A DRO is probably one of the most important upgrades you can make to a manual mill. By removing concerns with screw backlash or losing count of hand wheel rotations, the DRO allows you to work faster with less chance of user error. Even compared to a new mill, the linear scales of a DRO system are much more accurate than typical mill lead screws. Add in a few advanced features such as center function, bolt circle function and the ability to easily switch from metric to imperial units and it's easy to see why a DRO system is such a popular upgrade.
After a ton of research, I decided to purchase a 3 axis DRO system with glass scales directly from China. The glass scales are very accurate and seem to be trouble free if installed correctly. Rather than buying the absolute cheapest no-name system, I decided to upgrade a bit and get a higher-end (for China) Easson system to avoid future problems. The DRO system was purchased directly from China mainly for the considerable cost savings. While it's true you have to do your homework beforehand as you will get limited customer support after the sale, it was well worth it as the system I bought cost 470 dollars shipped, where the exact same system purchased stateside would be over 1000 bucks.
Through AliExpress, I ordered a 3 axis Easson DRO system with a ES-12B controller and glass scales from Siton Technology. The seller was able to substitute Slimline Scales for the standard scales at no additional cost. The Slimline Scales, as the name implies, are a bit smaller than standard scales which could only help during installation. All the scales are 0.005mm resolution (.0002 inch), which is plenty accurate for a manual mill.
Within certain limits, they will make the scales any length you want. These linear scales have an absolute length and a travel (measuring) length. Do your homework, carefully measure your specific machine and make sure you and the seller understand what your are ordering before you commit.
Here's the exact scales I ordered for my Grizzly G0678 mill:
These are all Easson GS30 Slimline scales!
- X Axis = 550mm travel (694mm total length)
- Y Axis = 250mm travel (394mm total length)
- Z Axis = 500mm travel (644mm total length)
In a few days the seller shipped the order and the scales were delivered via FedEx in under a week.
Everything was well packed in two boxes.
All 3 linear scales and back plates in one box.
The controller, instructions and some hardware in the other box. While I wouldn't say you receive a lot of hardware, for my challenging installation I knew I was going to have to customize almost everything anyway and what they did provide came in handy.
Did a quick function check on the workbench and happily everything was working OK.
If you look closely at the scales, you will see a black piece of plastic at the reading head that is used for protect the scales during shipping. Don't throw these out! They are very handy to set the correct distance between the head and scales during installation as well as protecting the scales during handling until they are permanently installed on the machine.
While planning the installation of the DRO, two outcomes were desired:
The installation will not limit the axis travels in any way.
I like the X, Y and Z travels exactly as they are from the factory. Reducing them in any manner, especially the rather small Y axis travel, will be unacceptable.
Add functionality to the machine, don't remove it.
I want to retain the current hard stops in the X & Y axes. Hard stops help eliminate mistakes in repetitious operations. I would also like to keep the limit switches for the X axis power feed to lower the possibility of damaging the unit by crashing into a stop. Merging the hard stops with the power feed limit switches will be a goal.
Achieving these outcomes while fitting 3 glass scales onto a somewhat small knee mill will be ambitious, but should be possible with careful planning. I could just slap on all 3 scales over a weekend, but where's the skill in that?
For more general information, check out this classic DoubleBoost video where he describes the DRO installation on his small knee mill, a highly modified Asian 6X26 mill which is very similar to the Grizzly. The DRO segment starts at 14:00.
In the next post the installation will begin.