Folks,
I'm doing a rehab on an Athearn Blue Box SD-9 chassis. There's a tapped coupler mounting hole that's a bit generous (as in loosey-goosey), presumably for a 4-40 screw (is there something metric a tad larger?). I'd like to reduce this bennie to a 2-56 if at all possible.
A couple of approaches occur to me:
1) clean it and fill it with some sort of epoxy or liquid metal, then redrill and tap for the 2-56 screw. I'm a bit leery with this approach as I don't know that there's a material that will take the fine work of a 2-56 tap - or the mechanical stress that goes along with it;
2) bore out the existing hole, snugly fit and CA an aluminum plug in it, then redrill and tap the plug.
Any idea's? Just thinking here. Hate to consign anything with but a single "wart" to the junk pile.
John
Hi, John
Back in my working days part of my millwright job was repairing gear boxes and pumps among other things.
We often used "helicoil" thread inserts when a hole was stripped or tapped too large. I wasn't sure how small they went but it appears you can get them down to #2, maybe even smaller.
Here is an example of a 4-40 thread insert kit. Home Depot sells these. Maybe you can find another supplier or one of the hardware stores.
https://www.ezlok.com/ezcoil-kit-SK20220
search ebay, too:
https://www.ebay.com/itm/New-PRECISION-4-40-X-168-Thread-Repair-Insert-Coils-12-Pack-P-N-83104-NOS/153411947976?hash=item23b8108dc8:g:ejkAAOSwDZ9bvOXE:sc:ShippingMethodStandard!44024!US!-1
Might be worth a look.
Good Luck, Ed
you could just run a 2.5 .45 mm tap in it and replace screw
Hi John,
If you have some epoxy available (who doesn't) why not try that first. If it turns out that you can't tap the epoxy cleanly all you have to do is run a 4-40 tap back through the hole to get rid of it. I think it would be very important to make sure that there are no oils or other contaminants in the existing hole before applying the epoxy.
As far as strength is concerned, I think the epoxy should be plenty strong enough to handle whatever loads it might experience. It's not like a butt joint that might break under stress. The epoxy is captive inside the frame. It's just acting like a spacer.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
Gidday John,
https://pratleyusa.com/products/pratley-steel-putty-125g
It's the bees knees!!
Cheers, the Bear.
"One difference between pessimists and optimists is that while pessimists are more often right, optimists have far more fun."
Thanks, guys. I think Dave has a good point: start cheap and simple and see what happens. I never tried drilling and tapping hardened epoxy. But if it can be done, that would likely work as I can't imagine a whole lot of shear stress in this application. And good fortune attends my case anyway - because the coupler is on the short hood, front end of an SP loco that is unlikely to ever be MU'd behind something else. If that doesn't work, I'll check out the helicoils at Home Depot or, better yet, a great old-time hardware store here in town that has rows upon rows of magical items.
Gidday John, https://pratleyusa.com/products/pratley-steel-putty-125g It's the bees knees!! Cheers, the Bear.
gmpullman Hi, John Back in my working days part of my millwright job was repairing gear boxes and pumps among other things. We often used "helicoil" thread inserts when a hole was stripped or tapped too large. I wasn't sure how small they went but it appears you can get them down to #2, maybe even smaller. Good Luck, Ed
Attuviando you think that the material in a 4-40 set screw can be drilled out and tapped?
Ouch! That sounds like an exercise in frustration and futility. Even a soft (brass or stainless are soft but they work-harden when trying to drill) set screw would try to spin out when the drill or tap grabs.
If you didn't go the helicoil route, the other suggestions about the epoxy would be next in line. There are some metal putty-type fillers out there (Devcon is one) but they are basically epoxy with a powdered metal filler.
Actually, I just took inventory and I have an old PRR Blue-Box SD-7 I'd be glad to send your way. The original couplers were held in with a plastic clip.
Cheers, Ed
this got me to thinking .seemes to me that i kinda rember that locktite has some striped thread product , might want to check it as i remember itmight work for you..
gmpullman Attuvian do you think that the material in a 4-40 set screw can be drilled out and tapped? Ouch! That sounds like an exercise in frustration and futility. Even a soft (brass or stainless are soft but they work-harden when trying to drill) set screw would try to spin out when the drill or tap grabs. Cheers, Ed
do you think that the material in a 4-40 set screw can be drilled out and tapped?
Attuvian Nice work, Mel. What do these cars weigh? John
https://www.mcmaster.com/93904a100
Drill it out for a 8-32. Insert the above threaded insert and your in business. We use these at work alot for screw that come in and out of aluminum parts. The steel wears better for threads than aluminum does.
Colorado Front Range Railroad: http://www.coloradofrontrangerr.com/
Seems to me to be a lot of fuss over trying to repair something which would better be replaced.
Why not simply cut-off the frame extension meant for coupler mounting? It's the main reason why all Athearn Blue Box locos had those gaping pilots.With the metal extensions gone, use successive layers of sheet styrene to build-up a platform which will put the coupler at the proper height, then drill and tap as necessary. You can then fill-in the rest of the gap in the pilot, and even add a snowplow, if you wish.
This example, on a heavily-modified Athearn U-Boat, isn't the clearest, but I think you'll get the gist of it...
All of the locomotives shown have BB frames with the coupler mounts replaced as mentioned. All have closed-in pilots with appropriate details. All of the body shells are easily removeable from their respective frames, and all of the couplers are removeable for service or replacement.
Wayne
Renegade1c https://www.mcmaster.com/93904a100 Drill it out for a 8-32. Insert the above threaded insert and your in business. We use these at work alot for screw that come in and out of aluminum parts. The steel wears better for threads than aluminum does.
Renegade,
It pushes the limits of the location but it would fit. I'm presuming that the top wings can be broken off after insertion.
The premier local hardware (non-chain) store may well have something like this. It's certainly in the running here.
Thanks!
I was going to say that doctor Wayne has used another solution for fixing truck mounts with similar issues, which is to drill a hole, and insert a piece of tubing that had been tapped. But I see that the doctor has posted a better solution!
Simon
doctorwayne Seems to me to be a lot of fuss over trying to repair something which would better be replaced. Why not simply cut-off the frame extension meant for coupler mounting? It's the main reason why all Athearn Blue Box locos had those gaping pilots.With the metal extensions gone, use successive layers of sheet styrene to build-up a platform which will put the coupler at the proper height, then drill and tap as necessary. You can then fill-in the rest of the gap in the pilot, and even add a snowplow, if you wish. Wayne
doctorwayne Seems to me to be a lot of fuss over trying to repair something which would better be replaced. Why not simply cut-off the frame extension meant for coupler mounting? It's the main reason why all Athearn Blue Box locos had those gaping pilots.With the metal extensions gone, use successive layers of sheet styrene to build-up a platform which will put the coupler at the proper height, then drill and tap as necessary. You can then fill-in the rest of the gap in the pilot, and even add a snowplow, if you wish. This example, on a heavily-modified Athearn U-Boat, isn't the clearest, but I think you'll get the gist of it... Wayne
Simple solution: Drill the whole all of the way through and then use a nut on the end of the machine screw bolt. I have done this on two blue box locomotives, a GP38 and a SD40-2. It worked perfectly.
RR_MelDo you have a easy way to align the coupler height?
I've done a lot of these too, Mel, and I use the back side of the Kadee couple height gauge to see how much shimming I have to do.
Mike.
My You Tube
That's certainly a better version of the photo, Mel.
It's been so long since I've done those locos, I don't recall the exact procedure, but I'd likely have measured, inside the loco, the approximate distance between the bottom of the end walkways and the bottom of the tongue to which the coupler would normally have been attached. I used stacked .060" sheet material (I buy it in 4'x8' sheets, so always have lots on-hand), and when I'm getting close to the proper height, simply lightly tack what might be of suitable thickness onto the stack already built. If it's too thin or thick, it can be easily removed and replaced with something more suitable.While each model of diesel might require a different stack of styrene to get to the proper coupler height, once you've done one, all multiples of that particular model should be the same. I had only three of those U-Boats, and five Athearn switchers, so not a lot of figuring-out to be done for mine.
I had to take a look at a couple of mine, but I think (at least it looks like) I just matched the height of the opening in the pilot.
I don't remember if I had to do any fine tuning with shims, or not. More than likely, I did, but looking at the Athearn BB locos I've done this to, I matched the excisting opening height in the pilot.
Of course I did this before the plow, ditch lights, hoses, etc were all added, while it was just the plain pilot.
Attuvian Thanks, guys. I think Dave has a good point: start cheap and simple and see what happens. I never tried drilling and tapping hardened epoxy. But if it can be done, that would likely work as I can't imagine a whole lot of shear stress in this application. And good fortune attends my case anyway - because the coupler is on the short hood, front end of an SP loco that is unlikely to ever be MU'd behind something else. If that doesn't work, I'll check out the helicoils at Home Depot or, better yet, a great old-time hardware store here in town that has rows upon rows of magical items. John
I KNOW you can drill and tap JB Weld.
Marlon
See pictures of the Clinton-Golden Valley RR
If the hole is off-centre from where it should be, it's usually a good idea to enlarge the hole before filling it, regardless of the filler used. That way, drilling and tapping is done in material with the same properties, and therefore less likely to be forced off-course by the harder or softer original material.
Attuvian Is this a "down under" product? And strong enough to be drilled and tapped?
Gidday John, it's a South African product and would appear to be available in the US, though perhaps not in your local hardware store.
Attuvian Is this a "down under" product? And strong enough to be drilled and tapped? Gidday John, it's a South African product and would appear to be available in the US, though perhaps not in your local hardware store. Cheers, the Bear.