Missing Change Gears

I find it a little strange that you have an English lead screw and threading name plate, but have gears that fit a metric shaft, 18mm? Similar to what @DAT510 showed. Maybe the lathe was designed for metric and then they just changed the lead screw and the gear teeth numbers to go to English. You measured 18mm, 10mm, 23mm: i.e. 18/25.4(*64ths)=.70866(*64ths)=45.35/64. If it were really an English size I would have expected the number of 64ths to be closer to an integer. If you have the gears off also measure the mounting shaft(s) just to be sure as it appears that you may have been measuring one of the gears that you had it sitting on top of the lathe in your first pictures.

Also, why not set the lathe up like the manual might indicate, set the gear box to a thread that easy to measure and let the machine make a light cut (scratch) so that you can see if it really makes the TPI you might expect. For example, 10TPI, 24TPI, or others are easy to measure or match to a known bolt. See pages 9-10 of your manual, and maybe page 13. Figure 10 shows a picture of your gear positions and at the left hand side of the table shows the gear set up that is suppose to be for that table. I cannot make out the bottom gear T number, but I looks like the top gear is a 40, the middle gear is 127, and the bottom gear is either another 40 or 48. Anyway, ratios would be 40/127, 127/127, and 127/46 or 40. The middle gear only transfers the motion since the same side is use for both of the others. So the over all ratio would be (40/127)*(127/127)*(127/(46 or 40))=40/(40 or 46). I would guess that it is the 40. So the ratio is simply 1! The manual also says that you have a set of English change gears (page 13) of 30, 32, 46 in the tool box in addition to the two 40's that are mounted on the lathe. These numbers agree with the numbers that @DAT510 posted. So on page 13 it also says you would need the following for the metric version of the lathe which would have the 3mm pitch lead screw. These would not work for you lathe since the lead screw is 8TPI.

Anyway, from all of the information that you have you can compute a set of tables of gear box gear ratios for every gear box setting. (spread sheet). Then from this you can figure out the TPI for each of the combinations of change gears that you have more might want.

You are lucky. You have a manual for your lathe! Although, some of the sentences read like they were written in China, not Canada! For example it refers to the "lead screw" as "screw leading stick"? Anyway, the tables look informative.

Have fun.
 
Do you know what Mod the gears are if metric or the DP or PA if imperial? You can measure the diameter of one of your gears and look up a chart for the number of teeth and diameter and figure out what you need to match what you have. That will give you the info to source spur gears from many sources. Dave
 
B2 said:
I find it a little strange that you have an English lead screw and threading name plate, but have gears that fit a metric shaft, 18mm? Similar to what @DAT510 showed. Maybe the lathe was designed for metric and then they just changed the lead screw and the gear teeth numbers to go to English. You measured 18mm, 10mm, 23mm: i.e. 18/25.4(*64ths)=.70866(*64ths)=45.35/64. If it were really an English size I would have expected the number of 64ths to be closer to an integer. If you have the gears off also measure the mounting shaft(s) just to be sure as it appears that you may have been measuring one of the gears that you had it sitting on top of the lathe in your first pictures.

Also, why not set the lathe up like the manual might indicate, set the gear box to a thread that easy to measure and let the machine make a light cut (scratch) so that you can see if it really makes the TPI you might expect. For example, 10TPI, 24TPI, or others are easy to measure or match to a known bolt. See pages 9-10 of your manual, and maybe page 13. Figure 10 shows a picture of your gear positions and at the left hand side of the table shows the gear set up that is suppose to be for that table. I cannot make out the bottom gear T number, but I looks like the top gear is a 40, the middle gear is 127, and the bottom gear is either another 40 or 48. Anyway, ratios would be 40/127, 127/127, and 127/46 or 40. The middle gear only transfers the motion since the same side is use for both of the others. So the over all ratio would be (40/127)*(127/127)*(127/(46 or 40))=40/(40 or 46). I would guess that it is the 40. So the ratio is simply 1! The manual also says that you have a set of English change gears (page 13) of 30, 32, 46 in the tool box in addition to the two 40's that are mounted on the lathe. These numbers agree with the numbers that @DAT510 posted. So on page 13 it also says you would need the following for the metric version of the lathe which would have the 3mm pitch lead screw. These would not work for you lathe since the lead screw is 8TPI.

Anyway, from all of the information that you have you can compute a set of tables of gear box gear ratios for every gear box setting. (spread sheet). Then from this you can figure out the TPI for each of the combinations of change gears that you have more might want.

You are lucky. You have a manual for your lathe! Although, some of the sentences read like they were written in China, not Canada! For example it refers to the "lead screw" as "screw leading stick"? Anyway, the tables look informative.

Have fun.
Click to expand...
Thank you for the in-depth response to my post. I got distracted for a few days playing with my Mill and dove back into the lathe today. I re read the manual today for probably the 4th time...and staring right back at me was the error I made. I miss read the manual partially dew to the poor English you touched base on and also my own hastiness.

When the manual is talking about change gears on page 13 it states "The Gear of the lathe that fit for English system screw are put in tool box. Those are (30t, 32t, 46t) each one piece, and have 2 pieces of 40t gear are set on machine.

It then goes onto say The Gear of the lathe that fit for Metric system screw are put in tool box. Those are (36t, 42t, 54t, 60t, 66t) each one piece, and have 2 pieces of 40t gear are set on machine.

I completely misinterpreted this and though the machine was supposed to come with a set of gears to cut metric threads. The machine has an 8TPI lead screw and I was mistaken in thinking it should have come with a set of gears to adapt the English lead screw to cut certain metric threads. (rookie mistake)

the mystery is solved! and I am content knowing the machine I purchased is a complete unit. Lots of good came out of this post. The YouTube video shared to this thread was especially helpful in wrapping my head around how change gears interface with actual thread cutting.
 
Great! Glad I could help. So someday when you really need to do a specific metric thread you can buy a few change gears that will get you a close approximation to the metric you want to make. Even a poor approximation will fit over a certain number of threads (length and looseness of the engaged thread plus the approximation error determines if they will fit. Or you can purchase a small set and get close to a lot of the standard metric threads. I have even been known, when in a pinch, to make a loose English TPI that is a close approximation to the metric thread that I need. If it is not a load bearing issue then you can just cut a few threads so that only a "few threads" are engaged and the two parts will turn together. Not a great solution, but when in a pinch you can make a "pinch" fit a little bit. I.e. We have all tried to put a metric bolt into an English nut of similar size before we notice the difference. They go in a little before binding! So "few threads" are defined! --- not what we would call "fine" or "high quality" machining.

It is a bit interesting to think about the loads on the threads and the desired material properties. If the two parts threads do not match then how is the load on the threads distributed? Even, if they are designed and made to match they will not be exact, so which threads bear the load. Important question: How flexible is the material of the threads? I.e. as they are loaded do they bend a little so that the next thread also engages? Is it linear and so recovers when undone. So does this not mean that that a strong, but spring like material would also be the strongest bolts. Steels are pretty much what springs are made from. The atomic bonds stretch before the atoms slip in position. So they are elastic, where as copper do not make good springs nor strong threads... It is soft, so that the atoms, especially at the grain boundaries, slip around rather than the atomic bonds stretching. On the other hand soft copper can sort of be mashed into shapes before it breaks. Ceramics are very hard an brittle. Poor elastic properties. Not good springs nor bolts. It is all about the elastic limit. Don't exceed it and a spring will come back to its original shape.

Dave
 
PS. All the more reason to have an electronic lead screw (ELS). Then you can drive the approximation to nearly accurate. See You Tube by Clough42 "Lathe Electronic Leadscrew"
 
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