3D-printed gear for Myford Super 7

Those of you who own Myford series 7 lathes will know that when confronted by odd screw threads a full range of change gears is the order of the day. However, some of the original series of change gears are no longer available, in particular, the 46-tooth change gear is no longer to be found. Without this particular gear one cannot cut either a 46 tpi or a 92 tpi screw thread.

Now let me be honest. I’m not really sure that I will ever need to cut either of these threads. But I somehow suspect that Murphy’s Law dictates that given enough time someone will ask me to cut one these threads for some odd bolt, shaft or stud that is needed for repair work.

Instead of burning up a lot of machining time to create this gear I chose for the cheap route and decided to try 3D-printing one of these gears in PLA plastic filament. I’m not the first to do this. There are various videos on Youtube of others who have done the same.

I opted to use the freeware program FreeCAD that has a built-in gear generator algorithm. The form I generated was passed into the Blender 3D software for inspection and cleanup and from there I wrote out a file in the .stl format which I sent to a friend of mine who has access to a 3D-printer. One day later he presented me with two copies of the gear.

The photos pretty much tell the rest of the story. The gear slid into place without any undo fettling. It meshed perfectly with the other metal gears in the train and (most important of all) didn’t fly to pieces when under power.

A test cut was made at 46 threads per inch. However, my thread gauge set can measure either 40 tpi or 48 tpi, but hasn’t provision for that elusive 46. So just to be sure, I held the points of a vernier caliper against the shaft and using a magnifier counted the threads for a measured distance along my work. Success!

So, now these plastic change gears will go into the drawer, there if I need them in the future.

Hope this inspires some of you.

A useful way of solving the problem - just keep an eye on the plastic gear in case it wears unexpectedly rapidly. (Might last for yonks - depends on the ratio, but change gears aren't heavily loaded.

Here's a challenge! Now a 3D-printer has shown what it can do for a lathe, how about using a Myford to make a 3D-printer? Apart from the electronics and the motors, I think it's doable.

Dave

A previous post about printed gears

Also someone has reported printing backgear for a SouthBend lathe and using it for years.by now.

Is the file for this gear available to others for printing? My son has printed gears with a carbon reinforced nylon, epacf30 , and the gears in the model rc car have lasted a very long time.

I would be glad to share the file with anyone who is interested.

I no longer have a personal web page. Is there a way to post that file on this forum?

Hi, I too would love to have that file please.

Martin

Can't post it here yet but if you wish to share you could put it on Thingiverse home to a million useful 3D printed objects.

John

Someone has beaten you to it on Thingiverse for most sizes, but not a 46-tooth as yet

Rob

Links to https://www.thingiverse.com/thing:2523313/files

I'm posting the gear file on Thingverse, but as a new user I'm informed by the system that my posting won't go live for 24 hours. When/if that happens successfully I'll post the link.

Rod made two printed tumbler gears for the Atlas 12 X 24 and they are perfect.

Please look online for software called GearDXF. To be fair, in this age of 3D printing, it is slightly misnamed, but it will output STL files suitable for 3DP, It will not do the keyway in the centre bore.

The gear file is now posted on Thingiverse.

Just follow this link: Myford 46-tooth gear at Thingiverse

Edited By Ignatz on 24/07/2022 21:59:36

Well done, Sir

MichaelG.

As you say in your orignal post, 46 tpi or 92 tpi are uncommon. However, if it will make 46 tpi threads, can it not be used for 23 tpi and 11 1/2 tpi? Of the four possiblities, 11 1/2 tpi is used on US NPT pipe threads above 1" nominal dia.

A chap I knew once told me that many years ago someone had asked him to make a batch of special pipe fittings that were 11½ TPI. It turned out the guy was selling kits for for bypassing gas meters. !!

I dont know how true that was.

Edited By Phil P on 25/07/2022 08:04:52

When I bought my elderly Smart and Brown lathe a couple of years ago, it came with a cabinet with all sorts of accessories but it did not have the additional gears for the thread dial indicator needed for the full range of metric threads, it having a metric leadscrew and gearbox. This is a great use of 3D printing, as you need a helical gear to mesh with the leadscrew but it takes virtually no load so wear and tooth strength is not a problem. Took more time figuring out the helix angle then figuring out how to turn a spur gear outline in F360 into a helix than it did to print. I did need to run a reamer through the bore to get a nice fit but the printed keyway was fine.

Edited By Nealeb on 25/07/2022 08:15:47

This opens up a whole new world of being able to produce the unusual tooth counts for the gears needed to cut various Metric threads on Imperial machines, and vice versa.

The files, presumably, will need modifying to take account of the different Pressure Angles, as well as tooth counts, but I am sure that there is sufficient expertise on here to cope with that!

(Neil has a file to print 100T gears for the mini lathe, so might be a starting point for 20 degrees P A gears )

Howard.

This is all available in the FreeCad - just fill in the table.

(Perhaps SOD who dod such excellent tutorials in basic use of FreeCad would like to cover this )

FreeCAD is rather too much of a learning curve for a simple gear.

Please have a look at:

https://evolventdesign.com/pages/gear-stl-generator

It does keyways and will also do profile shifting so, for example, if you want a 20t gear and a 21t gear with the same OD (to save having to alter carrier centres on a banjo) it will oblige.

Gears of differing tooth count but the same pitch diameter are very useful on metric thread dial indicators - a 35t and 36t made on a 35 1/2 pitch diameter make changing gears a simple sliding action, axial position controlled by a detent.

You could also make something with a 15 degree pressure angle to mesh with a metric trapezoidal thread.