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Metric Change Gears   For those who do not have extra gears for the Taiwan 7x10 Mini Lathe This data is from J.W. Early's Excel spread sheet. It has had the cells holding calculations removed and only the important data left. Some terminology has been changed slightly in the hopes that it would make this chart more understandable. At the right there is a crude ascii drawing depicting the positions of the change gears. You can cut perfect Metric Threads without any added gears On the 7x10 Mini Lathe. It is interesting that though the 9x20 has double compound gearing for thread cutting and three gears that the 7x10 does not have (shown in bold 25, 70 & 75) in most cases the gear combinations in its manual are no better than the 7x10 with single compound gearing. In all cases where Varmint Al shows a 21t gear you will have a more accurate thread than other inch lead screw machines that do not use either a 21t or a 127t gear in the setup. In almost all cases if you could fit in a 127t gear it gives the ideal ratio. The gear combinations in the 7x10 chart below will give you metric threads that will work very well and with 1 or 2 clean up passes they will fit certified ring gages perfectly.   J.W.Early																			+---- +---+ | | | | H +-+ +-------| E | | A | STUD | A +-+ +-------| D | | | +---+ | S | | | T +---+| | | O | || | | C ++ ++ +-------| K || C || B | | ++ ++ +-------| | || | | +---+| | | | || | | | |+---+ | ++ ++===+-------+---- || D || H | LEAD SCREW ++ ++===+-------+---- | | | | | +---+
Standard Gears that come with 7x10 MiniLathe
Ideal Ratio	0.3150			0.4409			0.4724			0.5039		0.6299		0.7874		0.9449		1.1024		1.2598		1.5750		1.8898
Actual Ratio	0.3158			0.4406			0.4723			0.5035		0.6294		0.7879		0.9455		1.1000		1.2571		1.5760		1.8909
Thread Pitch	0.5			0.7			0.75			0.8		1.0		1.25		1.5		1.75		2.0		2.5		3.0
Position	IN		OUT	IN		OUT	IN		OUT	IN	OUT	IN	OUT	IN	OUT	IN	OUT	IN	OUT	IN	OUT	IN	OUT	IN	OUT
Stud A			20			35			35		30		45		40		40		40		40		40		80
B , C	45		50	45		55	50		57	60	55	50	55	65	60	65	50	55	50	55	50	65	55	65	50
Screw D	57		H	65		H	65		H	65	H	65	H	55	H	55	H	40	H	35	H	30	H	55	H
With 21t Gear ( Module 1.0 Metric NOT Supplied Possible Source )
Ideal Ratio	0.3150			0.4409			0.4724			0.5039		0.6299		0.7874		0.9449		1.1024		1.2598		1.5750		1.8898
Actual Ratio	0.3150						0.4725					0.6300				0.9450				1.2600
Thread Pitch	0.5			0.7			0.75			0.8		1.0		1.25		1.5		1.75		2.0		2.5		3.0
Position	IN		OUT	IN		OUT	IN		OUT	IN	OUT	IN	OUT	IN	OUT	IN	OUT	IN	OUT	IN	OUT	IN	OUT	IN	OUT
Stud A			30						45				60				45				60
B , C	21		40				21		40			21	40			21	20			21	20
Screw D	50		H				50		H			50	H			50	H			50	H
With 127t Gear ( THEORETICAL GEAR Would not fit 7x10 as it would be ~5in. Dia.)
Ideal Ratio	0.3150			0.4409			0.4724			0.5039		0.6299		0.7874		0.9449		1.1024		1.2598		1.5750		1.8898
Actual Ratio	0.3150			0.4409			0.4724			0.5039		0.6299				0.9449				1.2598				1.8898
Thread Pitch	0.5			0.7			0.75			0.8		1.0		1.25		1.5		1.75		2.0		2.5		3.0
Position	IN		OUT	IN		OUT	IN		OUT	IN	OUT	IN	OUT	IN	OUT	IN	OUT	IN	OUT	IN	OUT	IN	OUT	IN	OUT
Stud A			40			35			60		40		80				60				80				80
B , C				80		50				80	50					40	20			40	20			60	20
Screw D			127	127		H			127	127	H		127			127	H			127	H			127	H

Last updated 10/12/1999

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