Characterizing the G0709 quick change gearbox

[mcdanlj]

Now that I can log in again... I have some caveats that I want to mention.

I counted teeth on only one gear; the one driven by the A/B/C selector. All the other counts are based on looking up the information in the parts list in the manual. Any mistakes or typos there will show up in mistakes here.

I did not disassemble the gearbox. Everything I wrote is based on turning things by hand with the selecting gears in the engaged positions and in intermediate positions that are disengaged.

I haven't tested this yet by calculating a gear train and validating it.

I can't trivially review correctness because I've closed the gearbox back up and refilled it with oil, so it will be a right mess again if I open it again.

I welcome feedback, correction, additional information.

 

[mcdanlj]

Feeds and Speeds​

Here’s all the data from the front plate, in mostly-textual form, to use to understand the ratios.

Note that this doesn’t cover the feed rate calculations because it doesn’t include the apron gears and the bed rack pitch. It only covers difference between feed rates.

The lead screw is 8 TPI. The input to the change gears turns 1:1 with the spindle. This should allow exact calculation for all lead-screw-driven pitches.

Change Gears

• F: 32:76 33:66
• G: 32:76 66:33
• H: 32:76 66:42 (Used only for worm cutting, as part of approximating pi

Z Feed (inches)​

				1	3	6	8
F	A	T	X	0.00168	0.0021	0.00252	0.00294
F	A	S	X	0.00336	0.0042	0.00504	0.00587
F	A	R	X	0.00671	0.00839	0.01007	0.01175
F	B	R	X	0.01679	0.02098	0.02518	0.02937
G	B	S	X	0.03357	0.04196	0.05035	0.05875
G	B	R	X	0.06714	0.08392	0.10071	0.1175

​

X Feed (inches)​

				1	3	6	8
F	A	T	X	0.00046	0.00057	0.00069	0.00081
F	A	S	X	0.00092	0.00115	0.00138	0.00162
F	A	R	X	0.00185	0.00231	0.00277	0.00323
F	B	R	X	0.00462	0.00577	0.00692	0.00808
G	B	S	X	0.00923	0.01154	0.01385	0.01615
G	B	R	X	0.01846	0.02307	0.02769	0.03231

​

mm threads​

				1	2	3	4	5	6	7	8
F	A	T	W	0.1		0.125			0.25
F	A	S	W	0.2	0.225	0.25			0.3		0.35
F	A	R	W	0.4	0.45	0.5	0.55		0.6	0.65	0.7
F	B	S	W						0.75		0.875
G	A	S	W	0.8	0.9		1.1		1.2	1.3	1.4
F	B	R	W	1		1.25			1.5		1.75
G	A	R	W	1.6	1.8
G	B	S	W	2	2.25	2.5	2.75		3	3.25	3.5
G	B	R	W	4	4.5	5	5.5	5.75	6	6.5	7

​

Threads/inch​

				1	2	3	4	5	6	7	8
G	C	T	Y	4	4.5	5	5.5	5.75	6	6.5	7
G	C	S	Y	8	9	10	11	11.5	12	13	14
G	B		Y	9.5	9.5	9.5	9.5	9.5	9.5	9.5	9.5
F	C	T	Y	16	18	20	22	23	24	26	28
F	C	S	Y	32	36	40	44	46	48	52	56
F	B		Y	38	38	38	38	38	38	38	38
F	C	R	Y	64	72	80	88	92	96	104	112

Module pitch (metric worms)​

				1	2	3	4	5	6	7	8
H	A	T	W	0.1		0.125			0.15		0.175
H	A	S	W	0.2	0.225	0.25	0.275	0.2875	0.3	0.325	0.35
H	B	T	W						0.375
H	A	R	W	0.4	0.45	0.5	0.55	0.575	0.6	0.65	0.7
H	B	S	W		0.5625	0.625	0.6875		0.75	0.8125	0.875
H	B	R	W	1	1.125	1.25	1.375		1.5	1.625	1.75

​

Diametral pitch (inch worms…)​

				1	2	3	4	5	6	7	8
H	C	T	Y	16	18	20	22	23	24	26	28
H	C	S	Y	32	36	40	44	46	48	52	56
H	B		Y	38	38	38	38	38	38	38	38
H	C	R	Y	64	72	80	88	92	96	104	112

 

[epanzella]

I'd love to have 27 tpi on my G0709, or be able to turn a knob on a whim to change the feed rate.

I don't know what change gears you have on your G0709 but on my G4003G I substitute 40t/40T change gears with a 40T/60T combination. Then 18tpi becomes 27tpi.
Ed P

 

[mcdanlj]

I don't know what change gears you have on your G0709

The huge graphic in the prior comment shows the change gear combinations available for the G0709, with all the change gears it ships with; there are no others in the set. To cut 27tpi would require either changing to an electronic lead screw or making a new 1.5 module change gear, either cutting one with a gear cutter or 3D printing one.

18TPI uses the F configuration, so maybe making a 48-tooth first gear would work (I think it could fit, but I haven't measure.) Alternatively, substitute a 22-tooth gear for the 33-tooth gear in the F configuration? I don't now whether that would reach; if not you might have to make two gears and replace both the 33-tooth and 66-tooth gears for it to reach.

 

[BGHansen]

18TPI uses the F configuration, so maybe making a 48-tooth first gear would work (I think it could fit, but I haven't measure.) Alternatively, substitute a 22-tooth gear for the 33-tooth gear in the F configuration? I don't now whether that would reach; if not you might have to make two gears and replace both the 33-tooth and 66-tooth gears for it to reach.

Let me answer the "will a 22-tooth gear sub'd for the 33-tooth gear reach"; it won't. Much to my chagrin, I learned this AFTER making a 22-tooth gear as a sub for the 33-tooth gear in F configuration. Oh well, it was shop time. I ended up making an arbor for the import gear cutter, gear blank, and a metric bushing for the broach.

As you noted, the 22-tooth gear can't reach the 61-tooth gear before the 76-tooth gear hits the axle for the 61-tooth gear. I considered cutting two additional gears: sub a 16-tooth for the 32-tooth and a 38-tooth for the 76-tooth gear. Problem with that idea is the distance between the normal 32-tooth shaft and the 66/42-tooth shaft is too great for the sub'd 16/38 to reach.

My last thought was to make a 99-tooth gear as a sub for the 66-tooth gear. I have a Tormach CNC mill with a 4th axis and a routine to cut any number of teeth. Yet another one on my "list of good intentions".

Bruce







Cutting a 22-tooth gear on my Bridgeport.

 

[mcdanlj]

I have now validated this characterization by using it to implement configuration for an ELS. Using this data, I worked out transmission ratios and configured the ELS, and 10 turns of the spindle (within 0.1° total error) got within 0.001" of 1" on a dial indicator.

If anyone else wants to do the same on a G0709, feel free to look at the source.

I'd love to have 27 tpi on my G0709, or be able to turn a knob on a whim to change the feed rate.

I now have 27 tpi on my G0709, and I can bump a button while the feed is going to change the feed rate. I love it!