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Dro For Mill
- Thread starter Mark_f
- Start date
- Joined
- Apr 28, 2014
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- 3,590
- Joined
- Dec 27, 2014
- Messages
- 658
I do not wish to step on any toes by saying controversial things.
I know a lot of people use iGaging scales and they do pretty fine work.
Just consider the published tolerance of their best scales before you buy:
http://www.igaging.com/page44.html
If +/-0.001" over 6" is acceptable to you, then run with it. Just keep in mind that the hand wheels on even the cheapest mill will be probably a whole order of magnitude more accurate.
I went shopping for inexpensive scales to use with OpenDro and I wound up with this:
http://www.aliexpress.com/item/3-ax...achine-3-pcs-1um-linear-scale/1556577283.html
I figured the worst that can happen is that he head unit will die and I will use the scales with OpenDro. The whole system is about the same cost as just two scales from DroPros (which has the cheapest domestic price I could find for glass scales). I checked it against my gauge blocks and it was dead on agreement with my Mitutoyo micrometer at 1" travel. I assume there is some error over longer distances, but so far it puts one hole dead inside a previous hole no matter how much I move the table around. So far it has been a good system, it arrived in 5 days, came with protective covers, brackets, etc, but I had to get some screws in the end.
I know a lot of people use iGaging scales and they do pretty fine work.
Just consider the published tolerance of their best scales before you buy:
http://www.igaging.com/page44.html
If +/-0.001" over 6" is acceptable to you, then run with it. Just keep in mind that the hand wheels on even the cheapest mill will be probably a whole order of magnitude more accurate.
I went shopping for inexpensive scales to use with OpenDro and I wound up with this:
http://www.aliexpress.com/item/3-ax...achine-3-pcs-1um-linear-scale/1556577283.html
I figured the worst that can happen is that he head unit will die and I will use the scales with OpenDro. The whole system is about the same cost as just two scales from DroPros (which has the cheapest domestic price I could find for glass scales). I checked it against my gauge blocks and it was dead on agreement with my Mitutoyo micrometer at 1" travel. I assume there is some error over longer distances, but so far it puts one hole dead inside a previous hole no matter how much I move the table around. So far it has been a good system, it arrived in 5 days, came with protective covers, brackets, etc, but I had to get some screws in the end.
- Joined
- Feb 1, 2015
- Messages
- 9,602
Interesting that the aliexpress link claims 1 micron scale accuracy but the scale is labeled as 5 micron. I have no personal experience with purchasing a DRO from a Chinese dealer but have read of issues regarding support.
Aside from that, the scale looks like a standard 5 micron glass scale. I have installed two three axis systems with these scales and have had no problem with them. As mentioned, they usually come with a fairly complete mounting package although I made fairly extensive modifications on both installs. In contrast, the iGaging scales have no protective covers for the scales which is not conducive to longevity.
I have installed a 3 axis iGaging scale system on my lathe using the TouchDRO readout app on my Android smart phone. The scales have a 10 micron (.0004") resolution.I have checked the accuracy of the readout and have generally found it to be within +/- .0005". I would expect that if I were dealing with a significant temperature swings, the accuracy of the aluminum backed scales would degrade but my shop holds a fairly consistent temperature year round (maybe 5F swing max.).
I have yet to work a mill or lathe that has less than .001" backlash. Additionally, the Chinese mills and lathes that I have used have metric lead screws so there is a built-in error in the hand wheel dials if using inch graduations. It is possible to correct for the difference between the displayed .040" and the actual .03937" on each dial revolution but it is a PITA and exposes the possibility of errors. I have also not seen a hand wheel dial with smaller than .001" graduations so trying to make any adjustments to sub thousandths accuracy requires interpolating between the marks.
A friend and business associate runs a CNC job shop with four six figure Haas machining centers and , IMO, one of the two best machinists that I have ever met. He will not guarantee better than +/- .002". He had done a significant amount of work for our company and is work is typically much better than that but his position is that if had had to stake is reputation on it, he quotes the conservative accuracy. I can read out position to .0001" on the Tormach and typically set my coordinates to the tenths of thousandths but I would be only fooling myself if I though I was better than a thousandth. Lost motion due to backlash, play in the ways, machine flexing, tool runout, and tool flexing all come into play.
In the final analysis, for most work, the .001" accuracy of the lower cost scales will meet the need. If I am machining something that required a more precise fit, I come up close to the final dimension and make a measurement. I then tweak the hand wheel slightly to finish the cut.
I like the 2.5 and 5 micron resolution on the Tormach and my mill/drill but it comes with a cost. If cost were not a consideration, I would go with a glass scale system. However, the money saved by going with an iGaging type DRO can be applied to some other piece of gear.
Bob
Aside from that, the scale looks like a standard 5 micron glass scale. I have installed two three axis systems with these scales and have had no problem with them. As mentioned, they usually come with a fairly complete mounting package although I made fairly extensive modifications on both installs. In contrast, the iGaging scales have no protective covers for the scales which is not conducive to longevity.
I have installed a 3 axis iGaging scale system on my lathe using the TouchDRO readout app on my Android smart phone. The scales have a 10 micron (.0004") resolution.I have checked the accuracy of the readout and have generally found it to be within +/- .0005". I would expect that if I were dealing with a significant temperature swings, the accuracy of the aluminum backed scales would degrade but my shop holds a fairly consistent temperature year round (maybe 5F swing max.).
I have yet to work a mill or lathe that has less than .001" backlash. Additionally, the Chinese mills and lathes that I have used have metric lead screws so there is a built-in error in the hand wheel dials if using inch graduations. It is possible to correct for the difference between the displayed .040" and the actual .03937" on each dial revolution but it is a PITA and exposes the possibility of errors. I have also not seen a hand wheel dial with smaller than .001" graduations so trying to make any adjustments to sub thousandths accuracy requires interpolating between the marks.
A friend and business associate runs a CNC job shop with four six figure Haas machining centers and , IMO, one of the two best machinists that I have ever met. He will not guarantee better than +/- .002". He had done a significant amount of work for our company and is work is typically much better than that but his position is that if had had to stake is reputation on it, he quotes the conservative accuracy. I can read out position to .0001" on the Tormach and typically set my coordinates to the tenths of thousandths but I would be only fooling myself if I though I was better than a thousandth. Lost motion due to backlash, play in the ways, machine flexing, tool runout, and tool flexing all come into play.
In the final analysis, for most work, the .001" accuracy of the lower cost scales will meet the need. If I am machining something that required a more precise fit, I come up close to the final dimension and make a measurement. I then tweak the hand wheel slightly to finish the cut.
I like the 2.5 and 5 micron resolution on the Tormach and my mill/drill but it comes with a cost. If cost were not a consideration, I would go with a glass scale system. However, the money saved by going with an iGaging type DRO can be applied to some other piece of gear.
Bob
- Joined
- Dec 8, 2013
- Messages
- 2,651
It would not be hard to interpolate a 5 micron scale to one micron. The actual accuracy at the system level will not be that good, of course.
- Joined
- Dec 3, 2014
- Messages
- 778
I used a Shooting Star on my Clausing mill for 5 years before I bought a BP size mill and sold the Clausing with the DRO. The problem for some (not necessarily wawoodman) is what happens when you take a field trip from one end of axis to the other, then back a few times. The Shooting Star type of scale which is a ground rack of teeth, is not accurate enough to give you repeatability with better than a couple thou. If that is good enough, then its fine, but for what they charge you can now buy a glass scale rig from China that is considerably more accurate. Having now used a Newall for 10 years I would say that is the gold ring, but since I bought mine they have gotten stupid expensive. 10 years later though its still works a new and has seen a lot of use. If money were an object and buying today I would go glass scales from China or pay twice as much and get the type scales that Newall uses on the Chinese clones from DRO PROs.
Not beating up on Shooting Star, they just have been passed by with the arrival of relatively inexpensive glass scales from Asia.
cheers
michael
- Joined
- Dec 27, 2014
- Messages
- 658
The scales I received are 1um, not 5um. I had the same reservation when I purchased them. This is doubly confirmed by the DRO advancing in 0.002" increments (EDIT: 0.0002"). Like I said, I checked it against a verified 1" gauge block and it read dead on, I also verified repeatability of returning to a previous spot and it was always within 0.0002" no matter how far I moved the table. From what I hear, the Chinese have really gotten glass scale manufacturing down, it is the electronics that suck.
As for the rest, the whole idea of a DRO is to eliminate or minimize all the other errors from backlash and the like. In theory, if the scale reads accurately and precisely, the only error will be the actual run out of the spindle + machine flex + the error of the read head (you do lock unused axis, and take spring cuts, right?). Your buddy will not guarantee under 0.001" because that is all a run of the mill CNC will do, your buddy is probably a far better machinist than his machine. There is a reason all that stuff goes to second ops machines when high precision is needed. With care and patience, a hobbyist can mill to half a thou consistently.
For $350.00, I was not especially worried about support - all I really wanted was the scales. I figured this was an entire set up that costs slightly more than two scales from DroPros, about the same as one Eason scale, and only about $100.00 more than 3 iGaging scales. It was pretty much a no-brainer. The same store sells complete 3-axis 5um kits for less than 3 iGaging scales. They also sell Eason, Sino, and Sinpro, and other kits. I did have to call my bank to get the international purchase approved, and resubmit the order - bit of a hassle, but worth it. The money goes in escrow until I approve the sale (you have 30 days or something like that). I figured the worse case would be I was out some cash for a few weeks until it got refunded, or the display would fail and I would do the Android thing like I originally planned.
Last edited:
- Joined
- Dec 18, 2013
- Messages
- 2,012
I went with the Dro Pros EL400 2 axis on my lathe and 3 axis on my mill. These use magnetic scales and are made in India. The smallest/thinness scales of any DRO and the scales can be easily cut to length. One word of warning, if you are mounting the X scale to the mill table that's fine, but these scales are far too flexible to mount directly to the cast knee, base, or column of a mill. Its doubtful those surfaces will be flat and the least little bit out of flat will twist/bow these scales. Pay no attention to the instructions blabbering about grub screws and blah blah just purchase a length of aluminum bar and mount the scale on that, then mount that to the mill way easier.
- Joined
- Nov 23, 2014
- Messages
- 2,606
I put a TPAC tools (tpactools.com) 4-axis (caliper type scale on the quill, glass slides on the table x/y/z) on my Jet JVM-830 for $485 delivered. The unit is from mTech, similar/same as Sinpo. Their 3-axis package is $455. I couldn't be happier with my unit. I had to make most of the mounting brackets which took around 8 hours. WELL worth the time! You'll love the addition to your shop regardless of what you chose.
Bruce
Bruce