Cutting a 3.5mm Pitch Thread on a G9249 Lathe

[Lancer4545]

Hi,

I have been trying to figure how I can set up my lathe to cut a Metric 3.5mm pitch thread and so far have drawn a blank. There must be some way to work out what change gears are needed to cut this thread but I don't know how to work it out.

I'm hoping there is someone who can point me in the right direction or knows what's needed

Thanks

Lance

 

[markba633csi]

That's not listed in the chart but it's 0.1377 inch pitch which is about 7.26 TPI. For a short thread you might could try 7 TPI and squeak by
Otherwise you'd most likely need to use a gear calculator program and change one of the stock 40 tooth gears by a tooth or two

 

[Downunder Bob]

Hi,

I have been trying to figure how I can set up my lathe to cut a Metric 3.5mm pitch thread and so far have drawn a blank. There must be some way to work out what change gears are needed to cut this thread but I don't know how to work it out.

I'm hoping there is someone who can point me in the right direction or knows what's needed

Thanks

Lance

Depends on what lathe you have. Most larger lathes will use a 127 tooth gear in the train. on my lathe I use a 127x120 This converts your imperial leadscrew to metric. can you post a picture of your lathe showing the change gear set up also the screw cutting gearbox and thread chart. Also what length of thread so you need?

 

[RJSakowski]

Looking at the manual for your lathe, in the metric threading configuration, replacing the 40t. gear driven by the spindle gear with a 28t. gear and with the 32t gear on the gear box input and using the 6A position on the QCGB, you should get a 3.5mm thread.

Unfortunately, the 28t, gear isn't one offered with the lathe so you would have to buy the gear from a third party or make one. It may be possible to find a part from another Grizzly lathe if you determined the module and pressure angle. SDP/SI sells metric gears at a reasonable price. 3D printing a gear is another option.

It's possible that with some other configuration with stock gears, you could get close but there wasn't an easy answer. There was a thread on HM some time ago where the poster had worked out a calculator where you entered in your gear options, your desired thread, and allowable error and it gave you the configuration options.

 

[OTmachine]

Note: when cutting Metric threads the thread dial will not indicate new start point.
After looking at the manual for your lathe, (https://cdn0.grizzly.com/manuals/g9249_m.pdf), I see that it has an 8 tpi lead screw. Since there are a lot of lathes from different sellers that yours is a copy of, I would think that there should be a 3D printed set of metric change gears availabl.

 

[OTmachine]

I bought this set for my SB9:
https://www.ebay.com/itm/124387115378?hash=item1cf60cc172:g:qSIAAOSwEkxfiDGz&amdata=enc:AQAIAAAA8BZHY+2pQUL48VlqVfia7+sSjZ1xUNUkLQ0YHmy/SbNSCGxh6b/NkR42jJCmf1vz0iHTa47DkXuivVSxNMYcrfP7IvsTTU4sWy8AWY0xcZvnN34z/X2VWgqtUCg8oAQEq84BZZZp0u3WsMpuQi9sL9JV9P8WhmDzwdHzIXpkbI/DNeTOjq8YpCr6UQtDv7lJ+vX9xz0ksZO28Vs8QHtCB3CX/ynsK/pkr+7E3sn3aoWpmaBAMhSHCJoT9zyj7t/Y85QdM099c7YMUW+RUBW1GAwsUQpGJcv+f07f+9bBtXxD4FX1+InjlcyjWJX4396nfg==|tkp:Bk9SR4Cd9YWaYw

Covers a wide range of threads including 3.5 mm

 

[DAT510]

A while back I created a Excel Spreadsheet to help me find additional tread combinations not listed on the Threading Table for my Jet 1024, which is in the same family as the G9249.

The closest I can find to 3.5mm is 3.5063mm pitch.

Change Gears:

Top Gear (Closest to spindle Drive) 30 tooth
Middle Gear (Combo) 120/127 (Top Gear 30 Drives 120 tooth) : (127 tooth Drives Bottom Gear 46 tooth)
Bottom Gear 46 tooth

QCGB
Lever A
Lever 4

I've attached my spreadsheet for your reference. It is a "live" sheet so changing certain cells will recalculate the table.

Hope this helps.