View Full Version : Metric change gears
02-13-2005, 03:17 PM
Boy have I been posting alot lately!
Any way, I just found out I am missing a 127 tooth change gear for my Takasawa lathe. I am sure I will not be able to buy one. Do these follow normal diametric pitch or angles? I wonder if I could find one at Boston gear and cut to fit? How do I figure out what I have, so I can either make one, or check with Boston gear?
[This message has been edited by Bob Quale (edited 02-13-2005).]
02-13-2005, 03:30 PM
I doubt this will be an exact match for your lathe, but you may be able to make something work, especially if you buy a matching gear. There is a fellow on eBay who frequently lists 127 tooth gear for the British Myford lathe. The gear is 3/8" wide, 20 diametral pitch, and 14 1/2 degrees pressure angle with a 5/8" diameter keyed hole in the middle. I bought one right after Christmas for about $40 including the shipping cost, when you are bidding beware that the English pound is almost two dollars.
I have never been able to find 127 tooth gear as a stock item, and consider modifying this one to fit my Logan to be a reasonable option considering the price of new ones. I believe that if you can find the gear to fit your lathe, the price will make you feel the same way.
02-13-2005, 03:39 PM
Given the make of lathe I would assume its equiped with metric gears. The DP or module to use the correct term you can find by measuring from the top of the tooth to the root or by measuring on of you gears over wires. A 120 tooth 1 module gears is 4.8208" over .068" pins, a 60 tooth is 2.458, a 30 tooth is 1.276. These figures are for 20D pressure angle gears. My SDP hand book does not list the pin sizes for 1.5 or larger modules vut they should be mulitples of the 1 module dimensions. The tip to root dimension for a module gear is 2.25 times the module
02-13-2005, 03:57 PM
I'm going to have to dig up a gear book. The one I have is very close to a 14.5 pressure angle and a 16DP. The width is .5 and the hub .010 over 7/8.
02-13-2005, 04:11 PM
There are a few other combinations that come extremely close to 127/100. For instance, a 47/37 combination would have an error of about .02%, plenty close for anything I can imagine making. Spend a few minutes with your calculator and you may find a set that will fit nicely in your gear train.
02-13-2005, 06:17 PM
127 and 100 no error
113 and 89 .03% error
108 and 85 .06%
99 and 78 .08%
94 and 74 .03%
80 and 63 .02%
66 and 52 .08%
61 and 48 .08%
47 and 37 .03%
33 and 26 .08%
02-13-2005, 07:56 PM
No need to dust off your calculator. There are programs on my page that deal
with this problem.
Assuming gears with between 15 and 100 teeth, the best choices for a single
pair of gears are:
47:37 => 1.270270 (0.021281%)
80:63 => 1.269841 (-0.012498%)
With two pairs of gears:
15:19 - 37:23 => 1.270023 (0.001802%)
24:22 - 78:67 => 1.270014 (0.001068%)
26:23 - 91:81 => 1.269995 (-0.000423%)
53:41 - 56:57 => 1.270004 (0.000337%)
59:53 - 81:71 => 1.269997 (-0.000209%)
89:63 - 89:99 => 1.270002 (0.000126%)
89:77 - 89:81 => 1.270002 (0.000126%)
Home Shop Freeware - Tools for People Who Build Things
02-13-2005, 09:17 PM
Don't know if I'm doing this right but here is what I have. The lathe calles for a combo 75-50-127.
I have 30-50-62-65-75-80-85-95-100-115-120.
The closest I can get is 85-62-115 I think?
How do you do the math with three gears and how close do you have to be?
The gears 65-100-115 don't seem to have a place in my threading chart, so I thought that they should be involved?
Thanks For all the help!
02-14-2005, 02:37 AM
I am not familiar with the lathe in question. I would like to know if it is a quick-change or a change-gear type and what the leadscrew pitch is? The list of gears kind of threw me.
02-14-2005, 10:26 AM
It is a gear head lathe. You have to change out gears to get to some threads, metric in particular. The lead screw is a 6TPI.
02-14-2005, 11:48 AM
If your gears are 16DP and 14.5 deg pressure angle you are in luck. Boston gear makes a 16DP change gear 14.5 angle 127 tooth. I just bought one and fitted it on my Clausing Colchester to cut metric threads. I had to bore it out to 7/8" to fit my arbor. I think it was .5 width. Be carefull about trying to use smaller combinations as the distance between the input and output gear may be too great. Take an existing gear add 2 to the number of teeth and divide by the gear OD. This will give you the gear DP. To check the pressure angle get a gauge or see if it meshes properly with a known gear.
[This message has been edited by Joe H (edited 02-14-2005).]
02-14-2005, 11:54 AM
I did some more math,
The closest I can get 85/62/115=.011921
The difference of .000110
First, am I doing the math right? and, is the difference acceptible? I think that would be a .01% error?
How do I figure what the error would be? would it be .01X one revolution of the lead screw?
Then thread I am cutting is about 1.5 inches long.
02-14-2005, 07:33 PM
The whole idea of the 127 tooth transposing gear is to convert your 6 tpi lead screw to metric pitch. The 127 tooth gear must be compounded (connected to on the same arbor with another gear)with typically a 100 or 120 tooth gear. Usually the 100 or 120 tooth gear is already on the lathe and connects the output of the gear box drive to the input of the quick change box. The compunded transposing gears must convert 25.4 (25.4 mm = 1 inch) to a whole number (usually even). For 127/100, 100/127 x 25.4 = 20 for, 127/120, 120/127 x 25.4 = 24. The output of the gear box drives the 127 tooth gear and 100 or 120 tooth gear drives the input gear of the quick change box. If this the way your lathe is setup you can see only certain size gears will physically fit the the drive train. The only 127 tooth gear currently made by Boston Gear is a 16DP 14.5 pressure angle change gear. My educated guess regarding your 75/50/127 combo is that the 127 tooth is compounded with the 120 or 100 and the 75 and 50 fit either the gear box output or the input for the quick change box. It sounds like the Boston gear (about $60 +shipping) maybe what you are looking for. You must determine the DP and pressure angle of your change gears.
02-14-2005, 07:47 PM
The gear combo of 75-50-127, works like this, the 75 is coneccted to the out put of the gear box, the 50 is on a sliding bracket, the 127 is on the input to the lead screw transmission, you then slide the 50 on the bracket until they mesh properly and tighten. Now the gear box with the 127, can be shiftes to give diferent threads, or shifted to the feed shaft and give different feeds. If I can fit the 85-62-115 combination, would it give me a workable solution?
The gears are metric, so the 16dp is close but not perfect, I could probably make it work if need be, but I thought the new gear combo was a great idea, if it will work. What do you think?
02-14-2005, 08:12 PM
Looking at the 75 / 50 / 127 combo. As you described it, the 50 has no effect on the gear ratio (it is only an idler). All it does is change the direction of rotation. The ratio of 75/127 x 25.4 = 15.
The 85 / 62 / 115 combo doesn't appear to work since the 85/115 ratio x 25.4 is not a whole number. The 62 tooth idler has no effect on the gear ratio.
One possibility is to compound your 50 tooth metric idler gear with a 50 tooth 16dp 14.5 PA change gear on the sliding bracket then drive a 127 tooth 16DP 14.5 PA change gear on the lead screw transmission.
If the gears are metric the PA is probably 20 deg. They will not mesh with 14.5 PA gears.
[This message has been edited by Joe H (edited 02-14-2005).]
02-14-2005, 08:47 PM
I got it!
I think the best avenue for me is going to be to make, or get the right size metric gear. I will detirmine the pitch tomorrow and go from there. Thanks for all the help!
02-15-2005, 10:00 AM
Try Maryland Metrics, in Baltimore.My old catalog gives 1-800-638-1830. They list 127t, 1.5 module, 20 deg pa. They're good people, and they know a lot. Might be worth a phone call?