Replacement worm wheel gear for Samhongsa Brass F3

[wcfn100]

I was going through my dad's stuff and found a A-B-A set of brass F3s by Samhongsa.  Upon inspection, four of the Delrin worm wheel gears are split.

Does anyone know if there's a replacement option of should I just try and sell these for parts.

Thanks,

Jason

[garethashenden]

Maybe https://nwsl.com/products/worm-gear-0-25mod-x-20-teeth-x-5-5mm-od-x-0-051-face-x-3-0mm-bore-delrin?_pos=1&_sid=055bdc1ab&_ss=r

It's for the Alco switchers that Key imported from Samhongsa, although your models are Hallmark. If they have the swiveling towers they may be the same worms, but I can't be sure. May be worth measuring the ones you have and see if they're the same dimensions. Spookshow is showing a second generation with different worms and trucks, but they're brass, not plastic.

[mmagliaro]

Well, I'll point you to my oft-used place, if you cannot get them from NWSL.

You need to measure the diameter, in mm, accurately with a caliper, and also the
gear thickness, and the bore hole.  Then count the teeth. 

diameter / (teeth + 2) = the "module" number.  I'm guessing it will be something like 0.3 or 0.4

Then you can go here and order a replacement:
https://shop.kkpmo.com/index.php?cat=c21_Spur-gear---Pinions---Worm-gears-Spur-gear--Gearwheel--Pinions.html

I swear, if that place ever stops selling gears, it will be heart-breaking.  It is such a handy service. 
They are not particularly "cheap"... on the order of $4 to $5 a gear if you only want one, but to get an engine back
in service, that's a bargain.

But I'd say do try NWSL first.  They make really nice stuff and you can call them on the phone.  And heck, they are USA made so...

[ChristianJDavis1]

I know everyone says you can't do it, but I've actually had success just gluing the gear back together while clamping it. I bought a GP7 with the same ailment and figured I wouldn't lose anything by trying so I glued it together; it has been running for I'd say about a good twelve hours or so with no signs of failing again (although it probably will eventually). If you just want to get them "back on the road" you can try gluing them back together with ACC (but you have to hold them together to get the teeth to line up correctly or you will have them "click" while running). This will let you run/test them while you figure out just what you need and you won't need to actually replace them unless they break again (so order the parts and as soon as the first one breaks, replace them all).

[wcfn100]

The gear in question measures like this -

14 teeth

.3 mm bore

5.7 mm diameter.

NWSL has a similar gear but with a 6mm diameter.  I don't know if that would be an option.

How important is the pitch on a gear this thin (1.5mm)?

Jason

[mmagliaro]

The gear in question measures like this -

14 teeth

.3 mm bore

5.7 mm diameter.

NWSL has a similar gear but with a 6mm diameter.  I don't know if that would be an option.

How important is the pitch on a gear this thin (1.5mm)?

Jason

 5.7 / (14+2) = .356
So it's actually a 72 diametrical pitch (or 0.35 mod)

This one here looks like it's your boy:
https://nwsl.com/collections/72-dp-gears/products/worm-gear-72dp-x-14-teeth-x-5-6mm-od-x-0-051-face-x-0-116-bore-delrin
(it also says, "fits f3 and f7")

I assume you meant 3mm bore, not 0.3mm

How positive are you about the thickness? Are you sure it's really 1.5mm (.0595"), or could it be .051" like this replacement?
If the replacement is a little thin, you might have to put some shim washers on either side to keep it centered, depending on how it's mounted in there (I have no idea how this assembly looks).

As for the pitch, it's hard to say, but since NWSL does accurately categorize gears as "spur" and "worm gear", and doesn't just call everything a "worm" or a "spur", and since they call this one a "worm gear", I bet it will work. 

[peteski]

I would think that pitch is critical for any meshing gears.  All gears meshing with each other need to be the same pitch.

[wcfn100]

This one here looks like it's your boy:
https://nwsl.com/collections/72-dp-gears/products/worm-gear-72dp-x-14-teeth-x-5-6mm-od-x-0-051-face-x-0-116-bore-delrin
(it also says, "fits f3 and f7")

I assume you meant 3mm bore, not 0.3mm

How positive are you about the thickness? Are you sure it's really 1.5mm (.0595"), or could it be .051" like this replacement?
If the replacement is a little thin, you might have to put some shim washers on either side to keep it centered, depending on how it's mounted in there (I have no idea how this assembly looks).

Thanks Max, not sure how I totally missed that one.

3mm yes.

Rechecking the thickness, if I squeeze, I can get down to 1.34mm.

Now to decide if the two busted ones are worth $40 to fix if I'm just going to sell them.

Thanks guys.

Jason

[mmagliaro]

I would think that pitch is critical for any meshing gears.  All gears meshing with each other need to be the same pitch.

In general, I agree.   I bet the NWSL worm wheel is made with the same pitch as the worm in that loco.  If it were my brass loco, I'd take a shot and expect a good chance of success.

[mark.hinds]

(Corrected 1/28/2021)

This appears to be what you want.  I bought 4 of them in 2016 as an experiment.  I never installed them, however, as I am still using the replacements provided by Samhongsa decades ago.  That Samhongsa replacement substituted an entirely brass worm gear assembly for the original brass-14-tooth / delrin-14-tooth assembly.  FWIW, the brass/brass replacements are slightly noisier (doesn't bother me), but produce the same performance including slow-speed creep.  However, the NWSL guy says the brass/brass replacements will result in greater gear wear, whereas his brass/delrin replacment worm gear assembly won't. 

The image shows what I got from NWSL.  Inside the package, the replacement is on the left, and on the right is one of the split-originals (the split is why it looks slightly larger).  I will also try to post my sketch of the exploded gear tower.  This sketch is for the Samhongsa micro-geared GP-9, but the general concept is the same as the F-units. 

MH

[wcfn100]

The image shows what I got from NWSL.  Inside the package, the replacement is on the left, and on the right is one of the split-originals (the split is why it looks slightly larger).  I will also try to post my sketch of the exploded gear tower. 

Thanks for the pictures Mark.  So the replacement shown on the left is pressed on the brass gear?

Jason

[mark.hinds]

(Corrected 1/28/2021)

Jason,

The NWSL replacement for the paired worm gear assembly may only include a replacement delrin gear, and may not include a new brass gear-with-brass-sleeve.  In the former case, you would need to press-fit the replacement on your original sleeve.  I say "may" because when I examine my gear stash, some packages contain black delrin replacement gears mounted on brass sleeves, and some do not (...).  I no longer remember whether this is because they came that way, or whether this is because I removed the original damaged paired worm gear assemblies, and replaced the split nylon gears with the NWSL delrin replacements.  FWIW. 

MH

[peteski]

Thanks for those pictures!  Now I understand how a plastic worm-wheel which is not normally press-fit onto its axle could split.  This is an unusual setup of a combination (double) gear, where the plastic worm-wheel has a large hole which is then press-fit onto the smaller brass gear.  That looks very prone to splitting, since there is not much 'meat" on that worm-wheel.

[peteski]

In general, I agree.   I bet the NWSL worm wheel is made with the same pitch as the worm in that loco.  If it were my brass loco, I'd take a shot and expect a good chance of success.

Just "in general"?  As I understand it, the pitch of a gear defines spacing between its teeth.  If there is even slight mismatch betwween the gears, the teeth will not fully or properly engage. Even it the combination works, it will likely wear out prematurely.

Also, I think that gear pitches follow some predefined specs. While there might be some unusual pitch values, in  general the majority of the gears fall into one of those often used pitch values.

[mmagliaro]

Just "in general"?  As I understand it, the pitch of a gear defines spacing between its teeth.  If there is even slight mismatch betwween the gears, the teeth will not fully or properly engage. Even it the combination works, it will likely wear out prematurely.

Also, I think that gear pitches follow some predefined specs. While there might be some unusual pitch values, in  general the majority of the gears fall into one of those often used pitch values.

Sorry... you said "pitch" and I was thinking "pressure angle".  The gear, as measured, works out to mod 0.35, and the NWSL gear is mod 0.35, so the pitch is the same and it should work.