. Thinking about drilling it with a 1.5mm bit.  I question the fit I will get. Have any of you had to drill out gears to fit different shafts?  How did they fit and or did you glue them to the shaft? 
Thanks for any advise
Paul

[Rasputen]

One way would be to use your 1.5mm bit and drill a hole in a scrap piece of brass.  You should be able to judge the fit onto the steel shaft without pressing it on very far.   I would also mike the drill bit and the shaft first, to see how close they are.

[Doug G.]

What you want to do is initially drill the hole undersize and work up to the final size. If you start with the 1.5mm bit, the hole will almost invariably end up a little oversize.

I agree with the Russian Svengali to practice on scrap brass first.

Doug

[Lemosteam]

^^^ Agreed.  The smaller diameter and smaller increments you can upsize the hole between, the smoother and more round the bore will be as well.  This is brass too, could you drill it at 1.25mm and then grind an HSS boring bar that could fit inside the 1.25mm hole and take light cuts inside while test fitting the motor new shaft with each pass?
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[rodsup9000]

  In most cases I would just buy the reamer. Over the last 25 plus years, I've bought a quite few reamers and I think that only one or two have been only used once. When making a piece like this, always bore the hole with a boring bar. I use Micro 100 boring bars and they have some as small as .020". The smallest I keep on hand is the .050"

 But when in a hurry and don't have time to wait for tooling, I turn a shaft that is a half of thousand (.0005") smaller than the shaft that the piece will go on. Using this as a gauge, I take very light cuts with a boring bar, till the gauge I made will barely go into the newly bored hole. This should give a slight press fit, but still use red (Loctite) thread lock of some sort.

 As they say "you'll spend way more in tooling than the cost of the machine". I'm guessing that over the last 25 years, I've spent well over $10,000 on tooling for both the mill and lathe. 


 BTW, the gear you turned looks very good and you did a great job on grinding the bit to cut it.
   

[mmagliaro]

You can actually buy 1.49mm drill bits ($5 - $10).  I have a few.  Then, as other suggested, use a 1.5mm chucking reamer to get the size up to exactly 1.5mm.   I know I paid under 10 bucks for my 1.5mm chucking reamer.  You can get by with a HSS steel one.  You are only reaming brass.   Hunt around on eBay and for the cheaper reamers from China.  Yes, I know, I know, they are not "top quality".  But for reaming out .01mm in a brass gear on a model train, they will work fine.  The precision of the meshes in these things doesn't require anything better.

[PaulP]

Thanks for the reply’s guys. 
My drill selection
#55  .052
#54  .055
1.5mm  .059
#53  .0595

My mistake was not experimenting with hole size before I turned the gear!
I was too excited about trying to make it and now I don’t want to take it out of the chuck
before finishing it. Rechecking is never as accurate.
Those boring bars sound interesting. I might pursue the reamer though.
I could also drill it and see how it turns out, it wasn’t that tough to make. I can always make more!

[narrowminded]

There's a very good chance that a carbide drill will drill on size or just over (1 to 2 tenths?) making a very nice slip fit.  Not sloppy at all but slip.  That's perfect for low strength Loctite that will hold as much as needed for this service but has the chance of being removed without wrecking the parts as happened to the originals.  That's my preferred way to make these kinds of fits, slip with loctite.  Totally adequate grip with fewer potential for difficulties, today or ever. 

If using on a motor shaft be careful not to loctite the bearing to the shaft.  Slide the gear onto the shaft, slip forward allowing the gear to overhang the end 1/2 to 3/4 of its length, apply a very small amount to the bore with a toothpick, slide on to position while giving it a half turn or so, and let set.  Do not apply ANY to the shaft ahead of the gear/ bushing.  If you do it WILL find its way into the bearing 9.9 times out of 10.

https://www.amazon.com/Loctite-22221-Purple-Strength-Thread/dp/B006GOL5CQ/ref=pd_sbs_469_t_0/137-4947886-1208146?_encoding=UTF8&pd_rd_i=B006GOL5CQ&pd_rd_r=8218fe57-316a-4e64-8ae6-fe258f3a7d58&pd_rd_w=pz5p8&pd_rd_wg=qjwGK&pf_rd_p=5cfcfe89-300f-47d2-b1ad-a4e27203a02a&pf_rd_r=RREEDGTJJ6BE2R2CWAM3&psc=1&refRID=RREEDGTJJ6BE2R2CWAM3

1/8" shank carbide circuit board drills.  Should have adequate drill length, infinite number of sizes, and relatively low cost.
https://drillbitsunlimited.com/

[narrowminded]

And for measuring holes consider pin gauge sets in .001" increments.  A .011" to .060" set and a .061" to .250" set will probably cover all of your modelling needs.  They come in plus and minus sets meaning that they are the marked size with a tolerance of  .0000"/ +.0002" (plus set) OR  .0000"/ -.0002" (minus set).

https://www.shars.com/catalogsearch/result/?cat=1271&q=PIN+GAUGES+SETS

[mmagliaro]

I agree that worrying about the bore being "press fit" is unnecessary for model worm gears.  And I too also prefer when they are just a slip fit so I don't have to wrestle it onto the motor shaft (which is a real problem if the motor doesn't have a backshaft like a lot of the coreless motors).  Better to drill out to 1.5mm, and just slip it on with Loctite.

And yes, narrowminded, boy do I know the perils of getting loctite near the shaft bearing.  The tiniest microdrop of that stuff and the shaft will stick fast.  Happened to me once on a coreless motor (ack!).  Luckily, it wasn't the RED stuff, and I was able to just keep swabbing it with acetone, holding the motor, gripping the shaft with small pliers, and "ootching" it back and forth until it finally let go.

I prefer to keep the motor with the shaft pointing DOWN when slipping the gear on, to keep any loctite from trying to run in there..  Also, putting a drop of oil right at the shaft/bearing entry will keep loctite from getting in there or setting there.

[PaulP]

Unreal. The reamer I ordered just showed up on the porch. I ordered it the other night and it said only $3.66 with free shipping so I figured it was from China. Only one left. Turns out it is an Alford Polk solid carbide CNC short length made in USA! And now it says to order again it’s $24.10! I guess I got lucky! Guess it’s time to try it out.

[woodone]

Well I don’t think that you will find drilling a hole to exact dimensions very good. Best to drill undersize and then ream.
You can get reamers on line for a small cost. Yes some will come from China, but these will give you a better fit than drilling. You better get some collets to hold your work too.   

[BuddyBorders]

Lots of great info in this thread. Many things I was going to suggest were already made. And it's nice to see I'm not the only ony one who has Loctited a motor together I wasted a 10X12 Sagami some years back.

One thing that hasn't been mentioned is making a D-Bit reamer. You get a rod the size you want, say from a scrap motor, and grind a flat halfway through the diameter. Taper the end some, say 15 degrees. If done well, it should ream a nice hole for you.

Keep up the nice work,

Buddy