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anyone willing to do some figuring?

DPittman

Ultra Member
Premium Member
Hi,
I have a Craftex cx700 lathe which is similar to the Grizzly and King 10 x 22 lathes.
I've have tried understanding the gear change XL spreadsheets that are out there but don't quite understand things well enough. Possibly they are not adaptable to my lathe?
I'm trying to understand if there are any more thread combinations with my lathe as is or if there would be additional gears that would increase possibilities.
There are "blanks" I my lathe gearing chart and I am assuming because they would be non sense threads?
Anyone have experience with these calculations/spreadsheets? I just don't have a good enough grasp of things (and mathematics) to figure this out.

Don
?
 

Janger

(John)
Administrator
Vendor
Hi,
I have a Craftex cx700 lathe which is similar to the Grizzly and King 10 x 22 lathes.
I've have tried understanding the gear change XL spreadsheets that are out there but don't quite understand things well enough. Possibly they are not adaptable to my lathe?
I'm trying to understand if there are any more thread combinations with my lathe as is or if there would be additional gears that would increase possibilities.
There are "blanks" I my lathe gearing chart and I am assuming because they would be non sense threads?
Anyone have experience with these calculations/spreadsheets? I just don't have a good enough grasp of things (and mathematics) to figure this out.

Don
?

Hey @Jimbojones how do you do this?
 

JohnW

(John)
I've built a couple of these spreadsheets. For an House of Tools 12x36 and for a Colchester 14x40 clone. In both cases, I came up with a few threading possibilities that were not documented for the machine, or which were close enough that it did not matter. i.e. an error of 0.001" in 10" will never matter in a real thread. Even an error of 0.001" in 1" is probably usable.

The key to calculating the threading possibilities is to determine how many times the lead-screw turns for each rotation of the chuck for every possible combination of gears. Then multiply that by the pitch of the lead-screw.

For figuring out the feed possibilities, you need to know what is happening inside the carriage as well, but that is usually not as interesting, except to verify the feed charts.

For instance, if the lead-screw has a 1/8" pitch (8 threads per inch), and it turns once for every rotation of the chuck (1:1), the carriage will advance 1/8" for every turn of the chuck, so it will do 8 TPI.

If the ratio is 1/2 turn of the lead-screw for every rotation of the chuck (2:1), it will be 16TPI.

With the HOT lathe, I put a turns counter in the chuck and at the end of the lead-screw and then ran the lathe for a couple of hundred chuck rotations for each combination of the selectable internal gears. That got me the final ratio and with a bit of head scratching, I figured out what each lever did. For one lever, the ratio was 2:1 between the H and L settings, so that was easy. There were some 3:2's and 4:5's, and I think a 3:7 or something like that. From that I figured out what the internal gear ratios were and filled out the spreadsheet for all the possible external gear configurations.

Remember, it doesn't matter if the gears are 18:36 or 17:34, they are both 1:2.

An idler gear does not matter, since if you have 18:36, and then 36:40, that is the same as 18:40, since the two 36's on the idler gear cancel out. The idler gear just changes direction in that case.

With the "Colchester", I had it apart anyway, so I counted the teeth on all the gears, so I didn't have to guess at the internal ratios.

Metric / imperial changeover is usually done with external (and sometimes with an internal gear) of 127:100 or something similar. They key is the 127 teeth. That works because 1" = (exactly by definition) 254mm. 254/2 = 127.

The Colchester and similar feed gearboxes (identified because they have four levers: ABC, DEF, WXYZ, and 1-8), are very cool using multiple power flow paths internally, but the result is that they do an approximate metric-imperial conversion, good to around 0.001" in 10". Once the patent ran out on that design, I think many lathe manufacturers stole the design, since it supports pretty much everything you would want to do on a lathe without any external gear changes. I'd bet any feed gearbox with three levers on the top with 3, 3, and 4 selections, and one at the bottom with 8 positions is effectively identical.

I have posted my HOT spreadsheet in the past. If you have come across it, it may seem very complex, because I used a Visual Basic function to do the math to make the spreadsheet a bit simpler, but I'm a software development kinda guy, so I think that is simpler, many people might not.

Did I make the situation better or worse for you?
 
Last edited:

DPittman

Ultra Member
Premium Member
I've built a couple of these spreadsheets. For an House of Tools 12x36 and for a Colchester 14x40 clone. In both cases, I came up with a few threading possibilities that were not documented for the machine, or which were close enough that it did not matter. i.e. an error of 0.001" in 10" will never matter in a real thread. Even an error of 0.001" in 1" is probably usable.

The key to calculating the threading possibilities is to determine how many times the lead-screw turns for each rotation of the chuck for every possible combination of gears. Then multiply that by the pitch of the lead-screw.

For figuring out the feed possibilities, you need to know what is happening inside the carriage as well, but that is usually not as interesting, except to verify the feed charts.

For instance, if the lead-screw has a 1/8" pitch (8 threads per inch), and it turns once for every rotation of the chuck (1:1), the carriage will advance 1/8" for every turn of the chuck, so it will do 8 TPI.

If the ratio is 1/2 turn of the lead-screw for every rotation of the chuck (2:1), it will be 16TPI.

With the HOT lathe, I put a turns counter in the chuck and at the end of the lead-screw and then ran the lathe for a couple of hundred chuck rotations for each combination of the selectable internal gears. That got me the final ratio and with a bit of head scratching, I figured out what each lever did. For one lever, the ratio was 2:1 between the H and L settings, so that was easy. There were some 3:2's and 4:5's, and I think a 3:7 or something like that. From that I figured out what the internal gear ratios were and filled out the spreadsheet for all the possible external gear configurations.

Remember, it doesn't matter if the gears are 18:36 or 17:34, they are both 1:2.

An idler gear does not matter, since if you have 18:36, and then 36:40, that is the same as 18:40, since the two 36's on the idler gear cancel out. The idler gear just changes direction in that case.

With the "Colchester", I had it apart anyway, so I counted the teeth on all the gears, so I didn't have to guess at the internal ratios.

Metric / imperial changeover is usually done with external (and sometimes with an internal gear) of 127:100 or something similar. They key is the 127 teeth. That works because 1" = (exactly by definition) 254mm. 254/2 = 127.

The Colchester and similar feed gearboxes (identified because they have four levers: ABC, DEF, WXYZ, and 1-8), are very cool using multiple power flow paths internally, but the result is that they do an approximate metric-imperial conversion, good to around 0.001" in 10". Once the patent ran out on that design, I think many lathe manufacturers stole the design, since it supports pretty much everything you would want to do on a lathe without any external gear changes. I'd bet any feed gearbox with three levers on the top with 3, 3, and 4 selections, and one at the bottom with 8 positions is effectively identical.

I have posted my HOT spreadsheet in the past. If you have come across it, it may seem very complex, because I used a Visual Basic function to do the math to make the spreadsheet a bit simpler, but I'm a software development kinda guy, so I think that is simpler, many people might not.

Did I make the situation better or worse for you?
Whoa! The task is as complex as I feared! I was hoping that maybe somebody had already figured out that with an additional gear of "x" teeth you can do "x" amount of additional threads. I know my gears and lead screw specs but I don't know how to figure out if there are any further possible combinations. Just kind of curious.

Don
 

Jimbojones

Active Member
Looks like I'm a bit late to the party but indeed, a bunch of math, logic and programming can grind you out some new gearing combinations; some unpublished and others that you would need differently toothed gears to achieve

I've got a CX701 and they didnt list 13TPI on the chart, nor 11 1/2 (NPT) but they are possible with additional change gear that Busy Bee actually can get for my model.

I checked out the CX700 manual and unless I got a dud copy, they dont publish the gearing/selector chart in the manual...wth?!? Part of why I wanted to see them was to get a sense of how the CX700 functions (and if its like the 701) where one of the selectors is simply a base TPI/.5x TPI/2x TPI selector. 11.5 TPI as a base speed is useful whereas 5.75 and 23 really arent so that would explain 'blanks' in the chart

If you can get me some hi-res photos of your charts/controls, I'd be interested in seeing how the machine is configured and then get a sense if the software I've written to generate my combos would be of any value to you. - PM directly, plz



Hey @Jimbojones how do you do this?
 

DPittman

Ultra Member
Premium Member
Looks like I'm a bit late to the party but indeed, a bunch of math, logic and programming can grind you out some new gearing combinations; some unpublished and others that you would need differently toothed gears to achieve

I've got a CX701 and they didnt list 13TPI on the chart, nor 11 1/2 (NPT) but they are possible with additional change gear that Busy Bee actually can get for my model.

I checked out the CX700 manual and unless I got a dud copy, they dont publish the gearing/selector chart in the manual...wth?!? Part of why I wanted to see them was to get a sense of how the CX700 functions (and if its like the 701) where one of the selectors is simply a base TPI/.5x TPI/2x TPI selector. 11.5 TPI as a base speed is useful whereas 5.75 and 23 really arent so that would explain 'blanks' in the chart

If you can get me some hi-res photos of your charts/controls, I'd be interested in seeing how the machine is configured and then get a sense if the software I've written to generate my combos would be of any value to you. - PM directly, plz
Ok I don't think I know how to pm an image but here is picture of the chart on my machine. PS. I found the B.B. manual for my lathe terribly poor and lacking, (much like after sales service).

Don
 

JohnW

(John)
What is the pitch of your leadscrew? 8tpi or 10tpi would be common if it is an imperial (vs metric machine).

Is there a lever that does "I", "II", and "III"? If so, I think something in the chart is wrong, since there is no reference to "I", and two references to "II" settings that give different results. On looking at it again, I see that one set is for carriage movement and the other is cross feed, so maybe the lever only does "II" and "III". More pictures would be good.

The difference between carriage and cross feed seems to be about .272727, which is 3/11, so in the carriage there is an additional, 3/11 gear ratio in the cross feed.
 

DPittman

Ultra Member
Premium Member
Ah that didn't work cuz I think the pic was too darn big...let's try thisView attachment 1014
So what my picture doesn't show is that I have 2 gear box control knobs, each with 3 positions, one labeled A,B, & C, and the other labeled I, II, & III. The "I" position I never used in any combination on the chart????
My lathe also has a separate lever for power cross feed and can also run the carraige that seems to run at half the rate of the threading lever...I should be able to double any given thread in the chart if I use that lever instead of the normal threading lever???
 

DPittman

Ultra Member
Premium Member
What is the pitch of your leadscrew? 8tpi or 10tpi would be common if it is an imperial (vs metric machine).

Is there a lever that does "I", "II", and "III"? If so, I think something in the chart is wrong, since there is no reference to "I", and two references to "II" settings that give different results. On looking at it again, I see that one set is for carriage movement and the other is cross feed, so maybe the lever only does "II" and "III". More pictures would be good.

The difference between carriage and cross feed seems to be about .272727, which is 3/11, so in the carriage there is an additional, 3/11 gear ratio in the cross feed.
John,my lead screw is 16tpi.
Don
 

JohnW

(John)
So, a starting point on figuring it all out is that when threading in CIII mode with the "a" gear at 48 teeth, you have a 1:1 ratio between the chuck on the lead screw, since it cuts 16tpi threads in that mode. The lead screw will rotate one turn for each rotation of the chuck to do that.

From the same chart, C:B is 2:1, and C:A is 1:2, so A:C:B provides 1:2:4 ratios. The thread pitch always doubles or halves when switching between those settings.

From the feed chart, the ratio between "II" and "III" is 0.4 or 2.5, depending on which way you go. The ratios listed range between .4035 and .3961, but average out to 0.3996, so I'll bet it is actually a 0.40000 gear ratio. 1/0.4 = 2.5. this is almost certainly generated by a set of gears with a 5:2 tooth ratio - maybe 50:20, 35:14, or some other multiple of 5 and 2. It doesn't matter, just remember that gear ratios must always come from the ratio of two integers (the number of teeth on each gear).

The threading charts do not make any use of the "II" setting, so there are all sort of possibilities there to use II when threading.

Using the CII setting as a 1:1 base that produced 16tpi, you can get twice or half that pitch by using A or B with III, and 0.4 times those pitches if you use II when threading.

I can't really make much sense of the gear configuration charts above. Maybe they make more sense when the machine is in front of you. You need to figure out what all the possible gear configurations that can be installed are. Then those ratios can be used to figure out all of the possibilities.
 
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