Found a source for Kumata plastic screws in N & Shoulder washers stuff

[u18b]

If you own a Hallmark brass SD40-2 made by Kumata or an Oriental E1 set, then you know what this is:




In the Kumata design for these locos, both of the gearboxes are charged (one to each rail).  So one of the gearboxes is insulated from the frame.    The way they secured it to the frame is with plastic screws.

But they rarely hold.  You have to torque them down very snug to get them to hold the gearbox properly...... but when you do that the pressure breaks the head.   

This situation is worsened by the fact that they only used two screws per gearbox instead of four.  Double whammy.   

If you have these locos... you already know all about this... and you know that finding replacement screws is a monumental challenge.

I recently repaired an SD40-2 for someone, and my solution was
--to just toss the old broken/weakened
--tap the two holes for 1-72 screws
--drill two extra holes and also tap them for 1-72
--secure with Walthers plastic 1-72 screws.


Much more secure.



But not everyone feels confident enough to disassemble a loco, and or drill and tap new screws in brass.
So just wish they could find new screws.

Well, I recently came across a source and thought I would share it for those interested.

The company is NBK.   


The page for plastic screws is:

https://www.nbk1560.com/en-US/products/specialscrew/nedzicom/plasticscrew/SPE-MC/

The screws you need for the SD40-2 and the E1 ATSF set are:  M1.6 screws.   I would get the 4 mm screws and cut off the excess as needed.

I have not bought from this source yet, but the real reason this interested me is the other sizes.

Kumata only uses M1.6 plastic screws in those two locos (which were their first).

After these first two locos, they switched their design.    They switched to all steel screws, but then had to insulate them from the gearbox.

So..... they added little insulating bushings.   These kept the screws from touching the gearbox (the gearbox has clear acetate to keep it from touching the frame).

These bushings are in LOTS of Kumata locos.   If you own a KMT loco, there's a good chance yours has these.

But once again, there is a problem.

Here is a photo.



The one on the right is still in pretty good shape.
But the one on the left is damaged and no longer useful.
These often split or get crushed.

At present, I have NOT found a source to find the tiny bushings. 
The size of the screws is  M1.4
Would love to find these bushings if I could.

But what I DID notice is that NBK sells tiny plastic screws.

In fact, they sell M1.4 plastic screws (and smaller!).

I have no idea how strong they would be, but it is nice to know that there is an alternative.
If you have a broken KMT loco, you could removed the steel screws and insulating bushings from the insulted gearbox and replace all four screws with plastic screws.


I may order some in the future to see how strong they are.

[mmagliaro]

Ron,
Is there anything special about these M1.6 plastic screws?   

Here's one source.  These guys all have nylon  M1.2, M1.4, and M1.6 (plus larger sizes):
http://www.solidspot.com/reny_screws.html  (claims their glass-filled nylon is stronger than any other plastic screw)

There are others.  The only size I really have big problems finding are M1.0.  I managed to get some, and I'm
using them in my engine, but now I cannot find them on the web and I don't remember where I got them!

[up1950s]

Found a source and list for collared nylon washers but doesn't have a cart . I would like some myself Ron .

https://www.wclco.com/plastic-components/spacers-shoulder-washers/nylon-shoulder-washers-nylon-metric-shoulder-washers/

[narrowminded]

Give me good dimensions or even better, a sample part of that plastic step washer, and I'll make you guys 10 or so machined in Delrin.  That is straight forward enough that it won't need discussed.  

[u18b]

Ron,
Is there anything special about these M1.6 plastic screws?   

Here's one source.  These guys all have nylon  M1.2, M1.4, and M1.6 (plus larger sizes):
http://www.solidspot.com/reny_screws.html  (claims their glass-filled nylon is stronger than any other plastic screw)

There are others.  The only size I really have big problems finding are M1.0.  I managed to get some, and I'm
using them in my engine, but now I cannot find them on the web and I don't remember where I got them!

No.  Nothing special.  Thanks for another source.

[u18b]

Found a source and list for collared nylon washers but doesn't have a cart . I would like some myself Ron .

https://www.wclco.com/plastic-components/spacers-shoulder-washers/nylon-shoulder-washers-nylon-metric-shoulder-washers/

For you and narrowminded....

I'll dig some parts out and do some measuring when I get a chance.

I have a calliper so I should be able to get some good dimensions.

[narrowminded]

Just let me know.  No drawing should be required. Just a description with the number.  For the tiny through hole you might have a better chance of getting a believable number with your number drill shanks if you have a set.  Even if you can give me two number drill sizes as a go, no go, we should be able to get something that's very workable.  I have about 200 drill sizes ranging from .0060" to .2660" in every imaginable number, letter, and metric size so we can get whatever is needed.    It's at least 1.6mm, I guess.   Then I'll need an address or two.

[up1950s]

I ordered the 1.6 and 2.0 sizes from this chap . At least now I will have something to work with should the need arise .

http://www.ebay.co.uk/itm/Packs-M1-6-M2-M3-M4-M5-M6-M8-M10-M12-M16-NYLON-Plastic-Shoulder-Washers-/181932246762

Thanks narrowminded for that offer . I should be good  once they clear up the airport in England and the post gets to me .

[u18b]

Found a source and list for collared nylon washers but doesn't have a cart . I would like some myself Ron .

https://www.wclco.com/plastic-components/spacers-shoulder-washers/nylon-shoulder-washers-nylon-metric-shoulder-washers/

YIKES!!!!!!    These shoulder washers from this website are all way to big.

Here are the measurements I made.
(they are so tiny that one even became an offering to the carpet gods  )

First- using this diagram from that website.



Ok, here is what I measured:

A (overall top surface)  2.45 mm/ .096"

B (lip)  KMT stock measures .47 mm/ .019"   

C Outside barrel (that must go into the gearbox hole)  1.47 mm / .0578"  (the hole in gearbox is 1.48mm)

D depth of barrel below lip (how much shank extend into hole) stock is REALLY thin at .47 mm  I think 1.00 mm / .39" better

E  inner hole  since my M1.4 screws actually measure 1.34mm across the threads, lets go with that as min.  So >1.34mm /.0527"

Because these are so tiny, and because they are so hard to find, this is why I was thinking some M1.4 mm plastic screws might possibly be a substitute.

edited:  and BTW, the wall thickness of these things is ( 1/2 of C-E)  .002"   2 mill  (.065 mm)

No wonder they are so fragile.

[u18b]

Give me good dimensions or even better, a sample part of that plastic step washer, and I'll make you guys 10 or so machined in Delrin.  That is straight forward enough that it won't need discussed.

Can you machine something that tiny?

If so......

[u18b]

I ordered the 1.6 and 2.0 sizes from this chap . At least now I will have something to work with should the need arise .

http://www.ebay.co.uk/itm/Packs-M1-6-M2-M3-M4-M5-M6-M8-M10-M12-M16-NYLON-Plastic-Shoulder-Washers-/181932246762

Too bad those folks don't go smaller to M1.4.    That would be the size I need.

I think I'll order a bag of the M1.4 screw from Max's source.

http://www.solidspot.com/reny_pan_head_micro_screws.html

It looks like the one with the strongest head and measured torque strength is:

RENY/LMCH M1.4-6   (6mmm long.... and then I'll cut off what I don't need)
CHEMIS Head Type 3
http://www.solidspot.com/shop/index.php?main_page=product_info&category=RENY%20CHEMIS%20Micro%20Head%20Type3%20Screw&products_model=RENYLM146&products_id=2471

Looks like 20 bucks plus shipping for a bag of 100.

[up1950s]

YIKES!!!!!!    These shoulder washers from this website are all way to big.

I was reading them as small . To me a .1mm is a tenth of a mm . Is M1 the same a 1.0mm ? They use , I think the big M for rod and screw , and the little mm for their nuts and holes . I like the idea of the metric system but I guess I haven't gotten the trick of how they mucked it up with how they wright it out all the time .

[up1950s]

1.2 and 1.4 mm screws and nuts found here .

http://www.tabcooptical.com/screws/new-category/

[narrowminded]

Can you machine something that tiny?

If so......

That is tiny.  But then, so are a lot of the parts I make.  

The wall thickness in that picture above looks like a lot more like .008"/ .010"  than .0015/ .002".  Maybe shadows? 

Forgive me if this question seems too elementary but did you use the inside calipers to measure the hole in the worm block to arrive at the shoulder diameter?  I ask because in those small numbers the inside calipers will read a few thousandths smaller than the hole, the smaller the hole the bigger the error, and if I look at your bushing picture above and scale from it to the known screw number (1.4) I'm guessing that wall to be more like .008"/ .010".  I have sets of pin gauges in .001" increments from .010" to .250" to measure small holes like that.  Could you or maybe did you measure the OD of the bushing if you have one that's clean enough to verify that dimension?  Absent actual pin gauges you can use drill shanks or anything that you can find that fits the hole and then measure its O.D.  For example, will a 1/16" drill easily go through the worm block hole but maybe not 5/64"?  And if you have a number drill index you can refine that quite a bit.  It can get you closer than the inside caliper in those small sizes.  The problem with that wall thickness in plastic is enough stability while you're machining it and it gets warm.  But if it is truly .0015" / .002" then we'll figure it out.

I have  1.35mm (.0531")  and  1.40mm (.055") drills. They are very sharp and tend to drill pretty much on size so I think the 1.4 will be the one to go with.  Even though the measurement over the thread will be as you measured, when you get up near and at the head, I expect the dimension will get closer to the 1.4mm number or greater at the transition radius and might tend to aggravate the distortion you've experienced, starting to yield the bushing before it even sees the screw load. 

How many do you need?

[u18b]

Your question is a good one.

Most of the measurements I gave are indirect (but better) measurements.

I first tried to get the inside diameter end of the calliper tips into the hole of the gearbox-  but the tips were not small enough for anything close.

So then I used the outside diameter ends and "eyeballed it."   Needless to say, that was not a good measure.
I then went searching for round objects that would be the size of that hole.

After several attempts, I found a standard N scale drive/worm shaft was absolutely perfect.  So I measured the shaft.   So the measure for C- the outside diameter of the barrel came from the worm shaft that just fit into the gearbox hole.

The size of E- the hole was also indirect.  It came from measuring one of the many M1.4 screws I have.

The size of B - the lip was exact.  I could measure that.

The measure of A- the diameter of the outside top lip.... was my suggestion.  I did not even measure the shoulder washer.  What I did was stick a screw with a larger than KMT size head in the hole.   The limitation of A is if it is too big, it will hit the wall of the gearbox.   But as long as it clears the wall, then bigger is actually better.   KMT made theirs too small.   If you see an old worn out one, you'll see that the head of the screw has started to sink down into the lip and deform it.  So bigger is better.  A is Ron Bearden's recommendation.

And D is as stated below.  Actual measure.  But they are too small.  So I gave my recommendation.