View Full Version : DRO - Inch or metric

David Morrow
11-15-2004, 11:50 PM
I'm looking at a Sherline mill and thinking about a DRO. In Canada, we're officially metric but the use of inch measures is still a reality. I thought I could buy an inch machine with a DRO and then the DRO would allow instant conversions between inch and metric. But, Sherline offers either an inch or a metric DRO and not one that does conversions. I emailed them and they said that it can't be done because :

"The system reads off the threads of the lead screws; therefore, if you had an inch machine and tried to read the DRO in metric your data would be
incorrect. The threads off the metric screws are finer than the threads off
inch lead screws, so using the DRO electronics in the incorrect mode would
result in information that could not accurately be used."

This doesn't make any sense to me at all. I don't want to start an arguement with Sherline but to me, the conversion should be electrical and done just before the LCD readouts. I've searched the web and inch / metric conversion seems to be almost universal on dro's.

Am I crazy or is Sherline just a bit out of step with the rest of the world ?

11-15-2004, 11:57 PM
Sounds like a cop out. I can make metric threads on my South Bend, converting is not a problem for even a slightly competent software designer. It could display in angstroms if they wanted.

11-16-2004, 12:02 AM
What may be the case is that encoders which they use may be coarse enough so that when used on one leadscrew vs the other, there is inadequate resolution (steps) for "normal" use. Professional DROs have resolutions down into the microns and there is no problem resolving inch or metric off the DRO scales. If Sherline is reading off leadscrew encoders, then this is probably where they have a limitation.

added - they do indeed use shaft encoders for each axis with resolutions of 0.0005" for inch and 0.01mm for metric. In any case, they could easily convert and that conversion would have an accuracy equivalent to the smallest step on the "native" system. Their problem is not obvious to me at this time of night http://bbs.homeshopmachinist.net//wink.gif


[This message has been edited by nheng (edited 11-15-2004).]

11-16-2004, 02:23 AM
I would not buy a DRO that can't work in both units. End of story. http://bbs.homeshopmachinist.net//biggrin.gif


11-16-2004, 02:44 AM
We have been metric in Australia since the mid seventies or should I say multimeasurents,we still go into the hardware store and buy imperial bolts with the nearest metric equivalent written on the bin.If you can get a dro that will read in both systems.

11-16-2004, 03:09 AM
Was thinking some more about wat you said about how the DRO worked off the lead screws. Hmm that sounds useless anyway even if you didn't want it to convert between met/inch. One of the other big advantages of a DRO especially on a mill is it helps with backlash errors. Reading off the lead screws will not even give you that benifit. I'm not fimilliar with the mill you are looking at but I guess it's fairly small, you may be better off just fitting a set of digital calipers to it. I have read posts here of people who have done this. Someone else might like to comment as this might be a better solution.


11-16-2004, 07:48 AM
Conversion to metric has nothing to do with the hardware, if you can resolve inch measurements to your satisfaction with the hardware offered for your mill then the resulting measurement is converted to metric by simple formula (math not machining) per Machinery Handbook 25 edition page 2453 1 inch equals 25.4 millimeters exactly they offer a chart and explanation for converting DRO's that convert just use a formula to change the resultant output to the display in effect they just do the math prior to it getting to you.

Disclaimer: All advise might be worth what you paid for it , no animals were hurt during the formation of this post. If you wish to disagree please keep it "civil" address the information given not the person who gave it. If the information makes you angry seek professional medical advise and appropriate medication.

11-16-2004, 09:39 AM
It sounds as though Sherline is using the leadscrew as the "standard" and simply giving you the equivalent of the dial graduations, instead of using a separate standard such as a glass scale or whatever.

Even so, as you say it's just math, and they ought to be able to interpose a multiply-by-25.4 in the electronics someplace. But that would cost more money.

11-16-2004, 11:06 AM
[QUOTE]Originally posted by David Morrow:
[B]I'm looking at a Sherline mill and thinking about a DRO."

Any DRO that reads from the lead screw will not take into account any back lash, therefore it's useless for accurate measuring. Instead get a DRO with a separate scale that will do both in/mm.


Paul Alciatore
11-16-2004, 12:38 PM
I would agree with and even go further than the above statements about "cop out" and the limited value of a "DRO" that uses the lead screw for it's input. Frankly, I would not call such a device a DRO in the same sense that the term is commonly used.

What's the sense of using the lead screw? You already have the dials and both dials and electronic readout will have all the errors of the lead screw including backlash, errors in pitch, wear, etc.

You would be better buying a real DRO and taking the trouble of installing it. Or even digital calipers or depth gauges could be adapted and would give you both English and metric at the touch of a button.

As for it being "impossible", that's just sales talk for "We don't have it. But we want you to buy our POS anyway."

Paul A.

11-16-2004, 04:28 PM
I wonder if you could use a Shooting Star dro? I do know they will fit the mini mills that grizzly and harbor freight sell.

www.star-techno.com (http://www.star-techno.com)

Paul in NE Ohio

11-16-2004, 08:45 PM
The real problem is currently there IS NO DECENT DRO MADE FOR A SMALL MILL PERIOD.
Let me define that a little better,no DRO that is moderately priced for the machines in question.
I have looked at the Shooting star and the ones sold by Little machineshop and others and all are either lacking in basic function or are horrible in price.
I added up all the componets for an import dro designed to fit my Mini-mill,$550.00 was what I got,too much considering you can get a full sized Mititoyo digimatic to fit a B-port mill for $750.
I like the idea of using the digital scales,but being able to see them is a problem,most times you can't.
So,what have I done? Mounted a couple of 2" throw dial indicators to the table on quick adjust slides,since most things made on the little machine are less than this it works good.

I wish someone would come up with a real DRO for these machines that cost something more reasonable like $50 an axis.

George Seal
11-16-2004, 10:32 PM
Yes Shooting Star DRO's will fit Micro Marks Mini-Mill. Installed one on mine and I am very happy with it. Chris Wood from Little Machine Shop has free drawings for the mounting brackets
WWW.Littlemachineshop.com (http://WWW.Littlemachineshop.com)

Remember the early bird gets the worm, BUT it's the second mouse that gets the cheese.

The Doctor
11-18-2004, 01:55 AM
Here is somebody selling a three axes display which I believe is designed to use the cheap Chinese scales. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3853683576 The use of a separate display unit like this would allow you to use the Chinese scales and not have problem seeing them so you could read them.

Here is somebody selling a similar display unit with three scales included http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3853565744 I did not check the specs of this closely, so I don't know if he supplies it with whatever length scales you need, but the price is not too bad. I am not in any way affiliated with either of these two sellers, nor have I ever dealt with them in the past. In other words, I cannot vouch for the quality or lack of quality of their services.

As to Sherline, I hate to badmouth an American company, but their DRO setup is completely half-ass! As others have said, part of the advantage of a DRO is the fact that it eliminates both backlash and lead screw errors. If the DRO cannot do this, all you're paying a great deal of money for is a glorified dial turns counter! For a lot less money you can simply put a metal ruler and pointer on each axes, and do your fine adjustment with the dial! This eliminates any possible error due to "dropping a turn", and provides every bit as much accuracy as Sherline's terrible system. As an added bonus a metal scales cost a lot less money :-)


Allan Waterfall
11-18-2004, 05:35 AM
I've got one of these on my mill,mine cost about £300.00 in the UK for a three axis system and Chinese scales.

www.shumatech.com (http://www.shumatech.com)

Also some good information on the site about Chinese scales.


11-18-2004, 09:54 PM
For any DRO, there should be a button or st of dip switches to go between met and inch. I had given to the shop some metric dro's, but found out the dips could be set to go either way. May want to check this out.