3D Printed Gears for Bachmann DDA40X....

I have a few of the Bachmann 2nd generation DDA40X locomotives. I saw them when they were new and I lived in Laramie, Wyoming so they are kind of special to me. The Bachmann's have dual motors like the originals and also most have a common fairly fatal flaw. The have the notorious Bachmann 'White Axle Gears' that split like in the next image. Bachmann no longer has these gears and as far as I can tell no one else has them either. James at James Trains has replacements for the Bachmann Doodlebug and might make them for the DDA40X's at some point also but as I write this (Aug 2023) doesn't as far as I know.

For some time I had thought about trying to design gears and 3D print them but thought designing gears had a 'black magic' like aspect to it. Recently searching about this I found that the free Fusion 360 I use has an also free add-on called GFGearGenerator that makes designing gears super easy. You do need to have some knowledge about gears to use it though.

I spent a couple hours searching and reading and view what I needed to use the program and in about 30 minutes with Fusion 360 I had an axle gear that I could print on an AnyCubic Photo M3 resin printer. 50 minutes of print time and a few minutes of cleanup and I had a number of gears to try out. The following takes it from there and if you find Part 1 to boring skip to Part 2.

===== Part 1 – What you need to design a gear =====

After you add GFGearGenerator to Fusion 360 you need a couple things to use it to design a gear, but not much and it will do the rest. You need to know the 'Standard' (metric/English); the 'Module' (metric) or 'Pitch- (English); 'Number of teeth'; 'Gear Height' (thickness) and the 'Pressure Angle'.

I knew the number of teeth from the stock gear. I knew the thickness of the gear from measuring the stock gear. I'd try a 14.5 pressure angle as that seems to be the common angle widely used. The only real unknown was what module or pitch do I use. The YouTube video ( HERE ) gave me the answer pretty quickly.

To determine the 'Pitch' you only need the number of teeth and the overall diameter of the gear in inches and the formula [ Pitch = (2 + # teeth)/ O.D. in inches ]. If you use Module you also only need the number of teeth and the overall diameter of the gear in mm). Pretty simple and explained in that video. I had the three stock gears (drive, idle & axle) that I knew the number of teeth on and could get close on the diameter of the gear. Using that and the video info I came up with a pitch of 63 on one gear, 65 on another and 64 on the third. All of the gears that mesh together, the larger drive gear in the gear tower and the axle gears and the idle gears have to be and are the same pitch. The small differences in the pitch numbers was due to accuracy in measuring the diameter to a thousands of an inch. Since 64 was a very common pitch I went with that and it seems to be right.

Using a pitch of 64 as the 'Pitch' in Fusion 360 I had a gear that ended up working first time in under 30 minutes. So much for 'Black Magic' although it still would be that without the GFGearGenerator add-on as it did all the heavy lifting.

With the basic gear designed by GFGearGenerator I only had to put the inner bore in the gear and the shoulders on both sides of the gear with Fusion 360, simple an quick to do. The gears were the first print I did with the AnyCubic Photon M3 and they came out great. The secret to that was I used the Siraya Tech's print profile for the M3 using their 'Build Sonic Grey' resin (love this resin so far). You can get the print profiles on Siraya Tech's site and add them to Chitubox which is the slicer I used. I chose light supports using it and the print was great right off the build plate. The gears snapped off the supports after I washed them on the build plate in the Elegoo 'Wash-n-Cure' station. After they were washed I put the gears alone back in the cure option of the station and cured them for about 2-3 minutes on each side. Next in part 2 the gears will be installed.

====== Part 2 – Installing & Testing the gears ======

The following will explain installing and testing the gears in the loco.



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I did get the loco running pretty will with one of the two trucks but not like you would want it as the gears in one truck would bind up and stop the loco at time. Not good on the motors.



I couldn't believe how well the gears printed and what little cleanup was needed after coming off the build plate and the wash and cure session which is very easy using the Elegoo 'wash-n-cure' station. No hand cleaning required with it.



Less than 30 minutes to design the gears in Fusion 360 once I spent a couple hours learning more about gears.



It is very important to bore the center of the gear out and doesn't take long using the three bits shown above. You want to end up with it spinning freely on the 3rd bit ( 1/16”). Don't overdo it though. You want the two axle half's to be a slight press-fit into the gear. If you don't clean the hole up the axle will probably crack/split the gear if it has to be forced in. After a couple you will get the feel. I wondered if I might have to end up using CA glue but so far that hasn't been necessary.



I start by testing the gear/axle combinations in the two bearing locations on the right above. You can put them there and spin the wheel/axles and turn the truck over and push it and see if the bearings and wheels are spinning freely. After you know they are then put two in under the drive gear (the worm gear on top of the large drive gear prevents you from spinning the two axles that are driven by the drive gear. Also once they are in place none of the gears will turn by hand as they are all connected via the idler gears.



Be sure and gauge the gear/axle combinations as you press the axle/wheels into the gears with a NMRA gauge.



I run the trucks on the workbench with the small 5v power supply on the end of a breadboard or take it over to the test layout and run the motors/trucks with some leads clipped to the track. This is good as you can run them at all speeds with the loco upside down. Clip the leads to each frame half. The gears/wheels might jump around a bit until you put the side truck frames on.

Above is a gear I cracked by pushing too hard on the axle while inserting it into the gear and the larger diameter step was forced into the gear and split it. Only time will tell how the gears stand up to longer run times on the layout. I'd like to hear your results if you print and use them and will pass that info on here. Contact me at ... contactsumner1 (at) gmail (dot) com



Click on the image above or ( HERE ) to see the gear test on the bench followed by testing on the test track.

I have no long term report at this point as to if the gears will hold up or not but so far I'm impressed and happy with them. Also they cost penny's to make and at this time I've had the loco apart and together and could replace all 8 axle gears and have the loco back on the track in about 30 minutes with new gears if needed.

I'll get the print file up soon.

Sumner

 

Very cool! Would you have any interest in selling these?

 

At this point in life not really interested in getting into sales/shipping/etc. but I'll have the files up soon. Want to test just a bit more. Once the files go up anyone could print and sell them if they want.

Sending you a PM also,

Sumner

 

Are you using Fusion 360? These are about the simplistic 3D printed project I've done. Basically only need to know how to add the gear package that is free and use a couple simple Fusion commands to design the gear. All very easy and I could help.

If you aren't using Fusion commercially it is all free and I think, not positive, that you can have up to $1000 of income a year as a result of using it and still not violate the terms (should check that).

Sumner

 

awesome. ive printed gears with filament print (i dont have resin printer yet ) and those came out very good.

 

Very impressive! And thanks for sharing your documentation of how you did this.

 

I have heard/read that the 3D printed gears sold as replacements for the Bachmann gears for the Northern, Consolidation, etc., online, also crack.

It's just a terrible design, stuffing an incompressible, metal material into a plastic tube which will always have weak spots that will eventually fail. The only way around it is to put sleeves around the plastic axle to reinforce/repair it (this is how I fixed my Northern and am in the process of fixing my Consolidation and Trolley) or make the assembly so there is no outward force placed upon the plastic tube.

Doug

 

It's not a bad design, it's a pretty standard model railroad locomotive design that generally works fine, it's just that Bachmann went through a phase where they were using a plastic that would shrink too much, putting too much stress on the gears.

 

It's a bad design. They should be the opposite with the plastic stuffed into a metal sleeve. This is how the original Con-Cor PA-1 was made and many other locomotive drivers. Most are made with plastic axles plugged into metal wheels.

If Bachmann had used the other way, their locomotives would all be running today.

Also, by saying this, I am not saying I hope Sumner's gears fail. I hope they work.

Doug

 

i think them original gears are inferior plastic an thats why the fail along with the pressure of not being exact on the hole size for the axle

 

Sumner,
You are an inspirational modeler! Always trying out new tech and new ideas and designs!
Nice work on the gears, great SBS, and thanks for sharing!

Scott

 

It could be that the plastic is inferior but it's still a bad design. I have seen other locomotives, with the same basic design, fail, too.

Doug

 

If Bachmann had done several small things different, they would have become a major player in N scale instead of the sad little company they have become...The Spectrum line is mostly great, but then they kind of stopped doing it and moved back into the 1970's (see latest caboose releases)

 

Then how do Atlas, Kato, Athearn, Intermoutain and others, including more modern Bachmannm, get away with it?

I believe most modern model locomotives, at least in N-scale, use the metal axle plugged into a plastic gear design.

 

Anybody got any pictures of these manufacturers' wheels and axles?

Google only gets me pictures of complete locomotives, plastic freight wheels and axles, and prototype wheels and axles.

Doug

 

Here's a few. The picture quality is horrible because my phone's camera glass cracked and I haven't fixed it yet, but I think it's clear enough. The one on the left is from a Kato ES44AC, the one in the middle is from an Atlas B36-7, and the one on the right is from an Intermountain F7.

 

The problem comes from plugging a metal axle into a plastic gear that is designed to be too small for a tight fit. Take constant pressure from the axle, add it to the built in stress points of the gear, and multiply that by time making the plastic more brittle (in the wrong type of plastic being used from the start) and that equals cracked gears. Most MFRs know to either not make the plastic to metal ratio too large or knurl the metal so it bites into the gear without causing too much pressure. There is a sweet spot here (tight but not too tight) that Bachmann never seems to have been able to find in some of their locomotives.

 

OK, those pictures indicate a much smaller diameter axle plugged into the plastic than Bachmann's sets, right? That's better. Much more strength in the thicker plastic.

I still say it's an unnecessary, inferior design.

Doug

 

Couple updates:

First I have no idea how long the gears I've designed/printed will last but I do know that I now have two locos that didn't run before that run now . I'm hoping that others that print these will take the time to post about the resin they used and the results they achieved. There are tons of different resins out there that have different properties. I'm using Siraya Tech 'Build Sonic Grey' and so far it is the only resin I've tried so lots of possibilities with different resins.

Second the gear's center bore are undersized as printed so you can't even get the axle in that way without breaking the gear. This was by design. I ream the gear out with first a #54 bit, then a #53 and finally a 1/16" bit. This takes about a minute to do. I spin the gear on the bit that I'm holding in the other hand. Don't want to use a drill as that is too aggressive. These gears are really small, just a hair over a 1/4" in diameter (6.8 mm).

I can stop rotating on the 1/16" bit early and the axle into the gear is a little more than snug fit in the gear. Turn it more and I can get to where if pops right in. I agree that the gear would of been better with a large diameter shoulder for more material between the axle and the outer part of the shoulder. But I'm not going to pursue that. I'll live with the stock setup.

What I am doing is running one loco with gears where the axle is a snug fit and doesn't need to be glued to the gear. The other loco I'll run with gears that have been reamed a little further and the axle really needs to be glued in. I have a procedure for doing that using a thin CA but you have to be fast with the last axle side getting it in and getting the NMRA gauge on it.

The main outcome I believe is that now there are gears one can print that might not be perfect and might not last for years but at least one can get a 'dead' loco running again. The gears cost practically nothing to make so even if you do have to replace them at some point it is only going to cost you a little time.




I'm also re-posting the first video above again (click the image or HERE ) as I didn't put the first one on the right YouTube account so deleted it and re-posted it ( HERE ).

Sumner