Adding a DRO to an X2 Mini-mill

[goober]

Ok folks, I've been threatening to post this for a while now but finally have the time to do it. I've had all the parts in hand for months, but travel and RealLife™ got in the way there for a bit.
This thread is a demonstration of one method for mounting scales and a DRO (Digital Read Out) on a mill. The mill in question is the Sieg X2 mini-mill clone sold by Harbor Freight (HF 44991), and also by Grizzly (G8689), ToolsNow/Cummins (7877), etc. See this comparison page for more info. It is an entry-level benchtop mill, costs about $350-500, and is about the smallest mill that is useful for most gunsmithing projects such as finishing 80% lowers, making custom parts, and such.
Pretty much all the lower-end (< $1500) mills available are Chinese-made and as such leave a bit to be desired in the fit & finish and precision categories. They are typical of ChiCom products: cheap and serviceable, but a bit crude and rough. One of the biggest shortcomings of these mills out of the box concerns the control of the X & Y movement of the table and Z movement of the spindle head: the mechanisms involved are not of the highest quality, and high-precision movement is difficult. Backlash is pretty much a given when changing directions, and can be hard to account for. On top of this, the lead screws that move the table sometimes have odd threads, so that one revolution of the turn crank may move the table 0.0625", or 0.060", or something weird like that, which can make it a pain to count turns in order to move the desired amount. These are all issues that can be dealt with/worked around to varying degrees, but the best way is to install a DRO. A DRO keeps track of where the cutter is in real XYZ space at all times. It allows one to move an exact amount in any or all dimensions, return back to the same spot again, etc. No more counting turns of the handle, and if there is backlash, it is accounted for. So if you have a mill, you want a DRO.
OK, enough explanation and justification. Let's get on with the demo. Having made the decision to add a DRO to one's mill, one must choose one. The available options range from complete packages including all scales, the display, mounting brackets, etc., to very DIY setups that require much more assembly and in some cases even electronics fabrication. As one would expect, prices vary accordingly, with some of the higher-end DROs costing in the thousands, and the very cheapest options a couple hundred. The DRO displays themselves range from simple 2- or 3-axis models that just show the current coordinates and can be zeroed, to actual small computers that can calculate the coordinates for round bolt patterns, take into account cutter diameter, and the like.
In the spirit of not putting Recaro seats in a Hyundai, it seems silly to spend more on a DRO that the mill cost to begin with, so I opted to buy the parts individually. I purchased electronic scales from Shars & a simple DRO display from CDCO.
Parts list:
Shars
12" Horizontal Digital Machine Scale     303-9307     1     $49.00
8" Horizontal Digital Machine Scale    303-9305    1    $39.00
12" Vertical Digital Machine Scale    303-9308    1    $56.00
Shipping cost $43.72
Total $187.72
CDCO
Item Number:   30011
Item Name:   3 - Axis DRO Display Unit ( Scales not included)
Price Each:   $189.00
Quantity:   1
Order Sub-Total: $189.00
Shipping Cost: $15.00
Total Cost: $204.00
 
Here are the scales and display (the cables that connect the scales to the display are not shown):

From bottom to top, the scales will be used for the X, Y, and Z axes, respectively.

[goober]

The scales will need to be mounted onto the mill such that the movable part will slide as its respective axis is moved. This will require some engineering, as the mill itself does not have any existing brackets or even dedicated locations for scale mounting. Rather than reinventing the wheel, I chose to use already proven mounting plans available on the interwebs. I'm using the fignoggle.com plans for mounting a DRO on an X2 clone mini-mill ($8.95). The plans include parts lists, drawings for the various mounts required, as well as installation instructions. As these plans are copyrighted, I will not show the drawings or any great detail regarding the mounts themselves, but you should get the idea anyway.

Most of the mounts are made from 2" x 0.5" 6061 aluminum bar stock. Here I'm cutting the stock on my ChiCom bandsaw:


And milling the brackets to shape according to the drawings. Needless to say, a bit of chicken-egg syndrome exists here; one can't help lamenting how much easier it would be to make these mounts if one had a DRO.... :p )
In this case one of the X-axis mounts:


and one for the y-axis:


And here are the finished mounts (one is made from aluminum angle stock):

[goober]

Once the mounting brackets are completed, we can attach the scales to the 3 axes of the mill. This will require some drilling and tapping for bracket attachment. First, remove the bellows-like chip guard on the front of the mill. (this is there to keep chips out of the y-axis ways; we will replace it once we get our brackets installed). There are a couple screws to be removed underneath the bellows:


Now, locate, punch, and drill 2 holes for the right side x-axis scale bracket:


And tap for 10-24 socket-head cap screws (SHCS):


Mount the right-side bracket on these holes and attach the middle bracket (the one made from angle stock) using the bellows attachment screws (replacing bellows):


Now the x-axis scale can be mounted up:



Note that the scale is only anchored to the table (moving part) on one end, and the sliding parts of the scale is attached to the main body of the mill (non-moving part). The reason for only attaching one end (instead of both) is to prevent binding or flexing should the scale/mill alignment be off just slightly.

[goober]

To mount the Y axis brackets, the X axis turn crank handle must be removed, and holes drilled/tapped for 10-24 SHCSs in the table assembly behind its location:


And in front of it on the base of the mill:


For the Z-axis, holes must be drilled/tapped near the base of the mill column:


And up on the spindle head assembly. Here are the Y & Z axis scales mounted up:


Plug in the DRO display and the installation is completed:

I've just temporarily "mounted" the display back there on the pegboard... I'll build a more functional mount for it, possibly on a flex/swing arm, eventually...
Next step will be to test the accuracy/precision of the readout in all axes, and then begin enjoying the benefits. I am really looking forward to not only how much easier this is going to make pretty much every operation, but also the improvement in the quality of my work, as well as the decreased anxiety that comes along with really knowing where one is.
Woohooo!

[lifeofahero]

Very nice!  I learned a lot and maybe, just maybe.. someday I'll take the DRO plunge. 

[B||ade]

Great, Thanks Goober I've been waiting for this. I do have one question though, could the Y axis slide be mounted on the opposite side so that there is clearance for the locking lever?

[goober]

Great, Thanks Goober I've been waiting for this. I do have one question though, could the Y axis slide be mounted on the opposite side so that there is clearance for the locking lever?

yeah, it could be. all of the scales are awful close to the locking levers, but they can still be manipulated. i may move it to the other side if needed. note that it should be mounted upside down if so, to keep the sign/direction thing right.

[B||ade]

I'm using your links to order my scales and display but I thought I would look around a bit. SO I went on to McMaster Carr and found the scales there. A 12" scale from McMaster is over $700 
Anyway, I should have my DRO setup by the weekend 

[goober]

I'm using your links to order my scales and display but I thought I would look around a bit. SO I went on to McMaster Carr and found the scales there. A 12" scale from McMaster is over $700 
Anyway, I should have my DRO setup by the weekend 

wow that's crazy if they are the same scales... but be aware there are lots of different kinds, and the ones i used are low-end (but decent). the higher-quality more accurate sealed glass type scales can be quite $pendy (and are overkill on mills like ours). good luck with the installation! 
are you going to use the fignoggle plans? there's lots of other good info & stuff on his site too.

[B||ade]

are you going to use the fignoggle plans? there's lots of other good info & stuff on his site too.

yep, Already got them printed out and I have the aluminum, and hardware sitting around the shop. I should be able to make the mounts tonight, the scales will be here tomorrow and the display on Thursday.
I can really see where the DRO is going to make thins much easier to track.

[goober]

are you going to use the fignoggle plans? there's lots of other good info & stuff on his site too.

yep, Already got them printed out and I have the aluminum, and hardware sitting around the shop. I should be able to make the mounts tonight, the scales will be here tomorrow and the display on Thursday.
I can really see where the DRO is going to make thins much easier to track.

cool 
BTW be careful with the cables that come with the display... the mini-DIN connectors that plug into the sockets on the display are really cheap and flimsy, and pretty much threaten to self-destruct anytime you go to disconnect them (at least mine did). once you can plug them in and leave them, they'll be fine, but if you're like me and want to immediately assemble and play with (erm.... TEST  ) things right out of the box, be gentle. just an FYI.

[B||ade]

Well, this has turned out to be a bit of a nightmare for me at least. The DRO I got from CDCO appears to be a somewhat used unit. The power cord for it has Linksys all over it. As most know, Linksys is a Mfg of network gear such as wireless routers and such. The end that plugs into the display does not fit correctly and vibration causes the display to cycle off and on. I called CDCO and his response was such that if I could have reached through the phone I would have choked him. I'l supposed to be in the Schaumburg area in a few weeks and this had better be resolved by then.
Secondly the 12" horizontal scale I got from Shars works fine until you plug the cable in. The contacts on the PCB are all not etched correctly and it shorts everything out. Here is a picture of it. Does this look normal to anyone else?

[goober]

yikes that stinks, sounds like you got hosed by two separate vendors 
i feel somewhat responsible, having recommended them 
but aside from the cheapo connectors on the cables i did not have any issues with my scales or DRO. i set them all up on my electronics bench prior to installation, to check for connector fit, make sure all the parts were there, test functionality, etc... i even left them set up and on for ~24 hrs to see if the readings would drift at all. everything seemed fine.
i'll take a look at my PS and the connector sockets on the scales to see if i can shed any light on your SNAFUs. really sorry man, i know how frustrating this kind of stuff can be when you're all stoked to get something set up and you hit these kind of roadblocks 
hang in there.

[B||ade]

No fault of yours Goober, I've dealt with things like this before. I would be curious to hear if your 12" scale shows the same as the one I posted and what kind of PS supply you got with the display. I did rectify the problem though, I have a ton of old power cords from various things and I have one that works perfectly. That solves one problem.
I will be able to run things, I'll just disconnect the X axis from the display and read it directly until it's resolved.

[goober]

Just thought I'd post a little followup. Before relying on my new DRO setup it seemed like a good idea to make sure they produce accurate measurements.
I did a quick & dirty test of the XY accuracy using something I had laying around that had some holes in it that are in known locations: namely, an AR15 drilling jig

First I clamped one half of the jig in the vise on some parallels. Then I chucked up a 1/4" drill bit and moved the table into position so that the bit was positioned over the pivot pin hole in the jig, and tested that it could be moved up and down freely through the hole w/o contacting the jig.
I then zeroed the X & Y axis readouts on the display.

Sorry for the hard to read display. Oh yeah, I also put together a mount for the display using a magnetic indicator base arm-thingy.

Many drawings/plans for AR15 lowers (such as the Ray-Vin guide) use the pivot pin location as a zero datum in X, Y, & Z. The locations of most other holes are then given from this point, like so:


So, I cranked the table over to X = -3.604", Y = -0.375", put a 5/32" bit in the chuck (this is the size for the hammer & trigger pin holes), crossed my fingers, and lowered the spindle...

BADA-BING! The bit passes right through the hammer pin hole like butter, no contact at all
I then tried with the trigger pin hole as well, and also returning to 0,0 to try again with the 1/4" bit in the pivot pin hole. All good. looks like the accuracy and precision of the DRO will serve my needs.

[fishfactor]

If you were to do away with the large display, how difficult is it to use the displays on the scales?  Maybe getting the scales, then updating to the display down the road.

[goober]

If you were to do away with the large display, how difficult is it to use the displays on the scales?  Maybe getting the scales, then updating to the display down the road.

possible but quite awkward. the x axis is easiest, but the Y is upside down and the Z is in the back on the right side of the column, so watching what you're doing while watching the readouts on the scales is tough. but if you had to do it that way, you'd still be better off than w/o DROs completely.