Need change gear help with a Vevor model YS-1835-A mini lathe!

[WobblyHand]

@WobblyHand

Not sure if this will help, but here is some info from a SIEG SC3 40T "POM" (Polyoxymethylene) plastic gear:

Keyway: 3mm wide, 2mm deep with 1.2mm of boss outside of that.
Centre boss: 18mm diameter by 7.6mm thick.
Gear is 7.75mm at the teeth

Seems odd to me that the boss is 0.15 narrower, but that is how it measured out and I did remeasure several times to confirm it.

There's tolerance and the like. I'd think that I'd defer to the OP's dimensions, because who knows what Vevor did. I made the dimensions close to nearest mm or .5 mm. With all of this stuff, there's going to be "some hand fitting required". Guess it's the nature of the beast. If it's slightly off, I can make another stl file for him to try, or a little judicious sanding. It's plastic, it won't take much to alter it if required.

Apparently, the workbench that I was using was replaced with something better. Anyways it only took 3 minutes to design the gear, so it's not a big deal to make another one. It's all extrusions and pockets to me.

 

[VicHobbyGuy]

For a 7x, all gears apart from the reverse tumbler gears are keyed. They have to be keyed since they drive the leadscrew and need to do so without slipping.

About 3D printed gears:
Yes, all the gears in standard sets are keyed.
For the intermediate gears in a gear train - the 'B' and 'C' gears - the keyway provides the means to 'lock' the stacked gears together, using a bushing with a keyway to match the smaller shaft on the intermediate gear position.
If the gear train has only 3 gears, A-idler-D, then another gear and the keyed bushing still need to be used to get the gear to fit on the shaft.
If you are 3D printing gears, it's easy to make extras without the keyway and with the smaller bore. Those gears are only used in the intermediate position. It's also possible to 3D print 'stacked' gears with the smaller bore, to save messing with that keyed bushing.
It's only a matter of a few dollars of filament to print an 'extra large' gear set.
BTW, gears without the boss seem to work fine in my machine. If the intermediate (free-turning) gears are too thick, they can bind on the attachment screw and washer.
A definite 'thumbs up' to @WobblyHand for the gear design work.
There are .stl files for the change gears at the online (free) file sites like printables.com and thingiverse.
There are lots of files online- here's one set I used:
https://www.printables.com/model/31195-lathe-change-gears-7x10-7x12-minilathe
I used the 'gear plug-in' at Onshape to design my non-standard gears. It was a nice gentle intro to CAD.

 

[WobblyHand]

I do have a mini-lathe. But I am NOT assuming that what I have (Sieg based) is what the original poster has. Which is why I asked the questions. More than happy to make a couple of designs, to help out, for a few missing gears. Not so keen to do a full set, well because that starts to look like work.. As noted above there's loads of change gears online, but it's not always obvious what their dimensions are, because stl's are tough to dimension from.

I figured the key way might be 3mm, but wasn't sure about the height of the key way. If I recall correctly, the needed gears were 55 & 65? Anyways, here's the stls for 55 and 65, with my best guess at dimensions. 3mm key width, 2.5mm long from radius to end of key. And the FreeCAD file if anyone wants to play with it. Just select the grey gear on the side and you can change how many teeth there are. Once you do, the gear is redrawn. Then export the Body to stl, or step. Easy peasy. Happy printing.

 

[VicHobbyGuy]

A beat-up Atlas would be a better choice because most all parts are available, the documentation can be depended on and the price is comparable to these new imports.

I don't know what Atlas you are referring to. I have never seen new spare parts for an older Atlas (or AA) lathe at reasonable prices. And most of those old, small lathes don't have nearly the capability of a 7x Chinese mini lathe in good running condition.
IMO, it needs a step up to a 9x or10x lathe like a SouthBend, Atlas, or Logan to get something more capable. And 'good luck' if you don't find one with the accessories you want, as they are all 'collectables'.

Since you also claim that Precision Mathews lathes are good alternatives to a 7x Vevor, 'market conditions' must vary a lot with geography.

 

[VicHobbyGuy]

Easy peasy. Happy printing.

Thanks, @WobblyHand .

 

[markba633csi]

The prices for used 9", 10" and 12" Atlas lathes have increased quite a bit in the last 10 years or so it's true. Parts also. It's made it
harder to find a whole machine for a decent price since many people want buy them cheap, part them out and make a profit.

They must not be too plentiful in Canada although I have seen that some members have them. After all they were made in USA.
Aside from wear and tear they just don't seem to have the kind of problems that plague some of these low-cost imports.

The gearset that they use is very standardized; well documented. Castings are good quality cast iron. Motors are chosen by
the user depending on what's available; another possible upgrade path and/or cost savings. Lots of good reasons to get an old lathe and fix it up.
I'm partial to the roller bearing headstocks since they practically eliminate spindle runout issues- one simple adjustment and off you go.

 

[WobblyHand]

Does someone need a 40? Haven't heard from the OP in a while.

 

[VicHobbyGuy]

The prices for used 9", 10" and 12" Atlas lathes have increased quite a bit in the last 10 years or so it's true.

That's a totally different class of machines from a Chinese 7x mini-lathe.
Bigger and heavier, and EVERYTHING for a larger lathe is more expensive.
I have a Logan 10" as well as my 7x Sieg Micromark - when I got the Logan the Vevor had to go.
Some Logan parts are still available, but the prices are very (very) high. I was lucky to get a Logan with a pretty good collection of the standard accessories -change gears, rests, etc. but that situation isn't common -especially at a reasonable price.
For people that don't have a lot of shop space or money or want to work on larger parts, smaller lathes make a lot of sense.
But, if a person doesn't like working on machinery, the 7x Chinese lathes won't be suitable. Neither will a clapped out fixer-upper that's missing parts, so a person could wait years for the 'right one to come down the road', depending on the location. I got lucky with my Logan.

 

[markba633csi]

Logans are nice and getting harder to find all the time- a very heavy and rigid machine for their size. They make an Atlas look like a wet noodle.
I'd love to have one, or a Boxford, or a Standard Modern. I'd really like a Hercus (like a South Bend with roller bearings) but they almost never show up here.
I think Ulma Doc had one for a while- I don't know where he finds this stuff LOL I can only dream

 

[6Sally5]

7x lathe change gears can be a devil to fit. I ended up running a reamer through all of the change gears, both the metal set for the lathe I am rebuilding as well as the plastic ones on the SC3. Made a world of difference and no more tapping to get them on or off.

Some gears have to be purchased separately to gain a full combination imperial and metric set.

Watch the key slots in the change gears too, they can either be too shallow, too narrow or a combination of both. I went with a four-square needle file to debur and open out the key-slots to ensure a good sliding fit.

Make sure you have plenty of lubrication on the twin-gear idler bush that carries the 80/20 gears. The one on my SC3 siezed to the shaft despite being lubricated because it was slightly undersized. I made a new one and ensured it had proper clearance, though I did rob the one from the lathe I am rebuilding to finish what I was doing at the time, then put it back once the replacement was fitted.

When changing the change-gears use a slip of 80gsm printer paper or a post-it note between them to set the mesh.

Another tip, always have at least one plastic gear in the chain. Better to strip the teeth of a plastic gear than to cause greater damage elsewhere. I left the idler gears on the reverse lever as the weak-point so those are the ABS/Plastic gears. Easier to replace and cheaper.

Most 7x lathes are supplied with metric lead screw, cross-slide and compound screws and rests. You can convert them to imperial if you wish to spend money on imperial lead screw, coss-slide screw and compound rest block, feed screw as well as replacement cross slide & compound slide dials. Metric dials have 40 divisions, Imperial dials have 50 divisions.

Imperial leadscrew is 16tpi, cross slide and compound slide screws are 3/8" 20tpi. Left handed for cross slide, right handed for compound rest and feed screw.

LittleMachineShop.com sell the parts to convert to imperial.

Great tips and info! Do you recall what size reamer you used? My SIL was able to make the 55 and 65 tooth gears using his 3D printer and the data from LMS. The bores though are .009” smaller than the factory gears.