View Full Version : Want to fit DRO to a lathe

03-08-2005, 04:37 AM
Anyone know how to go about fitting a DRO to a conventional lathe? Any websites??


03-08-2005, 07:38 AM
Here is how I did it using rotary encoders:


03-08-2005, 08:25 AM
You should be able to fit pretty well any linear scale (DRO) system to any lathe with a little ingenuity and mount bracket fabrication.
It's definately not rocket science if you go by the way the "factory" installers mount this stuff *shudder*.
I usually end up re-doing all my new installs due to the crappy workmanship of those guys.

Bubba's method is great, but sometimes you can lose needed resolution on a long axis because the LRT encoders work on a percentage of stroke resolution. eg 10 volts over 10" = 1v/1"; 10 volts over 1" = 1v/.1".
You can do it man!

03-08-2005, 11:30 PM
Thanks guys,
I was thinking on bubba's line too, except that I intended using an open ended timing belt instead of cable. My worry is about backlash in the timing pulley & belt and I'm awaiting a reply from the timing belt mfr. on this one. Linear scale seems to be an easier option, but is it more expensive than a rotary encoder and a counter? I spoke to a rotary encoder mfr. and they suggested a 1000 ppr encoder to get an accuracy of 0.01mm - provided I take care of the mech. backlash.


03-09-2005, 07:06 AM
From what I have read, backlash should not be a problem with the timing belt. However, you also need to realize the timing pulley will have a significant diameter to it and this will affect the resolution that you will get. Its the Pi D thing. One revolution will take Pi*D of the pulley to rotate the counter wheel. Example (if I can do the math right) 1" PD pulley * PI = 3.14159" of travel to make one revolution of the encoder.
Using a 1000 line encoder (4000 quadrature) gives you a resolution of 3.14159/4000 or 0.00078". Is this good enough for your use? Of course, you can play with the diameter and see different effects. A rule of thumb that I was taught is...You want your resolution to be 10X greater than the accuracy that you want. So in this case, your accuracy would be on the order of 0.0078". On my system, I was dealing with a 5mm shaft and was struggling to get it below .0001" resolution so I could hopefully have 0.001" accuracy. And all of this assumes that you setup the program parameters correctly and thats a whole nuther ballgame:)

03-09-2005, 07:56 AM
Thanks Bubba

What you say about the resolution is absolutely correct. I plan to use a 3mm pitch belt with a 15 teeth sprocket. I will have a 90 teeth sprocket fit on the shaft of the 15 teeth and the 90 teeth will drive a 15 teeth sprocket fit on encoder shaft. I guess for every 45 mm tavel of the carriage, the encoder will rotate 6 times, therefore I will get 1 revolution of encoder for every 7.5mm travel of the carriage. As per the calculation, I get a resolution of 0.0019 mm or 0.0000738" - is this ok if I'm looking for a max. resolution of 0.01 mm? Another alternative would be to increase the ratio of 90:15 to maybe 120:12 or something on those lines.

03-09-2005, 10:08 AM
Should work:cheers:

From what I am reading, you will be driving the encoder with a "jackshaft" arrangement to increase the rotation of the encoder? You will be using a small pulley as a driver for the large one which will then drive the small one on the encoder????
Also, I would try to limit it to one set of increasers as this will minimize any play (backlash) in the system.

03-09-2005, 04:41 PM
look at Home shop machinist, I think the shooting star.........
CBX Digital Readout - Home Page

CBX and CBX 3d - The first low-cost Digital Readout System for owners of mills, lathes, mill drills and 3 in 1's.

03-09-2005, 09:37 PM
I made a redneck dro on my small emco 5 lathe.
I only did one axis at this time. I bought a digital depth mike similar to a set of calipers.
Then I made 2 clamping fixtures. Mounted one to the bed and the other
to the saddle. I get 8 inches of travel from this setup.
Total cost $21.00.

03-10-2005, 12:27 AM
Thanks guys
the CBX has really got me thinking! The only hitch is that i'm looking at a resolution of atleast 0.002mm to get a fairly accurate least count of 0.01mm, but the CBX offers a resolution of 0.005" (0.0127mm) which would be a little less!

The system I'm planning works out to the same cost or maybe slightly cheaper than the CBX but with little extra work.


05-23-2005, 11:29 AM
Has anyone used the Meister DRos from Singapore via ebay?

01-16-2006, 01:56 AM
Anyone know how to go about fitting a DRO to a conventional lathe? Any websites??

is`t japan lathe machine or others,what type of dro did you used to install.sony,accurite..etc