# Question G1003 change gears



## tujungatoes (Feb 12, 2021)

New here.  Be gentle this is my first post.  I recently acquired my first lathe, a Shen Wai sw-900b. From what I’m reading it’s basically the same as the g1003(and numerous others).  It came with all the original equipment except the 30t and 32t metric threading gears. I know grizzly hasn’t supported these machines in forever.  Does anyone here know of a source for replacements, or specs on the gears for making replacements?  Sorry if this has been asked/answered before.  I swear I looked.


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## Mitch Alsup (Feb 13, 2021)

Metric has 25.4mm per inch
So big lathes use a 240/254 tooth gear, not so big lathes use a (254/2 =) 127 tooth gear and get essentially perfect pitch matching. Next size down uses 86/91.

My 12×36 lathe uses a 86 tooth gear for english threads and the 91 tooth gear for metric. And has tables of gear box selection for each set of back gearings. The manual downloaded from Grizzly G4003G shows a set of 86/91 teeth gears. 120/127×91/86 = 0.99981 or less than 0.1% "off"

What gears did you receive ?? There may be a way of cutting metric threads by using different gears and chosing the set up on the Norton Gear Box differently. G4003G has 26, 27, 35, 36, 40 installed, 45, 50, 60, 86/91 installed; in the kit which comes with the lathe, so I don't see a 30 and 32 available.


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## Ken226 (Feb 13, 2021)

tujungatoes said:


> New here.  Be gentle this is my first post.  I recently acquired my first lathe, a Shen Wai sw-900b. From what I’m reading it’s basically the same as the g1003(and numerous others).  It came with all the original equipment except the 30t and 32t metric threading gears. I know grizzly hasn’t supported these machines in forever.  Does anyone here know of a source for replacements, or specs on the gears for making replacements?  Sorry if this has been asked/answered before.  I swear I looked.




Alot of chinese machines in this size range are descendants and modifications of of just a few old designs.   As such, there are as many things interchangeable as are not.

Measure the size of the hole / shaft,  keyway width, and get the diameter/tooth count of one of your existing gears.

I'll probably be able give you some grizzly lathe model#s that will work with your lathe.  Then you can order them from Grizzly.

I have bought and sold a few chinese lathes over the years, and still have gears from all of them.  They all fit my current lathe.

I designed and modeled some involute gears in uncommon tooth count sizes  so I could cut some weird english and metric thread pitches.  They are uploaded  to thingiverse.  Anyone who's interested can 3d print and use them.    I modeled them to work with the Enco, Grizzly, Shop Fox, Birmingham, etc versions of my Birmingham ycl1340gh.  Search my username on thingiverse and you'll find them easily.

That model was sold by Shop Fox as the m1019, Grizzly as the G4016, etc.   The gears from my old Smithy 12x37 and even a mid 80s Smithy AT300 I one owned fit it.  At least, they fit the gearbox input shaft.

The gear/pitch spreadsheet I included with the gear files won't likely match your lathe though. It calculates based on my lathes gearbox ratios.


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## Ken226 (Feb 13, 2021)

FYI:  the info for the gears I mentioned above seems common to the 13x40 and 14x40 lathes are:  

Module 1, diametral pitch 20,  bore diameter 19mm,  keyway 5mm.   Gear width is 10mm.  The gears have an integral 10mm spacer, for an overall width of 20mm, pressure angle 20°.

If you measure one of your gears, it'll be easy to figure out if your lathe uses the same gears.


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## tujungatoes (Feb 13, 2021)

Thanks for the replies guys.  The gears I received are the inch threading gears.  According to the chart, some limited metric threading can be done, with them in different configurations, but for most I’ll need the other two. The inch gears are both 40 tooth and mic out at 52.489mm.  I’ve tried plugging them into some formulas to figure out the DP or module...but I got some odd numbers so I’m pretty sure I’m getting lost in the math. I have no clue on pressure angle or how to measure it.... did I mention I’m still super green

 It would be great if some of the gears you modeled worked Ken. I have a friend that could print some testers for me.

I’ll attach a pic(not mine) of the setup behind the headstock. it’s very simple. 
40t—>127/120–>40


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## Ken226 (Feb 13, 2021)

tujungatoes said:


> Thanks for the replies guys.  The gears I received are the inch threading gears.  According to the chart, some limited metric threading can be done, with them in different configurations, but for most I’ll need the other two. The inch gears are both 40 tooth and mic out at 52.489mm.  I’ve tried plugging them into some formulas to figure out the DP or module...but I got some odd numbers so I’m pretty sure I’m getting lost in the math. I have no clue on pressure angle or how to measure it.... did I mention I’m still super green
> 
> It would be great if some of the gears you modeled worked Ken. I have a friend that could print some testers for me.
> 
> ...



Mine uses a 40t output and input as well.  A 127 and 120 idler set too.

Just those gears alone will let you cut pretty much all common inch, and most metric threads.

Take a pic of your inch and metric pitch chart.  I can tell if it has the same gearbox ratios as mine...

Based on your 40t having a diameter of 52.489mm,  it is a module 1 with a diametral pitch of 20. Same as mine.

What's the bore diameter?

If your gears have a 19mm bore, my 3d print gears will fit.  Also, you can order the 30t from grizzly. The part# is p4016352.   Discontinued, but they still have some in stock, though it's 40$

Also, I'm pretty confident that the G0709 uses the same size gears as well.  They are cheap enough that it's worth a shot.  The pn# for the G0709 32t is p07090203. Also in stock. 13$

Just search the part# on grizzlies website.


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## tujungatoes (Feb 13, 2021)

Ken226 said:


> Mine uses a 40t output and input as well.  A 127 and 120 idler set too.
> 
> Just those gears alone will let you cut pretty much all common inch, and most metric threads.
> 
> ...



Unfortunately, mine has an 18mm hub.  I don’t think that’s going to be a deal breaker though. I don’t see why I couldn’t fab a little bushing to make up the difference.  I’m definitely going to check out your files on thingiverse too. I should be able to change the hub dimension and get my buddy to print me a couple to test before I throw money at grizzly.  Thanks a lot!  I’ll report back when I get something going.


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## tujungatoes (Feb 14, 2021)

Oh, and here’s that pic of my threading charts.


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## Ken226 (Feb 14, 2021)

Our gearboxes have the same ratios as well.




The spreadsheet file I have on thingiverse will be correct for you lathes  gearbox lever positions.  

Just fill in the gear tooth count field in the upper right,  and the gear lever chart autopopulates all of the pitches for that gear combo.


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## tujungatoes (Feb 14, 2021)

After some Staring at charts and your spreadsheet, it would appear that out gear boxes are only MOSTLY the same. 3, 4, and 5 are just slightly different. Still think I ought to be able to make it work with some little tweaks.


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## Ken226 (Feb 14, 2021)

The charts are a little different, but what I meant is that the actual gearbox ratios are the same.   But, it looks like your right,  there are a few actual differences

My phone won't let me open both charts side-by-side.   Opening and looking at them 1 at a time, it's easy to miss the small differences.

I have change gears in 28t, 30t, 32t, 46t, 50t, and a half dozen others.   Knowing the actual gearbox lever ratios is very useful for calculating and cutting the weird, non-standard threads that occasionally pop up on proprietary designs.

I have a list of the actual ratios somewhere, I'll post it up in a minute.


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## Ken226 (Feb 14, 2021)

Yea, looks like your correct.  A couple slight differences.


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## Ken226 (Feb 14, 2021)

Here are a few formulas you might find helpful, for creating a ratio chart for your gearbox and calculating thread pitches.   It'll also help you determine which of your pitches are exact, and which are approximations.

If your lathe has an 8tpi inch leadscrew, which is almost certain given your 40/127/40 (1:1 ratio)  gear arrangement for inch threads.

For each lever setting in your gearbox, divide the leadscrew tpi by the pitch given in the chart.

For example, A1 shows 4 tpi, so 8/4=2   A1 is a 2:1 ratio.  2 output shaft rotations per input rotation.
B1 shows 8 tpi,  so 8/8=1  B1 has a 1:1 ratio
C1  shows 16 tpi,  8/16=0.5  so, C1 has a .5 ratio
D1 shows 32 tpi, 8/32=0.25, so the ratio for D1 is .25

Once you have those gearbox ratios, the metric side is easy.

For the metric, the 8tpi leadscrew pitch becomes 3.175mm(1/8")(25.4)=3.175mm

So, first the change gear ratio. Example 40/127x120/40=.944882

Now, the change gear ratio (.944882) times the gearbox ratio (lever setting A1 = 2).   So 0.944882 x 2 = 1.89764 (this is the overall ratio, through both the change gears and gearbox

Now, multiply the ratio times the leadscrew pitch (mm). So 1.89764 x 3.175= 6.025007.    so, A1 is a slight approximation, but gives you a metric pitch of 6mm. 

Also, some or all of that extra .025007mm is probably rounding error from rounding to the nearest millionth.


Keep in mind that many of the thread pitches are approximations.   Approximations are unlikely to ever be a problem. 
For most threaded things, one or the other part is short.  A short nut on a long shaft, or a short screw into a hole.   Rarely ever would a 3foot long nut, or 3ft long screw be thread with engagement down its entire length.


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## tujungatoes (Feb 14, 2021)

Thanks again.  It was pretty easy to turn the equations around and work out what I needed.... once I finally figured out how to modify the spreadsheet.  I'll try and attach the altered version on the off chance anybody finds themselves similarly ignorant in the future.








						Lathe_Gearing_Spreadsheet (shenwai)
					

Sheet1  Enter the number of teeth on each gear for each gear set (A/B),Gear Combo,Gear A,Gear B,Gear C,Gear D,Reduction Ratio and (C/D) in the gear fields.  ---->,Inch,40,127,127,40,1 Metric,40,127,120,40,0.9448818898 The available thread pitch for each lever position will populate below. If only...




					docs.google.com
				




I should have a printed gear to try out tomorrow.


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## Ken226 (Feb 14, 2021)

Awesome!  

Now,  when you get brave and wanna try cutting metric threads to a shoulder, using both your half-nut and your inch thread dial (don't listen to any of the guys who say it can't be done).

Watch Adom do it here.  I've been using this method for 10+ years.  It's fantastic!

He's like a robot though!   I wouldn't dare do it @ 400 rpm.   I go about a hundred rpm.


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## tujungatoes (Feb 14, 2021)

Ken226 said:


> Awesome!
> 
> Now,  when you get brave and wanna try cutting metric threads to a shoulder, using both your half-nut and your inch thread dial (don't listen to any of the guys who say it can't be done).
> 
> ...


I like that technique.  I’m sure I’ll f**k it up at first, but it makes all kinds of sense.


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## tujungatoes (Feb 27, 2021)

update.  I went ahead and ordered the cheaper of the two gears from grizzly.  Unfortunately it’s not a match.  I believe the pitch is too coarse.  It looks like I’ll have to actually learn to measure gears. My 40 on the left and grizzly 32 on the right.


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## tujungatoes (Mar 3, 2021)

Continuing to update. I finally managed to figure out that the gears I need are 20° pressure angle, module 1.25. Semi uncommon I guess.:shrug:  I made one up in fusion 360 and had my buddy to print it.  Works like a charm!  I’m pretty stoked.  I’m going to do the 40, 32, and 30 tooth next.  I’ll post them up on thingiverse when I’m done, and add a link here on the off chance someone else needs them in the future.


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## Ken226 (Mar 3, 2021)

tujungatoes said:


> Continuing to update. I finally managed to figure out that the gears I need are 20° pressure angle, module 1.25. Semi uncommon I guess.:shrug:  I made one up in fusion 360 and had my buddy to print it.  Works like a charm!  I’m pretty stoked.  I’m going to do the 40, 32, and 30 tooth next.  I’ll post them up on thingiverse when I’m done, and add a link here on the off chance someone else needs them in the future.




That's great!

Now that you can get gears in any tooth count you desire,  there no limit to the feeds and pitches available.


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## tujungatoes (Mar 4, 2021)

Ken226 said:


> That's great!
> 
> Now that you can get gears in any tooth count you desire,  there no limit to the feeds and pitches available.


Yeah. It’ll be interesting to see what I come up with using your spreadsheet. I’ve already tried a few test threads on aluminum as some old rifle barrel stubs I have laying around.. They work ok, but kinda choppy looking. Long way to go before I do any real work.


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